JP2003209450A - Automatic gain control circuit and automatic gain control method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] When a received signal includes an interference wave in addition to a desired signal,
The saturation period at the input end of the A / D converter due to the interference wave is reduced, and good reception characteristics are maintained. SOLUTION: A received signal amplified or attenuated by a gain based on a control signal in a gain control amplifier 1 is A / D-converted.
The signal is converted into a digital signal in the converter 2, and unnecessary components are removed from the digital signal by the digital filter 3. The signal level determiner 10 determines the signal level of the digital signal, and sets a gain setting unit 11A.
Sets an amplification factor in the digital amplifier 9 according to the determined signal level. The output from the digital filter 3 is amplified by the digital amplifier 9 at the amplification rate, and the control signal generating means smoothes the difference signal between the amplified signal level and a predetermined reference value to output a control signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic gain control circuit and an automatic gain control for controlling the amplitude of a received signal in order to demodulate a digital modulation signal such as a polyphase phase modulation signal or a polyphase quadrature amplitude modulation signal. Regarding the method.

[0002]

2. Description of the Related Art In recent years, satellite digital broadcasting, terrestrial digital broadcasting, digital CATV, etc. using a polyphase phase modulation system or a polyphase quadrature amplitude modulation system have been put into practical use.
Generally, in a broadcasting system and a communication system using a digital modulation method, since it is a method of transmitting information by modulating the phase and amplitude of a carrier wave, in order to realize stable demodulation operation on the receiving side, the received signal Must be controlled to a constant amplitude and input to the demodulator.

FIG. 11 is a block diagram showing a configuration example of a conventional automatic gain control circuit.

The automatic gain control circuit shown in FIG. 11 includes a gain control amplifier 1 for amplifying or attenuating a received signal, and an A / A
A D converter 2, a digital filter 3 that passes only a signal of a reception channel (hereinafter referred to as "reception channel signal") from a reception signal, a signal level detector 4 that detects a signal level of the reception channel signal, and a signal level To standard value 6
, A loop filter 7 for smoothing the subtraction result, and a D / A converter 8 for D / A converting the smoothed subtraction result and outputting a control signal to the gain control amplifier 1.
Includes and. The reference value 6 means a desired signal level value as the signal level of the reception channel signal, and does not mean a specific value.

The specific operation of the automatic gain control circuit shown in FIG. 11 will be described below.

First, the received signal is amplified or attenuated by the gain control amplifier 1 and converted into a digital signal by the A / D converter 2. The received signal converted into the digital signal is subjected to the digital filter 3 to remove the interfering wave existing in the vicinity of the received channel signal included in the received signal, and to limit the band to prevent intersymbol interference of the digital signal. Is output. Signal level detector 4
Detects the signal level of the reception channel signal and inputs the detection result to the subtractor 5. The subtractor 5 subtracts the reference value 6 from the signal level of the detected reception channel signal and outputs the difference. The loop filter 7 smoothes the difference and outputs it to the D / A converter 8. The D / A converter 8 converts the smoothed difference into an analog signal and outputs the analog signal to the gain control amplifier 1 as a control signal for controlling the gain in the gain control amplifier 1.

When the signal level of the reception channel signal is lower than the reference value 6, the D / A converter 8 generates a control signal for increasing the gain of the gain control amplifier 1,
The gain control amplifier 1 operates so as to increase the gain of the received signal. On the other hand, when the signal level of the reception channel signal is higher than the reference value 6, the D / A converter 8 generates a control signal for decreasing the gain of the gain control amplifier 1, so that the gain control amplifier 1 receives the reception signal. Operates to reduce gain. As described above, even if the signal level of the received signal fluctuates, the signal level of the received channel signal is controlled to be constant by controlling the gain of the gain control amplifier 1. Therefore, the input amplitude to the demodulator can be kept constant and stable reception characteristics can be secured.

[0008]

Here, there is an interfering wave of high power with respect to the desired wave in a channel adjacent to the receiving channel within the receiving frequency band, and both the desired wave and the interfering wave are received. Think of if.

A received signal composed of a desired wave and an interfering wave is converted into a digital signal via a gain control amplifier 1 and an A / D converter 2. The received signal including the desired wave and the disturbing wave is removed by the digital filter 3 so that only the desired wave is output as the receiving channel signal. Then, as described above, the gain in the gain control amplifier 1 is controlled by the control signal via the signal level detector 4, the subtractor 5, the loop filter 7, and the D / A converter 8.
At this time, even though the desired signal and the interfering wave are received in the received signal, the interfering wave is removed by the digital filter 3. Therefore, the control obtained based on the signal level of only the desired wave. Gain control amplifier 1 by signal
The gain at is controlled. When the signal level of the reception channel signal is lower than the reference value 6, the gain control amplifier 1 operates so as to increase the gain of the reception signal. However, since the reception signal input to the gain control amplifier 1 includes the desired wave and the interfering wave, not only the desired wave is amplified but also the interfering wave is amplified.
The input terminal of the / D converter 2 is saturated and normal reception characteristics cannot be obtained, resulting in deterioration of the bit error rate in digital communication. Moreover, if the saturation operation time of the A / D converter 2 continues for a long time, the reception cannot be performed.

Next, consider the case where the signal level of the received signal is weak power.

As described above, the received signal is output as a received channel signal via the gain controlling amplifier 1, the A / D converter 2 and the digital filter 3. Further, the gain in the gain control amplifier 1 is controlled by the control signal via the level detector 4, the subtractor 5, the loop filter 7, and the D / A converter 8. When the received signal has weak power, the gain in the gain control amplifier 1 is increased to control the signal level of the received channel signal to the reference value. However, even if the gain in the gain control amplifier 1 is increased, when the maximum amplification factor of the gain control amplifier 1 is reached, further amplitude control cannot be performed and it becomes impossible to follow the level fluctuation of the received signal. That is, when the received signal has weak power, the reception limit performance is determined by the maximum amplification factor of the gain control amplifier 1.

An object of the present invention is, firstly, to reduce the saturation period at the input end of the A / D converter when the received signal includes a desired wave and an adjacent high-power interfering wave. It is another object of the present invention to provide an automatic gain control circuit and an automatic gain control method capable of maintaining good reception characteristics.

Secondly, when the received signal has weak power,
To provide an automatic gain control circuit and an automatic gain control method capable of following a level variation of a received signal even when the amplification factor in the gain control amplifier is equal to or higher than the maximum amplification factor.

[0014]

In order to solve the above problems, an automatic gain control circuit according to a first aspect of the present invention includes a gain control amplifier for amplifying or attenuating a received signal with a gain based on a control signal, and the gain. A / D for converting the received signal amplified or attenuated by the control amplifier into a digital signal
A converter, and a signal level determiner for determining the signal level of the digital signal output from the A / D converter,
A digital filter that removes unnecessary components from the digital signal output from the A / D converter, a digital amplifier that amplifies the signal output from the digital filter at a predetermined amplification factor, and a signal level determiner. A gain setting unit that sets the predetermined amplification factor in the digital amplifier based on the determined signal level, a signal level detector that detects a signal level of a signal output from the digital amplifier, and the signal level detection And a control signal generating means for smoothing a difference signal corresponding to the difference between the signal level detected by the detector and a predetermined reference value, and outputting the smoothed signal as the control signal to the gain control amplifier.

According to the present invention, the signal level judging device judges the signal level of the digital signal from the A / D converter, and the gain setting section sets the amplification factor of the digital amplifier according to the signal level. . Then, the gain of the gain control amplifier is controlled so that the signal level output from the digital amplifier becomes a predetermined reference value. Therefore, when the received signal includes the desired wave and the adjacent high-power disturbing wave, the saturation period at the input end of the A / D converter is reduced to maintain good reception characteristics, which in turn results in digital reception. It is possible to suppress deterioration of bit error rate in communication.

According to a second aspect of the present invention, in the automatic gain control circuit according to the first aspect, the control signal generating means sets a predetermined initial value corresponding to the predetermined amplification factor set by the gain setting section. Further comprising an initial value control unit, wherein the control signal generation means smooths the initial value set by the initial value control unit and outputs it as the control signal to the gain control amplifier, and a predetermined time elapses. After that, the difference signal is smoothed and output as the control signal to the gain control amplifier.

According to the second aspect of the invention, the initial value control section sets the initial value corresponding to the amplification factor set by the gain setting section in the control signal generating means. Therefore, the loop delay can be reduced and the gain control response can be made faster.

According to a third aspect of the invention, in the automatic gain control circuit according to the first or second aspect, the signal level determiner has a first threshold value and a second threshold value larger than the first threshold value. Each of the thresholds is compared with the signal level of the digital signal output from the A / D converter, and the gain setting unit determines the digital level when the signal level of the digital signal is higher than the second threshold. First higher than the current amplification factor of the digital amplifier
When the signal level of the digital signal is smaller than the first threshold value, the second amplification factor lower than the current amplification factor of the digital amplifier is set in the digital amplifier. To do.

