JP2010011380A - Variable gain amplifier and receiving apparatus - Google Patents

Abstract

There is provided a variable gain amplifier that suppresses a fluctuation of a direct current component of an output signal and improves a distortion characteristic when an input signal level becomes the highest to realize a good distortion characteristic.
A variable gain amplifier 60 according to the present invention suppresses fluctuations in a DC component of an output terminal by controlling output currents of variable current sources 30 and 31 serving as bias currents according to a gain. Specifically, when the gain is high (that is, when the amplitude of the input signal to the variable gain amplifier 60 is low), the bias current is reduced to suppress a decrease in the output DC voltage, and when the gain is low (that is, the input signal). When the amplitude is high), increase the output DC voltage by increasing the bias current. Thereby, the fluctuation | variation of an output DC voltage can be suppressed. Further, the distortion characteristic can be improved by increasing the bias current when the gain is low.
[Selection] Figure 3

Description

  The present invention relates to a variable gain amplifier, and more particularly to a variable gain amplifier integrated on a semiconductor integrated circuit and used for automatic gain control.

  FIG. 7 shows a main configuration of a general semiconductor integrated circuit receiving device 100. The receiving apparatus 100 receives, for example, a television broadcast signal (hereinafter referred to as “received signal”), and performs processing such as frequency conversion and amplification in order to perform demodulation processing and the like on the received signal in a subsequent circuit. This tuner IC is used to be mounted on a mobile phone or a television receiver. The receiving apparatus 100 can also be used as a satellite broadcast receiving tuner IC.

  As shown in FIG. 7, the receiving apparatus 100 includes a received signal input terminal 1, a high frequency variable gain amplifier 2, a frequency converter 3, a low frequency variable gain amplifier 4, a low pass filter 5, and an output amplifier 6. A local signal generator 7, an output signal level detection circuit 9, a gain control signal generation circuit 10 of the high frequency variable gain amplifier 2, and a gain control signal generation circuit 11 of the low frequency variable gain amplifier 4.

  The received signal input from the input terminal 1 is amplified or attenuated by the high frequency variable gain amplifier 2 and input to the frequency converter 3. The frequency converter 3 frequency-converts the input signal based on the local signal supplied from the local signal generation circuit 7 to a desired frequency, and outputs it to the low frequency variable gain amplifier 4. The low-frequency variable gain amplifier 4 amplifies or attenuates the input signal with a gain that gives a constant signal level and outputs the amplified signal to the low-pass filter 5. The output of the low-pass filter 5 is amplified by the output amplifier 6 and output to the output terminal. 8 is output.

  The output signal level detection circuit 9 connected to the output terminal 8 outputs the detection result of the output signal level to the gain control signal generation circuits 10 and 11. The gain control signal generation circuits 10 and 11 feedback control the gains of the variable gain amplifiers 2 and 4 based on the detection result provided from the output signal level detection circuit 9, respectively, so that the output signal output to the output terminal 8 is output. The level is kept constant.

  Here, the low frequency variable gain amplifier 4 is considered. FIG. 8 shows a general configuration of the low-frequency variable gain amplifier 4.

  As shown in FIG. 8, the low frequency variable gain amplifier 4 includes signal input terminals 12 and 13, gain control signal input terminals 14 and 15, a power supply terminal 16, transistors 17 to 22, and a low frequency variable gain amplifier 4. A resistor 23 relating to the input dynamic range, load resistors 24 and 25, current sources 26 and 27 for determining a bias current of the low-frequency variable gain amplifier 4, and signal output terminals 28 and 29.

  The transistors 17 to 22 are NPN type bipolar transistors. An input signal (the output signal of the frequency converter 3 when the receiver 100 is provided) is input to the bases of the transistors 17 and 18 via the signal input terminals 12 and 13, and gains are supplied to the transistors 19 to 22. A gain control signal (the output signal of the gain control signal generation circuits 10 and 11 when the receiving apparatus 100 is provided) is input via the control signal input terminals 14 and 15 and used for gain control. The input dynamic range of the low frequency variable gain amplifier 4 is determined approximately by the product of the resistor 23 and the bias current of the current sources 26 and 27, and the maximum gain is determined approximately by the ratio of the resistor 23 and the resistors 24 and 25.

  Input signals are input from the signal input terminals 12 and 13 and converted into collector currents of the transistors 17 and 18 by the transistors 17 and 18. The collector current of the transistor 17 is the emitter current of the transistors 19 and 20, and the collector current of the transistor 18 is the emitter current of the transistors 21 and 22. The ratio of the current flowing as the emitter current of the transistors 19 and 20 in the collector current of the transistor 17 is determined by the gain control signal input from the gain control signal input terminals 14 and 15. The same applies to the collector current of the transistor 18 and the emitter currents of the transistors 21 and 22.

  By the operation of the transistors 19 to 22, the gain of the low-frequency variable gain amplifier 4 is determined by a decrease from the maximum gain determined from the resistor 23 and the load resistors 24 and 25. Further, since both the signal component and the DC component are included in the collector current of the transistor 17, the signal component and the DC component are similarly included in the current flowing through the load resistor 24.

