JP2001326549A - Automatic gain control circuit and receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that there is a risk that a desired wave is distort ed due to the influence of an interfering wave. SOLUTION: An automatic gain control circuit for performing the gain control of a received signal on the basis of the detection output of the received signal is provided with: a variable attenuating means for deciding the attenuation quantity of the received signal according to the instruction of a control signal; a detecting means for receiving the received signal attenuated by the variable attenuating means and detecting the signal level of the desired wave from the received signal; and a gain control means for controlling the attenuation quantity of the variable attenuating means on the basis of the respective signal levels of the desired wave and interfering wave included in the received signal outputted from the variable attenuating means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a receiver having a power control function of a received signal and an automatic gain control circuit for realizing the control function. For example, modulation methods involving amplitude fluctuations (amplitude modulation such as ASK, phase modulation such as QPSK, FS
The present invention can be applied to a wireless device that realizes digital communication by frequency modulation of K or the like.

[0002]

2. Description of the Related Art At present, digital communication systems include QP
A modulation method such as SK, 4 / π shift QPSK or the like, which puts information on a phase or amplitude, is generally used. By the way, in this type of communication system in which the modulation waveform becomes an amplitude modulation waveform, demodulation cannot be performed when the receiving circuit is saturated, so that an automatic gain control technique is employed to prevent such a situation from occurring. I have.

For example, in the case of a radio communication system such as a mobile phone system, it is inevitable that the received electric field fluctuates due to the influence of the distance between the mobile station and the base station, multipath fading, and the like. However, an automatic gain control technique is employed to prevent the saturation of the reception electric field and obtain a maximum output to the baseband processing unit so as to keep the reception output constant.

FIG. 4 shows a conventional device configuration of a receiver provided with this kind of gain control technique. This figure relates to a receiving unit of a wireless communication device. The signal S1 input from the antenna 1 is amplified with a fixed gain in the power amplifier 2 and output to the variable attenuator 3. The signal S2 output from the power amplifier 2 is arbitrarily attenuated by the control signal S12 of the variable attenuator 3 using the output of the subtracter 12 as a control voltage, and is output as a signal S3.

The signal S3 is multiplied by a local oscillation output S4 supplied from a local oscillator 5 in a mixer (hereinafter referred to as "MIX") 4 and frequency-converted to a predetermined intermediate frequency band. The signal after the frequency conversion is provided to a band pass filter (hereinafter, referred to as “BPF”) 6 as S5. The signal S5 is band-limited by the BPF 6, and the signal S6
Is output as The signal S6 is multiplied by the local oscillation output S7 provided from the local oscillator 8 in the MIX 7, and frequency-converted into a baseband band. Thereafter, the signal after the frequency conversion is output to the BPF 9 as S8 and band-limited.

[0006] The signal S9 after this band limitation is
The signal is amplified by the F amplifier 10 to an amplitude that allows baseband processing, and output to a subsequent circuit (not shown) (OU in the figure).
It is output from the terminal indicated by T. ). The above is the signal flow in the main signal processing system.

[0007] The amplified signal S10 is also output to a detector 11 constituting an automatic gain control system. The detector 11 performs envelope detection of the signal S10. This detection output S11 is input to the subtractor 12. The subtracter 12 calculates a difference voltage between the detection output S11 and a reference voltage Vref (corresponding to Vref1 + H level in the embodiment) indicating a reference value of power at which the IF amplifier 10 does not saturate.

Here, the subtractor 12 outputs the reference voltage Vref.
When the detection output S11 is higher than the reference voltage Vref, the control signal S12 is output so as to increase the attenuation in the variable attenuator 3.
Is smaller, the control signal S12 for reducing the amount of attenuation in the variable attenuator 3 is output. By this control operation, the output S3 of the variable attenuator 3 becomes an output having a substantially constant amplitude regardless of the fluctuation of the received electric field.

[0009]

However, such a conventional apparatus has the following problems.

That is, in the above-described control method, a signal wave having a received electric field larger than the desired wave exists in the adjacent or next adjacent channel to the desired wave due to the positional relationship with respect to a plurality of mobile stations or base stations or the influence of fading. If you do
There is a problem that the waveform of the desired wave cannot be prevented from deteriorating due to the influence of the signal wave.

[0011] This is for the purpose of the receiver shown in the figure to sufficiently reduce the influence of the interference wave input to the IF amplifier 10 by the frequency selection operation by the BPFs 6 and 9 and the frequency conversion operation by the MIX 7. Although the deterioration of the desired wave due to the saturation of the IF amplifier 10 can be reduced, the conventional method of controlling the attenuation of the variable attenuator 3 only by the signal level of the desired wave whose band is limited by the BPFs 6 and 9 causes the interference. It is considered that the saturation of MIX4 due to the influence of the wave cannot be avoided.