According to the invention of claim 3, the signal level judging device compares the signal level of the digital signal from the A / D converter by using the first threshold value and the second threshold value, and the gain setting section is When the signal level is higher than the second threshold value, the amplification factor of the digital amplifier is set to the higher amplification factor, and when the signal level is lower than the first threshold value, the amplification factor of the digital amplifier is set to the lower amplification factor. To do. Therefore, A / D
Since the amplification factor of the digital amplifier is set so that the signal level from the converter finally falls between the first threshold value and the second threshold value, saturation at the input terminal of the A / D converter is achieved. It is possible to reduce the period and maintain good reception characteristics.

According to a fourth aspect of the present invention, in the automatic gain control circuit according to the third aspect, the initial value control section sets the gain when the signal level of the digital signal is larger than the second threshold value. An initial value corresponding to the first amplification factor set by the unit is set in the control signal generating means, and when the signal level of the digital signal is smaller than the first threshold value, it is set by the gain setting unit. An initial value corresponding to the second amplification factor is set in the control signal generating means.

According to a fifth aspect of the present invention, in the automatic gain amplifier according to the third aspect, the second threshold value is A / when the signal level of the digital signal is higher than the second threshold value. The D converter is a value that is determined to be in a saturation operation, and the first threshold value is the digital value set by the gain setting unit when the signal level of the digital signal is smaller than the first threshold value. When the second amplification factor is set in the amplifier, it is assumed that the A / D converter does not cause the saturation operation.

According to the invention of claim 5, since the respective threshold values are set as described above, the saturation period of the A / D converter can be shortened. Also, in this case, the S / N ratio of the received signal becomes advantageous,
It is possible to suppress the deterioration of the bit error rate.

According to a sixth aspect of the present invention, in the automatic gain control circuit according to the first or second aspect, the signal level determiner has a threshold value from a first threshold value to a Kth threshold value (K is an integer of 3 or more). And the signal level of the digital signal output from the A / D converter are compared, and the gain setting unit determines that the signal level of the digital signal is i-th (i is 3).
If it is greater than or equal to the (K-1 or less integer) threshold value and greater than the (i-1) th threshold value, the digital amplifier is provided with a third threshold value corresponding to the i-th threshold value higher than the current amplification factor of the digital amplifier. When the signal level of the digital signal is smaller than the first threshold value, the second amplification factor lower than the current amplification factor of the digital amplifier is set in the digital amplifier. To do.

According to the sixth aspect of the present invention, the signal level determining unit determines whether the signal level of the digital signal from the A / D converter is in the range from the second threshold value to the Kth threshold value, and sets the gain. The unit sets the amplification factor in the digital amplifier according to the range of the signal level from the second threshold value to the Kth threshold value, and lowers the amplification factor when the signal level is lower than the first threshold value. Set the amplification factor. Therefore, the amplification factor of the digital amplifier can be instantaneously set so that the signal level from the A / D converter falls within the range between the first threshold value and the second threshold value. It is possible to further reduce the saturation period at the edge and maintain good reception characteristics.

According to a seventh aspect of the present invention, in the automatic gain control circuit according to the sixth aspect, the initial value control section has a signal level of the digital signal equal to or lower than the i-th threshold value, and thus the (i-1) -th signal is obtained. Is greater than the threshold value of, the initial value corresponding to the third amplification factor set by the gain setting unit is set in the control signal generating means, and the signal level of the digital signal is higher than the first threshold value. When it is smaller, the initial value corresponding to the second amplification factor set by the gain setting unit is set in the control signal generating means.

According to an eighth aspect of the invention, in the automatic gain control circuit according to the sixth aspect, the second to Kth thresholds among the first to Kth thresholds are signals of the digital signal. If the level is less than or equal to the i-th threshold value, the (i-1) -th level
When the third amplification factor is set in the digital amplifier by the gain setting unit when it is larger than the threshold value of, the A / D converter is a value at which the saturation operation does not occur, and the first threshold value is When the signal level of the digital signal is smaller than the first threshold value and the second gain is set in the digital amplifier by the gain setting unit, the A / D converter has a value that does not cause a saturation operation. There is.

According to the invention of claim 8, since the respective threshold values are set as described above, the saturation period of the A / D converter can be shortened, and the S / N ratio of the received signal becomes advantageous, resulting in a bit error rate. Can be suppressed.

According to a ninth aspect of the present invention, in the automatic gain control circuit according to the first or second aspect, the maximum value of the gain of the gain control amplifier and the smoothed signal by the control signal generating means. The signal level determiner further includes maximum gain detection means for detecting whether or not the gain of the gain control amplifier reaches a maximum value by comparing with a difference signal or the initial value. And the signal level of the digital signal output from the A / D converter is compared, and the gain setting section detects that the gain of the gain control amplifier has the maximum value by the maximum gain detecting means. Further, when the signal level determiner determines that the signal level of the digital signal is smaller than the first threshold value, the digital amplifier detects the digital level. It shall set fourth amplification factor of raised than the current amplification factor of the width unit.

According to the ninth aspect of the present invention, the maximum gain detecting means detects whether or not the gain of the gain control amplifier reaches the maximum value, and the signal level judging device detects the digital signal from the A / D converter. If the signal level is smaller than the first threshold and the gain of the gain control amplifier is maximum, the gain setting unit compares the level with the first threshold and
The value with the increased amplification factor is set in the digital amplifier. Therefore, even when the signal level of the received signal is weak and the gain control amplifier has the maximum gain, control that can follow the level fluctuation of the received signal becomes possible.

According to a tenth aspect of the present invention, in the automatic gain control circuit according to the ninth aspect, the initial value control unit detects that the gain of the gain amplifier has a maximum value by the maximum gain detection means. And the signal level determiner determines that the signal level of the digital signal is smaller than the first threshold value, an initial value corresponding to the fourth amplification factor set by the gain setting unit. Is set in the control signal generating means.

According to a tenth aspect of the present invention, in the automatic gain control circuit according to the ninth aspect, the first threshold is such that the signal level of the digital signal is smaller than the first threshold and the maximum value is the maximum. If the gain setting unit sets the fourth amplification factor in the digital amplifier when the gain of the gain amplifier is not detected to be the maximum value, the A / D converter operates in saturation. Shall be a value that does not.

According to a twelfth aspect of the present invention, in the automatic gain control circuit according to any one of the first to eleventh aspects, the signal level determiner determines the A / A ratio within a predetermined time.
The signal level of the digital signal from the D converter is determined by measuring the number of times the digital signal exceeds a predetermined reference value.

According to the twelfth aspect of the invention, the signal level can be determined with a simple circuit configuration.

According to a thirteenth aspect of the present invention, in the automatic gain control circuit according to any one of the first to eleventh aspects, the signal level determiner uses the gain setting unit to set the predetermined level of the digital amplifier. The signal level of the digital signal is not judged for a predetermined time after the setting of the amplification factor is changed.

According to the thirteenth aspect of the present invention, since the signal level is not judged for a predetermined period after the setting of the amplification factor of the digital amplifier is changed, the signal level judgment which occurs when the amplification factor is sharply changed. It is possible to prevent erroneous setting of the amplification factor due to erroneous determination of the container.

According to a fourteenth aspect of the present invention, in the automatic gain control circuit according to any one of the second to eleventh aspects, the initial value control unit controls the gain of the gain control amplifier with respect to the control signal. Considering the characteristics, the predetermined initial value is set in the control signal generating means.

According to the fourteenth aspect of the present invention, since the setting of the initial value can be changed in the control signal generating means in accordance with the gain characteristic with respect to the control signal in the gain control amplifier, it is possible to shorten the convergence time of the automatic gain control. To do.

Further, in order to solve the above-mentioned problems, in the automatic gain control method according to the fifteenth aspect, the received signal amplified or attenuated by the gain based on the control signal in the amplification step for gain control is A / D conversion step. The signal, which has been converted into a digital signal in the above step, and in which unnecessary components have been removed from the digital signal, is amplified by a predetermined amplification factor in the digital amplification step, and the signal level after the amplification and a predetermined reference value are set in the control signal generation step. An automatic gain control method of smoothing the differential signal of the control signal in the gain control amplification step, the signal level determination step of determining the signal level of the digital signal, and the signal level determination step of determining the signal level of the digital signal. The predetermined level in the digital amplification step based on the signal level. In which and a gain setting step of setting the width ratio.

According to a sixteenth aspect of the present invention, in the automatic gain control method according to the fifteenth aspect, a predetermined initial value corresponding to the predetermined amplification factor set in the gain setting step is set to the control signal generating step. Further comprising an initial value control step, wherein the control signal generating step smoothes the initial value given by the initial value control step as the control signal in the gain control amplifying step, and after a predetermined time elapses, The differential signal is smoothed and used as the control signal in the gain control amplification step.

