JPH0244166B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gain control amplifier whose gain varies linearly in response to a gain control signal such as a control voltage.

This type of gain control amplifier usually has a non-feedback configuration because its purpose is to change the gain. For this reason, this type of gain control amplifier generally has the disadvantage of extremely high distortion (for example, total harmonic distortion is about 0.1%), so it is not suitable for applications such as audio, where high fidelity is required. , it was inappropriate to use it as an electronic volume or the like.

The present invention was made in view of the above-mentioned circumstances, and its purpose is to provide a gain control amplifier that has a non-feedback configuration, has extremely low distortion, and can therefore be used as an electronic volume for audio equipment. It's about doing. In order to achieve this objective, the gain control amplifier according to the present invention has the following features:
a variable gain amplification section comprising differentially configured transistors and a variable current source that changes a common emitter current of these transistors in accordance with a gain control signal; at least one pair of semiconductor rectifiers inserted in parallel and with current directions opposite to each other in the path of an input signal applied to the input signal, and between the power supply and the signal input side of each of the pair of semiconductor rectifiers, respectively. A distortion canceling circuit having a DC bias adjustment circuit inserted therein is provided, and the output is taken out from the collector side of the differentially configured transistor.

With this configuration, the distortion generated in the variable gain amplifier can be canceled out by the distortion generated by the distortion canceling circuit, and a gain control amplifier with low distortion can be realized. Furthermore, even if the characteristics of each of the semiconductor rectifying elements vary,
Since the bias of each semiconductor rectifying element can be adjusted by the corresponding DC bias adjustment circuit, it is possible to adjust the bias so that distortion is canceled out regardless of whether a positive or negative polarity signal is input.

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a circuit diagram showing the basic configuration of a gain control amplifier according to the present invention when the input signal is positive. In this diagram,
Reference numeral 1 indicates a variable gain amplification section, and reference numeral 2 indicates a distortion canceling circuit. In the variable gain amplification section 1, numerals 3 and 4 are differentially configured transistors, both of which are NPN transistors. Both emitters of these transistors 3 and 4 are commonly connected and connected to a negative power supply terminal 6 via a variable current source 5.
(The power supply voltage is -Vcc). The current _I0 of the variable current source 5 is designed to change in proportion to the control voltage Vc (gain control signal) applied to the control input terminal 5a. The collector of the transistor 3 is connected to an inverting input terminal of an operational amplifier 7, and is also connected to a positive power supply terminal 9 (power supply voltage is +Vcc) via a resistor 8. The base of the transistor 4 is grounded via a resistor 10, and the collector of the transistor 4 is connected to a non-inverting input terminal of an operational amplifier 7 and also to a positive power supply terminal 9 via a resistor 11. The non-inverting input terminal of the operational amplifier 7 is grounded via a resistor 12, and the output terminal of the operational amplifier 7 is connected to the signal output terminal 13 and connected to the inverting input terminal of the operational amplifier 7 via a feedback resistor 14. It is connected to the.

Further, in the distortion canceling circuit 2, 14 is a diode (semiconductor rectifying element), and this diode 1
The anode of the diode 14 is connected to the signal input terminal 15, and the cathode of the diode 14 is grounded via resistors 16 and 17 in sequence. The connection point between the resistors 16 and 17 is connected to the base of the transistor 3.

Next, the operation of this gain control amplifier having the above configuration will be explained.

First, the operation of the variable gain amplification section 1 will be explained.
Let us now assume that the voltage of the signal supplied from the connection point of the resistors 16 and 17 in the distortion canceling circuit 2 to the base of the transistor 3 is Va, and the voltage of the output signal obtained at the signal output terminal 13 is _V0 . Here, considering the case where the control voltage Vc is a certain constant value and therefore the current I ₀ is constant, the rate of change of the voltage V ₀ with respect to the voltage Va, that is, the gain G ₁ ( Here, the characteristic curve of G ₁ =V ₀ /Va) is as shown by the solid line a in FIG. That is, in this case, the gain G ₁ of the variable gain amplification section 1 exhibits a nonlinear characteristic such that it decreases as the voltage Va increases due to the effect of the base-emitter voltages of the transistors 3 and 4.
Then, when the control voltage Vc is changed, the current
Since I ₀ changes, the gain G ₁ maintains the nonlinear characteristics described above, and the control voltage It changes linearly according to Vc.

Next, in the distortion cancellation circuit 2, the diode 1
The forward resistance Rd of the diode 4 decreases as the forward voltage Vd of the diode 14 increases, as shown in FIG. The characteristic curve of G ₂ (here G ₂ =Va/Vi) is as shown in FIG. That is, in this case, the gain G ₂ of the distortion canceling circuit 2 is reduced by the voltage Vi due to the action of the diode 14.
It exhibits a nonlinear characteristic that increases as G increases, and this nonlinear characteristic has an inverse relationship to the nonlinear characteristic of the gain G ₁ in the variable gain amplification section 1 described above.