  Here, when the gain control signal level input from the gain control signal input terminal 15 is higher than the gain control signal level input from the gain control signal input terminal 14, more current flows through the transistor 19 than through the transistor 20. The amount of current flowing through the load resistor 24 increases. From this, it can be seen that the gain for the signal component is variable and the output DC voltage also changes in accordance with the gain.

  In order to remove a DC component by passing a signal, a method of inserting a capacitor in series is usually employed. However, it is difficult to install a capacitor having a large capacitance value on a semiconductor integrated circuit. Therefore, it is difficult to remove the DC component of the low frequency signal. Therefore, in the receiving apparatus 100, it is necessary to design the low-pass filter 5 and the output amplifier 6 so that desired characteristics can be obtained even with respect to changes in the output DC voltage component of the low-frequency variable gain amplifier 4. This is a constraint on the design of the filter 5 and the output amplifier 6. As a countermeasure against this problem, for example, methods described in Patent Document 1 and Patent Document 2 have been proposed.

  Specifically, in the variable gain amplifier circuit disclosed in Patent Document 1, transistors Q7 and Q8 and a constant voltage source V2 are provided, and the gain of the variable gain amplifier circuit is increased by the transistors Q7 and Q8 and the constant voltage source V2. Even if it fluctuates, the DC component of the output voltage is made constant by setting the DC component of the current flowing through the load resistors R1, R2 to a constant value (see paragraphs [0040] to [0061] and FIG. 1).

  In the variable gain amplifier disclosed in Patent Document 2, the bias potentials of the output terminals 6 and 7 are made constant regardless of the control voltage VA applied between the terminals 4 and 5 due to the circuit configuration (paragraph [ 0014] to paragraph [0028] and FIG.

  Next, the distortion characteristics of the low frequency variable gain amplifier 4 will be considered.

  When the receiving apparatus 100 needs to receive an input signal in a wide signal level range, the receiving apparatus 100 needs to realize a level diagram as shown in FIG. 9, for example. Further, the relationship of gain change between the high frequency variable gain amplifier 2 and the low frequency variable gain amplifier 4 is designed as shown in FIG.

  Here, a case is considered in which the signal level increases from the state where the input signal level to the receiving apparatus 100 is the lowest, that is, the gain of the entire receiving apparatus 100 is maximum. First, in order to reduce the gain of the entire receiving apparatus 100 without deteriorating the NF of the entire receiving apparatus 100, it is desirable not to decrease the gain of the previous stage. Therefore, the gain of the high-frequency variable gain amplifier 2 is variable without reducing the gain. The gain of the gain amplifier 4 is lowered. If the input signal level further increases and the gain of the low frequency variable gain amplifier 2 is lowered too much, the output signal level of the high frequency variable gain amplifier 2, the input / output signal level of the frequency converter 3, and the input of the low frequency variable gain amplifier 4. The signal level becomes high and a problem occurs in the distortion characteristics. Therefore, the gain reduction of the low frequency variable gain amplifier 4 is stopped within a range satisfying the required distortion characteristics, and the overall gain is lowered by reducing the gain of the high frequency variable gain amplifier 2. By performing such an operation, the receiving apparatus 100 as a whole is configured as a receiving apparatus having no problem in noise characteristics and distortion characteristics.

  Next, consider the distortion characteristics of the receiving apparatus 100 at a relatively low input signal level. When the input signal level is relatively low, the distortion characteristics of the high-frequency variable gain amplifier 2 can be designed so as not to be a problem. The reason for this will be briefly described below. In general, in a certain circuit, the larger the input signal, the greater the distortion component generated at the input section, and the larger the output signal, the greater the distortion component generated at the output section. From FIG. 9, considering the operation of the high-frequency variable gain amplifier (RFVGA) 2 at a relatively low input signal level, both the input signal and the output signal are lower than the signal level when the input signal level is higher. Therefore, when the input signal level is relatively low, the distortion characteristic of the high frequency variable gain amplifier 2 can be designed so as not to be a problem. 9, since the input / output signal levels of the low-pass filter (KPF) 5 and the output amplifier (AMP) 6 do not change even when the input signal level of the receiving apparatus 100 changes, the low-pass filter 5 and the output amplifier 6 Therefore, a constant distortion characteristic is always required. The frequency converter (MIXER) 3 must satisfy the distortion characteristics at the maximum input signal level and the maximum output signal level to the frequency converter 3 shown in FIG.