The invention according to claim 17 is the automatic gain control method according to claim 15 or 16, wherein the signal level determining step includes a first threshold value and a second threshold value larger than the first threshold value. Each of the threshold values is compared with the signal level of the signal converted into the digital signal in the A / D conversion step, and the gain setting step is performed when the signal level of the digital signal is higher than the second threshold value. When the first amplification rate which is higher than the current amplification rate of the digital amplification step is set as the predetermined amplification rate in the digital amplification step, and the signal level of the digital signal is smaller than the first threshold value , Lower than the current amplification factor of the digital amplification step as the predetermined amplification factor in the digital amplification step It shall be set a second amplification factor.

The invention of claim 18 is the automatic gain control method according to claim 17, wherein in the initial value control step, the gain setting is performed when the signal level of the digital signal is larger than the second threshold value. An initial value corresponding to the first amplification factor set by the step is given to the control signal generating step, and when the signal level of the digital signal is smaller than the first threshold value, it is set by the gain setting step. An initial value corresponding to the second amplification factor is given to the control signal generating step.

According to a nineteenth aspect of the present invention, in the automatic gain control method according to the seventeenth aspect, when the signal level of the digital signal is larger than the second threshold value, the second threshold value is A. In the / D conversion step, it is determined that a saturation operation is occurring, and the first threshold value is set by the gain setting step when the signal level of the digital signal is smaller than the first threshold value. When the second amplification factor is set as the predetermined amplification factor in the digital amplification step, it is assumed that the saturation operation does not occur in the A / D conversion step.

Further, the invention of claim 20 is the automatic gain control method according to claim 15 or claim 16, wherein the signal level determining step includes threshold values from the first to the Kth (K is an integer of 3 or more). And the signal level of the signal converted into the digital signal in the A / D conversion step, and in the gain setting step, the signal level of the digital signal is i-th (i is 3 or more and K or less). If it is less than or equal to the (integer) threshold value and greater than the (i−1) th threshold value, the predetermined amplification factor in the digital amplification step corresponds to the i-th threshold value higher than the current amplification factor in the digital amplification step. The third amplification factor is set, and when the signal level of the digital signal is smaller than the first threshold value, the predetermined increase in the digital amplification step is performed. It shall be set a second amplification factor lower than the current amplification factor of the digital amplification step as a percentage.

Further, the invention of claim 21 is the automatic gain control method according to claim 20, wherein in the initial value control step, the signal level of the digital signal is equal to or lower than the i-th threshold value and the (i-1) th value is satisfied. Is greater than the threshold value of, an initial value corresponding to the third amplification factor set by the gain setting step is given to the control signal generating step,
When the signal level of the digital signal is smaller than the first threshold value, an initial value corresponding to the second amplification factor set by the gain setting step is given to the control signal generating step.

According to a twenty-second aspect of the present invention, in the automatic gain control method according to the twentieth aspect, among the first to Kth threshold values, the second to Kth threshold values are signals of the digital signal. If the level is equal to or lower than the i-th threshold value, the (i-
If the third amplification factor is set as the predetermined amplification factor in the digital amplification step by the gain setting step when it is larger than the threshold value of 1), the saturation operation does not occur in the A / D conversion step. If the signal level of the digital signal is smaller than the first threshold value, the first threshold value is set to the second amplification factor as the predetermined amplification factor in the digital amplification step by the gain setting step. When set, the saturation operation does not occur in the A / D conversion step.

The invention of claim 23 is the automatic gain control method according to claim 15 or claim 16, wherein the maximum value of the gain in the gain control amplification step and the control signal generation step are smoothed. The method further comprises a maximum gain detection step of detecting whether or not the gain in the gain control amplification step reaches a maximum value by comparing the differential signal or the initial value with the signal level determination step. The threshold value is compared with the signal level of the digital signal output from the A / D converter, and the gain setting step detects the maximum gain in the gain control amplification step by the maximum gain detection step. And the signal level of the digital signal is determined by the signal level determination step to be the first threshold value. If it is determined that remote small, establish a fourth amplification factor of raised than the current amplification factor of the digital amplification step as the predetermined amplification factor of the digital amplification step.

The invention of claim 24 is the automatic gain control method according to claim 23, wherein in the initial value control step, the gain in the gain control amplification step is maximized by the maximum gain detection step. Is detected, and when the signal level determination step determines that the signal level of the digital signal is smaller than the first threshold value, it corresponds to the fourth amplification factor set by the gain setting step. An initial value is given to the control signal generating step.

The invention of claim 25 is the automatic gain control method according to claim 23, wherein the first threshold value is such that the signal level of the digital signal is smaller than the first threshold value, and the maximum value. When the gain detection step does not detect that the gain in the gain amplification step reaches the maximum value, the gain setting step sets the fourth amplification rate as the predetermined amplification rate in the digital amplification step. It is assumed that the saturation operation does not occur in the A / D conversion step.

The invention of claim 26 is the automatic gain control method according to any one of claims 15 to 25, wherein the signal level determination step is performed by the A / D conversion step within a predetermined time. The signal level of the digital signal is determined by measuring the number of times the converted digital signal exceeds a predetermined reference value.

The invention of claim 27 is the automatic gain control method according to any one of claims 15 to 25, wherein the signal level determination step is the predetermined step in the digital amplification step by the gain setting step. A predetermined time after the setting of the amplification factor of is changed,
The signal level of the digital signal is not judged.

Further, the invention of claim 28 is the automatic gain control method according to any one of claims 16 to 25, wherein the initial value control step is a gain for the control signal in the amplification step for gain control. The predetermined initial value is given to the control signal generating step in consideration of the characteristics of.

According to the automatic gain control method according to any one of claims 15 to 28, the action can be obtained that corresponds to the automatic gain control circuit according to any one of claims 1 to 15.

[0053]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

The same or corresponding portions in the drawings referred to in each embodiment are designated by the same reference numerals, and the description thereof will not be repeated.

(First Embodiment) <When Received Signal Contains Interfering Waves in addition to Desired Wave>
FIG. 1 is a block diagram showing a configuration example of an automatic gain control circuit of the present invention in the first embodiment.

The automatic gain control circuit shown in FIG. 1 comprises a gain control amplifier 1 for amplifying or attenuating a received signal, and an A / D.
A converter 2, a digital filter 3 that removes unnecessary signal components from the received signal and passes only the received channel signal, a signal level detector 4 that detects the signal level of the received channel, a reference value 6 from the detected signal level. And a D / A converter 8 (included in the control signal generating means) for outputting a control signal to the gain control amplifier 1 are included. . The reference value 6 means a desired signal level value as the signal level of the reception channel signal, and does not mean a specific value.

Further, the automatic gain control circuit shown in FIG.
It is within a predetermined setting range by measuring the signal level of the digital amplifier 9 which amplifies the reception channel signal with a predetermined amplification factor set and the signal obtained by converting the reception signal into a digital signal by the A / D converter 2. A signal level determiner 10 for determining whether or not the gain setting unit 11A sets a predetermined amplification factor of the digital amplifier 9 based on the determination result of the signal level determiner 10, and an amplification factor set by the gain setting unit 11A. An initial value control unit 12 that outputs an initial value corresponding to the change amount, a loop filter 13 (included in the control signal generating means) that has a function of smoothing the subtraction result from the subtractor 5 and setting the initial value. Is further included.

The specific operation of the automatic gain control circuit shown in FIG. 1 will be described below.

First, the received signal is amplified or attenuated by the gain control amplifier 1 with a gain based on the control signal, and A / A
It is converted into a digital signal by the D converter 2. The received signal converted into a digital signal is band-limited by the digital filter 3 to remove interfering waves existing in the vicinity of the receiving channel included in the received signal and to prevent intersymbol interference of the digital signal. The digital amplifier 9 amplifies the output from the digital filter 3 and outputs it as a reception channel signal. Signal level detector 4
Detects the signal level of the reception channel signal and inputs the result to the subtractor 5. The subtractor 5 subtracts the reference value 6 from the detected signal level of the reception channel signal, and outputs the difference as a difference signal. Then, the loop filter 13 smoothes the difference signal and outputs it to the D / A converter 8, and the D / A converter 8 converts the output from the loop filter 13 into an analog signal, and a gain control amplifier as a control signal. Output to 1. The gain control amplifier 1 controls the gain for the received signal based on the control signal.

Further, the signal level judging device 10 is
It is determined whether the signal level of the digital signal from the converter 2 is within a predetermined setting range. The gain setting unit 11A inputs the determination result of the signal level determiner 10 and sets the amplification factor of the digital amplifier 9. Further, the initial value control unit 12 sets an initial value in the loop filter 13 based on the set amplification factor.

Here, when the signal level of the reception channel signal is lower than the reference value 6, a control signal for increasing the gain in the gain control amplifier 1 is generated from the D / A converter 8, so that the gain control amplifier is generated. 1 operates to increase the gain of the received signal. When the signal level of the reception channel signal is lower than the reference value 6, the D / A converter 8 generates a control signal for reducing the gain in the gain control amplifier 1, so that the gain control amplifier 1 receives the reception signal. It works to reduce the gain of.