When MIX4 is saturated by the influence of an interference wave, the adjacent channel power of the interference wave is distorted and deteriorated.
It falls into the desired wave band and acts on the desired wave as an interference wave. As a result, the quality of the desired wave deteriorates.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and proposes the following means to solve the problems.

(A) As a first means, an automatic gain control circuit having the configuration shown in FIG. 1 is proposed.

That is, in an automatic gain control circuit for controlling the gain of a received signal based on the detection output of the received signal, a variable attenuating means (101) for determining the amount of attenuation of the received signal in accordance with an instruction of the control signal; Detecting means (102) for inputting the received signal attenuated by the means and detecting the signal level of the desired wave from the received signal; and detecting each of the desired wave and the interference wave contained in the received signal output from the variable attenuating means. A gain control means (103) for controlling the attenuation of the variable attenuation means based on the signal level is proposed.

(B) As a second means, an automatic gain control circuit having the configuration shown in FIG. 2 is proposed.

That is, in an automatic gain control circuit for controlling the gain of a received signal based on the detection output of the received signal, a variable attenuating means (101) for determining the amount of attenuation of the received signal according to an instruction of the control signal; Means for receiving the received signal attenuated by the means, and detecting the signal level of a desired wave from the received signal; and receiving the signal attenuated by the variable attenuating means. Second detection means (103A) for detecting a signal level including not only a desired signal but also an interference signal as long as the signal exists.
And calculating the signal level of the interference wave included in the received signal based on the detection outputs of the first and second detection means. If the signal level of the interference wave exceeds an allowable level, the first
The reference voltage to be compared with the detection output of the detecting means is changed in a direction in which the instruction of the attenuation amount to the variable attenuating means is likely to increase, and the comparison result between the changed reference voltage and the detection output of the first detecting means (large or small) Gain control means (103) for controlling the attenuation amount of the variable attenuation means based on the relationship or the magnitude relationship and the difference amount)
B) are proposed.

According to the second means, when an interference wave does not exist or does not exceed a predetermined allowable level, a normal reference voltage (variable attenuation means is used because the signal level of the interference wave exceeds the allowable level). The control of the amount of attenuation for the variable attenuating means is performed based on the reference voltage before the instruction of the amount of attenuation for (101) is changed to a direction in which it is likely to increase. Therefore, in the first detecting means (102A), a detection operation of the desired wave is performed in the same manner as in the related art.

On the other hand, when the signal level of the interfering wave exceeds the allowable level, the instruction of the amount of attenuation to the variable attenuating means (101) is made to the variable attenuating means based on the reference voltage changed in a direction that tends to increase. Control of the amount of attenuation is performed. For this reason, the signal level of the interfering wave input to the first detection means (102A) can be suppressed to within an allowable level. Of course, the reference voltage after the change is stricter in condition than the normal reference voltage, so that a good detection result of the desired wave is guaranteed.

(C) As a third means, an automatic gain control circuit having the configuration shown in FIG. 3 is proposed.

That is, in an automatic gain control circuit for controlling the gain of the received signal based on the detection output of the received signal, a first variable attenuating means (101A) for determining the amount of attenuation of the received signal in accordance with the instruction of the control signal; A first detection means (102A) for receiving a reception signal attenuated by the variable attenuation means and detecting a signal level of a desired wave from the reception signal;
And the detection output of the first detection means and the first reference voltage, and the comparison result (a magnitude relation or a magnitude relation and a difference amount)
Gain control means (103C) for controlling the amount of attenuation such that the signal level of the desired wave output from the second variable attenuation means (101B) in the first detection means is substantially constant based on And a second detection means (103D) for receiving the received signal attenuated by the first variable attenuating means and detecting a signal level including not only a desired wave but also an interfering wave from the received signal as long as the signal is present. And the signal level of the interference wave included in the received signal is calculated based on the detection outputs of the first and second detection means, and the signal level of the interference wave and the second
Based on the comparison result (the magnitude relation or the magnitude relation and the difference amount) with the reference voltage, so that the signal level of the interference wave included in the reception signal output from the first variable attenuation means becomes substantially constant. Second gain control means for controlling (103E)
Are proposed.

In the third means, the first variable attenuator (1) is controlled by the second gain control means (103E).
01A) can restrict the signal level of the interfering wave included in the signal output from the predetermined level to a predetermined level or less. At this time, there is a possibility that the desired wave is attenuated more than necessary. However, for the desired wave, the second variable attenuator (in the first detecting means) located after the first variable attenuator (101A). There is (1)
Since the signal level at the output stage of 01B) is controlled to be substantially constant, when the signal is to be detected by the first detection means (102A), the signal is processed as an appropriate signal level signal. .