Next, considering the low frequency variable gain amplifier (BBVGA) 4, when the input signal level changes, the output signal level of the low frequency variable gain amplifier 4 is always constant, but the input signal of the low frequency variable gain amplifier 4 is constant. It can be seen from FIG. 9 that the level changes. Therefore, with regard to the low frequency variable gain amplifier 4, when the input signal level to the low frequency variable gain amplifier 4 becomes the highest, that is, when a signal having a relatively low input signal level or higher is input as the receiving apparatus 100, the distortion on the input side. The characteristics must be designed to meet the required values. Further, considering that the distortion characteristics of the entire receiving apparatus 100 are influenced by the circuit block having the worst distortion performance among the circuit blocks constituting the receiving apparatus 100, the distortion characteristics of the low-frequency variable gain amplifier 4 are considered. Must meet the required performance at relatively low input signal levels.
JP 5-218767 (published August 27, 1993) JP-A-6-152283 (published on May 31, 1994)

  As described above, it is difficult to remove a DC component of a low-frequency signal in a semiconductor integrated circuit, and therefore, the design of a circuit subsequent to the circuit in which the DC component of the output signal changes is restricted. Produce. Variable gain amplifiers that can solve this problem have been proposed in Patent Documents 1 and 2 described above, but these variable gain amplifiers have the following problems.

  First, in the circuit configuration of the variable gain amplifier circuit disclosed in Patent Document 1, all the transistors that constitute the circuit when the number of vertically stacked transistors is large and the power supply voltage is low as compared with a general variable gain amplifier circuit. It is difficult to operate the transistor under an appropriate bias condition. Also, when the gain performance of the variable gain amplifier circuit is not good and a low gain is required, that is, when the input signal to the variable gain amplifier circuit is large and good distortion characteristics are required, an appropriate design cannot be made, and distortion When the characteristics are not required, an unnecessary current is passed, resulting in a waste of current consumption.

  Next, the circuit configuration of the variable gain amplifier disclosed in Patent Document 2 also has a large number of vertically stacked circuit stages compared to the configuration of a general variable gain amplifier (low frequency variable gain amplifier 4), and the power supply voltage is compared. When the power supply voltage is low, a sufficient operating voltage range cannot be secured in the amplifier, and the input dynamic range is fixed. Therefore, the current consumption cannot be suppressed while designing the distortion characteristics appropriately.

  The present invention has been made in view of the above problems, and suppresses fluctuations in the direct current component of the output signal and improves the distortion characteristics when the input signal level is the highest to achieve good distortion characteristics. It is an object of the present invention to provide a variable gain amplifier and a receiving apparatus including the same.

  In order to solve the above-described problem, a variable gain amplifier according to the present invention includes a first differential pair including first and second transistors to which an input signal is input to a base, and the first transistor A second differential pair composed of third and fourth transistors whose emitters are connected to the collector, and fifth and sixth transistors whose emitters are connected to the collector of the second transistor A third differential pair; a first resistor connected between the emitters of the first and second transistors; a connection point between the emitter of the first transistor and the first resistor; and a ground. A first current source connected in between; a second current source connected between a connection point between the emitter of the second transistor and the first resistor and the ground; and the third transistor Collector and power supply end And a third resistor connected between the collector of the sixth transistor and the power supply terminal, and the collectors of the fourth and fifth transistors are The bases of the third and sixth transistors are connected to each other, the bases of the fourth and fifth transistors are connected to each other, and the thirds connected to each other are connected to the power supply terminal. A gain control signal is input to the bases of the fourth and fifth transistors connected to the bases of the sixth transistor and the sixth transistor, respectively, and output terminals from which collectors of the third and sixth transistors extract output signals In the variable gain amplifier used as the above, it comprises current control means for controlling the output currents of the first and second current sources, and the current control means comprises: Based on the gain control signal, when the gain of the variable gain amplifier increases, the output currents of the first and second current sources are decreased, and when the gain of the variable gain amplifier decreases, the first and second current sources are decreased. The output current of the second current source is increased.

  According to the above configuration, the variable gain amplifier according to the present invention suppresses fluctuations in the DC component of the output terminal by controlling the output currents of the first and second current sources, that is, the bias current, according to the gain. Specifically, when the gain is high (that is, when the input signal amplitude to the variable gain amplifier is low), the bias current is reduced to suppress a decrease in the output DC voltage, and when the gain is low (that is, the input signal amplitude). Increase the bias current to suppress the output DC voltage from rising. Thereby, the fluctuation | variation of an output DC voltage can be suppressed. Further, the distortion characteristic can be improved by increasing the bias current when the gain is low.

  As described above, the variable gain amplifier according to the present invention is a variable gain amplifier that suppresses the fluctuation of the DC component of the output signal and improves the distortion characteristic when the input signal level becomes the highest, thereby realizing a good distortion characteristic. There is an effect that it can be provided.

  In the variable gain amplifier according to the present invention, a collector of the seventh transistor as the first current source is connected to a connection point between the emitter of the first transistor and the first resistor, and the second transistor The collector of the eighth transistor as the second current source is connected to the connection point between the emitter of the transistor and the first resistor, and the bases of the seventh and eighth transistors are connected to each other. It is preferable that the current control circuit changes a reference current that is input to the first current mirror circuit and serves as an output reference.

  The first and second current sources must always flow the same current, including changes due to the control of the current control means. For this reason, if the first and second current sources are configured with a current mirror circuit (first current mirror circuit) as in the above configuration, the first and second current sources are appropriately and It can be realized easily. The variable gain amplifier can be realized appropriately and easily by performing such control by changing the reference current input to the first current mirror circuit by the current control means.