FIG. 2 is a block diagram showing a configuration example of the signal level determiner 10, the gain setting unit 11A, and the initial value control unit 12.

First, in the signal level judging device 10,
A first threshold value and a second threshold value larger than the first threshold value are set in advance, and the signal level of the digital signal from the A / D converter 2 is compared with these threshold values. And
The second threshold value is set to a value at which the input end of the A / D converter 2 is determined to be in a saturation operation when the signal level of the received signal is higher than this value. Further, when the signal level of the received signal is smaller than this value, the first threshold value is set to a value at which the input end of the A / D converter 2 does not perform the saturation operation even if the amplification factor of the digital amplifier 9 is lowered by one step. It is set.

More specifically, for example, the signal level judging device 10 includes two comparators 10a and 10b,
The comparator 10a compares the second threshold with the signal level of the digital signal, and the comparator 10b compares the first threshold with the signal level of the digital signal. At this time, the comparator 10
As the output x from a, 0 is output when the signal level is equal to or lower than the second threshold value, and 1 is output when the signal level is higher than the second threshold value. The output y from the comparator 10b is the first
If it is equal to or more than the threshold value of 1, 1 is output, and if it is smaller than the first threshold value, 0 is output. That is, as a combination of x and y, it means that the signal level is smaller than the first threshold value when y = 0 is output at x = 0, and when y = 1 is output at x = 1. It means that the signal level is higher than the second threshold value, and when y = 0 is output at x = 0, it means that the signal level is in the range above the first threshold value and below the second threshold value. ing.

When it is determined that the signal level measured by the signal level determiner 10 is larger than the second threshold, the gain setting section 11A sets the amplification factor of the digital amplifier 9 to the maximum settable amplification factor. Set. On the other hand, when it is determined that it is smaller than the first threshold value, the amplification factor of the digital amplifier 9 is lowered by one step from the current set value. If the signal level is between the first threshold value and the second threshold value, the current set value is held. Note that, here, the case where the signal level is determined to be higher than the second threshold value and the amplification factor of the digital amplifier 9 is set to the maximum configurable amplification factor is described, but the present embodiment is not limited to this. The present invention is not limited to this, and can be similarly implemented even when the amplification factor is increased to a certain amplification factor.

More specifically, for example, the gain setting unit 1
1A is a selector 11a, a register 11b, a ΔA detector 1
1c is provided. Then, the selector 11a sets y when x = 1.
If = 1 is input, the maximum value of the amplification factor Amax (corresponding to the first amplification factor) is input. If y = 0 is input at x = 0, the amplification factor An-1 (the first amplification factor An-1) which is one step lower than the current amplification factor An (Corresponding to the amplification factor of 2) is input to y = 1 with x = 0, the current amplification factor An is output to the digital amplifier 9 via the register 11b as the amplification factor to be set next. The gain setting unit 11A further calculates the amount of change in the amplification factor and outputs the calculated value to the initial value control unit 12, the specific operation of which will be described later.

By doing so, when there is an interfering wave of higher power than the desired wave in the channel adjacent to the receiving channel and the interfering wave is received together with the desired wave, the signal level judging device When it is determined by 10 that the signal level exceeds the second threshold value and the input end of the A / D converter 2 is in saturation operation, the gain setting unit 11 sets the maximum amplification factor of the digital amplifier 9 that can be set. Set to the amplification factor of. Further, as the output from the A / D converter 2, only the desired wave from which the interfering wave has been removed by the digital filter 3 is output, and the desired wave is amplified by the digital amplifier 9 at the maximum amplification factor and the received channel signal is obtained. Is output as. Then, based on the signal level of this amplified desired wave, the signal level detector 4, the subtractor 5, the loop filter 13, D
When the gain in the gain control amplifier 1 is controlled via the / A converter 8, the signal level at the input end of the A / D converter 2 is attenuated by the reciprocal of the amplification factor of the digital amplifier 9. , The saturation operation of the A / D converter 2 can be eliminated.

Considering the next stage, since the signal level at the input end of the A / D converter 2 is attenuated to 1 / amplification rate by setting the amplification rate of the digital amplifier 9 to the maximum, When it is determined by 10 that the signal level of the digital signal from the A / D converter 2 is lower than the first threshold value, the gain setting unit 11 lowers the amplification factor of the digital amplifier 9 by one step from the current setting value. .
In the next step, the signal level at the input end of the A / D converter 2 is amplified by lowering the amplification factor of the digital amplifier 9 by one step, but the signal level of the digital signal from the A / D converter 2 is When it is determined that the threshold value of 1 is small, the gain setting unit 11 further lowers the amplification factor of the digital amplifier 9 by one step from the current setting value. Repeating in this way, when the output signal level of the A / D converter 2 finally falls between the first threshold value and the second threshold value, the amplification factor of the digital amplifier 9 is held. Will be done.

Now, consider the power-to-noise power ratio (S / N ratio) of the digital signal from the A / D converter 2. Generally, the S / N ratio is bad if the signal level is low, and the A / N ratio is
Since the deterioration occurs when the input end of the D converter 2 is saturated, the S / N ratio is the best if the signal level is increased in a range where the input end is not saturated. Further, the bit error rate in digital communication is closely related to the S / N ratio, and there is a characteristic that the bit error rate deteriorates when the S / N ratio decreases. Therefore, in the present embodiment, the state where the amplification factor of the digital amplifier 9 is finally held is because the input signal level is high within the range where the input terminal of the A / D converter 2 is not saturated. It is possible to suppress deterioration of the bit error rate because the / N ratio becomes the best value.

Further, another configuration example of the above-mentioned signal level judging device 10 will be described. As threshold values for determining the signal level, K kinds of threshold values from the first threshold value to the Kth threshold value (K is an integer of 3 or more) are set, and the amplification factor of the digital amplifier 9 corresponding to each threshold value is set in advance. . When the signal level is lower than the first threshold value or higher than the second threshold value, the signal level among the second to Kth threshold values is i-th (i is It is determined that it is in the range greater than or equal to 3 and less than or equal to K and less than the (i-1) th threshold. Here, when the signal level exceeds the second threshold value and is equal to or lower than the third threshold value, if the amplification factor of the digital amplifier 9 is raised by one step from the current set value (corresponding to the third amplification factor), A / When the input end of the D converter 2 is set to a value that does not cause the saturation operation and exceeds the third threshold value and is equal to or less than the fourth threshold value, if the amplification factor of the digital amplifier 9 is increased by two steps from the current setting value. The input terminal of the A / D converter 2 (corresponding to the third amplification factor) is set to a value at which the saturation operation does not occur, and similarly, the input terminal of the A / D converter 2 exceeds the (K-1) th threshold value and is equal to or less than the Kth threshold value. In this case, if the amplification factor of the digital amplifier 9 is increased by (K-1) steps from the current set value (the third value).
The input terminal of the A / D converter 2 (corresponding to the amplification factor of 1) is set to a value at which saturation operation does not occur. The first threshold value is A / even if the amplification factor of the digital amplifier 9 is lowered by one step.
The input end of the D converter 2 is set to a value that does not cause saturation operation.

As described above, the signal level judging device 10
The signal level of the digital signal from the / D converter 2 is the second
It is determined that the input terminal of the A / D converter 2 is in a saturation operation by exceeding the threshold of, and the signal level of the digital signal of the A / D converter 2 falls between which threshold and which threshold. To judge. For this reason, the gain setting unit 11 can optimally set the amplification factor of the digital amplifier 9 according to the signal level of the digital signal from the A / D converter 2, so that the gain level of the signal level equivalent to the reference value of the reception channel signal is set. The reception channel signal can be obtained instantaneously. As a result, the saturation operation at the input end of the A / D converter 2 can be prevented quickly, and the state with the best S / N ratio can be quickly set.

Further, the signal level judging device 10 described above is
As a method of determining the signal level of the digital signal from the A / D converter 2, the following determination can be made. That is, the signal level determiner 10 is the A / D converter 2
By monitoring the value of the output signal of and counting the number of times exceeding the preset determination value within the preset time, the signal level can be determined according to the counted value. If the gain setting unit 11A sets the amplification factor according to the measured signal level, the signal level is determined by a simple circuit configuration without determining the signal level by comparison with each threshold value. be able to.

Next, the operation of the initial value controller 12 will be described.

First, the gain setting unit 11A calculates the amount of change in the amplification factor and outputs it to the initial value control unit 12. For example, as shown in FIG. 2, the ΔA detector 11C in the gain setting unit 11B outputs A. By calculating ₂ / A ₁ , the change in amplification factor ΔA
Is output to the initial value control unit 12.