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (A) First Embodiment Here, an example of an embodiment that embodies the second and fourth means of the present invention will be described. The first means in the above-mentioned solving means is a solving means as a general concept of the second means and the third means (corresponding to the second embodiment as described later).

(A-1) Configuration of Automatic Gain Control Circuit and Receiver FIG. 5 shows the configuration of the receiver and the automatic gain control circuit according to the first embodiment. This receiver includes an antenna 1, an automatic gain control circuit, a signal system for processing the output of the circuit, and a transmission system for transmitting information such as audio and video to the other party as required, and a reception system. And an output system for providing a signal as audio or video to the user.

In this embodiment and the following embodiments, a radio receiver will be described as an example, but a wired receiver is not excluded unless the influence of an interference wave can be ignored.

The difference of this receiver from the conventional example is that, in addition to the first detection system for detecting the reception level of only the desired signal, like an automatic gain control circuit as the second means of the solution, A second detection system for detecting the reception level including the interference wave is newly provided, the reception level of the interference wave is calculated from the detection outputs of the first and second detection systems, and the interference wave level exceeds the allowable level. In case, change the reference voltage of automatic gain control,
The point is that the sensitivity deterioration due to the interference wave is more unlikely to occur.

The configuration shown in FIG. 5 will be specifically described. This receiver comprises an antenna 1, a power amplifier 2 constituting an automatic gain control circuit, a variable attenuator 3, a MIX 4, a local oscillator 5, a BPF 6, a MIX 7, a local oscillator 8, a BPF 9,
F amplifier 10, detector 11, BPF25, MIX26,
BPF 27, IF amplifier 28, detector 29, subtractor 3
0, a comparator 31, an adder 32, and a subtractor 33.

Of these, BPF6, MIX7, BPF
9, an IF amplifier 10 and a detector 11 constitute a first detector (102A) for detecting an envelope of a desired wave.

Also, BPF25, MIX26, BPF2
7. The IF amplifier 28 and the detector 29 constitute a second detector (103A) for detecting the envelope of the received wave including not only the desired wave but also the interfering wave. Here, the pass bands of the BPFs 25 and 27 correspond to the corresponding BPFs 6 in the first detector.
And 9 are set to be wider than the passbands, so that signals of adjacent channels, and in some cases, signals of the next adjacent channel may be set to pass. Of course, the setting of this pass band is selected appropriately according to the system to which it is applied.

Further, the subtractor 30, the comparator 31, the adder 32 and the subtracter 33 constitute a gain control section (103B). Here, the gain control unit detects the reception level of the interference wave by comparing the outputs detected by the first and second detection units, and the reception level of the interference wave is MIX.
If it is confirmed that the control signal 4 is at a level that saturates the control signal 4, the control signal to the variable attenuator 3 operates so that the amount of attenuation is larger than that of the control using only the desired wave.

On the other hand, the gain control section detects the reception level of the interference wave by comparing the output detected by each of the first and second detection sections.
When it is confirmed that the level is not at a level that saturates IX4, the operation is performed so that the IF amplification unit 10 is not saturated by a desired wave.

(A-2) Reception Operation and Gain Control Operation The antenna 1 receives, for example, a 4 / πQPSK modulated wave IN and outputs it to the power amplifier 2 as a signal S1. The power amplifier 2 outputs a signal S1 with a fixed gain (for example, 10 dB).
, And outputs the amplified signal S2 to the variable attenuator 3.

The variable attenuator 3 controls the control signal S34 from the subtractor 33 which is input to the control voltage input terminal for instructing the amount of attenuation.
The signal S2 output from the power amplifier 2 is attenuated according to the following equation.

As described later, MIX4 is not saturated unless there is an adjacent channel signal (that is, no interference wave). In this case, the output of the IF amplifier 10 is a reference voltage (Vref1 + H level) for obtaining the maximum output level. ), The attenuation of the variable attenuator 3 is automatically controlled so that the same detection voltage as in the case of using) is obtained.

The MIX 4 and the local oscillator 5 generate the modulated wave IN
BPF6 and BPF2
5 to output a signal S5. BPF6 selects the desired wave,
It operates so as to attenuate the signal of the adjacent channel (that is, an interference wave) to prevent the sensitivity from deteriorating.

The MIX 7 and the local oscillator 8 convert the signal S6 to an intermediate frequency in a lower baseband and output it as a signal S8. The BPF 9 controls the band-limited signal S
9 is output to the IF amplifier 10. As a result, a modulated wave of only a desired channel can be obtained from a plurality of channels.