  In the variable gain amplifier according to the present invention, the current control means includes a voltage conversion circuit that converts the gain control signal into a desired voltage, and a voltage generated by the voltage conversion circuit is applied to a base. And a transconductance amplifier circuit comprising at least a fourth differential pair composed of the tenth transistor and a current source connected to the emitters of the ninth and tenth transistors, respectively. A voltage corresponding to the gain control signal generated by the voltage conversion circuit and input to the bases of the third and sixth transistors connected to each other is input to the base of the ninth transistor. The bases of the ten transistors are connected to the bases of the fourth and fifth transistors connected to each other generated by the voltage conversion circuit. Voltage corresponding to the force to gain control signal is inputted, it is preferable to generate a reference current of the first current mirror circuit from the collector current of the tenth transistor is an output current of the transconductance amplifier circuit.

  According to the above configuration, since the reference current of the first current mirror circuit is generated using the gain control signal, the variable gain amplifier that performs control according to the gain can be realized appropriately and simply. Can do.

  In the variable gain amplifier according to the present invention, the current control means further includes a third current source that outputs a constant current, and an output current of the third current source and an output of the transconductance amplifier circuit. It is preferable to generate the reference current of the first current mirror circuit from the current summed with the current.

  According to the above configuration, a third current source is further provided, and a reference current of the first current mirror circuit is calculated from a sum of an output current of the third current source and an output current of the transconductance amplifier circuit. By generating the above, it is possible to prevent the current of the variable gain amplifier from becoming smaller than an allowable value for appropriate operation.

  In the variable gain amplifier according to the present invention, the current control means a second current mirror that amplifies the sum of the output current of the third current source and the output current of the transconductance amplifier circuit at a constant magnification. It is preferable that the circuit further includes a circuit, and the output current of the second current mirror circuit is the reference current of the first current mirror circuit.

  According to said structure, it is further provided with the 2nd current mirror circuit, The electric current of the sum of the output current of the said 3rd current source, and the output current of the said transconductance amplifier circuit using the said 2nd current mirror circuit Is amplified at a constant magnification and used as the reference current of the first current mirror circuit, so that the current flowing in the circuit constituting the current control means such as the transconductance amplifier circuit can be reduced. The gain amplifier can be realized appropriately, simply, and with low current consumption.

  In the variable gain amplifier according to the present invention, the current source and the third current source in the transconductance amplifier circuit are preferably constituted by a third current mirror circuit to which a common reference current is input.

  According to the above configuration, the variable gain amplifier is configured by configuring the current source and the third current source in the transconductance amplifier circuit by the third current mirror circuit to which a common reference current is input. It can be realized appropriately and easily.

  In the variable gain amplifier according to the present invention, it is preferable that the voltage conversion circuit is an emitter follower circuit.

  In the variable gain amplifier, in order to operate each transistor with an appropriate bias in terms of its circuit configuration, the ninth and tenth transistors are different from the third transistor to the sixth transistor. Since it is desirable to apply a low DC voltage, the variable gain amplifier can be realized appropriately and simply by configuring the voltage conversion circuit with an emitter follower circuit as in the above configuration.

  The receiver according to the present invention is characterized by using the variable gain amplifier in order to solve the above-described problems.

  Since the receiving apparatus according to the present invention uses the variable gain amplifier as described above, a circuit (for example, a circuit subsequent to the variable gain amplifier) without increasing the allowable range of the DC voltage more than necessary. Filter and output amplifier) can be designed, and a receiver having good distortion characteristics and low current consumption can be realized.

  The variable gain amplifier according to the present invention suppresses fluctuations in the DC component of the output terminal by controlling the output currents of the first and second current sources serving as bias currents according to the gain. Specifically, when the gain is high (that is, when the input signal amplitude to the variable gain amplifier is low), the bias current is reduced to suppress a decrease in the output DC voltage, and when the gain is low (that is, the input signal amplitude). Increase the bias current to suppress the output DC voltage from rising. Thereby, the fluctuation | variation of an output DC voltage can be suppressed. Further, the distortion characteristic can be improved by increasing the bias current when the gain is low. As described above, the variable gain amplifier provides a variable gain amplifier that suppresses the fluctuation of the direct current component of the output signal and improves the distortion characteristics when the input signal level becomes the highest, thereby realizing good distortion characteristics. Can do.

  Since the receiving apparatus according to the present invention including the variable gain amplifier as described above uses the variable gain amplifier, the subsequent stage of the variable gain amplifier without increasing the allowable range of the DC voltage more than necessary. Circuit (for example, a filter and an output amplifier) can be designed, and a receiver having good distortion characteristics and low current consumption can be realized.

[Embodiment 1]
An embodiment of the present invention will be described below with reference to FIGS.

  FIG. 1 shows a partial circuit configuration of a variable gain amplifier 60 according to the present embodiment, and FIGS. 2 and 3 show a more specific circuit configuration of the variable gain amplifier 60. For convenience of explanation, members having the same functions as the members of the low-frequency variable gain amplifier 4 shown in FIG.