The initial value control unit 12 includes a gain setting unit 11A.
Input the change amount ΔA of the amplification factor of the digital amplifier 9 and store a value based on a preset mathematical expression to be described later in the memory, and the change amount ΔD of the control value corresponding to the input change amount ΔA of the amplification factor. Loop filter 1 with initial value
Set to 3. The reason for doing this is as follows. That is, when the amplification factor of the digital amplifier 9 is increased, the gain in the gain control amplifier 1 is decreased by the increase amount of the amplification factor, and when the amplification factor of the digital amplifier 9 is decreased, the amplification factor is increased. The gain in the gain control amplifier 1 increases by the decrease in the rate. The amplification factor of the digital amplifier 9 is instantly changed by the setting of the gain setting unit 11, but the gain control amplifier 1
A loop delay is caused in the gain in 1 by a loop that controls the gain via the signal level detector 4, the subtractor 5, the loop filter 13, and the D / A converter 8. Therefore, in order to reduce this loop delay, the initial value control unit 12 changes the gain change in the gain control amplifier 1 corresponding to the change in the amplification factor of the digital amplifier 9 to the loop filter 13.
Given as an initial value to. The initial value control unit 12 changes the setting of the initial value in the loop filter 13 every time the gain setting unit 11A changes the setting of the amplification factor of the digital amplifier 9. The selector in FIG. 3 can receive the control signal from the outside which indicates the change of the setting of the amplification factor.

Then, the gain controlling amplifier 1 controls the gain of the received signal by the control signal based on the initial value sequentially given by the loop filter 13, and after a lapse of a predetermined time, the difference signal from the subtractor 5 is obtained. Based on the control signal, the gain of the received signal is controlled. The selector in the loop filter 13 also performs such control switching according to the control signal. For example, a control signal can be output so that the control is switched after the lapse of the time by externally measuring the time corresponding to the loop delay as the predetermined time.

Now, the relationship between the gain change amount of the digital amplifier 9 and the gain change amount of the gain control amplifier 1 will be described with reference to the following mathematical expressions.

FIG. 3 is a diagram showing the gain characteristic of the gain control amplifier 1 with respect to the control signal.

The figure shows a case where the decibel value of the gain is proportional to the control signal. The relationship between control signal and gain is

[0080]

[Equation 1]

It is represented by

In the first state, the amplification factor of the digital amplifier 9 is set to A ₁ times, the value of the control signal input to the gain control amplifier 1 is D ₁ , and the gain control in this case is controlled. It is assumed that the gain in the amplifier 1 is G ₁ . Then, consider a case where the amplification factor of the digital amplifier 9 is changed to A ₂ times according to the determination result of the signal level determiner 10. The change amount ΔA of the amplification factor of the digital amplifier 9 is

[0083]

[Equation 2]

From this, the gain variation ΔG of the gain control amplifier 1 is

[0085]

[Equation 3]

It becomes Based on this gain change amount ΔG, the gain G ₂ in the gain control amplifier 1 after the amplification factor of the digital amplifier 9 is changed to A ₂ times is

[0087]

[Equation 4]

It can be predicted that the value of the control signal D _{2 at} this time is

[0089]

[Equation 5]

It can be obtained by Further, the control value change amount ΔD corresponding to the gain change amount ΔG is

[0091]

[Equation 6]

It can be obtained by Therefore, when the gain setting unit 11A changes the setting of the amplification factor of the digital amplifier 9, the initial value control unit 12 loops the control value change amount ΔD corresponding to the gain change amount ΔG in the gain control amplifier 1 by the loop filter. It is given as an initial value of 13. Therefore, the loop delay described above can be reduced.

Another configuration example of the initial value control unit 12 will be described with reference to FIG.

FIG. 4 is a diagram showing another gain characteristic of the gain control amplifier 1 with respect to the control signal.

Generally, in order to obtain a wide range of gain control, a plurality of gain control amplifiers 1 can be cascade-connected in multiple stages. At this time, if the gain characteristics of the gain control amplifiers 1 with respect to the control signal are different, as shown in FIG. 3, the gain decibel value is not proportional to the control signal.

In such a case, the initial value control unit 12 can be realized by storing the control signal and the slope indicating the gain characteristic of the gain control amplifier 1 at that time in the memory. That is, for example, the gain characteristic of the gain control amplifier 1 is monitored by an external device, and the initial value control unit 12
The value of the control signal is used as an address in the internal memory, and the slope of the gain characteristic of the gain control amplifier 1 corresponding to the address is stored. Then, by substituting the slope of the gain characteristic into the constant α of Equation 1 above, the control value change ΔD corresponding to the gain change ΔG in the gain control amplifier 1 given to the loop filter 13 is approximately obtained. You can

Similarly to the above, in the first state, the amplification factor of the digital amplifier 9 is set to A ₁ times,
The value of the control signal in the gain control amplifier 1 is D ₁ , and the gain in the gain control amplifier 1 in that case is G ₁
Suppose Then, consider a case where the amplification factor of the digital amplifier 9 is changed to A ₂ times according to the determination result of the signal level determiner 10. The change ΔA in the amplification factor of the digital amplifier 9 can be obtained by the equation 2, and the gain change ΔG in the gain control amplifier 1 can be obtained by the equation 3 in the same manner as described above. Then, the control value change amount ΔD corresponding to the gain change amount ΔG can be approximately obtained by substituting the slope of the gain characteristic into the constant α in the equation (6).

FIG. 5 is a diagram showing a transient response of a control signal in the gain control amplifier 1 when the initial value is set in the loop filter 13 by the initial value control unit 12.

As the first state, a gain control amplifier is used.
The value of the control signal of 1 is D₁Suppose After that, time T₁
When the amplification factor of the digital amplifier 9 is changed in
The initial value is set in the loop filter 13, and the gain control gain is increased.
The value of the control signal of width 1 is D ₂Controlled to be.
Also, time T₂The amplification factor of the digital amplifier 9 is
When changed, the initial value is set in the loop filter 13.
And the value of the control signal of the gain control amplifier 1 is D₃Will be
Controlled.

At the instant when the initial value is set in the loop filter 13 at time T ₁ or T ₂ , the gain in the gain control amplifier 1 is momentarily high due to the abrupt change in the value of the control signal. Therefore, the value of the control signal may oscillate for a while thereafter. Since this oscillation changes the gain in the gain control amplifier 1, the signal level determiner 10 caused by this gain change is generated.
It is necessary to avoid erroneous judgment of. Therefore, the signal level determiner 10 controls the gain control amplifier 1 after the gain setting unit 11A changes the setting of the amplification factor of the digital amplifier 9, that is, after the loop filter 13 is set to the initial value. The digital signal level from the A / D converter 2 is not judged for a predetermined time until the vibration of the value of is eliminated. For example, by presetting a predetermined time until the vibration corresponding to the control value change ΔD disappears, the signal level determiner 10 can prevent the signal level from being determined for this predetermined time. it can. As a result, it is possible to avoid erroneous determinations in the signal level determiner 10 caused by a sudden gain change, and prevent erroneous gain setting in the gain setting unit 11A.

(Second Embodiment) <When Received Signal has Weak Power> FIG. 6 is a block diagram showing a configuration example of an automatic gain control circuit according to the present invention in a second embodiment.

The automatic gain control circuit shown in FIG. 6 includes, in addition to the components included in the automatic gain control circuit shown in FIG. 1, whether the output from the loop filter 13 exceeds the maximum value of the gain of the gain control amplifier 1. It further includes maximum gain detection means 14 for detecting whether or not it is.

Now, even when the signal level of the reception signal input to the gain control amplifier 1 is weak power, it is output as a reception channel signal through the A / D converter 2, the digital filter 3, and the digital amplifier 9. It Furthermore, the signal level detector 4, the subtractor 5, the loop filter 13, D /
The gain in the gain control amplifier 1 is controlled via the A converter 8. When the received signal has weak power, the automatic gain control circuit operates so that the gain of the gain control amplifier 1 is increased and the signal level of the received channel signal becomes the reference value 6. At this time, the maximum gain detection means 14 is preset with a value corresponding to the maximum gain of the gain control amplifier 1, and when the output of the loop filter 13 exceeds this set value, the gain in the gain control amplifier 1 is increased. Is detected to be the maximum value, and the detection result is input to the gain setting unit 11B. Then, when it is determined by the signal level determiner 10 that the signal level of the digital signal from the A / D converter 2 is smaller than the first threshold value, and the maximum gain detection means 14 is used in the gain control amplifier 1. When the gain is the maximum value, the gain setting unit 11B sets the amplification factor of the digital amplifier 9 (corresponding to the fourth amplification factor) which is one step higher than the current setting value in the digital amplifier 9.

When the signal level of the received signal is weak power, it is detected by the maximum gain detecting means 14 that the gain of the gain controlling amplifier 1 reaches the maximum value, and the maximum value of the gain of the gain controlling amplifier 1 is detected. Even if the received signal is amplified, the signal level of the digital signal from the A / D converter 2 in the signal level determination unit 10 may be smaller than the first threshold value. In this way, when the gain in the gain control amplifier 1 has the maximum value and the signal level of the digital signal from the A / D converter 2 becomes smaller than the first threshold value, the gain setting unit 11B causes the digital amplifier 9 to operate. By increasing the amplification factor of by one step from the current setting value,
The reception channel signal output from the digital amplifier 9 is amplified.