As a result of the above, the overall gain G (here, G=V ₀ /Vi) of this gain control amplifier, expressed as the product of gain G ₁ and gain G ₂ , is determined by the nonlinearity of gain G ₁ and the gain G ₂ . The nonlinearity cancels out and becomes approximately linear. In this way, according to the basic configuration shown in FIG. 1, it is possible to realize a gain control amplifier with extremely low distortion even though it has a non-feedback configuration.

Next, we will create a fifth concrete circuit based on this basic configuration.
As shown in the figure. In this figure, parts corresponding to those in FIG. 1 are given the same reference numerals.

In the distortion canceling circuit 2 shown in FIG. 5, a DC blocking capacitor 18a and a diode 14a are serially connected between the signal input terminal 15 and the resistor 16, with the cathode of the diode 14a facing the resistor 16. A capacitor 18b for DC blocking and a diode 14b are inserted in series in parallel with this, with the anode of the diode 14b facing the resistor 16. Capacitor 18a
The connection point between and the diode 14a is a resistor 19a,
It is connected to the positive power supply terminal 9 through the variable resistor 20a in order, so that an adjustable DC bias current can be supplied to the diode 14a. Further, the connection point between the capacitor 18b and the diode 14b is connected to the negative power supply terminal 6 via a resistor 19b and a variable resistor 20b in order, so that an adjustable DC bias current can be supplied to the diode 14b.

In this case, when the input signal Vi is positive, the input signal is given distortion characteristics by the diode 14a and is supplied to the base of the transistor 3 (at this time, the diode 14b is in a non-conducting state); When Vi is negative, the same input signal is connected to diode 1
4b imparts distortion characteristics to the transistor 3.
(at this time, the diode 14a
becomes non-conducting). In this case, the distortion characteristics imparted by the diodes 14a and 14b are as follows:
By changing the DC bias current supplied to these diodes 14a, 14b using variable resistors 20a, 20b, it is possible to set the optimum state to cancel the distortion of variable gain amplifier section 1.

Next, in the variable gain amplifier section 1, each emitter of the transistors 3 and 4 is connected to a diode _21-1 to _21-6.
and diodes _22-1 to _22-6 , respectively, and then NPN transistor 23 and resistor 2.
4 in turn to the negative power supply terminal 6.
This part consisting of the transistor 23 and the resistor 24, and the diode-connected NPN transistor 2
5 and the emitter resistor 26 of the transistor 25 constitute a current mirror circuit, and the transistor 25 in this current mirror circuit includes a variable resistor 27 and resistors 28 to 3.
A constant current I ₀ corresponding to the control voltage Vc is supplied from a variable constant current circuit including a PNP transistor 31.

According to this specific circuit, the input signal supplied to the signal input terminal 15 is transferred to the control input terminal 5a.
When amplifying at a gain according to the control voltage Vc applied to the signal output terminal 13 and outputting the signal from the signal output terminal 13, the distortion generated in the variable gain amplifying section 1 is canceled by the distortion generated in the distortion canceling circuit 2. can do.

As is clear from the above description, the gain control amplifier according to the present invention includes differentially configured transistors and a variable current source that changes the common emitter current of these transistors in accordance with a gain control signal. at least one pair of semiconductor rectifying elements with current directions opposite to each other and inserted in parallel in a path of an input signal applied between both bases of the differentially configured transistor; a distortion canceling circuit having a DC bias adjustment circuit inserted between the power supply and the signal input side of each of the pair of semiconductor rectifying elements, and the collector side of the differentially configured transistor. Since the output is taken out from the variable gain amplifier, the distortion in the variable gain amplifier section is canceled out by the distortion in the distortion canceling circuit, making it possible to realize a gain control amplifier with extremely low distortion. Also,
According to this invention, even if the characteristics of each of the semiconductor rectifying elements vary, the bias of each semiconductor rectifying element can be adjusted by the corresponding DC bias adjustment circuit. can be adjusted so that the distortion is canceled even when input. Furthermore, since the gain control amplifier according to the present invention has a non-feedback configuration and a simple circuit configuration, it has the advantage of being able to vary the gain extremely efficiently and being inexpensive. Suitable as an electronic volume.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the basic configuration of a gain control amplifier according to the present invention, FIG. 2 is a characteristic diagram showing gain changes of the variable gain amplifier section 1 in the same basic configuration, FIG. 3 is a characteristic diagram of a diode, and FIG. FIG. 4 is a characteristic diagram showing the gain change of the distortion canceling circuit 2 in the basic configuration, and FIG. 5 is a circuit diagram showing an example of a specific circuit of the gain control amplifier according to the present invention. 1... variable gain amplifier, 2... distortion canceling circuit, 3,
4... Differentially configured transistor, 5... Variable current source.

Claims (1)

[Scope of Claims] 1. A variable gain amplification section comprising differentially configured transistors and a variable current source that changes the common emitter current of these transistors in accordance with a gain control signal; 2. at least one pair of semiconductor rectifiers inserted in parallel and with current directions opposite to each other in the path of an input signal applied between both bases of the configured transistor; and a power supply and each of the pair of semiconductor rectifiers. a distortion canceling circuit each having a DC bias adjustment circuit inserted between the signal input side and the signal input side, and configured to take out an output from the collector side of the differentially configured transistor. Control amplifier.