  As shown in FIG. 1, the variable gain amplifier 60 has a variable current source 30 (first current source) that can change the output current value, instead of the current sources 26 and 27 in the low frequency variable gain amplifier 4. 31 (second current source), and by controlling the output current (that is, bias current) of the variable current sources 30 and 31 according to the gain, the DC component of the output signal output from the signal output terminals 28 and 29 The effect of the gain control signal input to the gain control signal input terminals 14 and 15 can be suppressed, and the fluctuation can be suppressed, that is, stabilized.

  Specifically, when the gain is high (that is, when the input signal amplitude to the variable gain amplifier 60 is low), the output current of the variable current sources 30 and 31 is decreased to increase the input dynamic range more than necessary. Without reducing the output DC voltage, and when the gain is low (that is, when the input signal amplitude is high), the output current of the variable current sources 30 and 31 is increased to increase the input dynamic range and the output DC voltage. Suppresses the rise. Thereby, the fluctuation | variation of an output DC voltage can be suppressed.

  Further, when the gain is set to be small, it means that the input signal level to the variable gain amplifier 60 is high as described above. Therefore, at this time, the output current of the variable current sources 30 and 31 is increased. Thus, the distortion characteristics of the circuit can be improved.

  In the circuit configuration of the variable gain amplifier 60, the gain is almost determined by the ratio between the resistor 23 and the load resistors 24 and 25, so that the gain change caused by changing the output current of the variable current sources 30 and 31 is almost zero. Instead, the gain is controlled based on the gain control signal input to the gain control signal input terminals 14 and 15. The input dynamic range of the variable gain amplifier 60 is determined by the product of the resistor 23 and the bias current of the variable current sources 30 and 31.

  In order for the variable gain amplifier 60 to operate properly, it is necessary that the variable current sources 30 and 31 always pass the same value of current including the change due to the control according to the gain as described above. Therefore, as shown in FIG. 2, the variable current sources 30 and 31 include a current mirror circuit (specifically, a current mirror circuit including the current input circuit 32 and the current output circuits 33 and 34 and a reference current in the current mirror circuit). The variable current source 35) is preferably configured by the current mirror circuit, and the variable current sources 30, 31 can be realized appropriately and easily. Control according to the gain is performed by changing a reference current that is input to the current mirror circuit and serves as a reference for output. Thereby, the variable gain amplifier 60 can be realized appropriately and easily. Hereinafter, a specific circuit configuration of the variable gain amplifier 60 will be described with reference to FIG.

  As shown in FIG. 3, the variable gain amplifier 60 has current input circuits 32, 37, current output circuits 33, 34, 36, a voltage conversion circuit 43, a transconductance with respect to the configuration of the low frequency variable gain amplifier 4. And an amplifier circuit 56. The current input circuit 32 and the current output circuits 33 and 34 constitute variable current sources 30 and 31. The current control means in the variable gain amplifier according to the present invention described in the claims includes a current output circuit 36, a current input circuit 37, a voltage conversion circuit 43, and a transconductance amplifier circuit 56.

  The current input circuit 32 includes an NPN bipolar transistor 32a and a resistor 32b. Similarly, the current output circuits 33 and 34 include one NPN type bipolar transistor and one resistor. The current output circuit 36 includes a PNP bipolar transistor 36a and a resistor 36b. Similarly, the current input circuit 37 includes one PNP-type bipolar transistor (hereinafter referred to as “transistor” as appropriate) and one resistor.

  The current input circuit 32 and the current output circuits 33 and 34 constitute a current mirror circuit (first current mirror circuit). A current is supplied to the current input circuit 32 via the voltage conversion circuit 43, the transconductance amplifier circuit 56, the current output circuit 37, and the current input circuit 36, and the current output circuits 33 and 34 are substantially the same as the current flowing through the current input circuit 32. Generate the same value of current. As described above, since the variable current sources 30 and 31 need to flow the same current in order to properly operate the variable gain amplifier 60, the current output circuits 33 and 34 have the same current. Although it needs to be designed to flow, the current values of the current input circuit 32 and the current output circuits 33 and 34 need not be 1: 1.

  The current input circuit 36 and the current output circuit 37 constitute a current mirror circuit (second current mirror circuit) 55. The mirror ratio (current ratio) of the current mirror circuit 55 may be 1: 1 for the input-to-output, but may be 1: n (n> 1). With this configuration, that is, by a configuration in which the current mirror circuit 55 amplifies the input current at a constant magnification, the current flowing through the transconductance amplifier circuit 56 that supplies current to the current mirror circuit 55 is reduced. Current consumption can be reduced.

  The voltage conversion circuit 43 is connected to the gain control signal input terminals 14 and 15, converts the gain control signal input to the gain control signal input terminals 14 and 15 into a desired voltage, and inputs the input signal of the transconductance amplifier circuit 56. Is generated. Specifically, the voltage conversion circuit 43 is configured by an emitter follower circuit (details will be described later). The variable gain amplifier 60 has a lower DC voltage than the transistors 19 to 22 in the transistors 38 and 39 constituting the transconductance amplifier circuit 56 in order to operate each transistor with an appropriate bias. Therefore, if the voltage conversion circuit 43 is composed of an emitter follower circuit, the variable gain amplifier 60 can be realized appropriately and easily.