Specific description will be made with reference to FIG.
That is, the gain setting unit 11B has the maximum gain detection means 14
When a signal indicating that the gain of the gain control amplifier 1 reaches a maximum value is received from the signal level control signal and a signal indicating that the signal level of the digital signal becomes smaller than the first threshold value is input from the signal level determination unit 10, the selector The amplification factor of An + 1, which is one step higher than the current amplification factor An, is selected by 11a and set in the digital amplifier 9. And this An +
Gain control is performed via the signal level detector 4, the subtractor 5, the loop filter 13, and the D / A converter 8 so that the signal level of the reception channel signal amplified by the amplification factor of 1 becomes the signal level of the reference value. The gain in the amplifier 1 is controlled.
That is, the maximum gain detecting means 14 detects that the gain controlling amplifier 1 has fallen below the maximum value of the gain, or the signal level judging device 10 detects that the signal level of the digital signal from the A / D converter 2 is the first value. The amplification factor of the digital amplifier 9 is increased step by step until it is determined that the threshold value is 1 or more. As a result, even if the signal level of the received signal is weak power, by amplifying the insufficient gain of the gain control amplifier 1 by the digital amplifier 9, it is possible to follow the level fluctuation of the received signal. It will be possible.

As described above, when the gain setting unit 11B sets the amplification factor An + 1, which is one step higher than the current amplification factor An, the initial value control unit 12 sets the ΔA in the gain setting unit 11B. The control value ΔD corresponding to the variation ΔA of the amplification factor obtained by calculating A ₂ / A ₁ by the detector 11C can be set in the loop filter 13 also in this embodiment.

Further, in the present embodiment, since it is assumed that the received signal has weak power, the case where the signal level judging device 10 judges using only the first threshold value has been described. Similar to the embodiment, the present embodiment can be implemented in the same manner even if the configuration is such that a second threshold larger than the first threshold and further K types of thresholds are used for the determination.

(Third Embodiment) <Automatic Gain Control Method-No. 1-> Hereinafter, an automatic gain control method in the automatic gain control circuit shown in the first embodiment will be described, but the above contents are assumed. And explain.

FIG. 8 is a flow chart for explaining an automatic gain control method for the automatic gain control circuit shown in FIG.

First, the gain control amplifier 1 amplifies or attenuates the received signal based on the control signal (corresponding to the gain control amplification step), and is converted into a digital signal in the A / D converter 2 (A / D). Corresponding to the D conversion step). The signal level determiner 10 is the A / D converter 2
The signal level P of the digital signal from is measured (step S1), and the signal level determiner 10 determines the signal level P from the second level.
Is compared with the threshold value K ₂ (step S2), and it is determined whether the input terminal of the A / D converter 2 is in the saturation operation (corresponding to the signal level determination step). In the digital amplification step, a signal from which unnecessary components have been removed from the digital signal from the A / D converter 2 is amplified based on the amplification factor set in the gain setting step described below.

When it is determined that the signal level P is higher than the second threshold value K ₂ (that is, the saturation operation is performed) (YES in step S2), the gain setting section 11A causes the digital amplifier 9 to operate in step S3. The gain A is set to the maximum gain Amax that can be set (corresponding to the gain setting step), and the initial value control unit 12 sets the gain of the digital amplifier 9 from the current set value An to the maximum gain Amax. A control value variation ΔD (obtained by the above-described mathematical expression) for the gain control amplifier 1 corresponding to the amplification factor variation ΔA when changing is given to the loop filter 13 as an initial value (corresponding to the initial value control step).

On the other hand, when it is determined that the signal level P is equal to or lower than the second threshold value K ₂ (no saturation operation is performed) (step S
NO 2), further in the step S4, corresponds to the signal level P and (signal level determination step of determining whether the first threshold value K ₁ and lower than the first threshold value K ₁ compares). Then, when it is determined that the signal level P is smaller than the first threshold value K ₁ (YES in step S4), the gain setting unit 11A sets the amplification factor A of the digital amplifier 9 from the current setting value An in step S5. The initial value control unit 12 changes the amplification factor of the digital amplifier 9 from the current setting value An to An-1 while setting it to An-1 which is lowered by one step (corresponding to the gain setting step). The control value change amount ΔD (determined by the above-described mathematical expression) corresponding to the amount ΔA is given to the loop filter 13 as an initial value (corresponding to the initial value control step).

Furthermore, step S3 or step S5
When setting the initial value to the loop filter 13 in
After the lapse of a predetermined time from the setting of the initial value until the oscillation of the value of the control signal in the gain control amplifier 1 disappears (step S6), the process returns to the first step S1. That is, the signal level determiner 10 newly determines the signal level P of the digital signal from the A / D converter 2 after a predetermined time has passed (step S1).

When it is determined that the signal level P is equal to or higher than the first threshold K ₁ (NO in step S4), in other words, the output signal level P of the A / D converter 2 is the first threshold K 1.
If it is within the range between ₁ and the second threshold value K ₂ , the first step S
Return to 1. That is, in this case, the gain setting unit 11A holds the current setting value An as it is.

FIG. 9 shows another configuration of the signal level determiner 10, in which the threshold for determining the signal level P is the first threshold K ₁
7 is a flowchart for explaining an automatic gain control method when using K types of threshold values from to Kth threshold value K _K. The description of the steps common to FIG. 8 will not be repeated.

In FIG. 9, the signal level judging device 10
And the signal level P is the second threshold value K ₂Greater than (satiated
When it is determined that the sum operation is performed (in step S12)
YES), in steps S13 to S16,
Further, the signal level P is the second threshold value K₂To the Kth threshold value K_K
Up to (the signal level
Corresponding to the judgment step). In step S14,
The signal level P is the (i + 1) th threshold value K_{i + 1}Is less than
If determined (YES in step S14), the gain setting
The constant section 11A sets the amplification factor A of the digital amplifier 9 to the current setting.
When set to An + i-1 which is (i-1) steps higher than the fixed value An
In both cases, the initial value controller 12 amplifies the digital amplifier 9.
Amplification when changing the rate from the current set value An to An + i-1
The control value change of the gain control amplifier 1 corresponding to the rate change ΔA
The fraction ΔD (which can be obtained by the above-mentioned mathematical expression)
It is given as an initial value to the loop filter 13 (step S
17). Then, the process proceeds to step S20. On the other hand, the signal level
Bell P is the second threshold K₂Below (saturation is not working)
If determined (NO in step S12), step S
The process from 18 to step S20 is the same as the process of FIG.
This is the same as the processing in steps S4 to S6.

(Fourth Embodiment) <Automatic Gain Control Method-Part 2-> An automatic gain control method in the automatic gain control circuit shown in the second embodiment will be described below. And explain.

FIG. 10 is a flow chart for explaining the automatic gain control method in the automatic gain control circuit shown in FIG.

First, the gain control amplifier 1 amplifies or attenuates the received signal based on the control signal (corresponding to the gain control amplification step) and is converted into a digital signal in the A / D converter 2 (A / D). Corresponding to the D conversion step). The signal level determiner 10 is the A / D converter 2
Signal level P of the digital signal from (step S21), the signal level determination device 10 compares the signal level P with the second threshold value K ₂ (step S22), and the input terminal of the A / D converter 2 It is determined whether or not the saturation operation is performed (corresponding to the signal level determination step). In the digital amplification step, a signal from which unnecessary components have been removed from the digital signal from the A / D converter 2 is amplified based on the amplification factor set in the gain setting step described below.

When it is determined that the signal level P is higher than the second threshold value K ₂ (saturation operation is being performed) (YES in step S22), the gain setting section 11B causes the digital amplifier 9 to operate in step S23. Is set to the maximum amplification rate Amax that can be set (corresponding to the gain setting step), and the initial value control unit 12
Is the gain change amount ΔA when the gain of the digital amplifier 9 is changed from the current set value An to the maximum gain Amax.
The control value variation ΔD of the gain control amplifier 1 (determined by the above-described mathematical expression) corresponding to the above is given to the loop filter 13 as an initial value (corresponding to the initial value control step).

On the other hand, when it is determined that the signal level P is equal to or lower than the second threshold value K ₂ (no saturation operation is performed) (step S
NO 22), further corresponding to the signal level P and (signal level determination step of determining whether the first threshold value K ₁ and lower than the first threshold value K ₁ by comparing in step S24).

Then, when it is determined that the signal level P is smaller than the first threshold value K ₁ (YES in step S24).
S), in step S25, the maximum gain detecting means 14
Determines whether the gain of the gain control amplifier 1 has the maximum value (corresponding to the maximum gain detection step). That is, the current output value Dn of the loop filter 13 and the preset value Dmax corresponding to the maximum value of the gain of the gain control amplifier 1 are compared (step S25), and the gain control amplifier 1 becomes the maximum gain. Determine whether or not. When the maximum gain is not detected (NO in step S25), the gain setting unit 11B sets the amplification factor of the digital amplifier 9 to An-1 which is one step lower than the current setting value An (gain setting in step S26). (Corresponding to the step), the initial value control unit 12 changes the amplification factor ΔA when the amplification factor of the digital amplifier 9 is changed from An to An-1.
The control value variation ΔD of the gain control amplifier 1 (determined by the above-described mathematical expression) corresponding to the above is given to the loop filter 13 as an initial value (corresponding to the initial value control step).