The IF amplifier 10 receives the input signal S9
At a fixed gain (for example, 60 dB) to an amplitude that allows baseband processing, and outputs the amplified signal S10 to the detector 11 and a demodulation circuit (not shown).

The detector 11 detects the envelope of the signal S10,
Detection signal S1 indicating reception intensity (power) of the modulated wave signal
1 is output to the subtractor 30. This detection signal S11 is
This is the detection output for the desired wave.

On the other hand, the detection operation of the modulated wave signal including the interfering wave is performed as follows. First, one of the two signals S5, which is the output of MIX4, is input to the BPF 25. The BPF 25 operates to selectively pass a desired wave. However, the pass band of the BPF 25 is set wider than that of the BPF 6, and adjacent interfering waves also pass. The MIX 26 and the local oscillator 8 convert the signal that has passed through the BPF 25 into a signal in an intermediate frequency band lower than the modulated wave, and outputs the signal as a signal S27.

The BPF 27 limits the band in the same manner as the BPF 25, and outputs a signal S28 to the IF amplifier 28. As a result, a modulated wave including an interference wave adjacent to the desired channel is obtained from the plurality of channels.

The IF amplifier 28 receives the input signal S28
At a fixed gain (for example, 60 dB).
The signal is amplified so that the output level becomes equal to 0, and the amplified signal S29 is output to the detector 29.

The detector 29 detects the envelope of the signal S29.
Detection signal S3 indicating reception intensity (power) of the modulated wave signal
0 is output to the subtractor 31. The detection signal S30 is a detection output including the desired wave and the adjacent interference wave.

The subtractor 30 subtracts the detection signal S11 obtained from the modulated wave including only the desired wave from the detection signal S30 obtained from the modulated wave including the interfering wave.
A signal S31 indicating the power of the interference wave is output to the comparator 31.

The comparator 31 has an interference wave level signal S31 and a reference voltage level Vref for giving the saturation level of MIX4.
2 and the reception intensity (power) of the interference wave is MIX4
Is determined to have reached the level at which is saturated.

The reference voltage level Vref2 here
Between the reference voltage level Vref1 and the aforementioned reference voltage level Vref1.
f2 ≧ Vref1> “H” level output of the comparator 31 (the same applies to the second embodiment).

Here, the comparator 31 determines that the signal level of the input interference wave level signal S31 is equal to the reference voltage level Vre.
If it exceeds f2, an output signal S32 of "L" level (0 [V] in this embodiment) is output. on the other hand,
Comparator 31 outputs an "H" level output signal S32 when the signal level of input disturbance wave level signal S31 does not exceed reference voltage level Vref2.

The adder 32 adds the signal S32 output from the comparator 31 to the "H" level output signal S32, and adds the result to the reference voltage Vref1 which gives the maximum level at which the desired wave is not saturated. , A new reference voltage Vref
(= Vref1 + “H” level). here,
When the output of the comparator 31 is at the “L” level (0 [V]), the reference voltage level Vref1 is used as the output of the adder 32.
Output itself.

That is, the input interference wave level signal S
When the signal level of the reference signal 31 exceeds the reference voltage level Vref2, the reference voltage level that provides a more severe reference voltage level (because the output signal S11 easily exceeds the reference voltage level) than when it does not exceed the reference voltage level Vref2. Vr
ef1 is output.

The adder 32 outputs the new reference voltage thus generated to the subtractor 33 as a signal S33.

The subtracter 33 outputs the output signal S3 of the adder 32.
3 and the output signal S11 of the detector 11 that outputs the detection output of the desired wave, and the output signal S11 is output signal S33.
If the output signal S11 is smaller than the output signal S33, the variable attenuation is increased (ie, the signal level of the desired wave is increased). That is, the control signal S34 is output (to lower the signal level of the desired wave). By this feedback control, the output signal S11 is controlled to be equal to the signal voltage of the output signal S33.

That is, when there is no interfering wave so as to saturate the MIX4, the "H" level is output as the output signal S32 of the comparator 31, and the reference voltage Vref1 + "H" level is output as the output of the adder 32. Is done. As a result, automatic gain control similar to that of the conventional device is performed.

On the other hand, when there is an interference wave enough to saturate MIX4, the output signal S
The “L” level (0 [V]) is output as 32, and Vref 1 itself is output as the output of the adder 32.