  The transconductance amplifier circuit 56 includes NPN bipolar transistors (hereinafter referred to as “transistors” as appropriate) 38 (9th transistor) and 39 (tenth transistor), a resistor 40, and current sources 41 and 42. A current to be supplied to the current output circuit 37 is generated.

  The base of the transistor (first transistor) 17 is connected to the signal input terminal 12, and the base of a transistor (second transistor) 18 that forms a differential pair (first differential pair) together with the transistor 17 is The signal input terminal 13 is connected. A resistor (first resistor) 23 is connected between the emitters of the transistors 17 and 18. The connection point between the emitter of the transistor 17 and the resistor 23 is connected to the collector of a transistor (seventh transistor) 33 a constituting the current output circuit 33, and the emitter of the transistor 33 a constitutes the current output circuit 33. The resistor 33b is grounded. The connection point between the emitter of the transistor 18 and the resistor 23 is connected to the collector of a transistor (eighth transistor) 34 a constituting the current output circuit 34, and the emitter of the transistor 34 a constitutes the current output circuit 34. It is grounded through a resistor 34b. The bases of the transistors 33a and 34a and the base of the transistor 32a constituting the current output circuit 32 are connected to each other, and the emitter of the transistor 32a is grounded via a resistor 32b constituting the current output circuit 32.

  The emitters of the transistors 19 (third transistor) and 20 (fourth transistor) constituting the differential pair (second differential pair) are connected to each other. Connected with collector. The emitters of the transistors 21 (fifth transistor) and 22 (sixth transistor) constituting the differential pair (third differential pair) are connected to each other. Connected with collector. The base of the transistor 20 and the base of the transistor 21 are connected to each other, and the bases connected to each other are connected to the gain control signal input terminal 14. The base of the transistor 19 and the base of the transistor 22 are connected to each other, and the bases connected to each other are connected to the gain control signal input terminal 15.

  The collector of the transistor 19 is connected to the power supply terminal 16 via a load resistor (second resistor) 24, and the collector of the transistor 20 is connected to the power supply terminal 16. The collector of the transistor 21 is connected to the power supply terminal 16, and the collector of the transistor 22 is connected to the power supply terminal 16 via a load resistor (third resistor) 25. A connection point between the collector of the transistor 19 and the load resistor 24 is connected to the signal output terminal 28, and a connection point between the transistor 22 and the load resistor 25 is connected to the signal output terminal 29.

  A resistor 40 is connected between the emitters of the transistors 38 and 39 constituting the differential pair (fourth differential pair). A current source 41 is connected between a connection point between the emitter of the transistor 38 and the resistor 40 and the ground, and a current source 42 is connected between a connection point between the emitter of the transistor 39 and the resistor 40 and the ground. Is connected. The collector of the transistor 38 is connected to the power supply terminal 16, and the collector of the transistor 39 is connected to the power supply terminal 16 via the transistor 37 a and the resistor 37 b that constitute the current output circuit 37.

  The emitter of the transistor 36a of the current input circuit 36 constituting the current output circuit 37 and the current mirror circuit 55 is connected to the power supply terminal 16 via the resistor 36b, and the collector of the transistor 36a is connected to the collector of the transistor 32a. Has been. A voltage corresponding to the gain control signal generated in the voltage conversion circuit 43 and input to the gain control signal input terminal 15 is input to the base of the transistor 38, and the voltage conversion circuit 43 is connected to the base of the transistor 39. The voltage corresponding to the gain control signal input to the gain control signal input terminal 14 is input.

  The variable gain amplifier 60 has the above-described configuration, that is, the level decreases when the gain of the variable gain amplifier 60 is increased, and the level increases when the gain of the variable gain amplifier 60 is decreased. The current supplied to the current input circuit 32 and the current output circuits 33 and 34, which function as the variable current sources 30 and 31 and constitute the current mirror circuit, using the gain control signal input to the gain control signal input terminal 14 Is generated. With this configuration, the variable gain amplifier 60 can realize control according to the gain as described above, and can realize the variable gain amplifier 60 appropriately and simply. The basic amplification operation of the variable gain amplifier 60 is the same as the amplification operation of the low-frequency variable gain amplifier 4, and therefore the description thereof is omitted here.

[Embodiment 2]
Another embodiment of the present invention is described below with reference to FIGS.

  FIG. 4 shows a circuit configuration of the variable gain amplifier 60a according to the present embodiment, and FIGS. 5 and 6 show more specific circuit configurations of the variable gain amplifier 60a. For convenience of explanation, members having the same functions as those of the variable gain amplifier 60 shown in FIG. 1 to FIG.

  The variable gain amplifier 60a outputs a constant current between the output terminal of the transconductance amplifier circuit 56, that is, the connection point between the collector of the transistor 37a and the collector of the transistor 39a, and the ground. A current source 44 is provided. By adding the current source 44, it is possible to prevent the current of the variable gain amplifier 60a from becoming smaller than an allowable value for appropriate operation.