On the other hand, when the maximum gain is detected in step S25 (YES in step S25), the gain setting unit 11B raises the amplification factor of the digital amplifier 9 by one step from the current setting value An in step S27. 1
(Corresponding to the gain setting step), the initial value control unit 12 controls the gain of the digital amplifier 9 corresponding to the gain change amount ΔA when the current set value An is changed to An + 1. The control value change ΔD of the operational amplifier 1 (obtained by the above-mentioned mathematical expression) is given to the loop filter 13 as an initial value (corresponding to the initial value control step).

Furthermore, step S23 or step S
26 or the loop filter 13 in step S27.
When the initial value is set to, after the predetermined time elapses from the setting of the initial value until the oscillation of the value of the control signal in the gain control amplifier 1 disappears (step S6), the process returns to the first step S21. Become. That is, the signal level determiner 10 newly determines the signal level P from the A / D converter 2 after a predetermined time has elapsed (step S
1).

When it is determined that the signal level P is equal to or higher than the first threshold value K ₁ (NO in step S24), in other words, the output signal level P of the A / D converter 2 is equal to the first threshold value K ₁ . If it is within the range of the second threshold value K _2, the process returns to the first step S21. That is, in this case, the gain setting unit 11A holds the current amplification factor An as it is.

Further, in the present embodiment, the case where the signal level P is larger than the second threshold value K ₂ and the gain setting section 11B sets the maximum amplification rate Amax at which the amplification rate of the digital amplifier 9 can be set will be described. However, after determining that it is larger than the second threshold value K ₂ as shown in FIG. 9,
The present invention can be similarly implemented even when the steps corresponding to steps S14 to S16 shown in FIG. 9 are inserted between steps S22 and S23 shown in FIG.

In all of the above embodiments, the amplification rate is increased or decreased step by step. However, the present invention is not limited to step by step, for example, two or three steps. It is needless to say that the present invention can be similarly implemented by moving up and down by predetermined steps such as.

[0128]

As described above, according to the present invention, in the case where the received signal includes the desired wave and the adjacent high-power disturbing wave, the disturbing wave causes a disturbance at the input end of the A / D converter. The saturation period is reduced to maintain good reception characteristics. As a result, it is possible to suppress deterioration of the bit error rate in digital communication.

Further, according to the present invention, when the received signal has weak power, it is possible to follow the level fluctuation of the received signal even when the gain control amplifier has a maximum amplification factor or more.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an automatic gain control circuit according to a first embodiment.

FIG. 2 is a signal level determiner 10 and a gain setting unit 11
FIG. 3 is a diagram showing an internal configuration example of A, an initial value control unit 12, and a loop filter 13.

FIG. 3 is a diagram showing gain characteristics of a gain control amplifier 1 with respect to a control signal.

FIG. 4 is a diagram showing another gain characteristic with respect to a control signal of the gain control amplifier 1.

FIG. 5 is a diagram showing a transient response of a control signal of the gain control amplifier 1.

FIG. 6 is a block diagram showing a configuration of an automatic gain control circuit according to a second embodiment.

FIG. 7 is a diagram illustrating an internal configuration example of a gain setting unit 11B.

FIG. 8 is a flowchart illustrating an automatic gain control method according to a third embodiment.

FIG. 9 is a flowchart for explaining another automatic gain control method in the third embodiment.

FIG. 10 is a flowchart for explaining an automatic gain control method in the fourth embodiment.

FIG. 11 is a block diagram showing a configuration example of a conventional automatic gain control circuit.

[Explanation of symbols]

1 Gain Control Amplifier 2 A / D Converter 3 Digital Filter 4 Signal Level Detector 5 Subtractor (Included in Control Signal Generation Means) 6 Reference Value 7 Loop Filter 8 D / A Converter (Included in Control Signal Generation Means 9 digital amplifier 10 signal level determiners 11A, 11B gain setting section 12 initial value control section 13 loop filter (included in control signal generating means) 14 maximum gain detecting means 15 signal level determiners S2, S4, S12, S18 , S22, S24 Signal level determination steps S3, S5, S17, S19, S23, S26, S27
Gain setting step and initial value control step S25 Maximum gain detection step

Claims (28)