As a result, the subtracter 33 outputs the normal (when there is no interfering wave) reference voltage Vref (= Vref1 + “H”).
The comparison result between the reference voltage Vref1 that is smaller than the reference voltage Vref1 and the signal level of the desired wave is output to the variable attenuator 3. This means that control is performed to give more attenuation than that controlled by Vref1, which leads to a decrease in the input level of the interfering wave input to MIX4.

Thus, the possibility that the MIX 4 is saturated due to the influence of the interference wave is further reduced, and the possibility that the desired wave is distorted can be reduced accordingly. Of course, IF amplifier 10
, No further saturation occurs, so that the reception quality can be further improved.

(A-3) Effects of the First Embodiment As described above, by using the receiver equipped with the automatic gain control circuit according to the present embodiment, the first stage is affected by the interference wave of the adjacent channel. Can be effectively avoided. As a result, the desired wave can be prevented from being distorted by the influence of the interfering wave, and the reception quality of the desired wave can be improved.

Further, the standard of linearity in the selection of MIX4 located at the first stage can be relaxed, and the mutual phase modulation characteristics can be improved.

(B) Second Embodiment Here, an example of an embodiment in which the third and fourth means of the solving means are embodied will be described.

(B-1) Configuration of Automatic Gain Control Circuit and Receiver FIG. 6 shows a configuration of a receiver and an automatic gain control circuit according to the second embodiment. This receiver also has an antenna 1, an automatic gain control circuit, a signal system for processing the output of the circuit, and a transmission system for transmitting information such as audio and video to the other party if necessary, and a reception system. And an output system for providing a signal as audio or video to the user.

In this embodiment and the following embodiments, a radio receiver will be described as an example, but a wired receiver is not excluded unless the influence of an interference wave can be ignored.

This receiver differs from the prior art in that a first detection system for detecting the reception level of only a desired signal, such as an automatic gain control circuit as a third means of the invention, A first gain control system for automatically controlling the gain of the first detection system based on the reception level of the desired wave from the first detection system and detecting the reception level including the interference wave based on the reception level. A second detection system to be performed, and a reception level of an interfering wave is calculated from detection outputs of the first and second detection systems, and a gain in the second detection system is automatically controlled based on the reception level. The provision of the gain control system makes it more difficult for sensitivity degradation due to an interfering wave to occur.

The configuration shown in FIG. 6 will be specifically described. This receiver comprises an antenna 1, a power amplifier 2 constituting an automatic gain control circuit, a variable attenuator 3, a MIX 4, a local oscillator 5, a BPF 6, a MIX 7, a local oscillator 8, a BPF 9,
F amplifier 10, detector 11, subtractor 12, variable attenuator 1
3, a BPF 25, a MIX 26, a BPF 27, an IF amplifier 28, a detector 29, a subtractor 30, and a subtractor 34.

Of these, BPF6, MIX7, BPF
9, an IF amplifier 10, a detector 11, and a variable attenuator 13 for detecting the envelope of a desired wave by a first detector (102
A, 101B). The feature of the first detector is that the variable attenuator 13 (1
01B).

A first gain control section (103C) in which the subtractor 12 controls the gain based on only the reception electric field level of the desired wave so that the signal level output from the variable attenuator 13 becomes a constant level. Is configured.

The BPF 25, MIX 26, BPF 2
7. The IF amplifier 28 and the detector 29 constitute a second detector (103D) for detecting the envelope of the received wave including not only the desired wave but also the interfering wave.

Here, the pass bands of the BPFs 25 and 27 are set to be wider than the corresponding pass bands of the BPFs 6 and 9 in the first detector, and the signals of the adjacent channels, and in some cases, the signals of the next adjacent channels are also passed. It shall be set as possible. Of course, the setting of this pass band is selected appropriately according to the system to which it is applied.

Further, the second gain control in which the subtractor 30 and the subtracter 34 control the gain based on only the reception electric field level of the interference wave so that the signal level output from the variable attenuator 3 becomes a constant level. (103E). Here, the second gain control unit detects the reception level of the interference wave by comparing the output detected by each of the first and second detection units, and determines that the reception level of the interference wave is MIX4.
Is controlled so that the level is not saturated.

(B-2) Reception Operation and Gain Control Operation The antenna 1 receives, for example, a 4 / πQPSK modulated wave IN and outputs it to the power amplifier 2 as a signal S1. The power amplifier 2 outputs a signal S1 with a fixed gain (for example, 10 dB).
, And outputs the amplified signal S2 to the variable attenuator 3.

The variable attenuator 3 receives a control signal S32 from a subtractor 34 input to a control voltage input terminal for instructing the amount of attenuation.
The signal S2 output from the power amplifier 2 is attenuated according to the following equation.