  The current source 44 can be constituted by a current output circuit 47 as shown in FIG. Similarly, the current sources 41 and 42 can also be configured by current output circuits 45 and 46. The current output circuits 45 to 47 constitute a current mirror circuit (third current mirror circuit) together with the current input circuit 48. The current input circuit 48 inputs a reference current as an output reference to the current mirror circuit. The current source 49 supplies current to the current input circuit 48.

  Further, as shown in FIG. 6, the voltage conversion circuit 43 includes NPN-type bipolar transistors 50 and 51 that constitute an emitter follower circuit, and current output circuits 52 and 53 that supply the emitter currents of the transistors 50 and 51, respectively. Can be configured. The current output circuits 52 and 53 constitute the current mirror circuit together with the current output circuits 45 to 47 and the current input circuit 48. With the configuration as described above, the variable gain amplifier 60a can be realized appropriately and easily. The current ratio of the current mirror circuit constituted by the current output circuits 45 to 47 and the current input circuit 48 is designed so that the gain and distortion characteristics of the variable gain amplifier 60a are set to desired values.

  The current output circuit 45 includes an NPN bipolar transistor 45a and a resistor 45b. Similarly, the current output circuits 46, 47, 52, 53 and the current input circuit 48 also include one NPN bipolar transistor and one resistor.

  The collector of the transistor 48a of the current input circuit 48 is connected to the power supply terminal 16 via a current source 49, and the emitter of the transistor 48a is grounded via a resistor 48b. The emitter of the transistor 53a of the current output circuit 53 is grounded via a resistor 53b, and the collector of the transistor 53a is connected to the emitter of the transistor 51. The base of the transistor 51 is connected to the gain control signal input terminal 14, and the collector of the transistor 51 is connected to the power supply terminal 16. A connection point between the collector of the transistor 53 a and the emitter of the transistor 51 is connected to the base of the transistor 39.

  The emitter of the transistor 52a of the current output circuit 52 is grounded via a resistor 52b, and the collector of the transistor 52a is connected to the emitter of the transistor 50. The base of the transistor 50 is connected to the gain control signal input terminal 15, and the collector of the transistor 50 is connected to the power supply terminal 16. A connection point between the collector of the transistor 52 a and the emitter of the transistor 50 is connected to the base of the transistor 38.

  The emitter of the transistor 45a of the current output circuit 45 is grounded via a resistor 45b, and the collector of the transistor 45a is connected to the connection point between the emitter of the transistor 38 and the resistor 40. The emitter of the transistor 46 a of the current output circuit 46 is grounded via a resistor 46 b, and the collector of the transistor 46 a is connected to the connection point between the emitter of the transistor 39 and the resistor 40. The emitter of the transistor 47a of the current output circuit 47 is grounded via a resistor 47b, and the collector of the transistor 47a is connected to the connection point between the collector of the transistor 37a and the collector of the transistor 39a. The bases of the transistors 45a to 48a, 52a, and 53a are connected to each other.

  The variable gain amplifier 60a having the above-described configuration converts the current supplied to the current input circuit 32 and the current output circuits 33 and 34 constituting the current mirror circuit, which functions as the variable current sources 30 and 31, into transconductance. This is the same as the variable gain amplifier 60 except that the sum of the output current of the amplifier circuit 56 and the output current of the current source 44 is generated via the current mirror circuit 56, and corresponds to the gain as described above. Control can be realized, and a variable gain amplifier can be realized appropriately and easily.

  As described above, the variable gain amplifier according to the present embodiment controls (increases or decreases) the output currents of the variable current sources 30 and 31 that are bias currents according to the gain, thereby increasing the gain of the DC component of the output signal. It is possible to realize a variable gain amplifier capable of obtaining necessary distortion characteristics while suppressing dependent fluctuations and suppressing waste of current consumption. Then, this variable gain amplifier (particularly, the variable gain amplifier 60a shown in FIG. 6 is most preferable) is used as the low frequency variable gain amplifier 4 of the receiving apparatus 100 shown in FIG. Therefore, it is possible to realize a receiving apparatus that can reduce the restriction on the input DC voltage of 6 and obtain necessary distortion characteristics while suppressing current consumption during actual use. In the above variable gain amplifier, the minute gain change depending on the bias current is absorbed by the feedback loop that keeps the output signal level constant, so this minute gain change affects the operation and characteristics of the receiving apparatus. do not do.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The variable gain amplifier according to the present invention suppresses fluctuations depending on the gain of the DC component of the output signal and obtains necessary distortion characteristics while suppressing waste of current consumption. It can be suitably used as a variable gain amplifier in a receiving apparatus that receives a television broadcast signal and performs processing such as frequency conversion and amplification in order to perform demodulation processing and the like on the received signal in a subsequent circuit. The receiving device according to the present invention provided with the variable gain amplifier can be suitably used as the receiving device.