[Claims] 1. A gain control amplifier for amplifying or attenuating a reception signal with a gain based on a control signal, and an A / D converter for converting the reception signal amplified or attenuated by the gain control amplifier into a digital signal. A signal level determiner for determining the signal level of the digital signal output from the A / D converter, a digital filter for removing unnecessary components from the digital signal output from the A / D converter, A digital amplifier that amplifies the signal output from the digital filter with an amplification factor of, and a gain setting unit that sets the predetermined amplification factor in the digital amplifier based on the signal level determined by the signal level determiner. A signal level detector for detecting the signal level of the signal output from the digital amplifier, Control signal generating means for smoothing a difference signal according to the difference between the signal level detected by the signal level detector and a predetermined reference value, and outputting it as the control signal to the gain control amplifier. Automatic gain control circuit. 2. The automatic gain control circuit according to claim 1, wherein a predetermined initial value corresponding to the predetermined amplification factor set by the gain setting unit is set in the control signal generating means. Further, the control signal generating means smoothes the initial value set by the initial value control unit and outputs it to the gain control amplifier as the control signal, and smoothes the difference signal after a predetermined time elapses. An automatic gain control circuit, which outputs the control signal to the gain control amplifier. 3. The automatic gain control circuit according to claim 1, wherein the signal level determiner includes a first threshold value and a second threshold value larger than the first threshold value, and the A / A ratio. The gain setting unit compares the signal level of the digital signal output from the D converter with the current level of the digital amplifier when the signal level of the digital signal is larger than the second threshold value. Is set to a first amplification factor higher than the amplification factor of, and when the signal level of the digital signal is smaller than the first threshold value, the digital amplifier is controlled to have a first amplification factor lower than the current amplification factor of the digital amplifier. An automatic gain control circuit characterized by setting an amplification factor of 2. 4. The automatic gain control circuit according to claim 3, wherein when the signal level of the digital signal is larger than the second threshold, the initial value control unit sets the first value set by the gain setting unit. An initial value corresponding to an amplification factor of 1 is set in the control signal generating means, and when the signal level of the digital signal is smaller than the first threshold value, the second amplification factor set by the gain setting unit. The automatic gain control circuit is characterized in that an initial value corresponding to is set in the control signal generating means. 5. The automatic gain amplifier according to claim 3, wherein the second threshold value causes the A / D converter to perform a saturation operation when the signal level of the digital signal is higher than the second threshold value. The first threshold value is a value that is determined to be caused, and the first threshold value is used by the gain setting unit to cause the digital amplifier to perform the second amplification when the signal level of the digital signal is smaller than the first threshold value. If you set the rate, A /
An automatic gain control circuit characterized in that the D converter has a value that does not cause a saturation operation. 6. The automatic gain control circuit according to claim 1 or 2, wherein the signal level determiner determines each of the threshold values from a first to a Kth (K is an integer of 3 or more) and the A / D. The gain setting unit compares the signal level of the digital signal output from the converter, and the gain setting unit determines that the signal level of the digital signal is equal to or less than an i-th threshold (i is an integer of 3 or more and K or less). -1) is larger than the threshold value, the third amplification factor corresponding to the i-th threshold value which is higher than the current amplification factor of the digital amplifier is set in the digital amplifier, and the signal level of the digital signal is set. An automatic gain control circuit, wherein when it is smaller than the first threshold value, a second amplification factor lower than a current amplification factor of the digital amplifier is set in the digital amplifier. 7. The automatic gain control circuit according to claim 6, wherein the initial value control unit, when the signal level of the digital signal is equal to or lower than the i-th threshold value and higher than the (i−1) th threshold value, An initial value corresponding to the third amplification factor set by the gain setting unit is set in the control signal generating means, and when the signal level of the digital signal is smaller than the first threshold value, the gain setting unit An automatic gain control circuit, wherein an initial value corresponding to the second amplification factor set by the above is set in the control signal generating means. 8. The automatic gain control circuit according to claim 6, wherein the second to the Kth thresholds among the first to Kth thresholds are selected.
When the signal level of the digital signal is less than or equal to the i-th threshold value and greater than the (i-1) th threshold value, the gain setting unit sets the third amplification factor to the digital amplifier. , The A / D converter is a value that does not perform a saturation operation, and the first threshold is set to the digital amplifier by the gain setting unit when the signal level of the digital signal is smaller than the first threshold. When the second amplification factor is set, the A /
An automatic gain control circuit characterized in that the D converter has a value that does not cause a saturation operation. 9. The automatic gain control circuit according to claim 1, wherein the maximum value of the gain of the gain control amplifier and the difference signal or the initial value smoothed by the control signal generating means. Further comprising maximum gain detection means for detecting whether or not the gain of the gain control amplifier has a maximum value, wherein the signal level determiner has a first threshold value and the A / D converter. Comparing the signal level of the digital signal output from the gain setting unit, the gain setting unit detects that the gain of the gain control amplifier has a maximum value, and the signal level determiner. When it is determined that the signal level of the digital signal is smaller than the first threshold value by the digital amplifier, the current amplification factor of the digital amplifier is added to the digital amplifier. Automatic gain control circuit and sets a fourth amplification factor of the raised remote. 10. The automatic gain control circuit according to claim 9, wherein in the initial value control unit, the maximum gain detection unit detects that the gain of the gain control amplifier has a maximum value, and When the level determiner determines that the signal level of the digital signal is lower than the first threshold value, the control signal generating means sets the initial value corresponding to the fourth amplification factor set by the gain setting unit. An automatic gain control circuit characterized by setting to. 11. The automatic gain control circuit according to claim 9, wherein the first threshold is such that the signal level of the digital signal is smaller than the first threshold, and the maximum gain detecting means controls the gain gain. When it is not detected that the gain of the amplifier reaches the maximum value, the gain setting unit sets the fourth amplification factor in the digital amplifier, and the A / D converter has a value that does not perform the saturation operation. Characteristic automatic gain control circuit. 12. The automatic gain control circuit according to claim 1, wherein the signal level determiner determines that the digital signal from the A / D converter has a predetermined value within a predetermined time. An automatic gain control circuit, characterized in that the signal level of the digital signal is judged by measuring the number of times a reference value is exceeded. 13. The automatic gain control circuit according to claim 1, wherein in the signal level determiner, the setting of the predetermined amplification factor of the digital amplifier is changed by the gain setting unit. The automatic gain control circuit is characterized in that the signal level of the digital signal is not judged for a predetermined time after the start. 14. The automatic gain control circuit according to claim 2, wherein the initial value control unit considers a gain characteristic of the gain control amplifier with respect to the control signal, An automatic gain control circuit, wherein a predetermined initial value is set in the control signal generating means. 15. A signal obtained by converting a reception signal amplified or attenuated by a gain based on a control signal in a gain control amplification step into a digital signal in an A / D conversion step and removing unnecessary components from the digital signal. Is amplified by a predetermined amplification factor in the digital amplification step, and the difference signal between the signal level after the amplification and a predetermined reference value is smoothed in the control signal generation step to be the control signal in the gain control amplification step. A gain control method, wherein the predetermined amplification factor in the digital amplification step is set based on the signal level determination step of determining the signal level of the digital signal and the signal level determined in the signal level determination step. A gain setting step. Control method. 16. The automatic gain control method according to claim 15, further comprising: an initial value control step of giving a predetermined initial value corresponding to the predetermined amplification factor set in the gain setting step to the control signal generating step. Further, the control signal generating step smoothes the initial value given by the initial value control step to be the control signal in the gain control amplifying step, and smoothes the difference signal after a predetermined time elapses to smooth the gain. An automatic gain control method, wherein the control signal is used in a control amplification step. 17. The automatic gain control method according to claim 15 or 16, wherein the signal level determining step includes a first threshold value and a second threshold value larger than the first threshold value and the A / A value. In the D converting step, the signal level of the signal converted into the digital signal is compared, and in the gain setting step, when the signal level of the digital signal is larger than the second threshold value, the gain in the digital amplifying step is As a predetermined amplification factor, a first amplification factor which is higher than the current amplification factor of the digital amplification step is set, and when the signal level of the digital signal is smaller than the first threshold value, the digital amplification step is performed. As the predetermined amplification factor, set the second amplification factor lower than the current amplification factor of the digital amplification step. Automatic gain control method comprising Rukoto. 18. The automatic gain control method according to claim 17, wherein, in the initial value control step, when the signal level of the digital signal is larger than the second threshold value, the gain value is set by the gain setting step. An initial value corresponding to an amplification factor of 1 is given to the control signal generating step, and when the signal level of the digital signal is smaller than the first threshold value, the second amplification factor set by the gain setting step is set. An automatic gain control method, wherein a corresponding initial value is given to the control signal generating step. 19. The automatic gain control method according to claim 17, wherein the second threshold value is a saturation operation in the A / D conversion step when the signal level of the digital signal is higher than the second threshold value. The first threshold value is the predetermined value in the digital amplification step by the gain setting step when the signal level of the digital signal is smaller than the first threshold value. An automatic gain control method, characterized in that when the second amplification factor is set as the amplification factor, a saturation operation does not occur in the A / D conversion step. 20. The automatic gain control method according to claim 15 or 16, wherein the signal level determination step is performed from the first to the Kth (K is 3).
Each of the threshold values up to the above integer) is compared with the signal level of the signal converted into the digital signal in the A / D conversion step, and in the gain setting step, the signal level of the digital signal is i-th ( If i is greater than or equal to 3 and less than or equal to a threshold value of K) and greater than the (i−1) th threshold value, the predetermined amplification factor in the digital amplification step is higher than the current amplification factor of the digital amplification step. And a third amplification factor corresponding to the i-th threshold value is set, and when the signal level of the digital signal is smaller than the first threshold value, the digital amplification step is performed as the predetermined amplification factor in the digital amplification step. The automatic gain control method is characterized by setting a second amplification factor lower than the current amplification factor. 21. The automatic gain control method according to claim 20, wherein in the initial value control step, when the signal level of the digital signal is equal to or lower than the i-th threshold value and higher than the (i-1) th threshold value, An initial value corresponding to the third amplification factor set in the gain setting step is given to the control signal generating step, and when the signal level of the digital signal is smaller than the first threshold value, the gain setting step is performed. An automatic gain control method, wherein an initial value corresponding to the set second amplification factor is given to the control signal generating step. 22. The automatic gain control method according to claim 20, wherein among the threshold values from the first to the Kth, the second to the Kth threshold values are used.
When the signal level of the digital signal is equal to or lower than the i-th threshold value and larger than the (i-1) th threshold value, the threshold value is set to the predetermined amplification factor in the digital amplification step by the gain setting step. When the amplification factor of 3 is set, the saturation operation does not occur in the A / D conversion step, and the first threshold value is the value when the signal level of the digital signal is smaller than the first threshold value. An automatic gain control method, wherein when the second amplification factor is set as the predetermined amplification factor in the digital amplification step in the gain setting step, the saturation operation does not occur in the A / D conversion step. 23. The automatic gain control method according to claim 15 or 16, wherein the maximum value of the gain in the gain control amplification step and the difference signal or the initial value smoothed in the control signal generation step are used. Further comprising a maximum gain detection step of detecting whether or not the gain in the gain control amplification step has a maximum value, wherein the signal level determination step includes a first threshold value and the A /
The signal level of the digital signal output from the D converter is compared, and in the gain setting step, the maximum gain detection step detects that the gain in the gain control amplification step has a maximum value, and When the signal level determination step determines that the signal level of the digital signal is smaller than the first threshold value, the predetermined amplification rate in the digital amplification step is higher than the current amplification rate in the digital amplification step. An automatic gain control method characterized by setting a fourth amplification factor. 24. The automatic gain control method according to claim 23, wherein in the initial value control step, the maximum gain detection step detects that the gain in the gain control amplification step has a maximum value.
In addition, when the signal level determination step determines that the signal level of the digital signal is smaller than the first threshold value, the initial value corresponding to the fourth amplification factor set in the gain setting step is set to the above-mentioned value. An automatic gain control method characterized by applying to a control signal generation step. 25. The automatic gain control method according to claim 23, wherein the first threshold is such that the signal level of the digital signal is smaller than the first threshold, and the maximum gain is detected by the maximum gain detection step. When it is not detected that the gain in the amplification step becomes the maximum value, the gain setting step sets the fourth amplification rate as the predetermined amplification rate in the digital amplification step, and the gain is saturated in the A / D conversion step. An automatic gain control method, characterized in that the value does not cause any operation. 26. The automatic gain control method according to any one of claims 15 to 25, wherein the signal level determination step is performed within the predetermined time by the A
An automatic gain control method, wherein the signal level of the digital signal is determined by measuring the number of times the digital signal converted by the / D conversion step exceeds a predetermined reference value. 27. The automatic gain control method according to claim 15, wherein in the signal level determination step, the setting of the predetermined amplification factor in the digital amplification step is changed by the gain setting step. The automatic gain control method is characterized in that the signal level of the digital signal is not determined for a predetermined time after the operation. 28. The automatic gain control method according to claim 16, wherein the initial value control step considers a gain characteristic with respect to the control signal in the gain control amplification step, An automatic gain control method, wherein the predetermined initial value is given to the control signal generating step.