As described later, when there is a signal of an adjacent channel (that is, an interfering wave), the value of the variable attenuator 3 is automatically controlled so as to be equal to the reference voltage Vref2 that provides a level at which the MIX 4 does not saturate.

The MIX 4 and the local oscillator 5 generate the modulated wave IN
The lower intermediate circumference is converted into a number, and BPF6 and BPF2
5 to output a signal S5. BPF6 selects the desired wave,
It operates so as to attenuate the signal of the adjacent channel (that is, an interference wave) to prevent the sensitivity from deteriorating.

The MIX 7 and the local oscillator 8 convert the signal S6 to an intermediate frequency in a lower baseband and output it as a signal S8. The BPF 9 controls the band-limited signal S
9 is output to the variable attenuator 13. This variable attenuator 13
Is a second-stage attenuation means on the signal path as viewed from the desired wave.

The variable attenuator 13 controls the control signal S1 from the subtractor 12 input to the control voltage input terminal for instructing the amount of attenuation.
3, the signal S9 output from the BPF 9 is attenuated. As will be described later, the variable attenuator 13 outputs a reference voltage V for obtaining the maximum output level of the IF amplifier 10.
The amount of attenuation is automatically controlled so that a detection voltage of the same level as ref (= Vref1 + H level) is obtained. As a result, a modulated wave of only a desired channel from a plurality of channels can be obtained at a desired level.

The IF amplifier 10 receives the input signal S10
At a fixed gain (for example, 60 dB) to an amplitude that allows baseband processing, and outputs the amplified signal S11 to the detector 11 and a demodulation circuit (not shown).

The detector 11 detects the envelope of the signal S11,
Detection signal S1 indicating reception intensity (power) of the modulated wave signal
2 is output to the subtractor 30 and the subtractor 12.

The subtractor 12 outputs the output value of the detector 11 and the IF
The output of the detector 11 is compared with a reference voltage Vref (= Vref1 + H level) indicating the reception intensity (power) at which the amplifier 10 does not saturate, and the output of the detector 11 is set to the reference voltage Vref (= Vref).
(1 + H level), the amount of attenuation instructed to the variable attenuator 13 is increased so that saturation does not occur in the IF amplifier 10.

On the other hand, when the output of the detector 11 is lower than the reference voltage Vref (= Vref1 + H level), the subtractor 13 controls the variable attenuator 13 so that the maximum output can be obtained within a range where saturation does not occur in the IF amplifier. To reduce the amount of attenuation instructed.

With this operation, the amplitude of the detection output output from the IF amplifier 10 is changed to the reference voltage Vref (= Vre
(f1 + H level).

On the other hand, the operation of detecting a modulated wave signal including an interference wave is performed as follows. First, one of the two signals S5, which is the output of MIX4, is input to the BPF 25. The BPF 25 operates to selectively pass a desired wave. However, the pass band of the BPF 25 is set wider than that of the BPF 6, and adjacent interfering waves also pass. The MIX 26 and the local oscillator 8 convert the signal that has passed through the BPF 25 into a signal in an intermediate frequency band lower than the modulated wave, and outputs the signal as a signal S27.

The BPF 27 limits the band in the same manner as the BPF 25, and outputs the signal to the IF amplifier 28 as a signal S28. As a result, a modulated wave including an interference wave adjacent to the desired channel is obtained from the plurality of channels.

The IF amplifier 28 receives the input signal S28
At a fixed gain (for example, 60 dB).
The signal is amplified so that the output level becomes equal to 0, and the amplified signal S29 is output to the detector 29.

The detector 29 detects the envelope of the signal S29,
Detection signal S3 indicating reception intensity (power) of the modulated wave signal
0 is output to the subtractor 30. The detection signal S30 is a detection output including the desired wave and the adjacent interference wave.

The subtracter 30 subtracts the detection signal S12 obtained for the modulated wave of only the desired wave from the detection signal S30 obtained for the modulated wave including the interfering wave.
A signal S31 indicating the power of the interference wave is output to the subtractor.

The subtractor 34 compares the interference wave level signal S31 with the saturation level reference voltage level Vref2 of the MIX 4 to determine whether or not the reception intensity (power) of the interference wave has reached a level at which the MIX 4 is saturated. . Here, when the signal level of the input interference wave level signal S31 exceeds the reference voltage level Vref2, the subtractor 34 outputs an output signal S32 for increasing the attenuation.

On the other hand, the subtractor 34 determines that the signal level of the input interference wave level signal S31 is equal to the reference voltage level Vref.
If it does not exceed 2, the output signal S32 for reducing the amount of attenuation is output.