1 is a circuit diagram showing a configuration of a part of a variable gain amplifier according to an embodiment of the present invention. FIG. 2 is a circuit diagram showing a more specific configuration of the variable gain amplifier shown in FIG. 1. FIG. 2 is a circuit diagram showing a more specific configuration of the variable gain amplifier shown in FIG. 1. It is a circuit diagram which shows the structure of the variable gain amplifier which concerns on other embodiment of this invention. FIG. 4 is a circuit diagram showing a more specific configuration of the variable gain amplifier shown in FIG. 3. FIG. 4 is a circuit diagram showing a more specific configuration of the variable gain amplifier shown in FIG. 3. It is a figure which shows a prior art and shows the structure of a receiver. It is a circuit diagram which shows the structure of the low frequency variable gain amplifier in the receiver shown in FIG. FIG. 8 is a level diagram of the receiving apparatus shown in FIG. 7. FIG. It is a schematic diagram of gain control of the receiving apparatus shown in FIG.

Explanation of symbols

16 Power supply terminal 17 Transistor (first transistor)
18 transistor (second transistor)
19 transistor (third transistor)
20 transistor (fourth transistor)
21 transistor (fifth transistor)
22 transistor (sixth transistor)
23 Resistance (first resistance)
24 resistance (second resistance)
25 Resistance (third resistance)
28, 29 Output terminal 30 Variable current source (first current source)
31 Variable current source (second current source)
33a Transistor (seventh transistor)
34a Transistor (eighth transistor)
38 transistors (9th transistor)
39 transistor (tenth transistor)
44 Current source (third current source)
55 Current mirror circuit (third current mirror circuit)
56 Transconductance amplifier circuit 60, 60a Variable gain amplifier 100 Receiver

Claims (8)

A first differential pair composed of a first transistor and a second transistor for inputting an input signal to a base, and a third transistor and a fourth transistor whose emitter is connected to the collector of the first transistor. A second differential pair, a third differential pair composed of fifth and sixth transistors whose emitters are connected to the collector of the second transistor, and the first and second transistors A first resistor connected between the emitters; a first current source connected between a connection point between the emitter of the first transistor and the first resistor and the ground; and the second transistor. A second current source connected between a connection point between the emitter of the first transistor and the first resistor and the ground, and a second resistor connected between the collector of the third transistor and the power supply terminal; , The sixth transistor A third resistor connected between the collector and the power supply terminal, the collectors of the fourth and fifth transistors being connected to the power supply terminal, and the bases of the third and sixth transistors. Are connected to each other, the bases of the fourth and fifth transistors are connected to each other, and the bases of the third and sixth transistors connected to each other are connected to each other. In a variable gain amplifier in which a gain control signal is input to each of the bases of the transistors, and the collectors of the third and sixth transistors are used as output terminals for extracting output signals.
Current control means for controlling output currents of the first and second current sources;
The current control means reduces the output current of the first and second current sources when the gain of the variable gain amplifier increases and decreases the gain of the variable gain amplifier based on the gain control signal. Increases the output currents of the first and second current sources. A collector of the seventh transistor as the first current source is connected to a connection point between the emitter of the first transistor and the first resistor, and the emitter of the second transistor and the first resistor are connected. Is connected to the collector of the eighth transistor as the second current source, and the bases of the seventh and eighth transistors are connected to each other to form a first current mirror circuit,
2. The variable gain amplifier according to claim 1, wherein the current control means changes a reference current that is input to the first current mirror circuit and serves as an output reference. The current control means includes
A voltage conversion circuit for converting the gain control signal into a desired voltage;
The voltage generated by the voltage conversion circuit is connected to the fourth differential pair composed of the ninth and tenth transistors to be applied to the base, and to the emitters of the ninth and tenth transistors, respectively. A transconductance amplifier circuit including at least a current source
A voltage corresponding to the gain control signal generated by the voltage conversion circuit and input to the bases of the third and sixth transistors connected to each other is input to the base of the ninth transistor, A voltage corresponding to the gain control signal generated by the voltage conversion circuit and input to the bases of the fourth and fifth transistors connected to each other is input to the base of the tenth transistor,
3. The variable gain amplifier according to claim 2, wherein a reference current of the first current mirror circuit is generated from a collector current of the tenth transistor which is an output current of the transconductance amplifier circuit.   The current control means further includes a third current source that outputs a constant current, and the current control means calculates the first current from the sum of the output current of the third current source and the output current of the transconductance amplifier circuit. 4. The variable gain amplifier according to claim 3, wherein a reference current of one current mirror circuit is generated.   The current control means further includes a second current mirror circuit that amplifies the sum of the output current of the third current source and the output current of the transconductance amplifier circuit at a constant magnification, 5. The variable gain amplifier according to claim 4, wherein an output current of the second current mirror circuit becomes a reference current of the first current mirror circuit.   6. The current source and the third current source in the transconductance amplifier circuit are configured by a third current mirror circuit to which a common reference current is input. The variable gain amplifier according to item.   The variable gain amplifier according to claim 3, wherein the voltage conversion circuit includes an emitter follower circuit.   A receiving device using the variable gain amplifier according to claim 1.

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