Thus, when there is no interfering wave (when there is no risk of saturating the MIX 4), the attenuation of the variable attenuator 3 is controlled to OdB, and when there is an interfering wave (the MIX 4 may be saturated). If it is a certain level), the control voltage is applied to the variable attenuator 3 so that the interference wave level does not exceed the reference voltage Vref2.

By this control, when there is no interference wave,
There is no attenuation in the variable attenuator 3, and the variable attenuator 13 operates so that the maximum gain is selected according to the desired wave level. When there is an interfering wave, the variable attenuator 3 at a level at which the MIX 4 does not saturate due to the interfering wave is controlled, while the variable attenuator 13 at the subsequent stage compensates for the attenuation of the variable attenuator 3 and the desired wave level is reduced. It is controlled to be the maximum.

(B-3) Effect of Second Embodiment As described above, by using the receiver equipped with the automatic gain control circuit according to the present embodiment, the first stage is affected by the interference wave of the adjacent channel. Can be effectively determined whether or not the MIX4 located at the position (1) is saturated. As a result, the desired wave can be prevented from being distorted by the influence of the interfering wave, and the reception quality of the desired wave can be improved.

The attenuation of the variable attenuator 13 provided at the subsequent stage can be controlled based on the detection level of the desired wave.
The signal level of the desired wave attenuated by the first stage variable attenuator 3 in consideration of the influence of the interfering wave can be supplemented by the control unit.

Further, the standard of linearity in the selection of MIX4 located at the first stage can be relaxed, and the mutual phase modulation characteristics can be improved.

(C) Other Embodiments In the first and second embodiments described above, the receiver of the double superheterodyne system (that is, the receiver of performing the frequency conversion twice) has been described. The present invention can also be applied to a single superheterodyne receiver (that is, a receiver that performs frequency conversion only once) and a direct conversion receiver. Further, the present invention can be used for an IF sampling digital type receiver.

In the first and second embodiments, the case where the transmission path of the modulated wave is a wireless path has been described. However, the signal (interference wave) of another adjacent channel is used.
Can be widely applied to a receiver using a system in which a wired path is used as a transmission path, as long as there is a possibility that these are mixed.

In the above-described first and second embodiments, the attenuation of the variable attenuator 3 is determined by the outputs of the subtracters 33 and 34 (the difference voltage between the reference voltage and the input signal, ie, the magnitude relationship and the difference). And the amount of attenuation of the variable attenuator 13 is controlled by the output of the subtractor 12 (the difference voltage between the reference voltage and the input signal, that is, the magnitude relationship and the difference amount). Alternatively, a method of controlling the amount of attenuation based on only the magnitude relationship between the reference voltage and the input signal may be employed.

[0093]

According to the first aspect of the present invention, as described above, in the automatic gain control circuit for controlling the gain of the received signal based on the detection output of the received signal, the signal is included in the received signal. Gain control means that controls the amount of attenuation of the variable attenuation means based on the signal levels of the desired signal and the interfering signal, enabling control of the amount of attenuation taking into account the signal level of the interfering signal Therefore, the possibility that the desired wave included in the received signal input to the detection means is distorted by the influence of the interference wave can be significantly reduced.

(B) As described above, according to the second aspect of the invention, the signal level of the desired signal is detected by the automatic gain control circuit that controls the gain of the received signal based on the detection output of the received signal. In addition to the first detecting means, there is provided second detecting means for detecting a signal level including not only a desired signal but also an interfering signal as long as the desired signal exists.
The signal level of the interference wave included in the received signal is calculated based on the detection output of the detection means, and when the signal level of the interference wave exceeds the allowable level, it is compared with the detection output of the first detection means. The reference voltage is changed in a direction in which the instruction of the amount of attenuation to the variable attenuating means is likely to increase, and the amount of attenuation of the variable attenuating means is controlled based on a comparison result between the changed reference voltage and the detection output of the first detecting means. By doing so, the possibility that the desired wave included in the received signal input to the first detection means is distorted by the influence of the interference wave can be significantly reduced.

(C) As described above, according to the third aspect of the present invention, the automatic gain control circuit for controlling the gain of the received signal based on the detection output of the received signal detects the signal level of the desired signal. In addition to the first detecting means, there is provided second detecting means for detecting a signal level including not only a desired signal but also an interfering signal as long as the signal is present, and further comprises a detecting output of the first detecting means and a first detecting means. And the amount of attenuation is controlled based on the comparison result such that the signal level of the desired wave output from the second variable attenuating means in the first detecting means is substantially constant. 1 gain control means;
And calculating the signal level of the interference wave included in the received signal based on the detection output of the second detection means, and calculating the first signal level based on the comparison result between the signal level of the interference wave and the second reference voltage.
And a second gain control means for controlling the amount of attenuation so that the signal level of the interference wave included in the received signal output from the variable attenuating means becomes substantially constant. The possibility that the desired wave included in the received signal is distorted due to the influence of the interfering wave can be remarkably reduced. Also,
Since the gain of the desired wave is separately adjusted by the first gain control means, it is possible to compensate for the attenuation of the desired wave by the second gain control means.

(D) According to the fourth aspect of the present invention, as described above, a receiver including the automatic gain control circuit according to any one of the first to third aspects is proposed to receive a signal as a receiver. Better quality can be achieved.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a configuration of a receiver according to a first means.

FIG. 2 is a functional block diagram showing a configuration of a receiver according to a second means.

FIG. 3 is a functional block diagram showing a configuration of a receiver according to a third means.

FIG. 4 is a diagram showing a conventional configuration.

FIG. 5 is a diagram illustrating a functional block configuration of a receiver according to the first embodiment.

FIG. 6 is a diagram illustrating a functional block configuration of a receiver according to a second embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Antenna, 2 ... Power amplifier, 3, 13, 101, 1
01A, 101B ... variable attenuator, 4, 7, 26 ... MI
X, 5, 8 ... local oscillator, 6, 9, 25, 27 ... BP
F, 10, 28: IF amplifier, 11, 29: detector, 1
2, 30, 33, 34 ... subtractor, 31 ... comparator, 32 ...
Adders, 102, 103A, 103D ... Detector, 10
3, 103B, 103C, 103E ... gain control units.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H04L 27/06 H04L 27/06 Z 5K062 27/14 27/14 Z 27/22 27/22 Z F term ( Reference) 5J100 JA01 JA03 KA05 LA03 LA09 QA02 SA02 5K004 AA03 AA04 AA05 AA08 DC06 DF00 DG01 ED06 EG00 EH02 FA05 FD06 FG00 FH04 JD06 JG00 JH03 5K020 AA08 DD01 DD09 EE01 EE11 GG12 EE13 GG3 EE05 EE13 GG3 AA10 BB12 CC08 CC11 CC14 CC52 5K062 AA01 AB04 AB06 AD04 AD09 AG01 AG02 AG03 BE08 BE09

Claims (4)

[Claims] An automatic gain control circuit for controlling a gain of a received signal based on a detection output of the received signal, wherein the variable attenuator determines an attenuation amount of the received signal according to an instruction of the control signal. Detecting means for receiving the attenuated received signal and detecting a signal level of a desired wave from the received signal; and detecting the signal level of the desired wave and the interference wave included in the received signal output from the variable attenuating means. A gain control means for controlling the amount of attenuation of the variable attenuation means. 2. An automatic gain control circuit for controlling a gain of a received signal based on a detection output of the received signal, wherein the variable attenuator determines an amount of attenuation of the received signal in accordance with an instruction of the control signal. A first detecting means for receiving the attenuated received signal and detecting a signal level of a desired wave from the received signal; and a receiving signal attenuated by the variable attenuating means, and receiving only the desired signal from the received signal. Second detection means for detecting a signal level including an interference wave as long as the signal is present, and calculating a signal level of the interference wave included in the received signal based on the detection outputs of the first and second detection means However, when the signal level of the interference wave exceeds the allowable level, the reference voltage to be compared with the detection output of the first detection means is likely to increase the indication of the amount of attenuation to the variable attenuation means. Gain control means for controlling the amount of attenuation of the variable attenuating means based on a comparison result between the changed reference voltage and the detection output of the first detecting means. Control circuit. 3. An automatic gain control circuit for controlling a gain of a received signal based on a detection output of the received signal, wherein the first variable attenuating means determines an attenuation amount of the received signal according to an instruction of the control signal; A first detection unit that receives the reception signal attenuated by the attenuation unit and detects a signal level of a desired wave from the reception signal; and compares a detection output of the first detection unit with a first reference voltage. First gain control means for controlling the amount of attenuation based on the comparison result so that the signal level of the desired wave output from the second variable attenuation means in the first detection means is substantially constant; A second detection means for receiving the received signal attenuated by the first variable attenuating means and detecting a signal level including not only a desired wave but also an interfering wave from the received signal as long as the signal is present; First and second inspection Calculating a signal level of an interference wave included in the received signal based on a detection output of the means, and outputting the signal level from the first variable attenuation means based on a comparison result between the signal level of the interference wave and a second reference voltage; And a second gain control means for controlling the amount of attenuation so that the signal level of an interference wave included in the received signal is substantially constant. 4. A receiver comprising the automatic gain control circuit according to claim 1.