JPS5829001B2 - gain control amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gain control amplifier circuit whose gain can be changed according to a voltage applied to a control input terminal.

Conventionally, the gain can be controlled by DC voltage.
Various types of so-called gain control amplifier circuits have been considered.

For example, FIG. 1 shows an example of this gain control amplification circuit, in which the gain changes according to an exponential function of the DC voltage applied to the control input terminal 11.

That is, in FIG. 1, the input signal applied to the input terminal 2 is inputted via the resistor 11 (value R1) to the amplifier 4 in which the transistor 3 is inserted in the feedback circuit, where it is subjected to voltage-to-current conversion. , is input to an amplifier 6 having a resistor 8 (value R2) in a feedback circuit via a transistor 5 whose emitter is commonly connected to the transistor 3, and is converted from current to voltage by the amplifier 6 and output from an output terminal 7.

Then, the DC control voltage applied to the control input terminal 1 is
The voltage is divided by a resistor 9 (value R3) and a resistor 10 (value R4) and applied to the base of the transistor 5.

Therefore, the gain Av of the gain control amplifier circuit having the above configuration is
1 is the DC control voltage applied to the control input terminal, Vc
Then, the gain A, V ] is determined according to the exponential function of the DC control voltage Vc.

Note that the method of deriving this formula is almost the same as the way to derive formula (11), which will be described later, so please refer to this.

In the above conventional example, amplifiers 4 and 6 are connected in series, and each amplifier 4 and 6 is provided with feedback, but only negative feedback is provided for each amplifier (not negative feedback for the entire circuit). Therefore, the amplifiers 4 and 6 are required to have the same gain and distortion rate and high performance, resulting in disadvantages such as increased cost and difficulty in achieving linearity due to the imbalance.

The present invention has been made to eliminate the above-mentioned disadvantages, and its purpose is to provide a high-performance gain control amplifier circuit regardless of the characteristics of the number of amplifiers used. The input signal current obtained in the first amplifier is applied to the non-inverting input terminal of the first amplifier and the collector of the first transistor, and the output signal of the first amplifier is supplied to the output terminal, and the second an inverting input terminal of an amplifier and a collector of a second transistor υ), supplying an output signal of the second amplifier to each emitter of the first and second transistors, and an inverting input terminal of the first amplifier; , each of the non-inverting input terminals of the second amplifier is grounded;
A control voltage is applied between the bases of the first and second transistors.

The present invention will be described in detail below with reference to the drawings.

FIG. 2 is a circuit diagram showing the configuration of a gain control amplifier circuit which is an embodiment of the present invention.
3 is connected to the non-inverting input terminal of an amplifier 15 (operational amplifier) via a resistor 14 (value R5), the inverting input terminal of this amplifier 15 is grounded, and its output terminal is connected to the output terminal 16. It has become.

This output terminal 16 is connected via a resistor 17 (value R6) to the collector of a transistor 18 and an amplifier 19 (operational amplifier).
The non-inverting input terminal of this amplifier 19 is grounded, and the output terminal thereof is connected to the common emitter of transistors 18 and 21 via a resistor 20.

The control input terminal 22 is connected to the base of a transistor 18 via a resistor 23 (value R7), and the base of this transistor 18 is grounded via a resistor 24 (value R8).
The base and collector of the transistor 21 are connected to ground and to the non-inverting input terminal of the amplifier 15, respectively.

In the above configuration, the transistor 21 constitutes the first circuit, the transistor 18 constitutes the second circuit, and the amplifier 1
9 and transistor 21 constitute a feedback loop of amplifier 15, and transistor 18 constitutes a feedback loop of amplifier 19.

Furthermore, these transistors 18 and 21 are configured as a pair of transistors in order to have the same characteristics.

Therefore, in the gain control amplifier circuit having the above configuration,
The collector currents of the transistor 21 and the transistor 18 are each Ic1 (input signal current) Ic2, and the base-emitter voltages are Vbe1 and Vbe2, respectively.
Then, the following equation holds true from the properties of the PN junction of the transistor.

That is, holds true.

However, in this equation, holds true, and taking the natural logarithm of both sides of the above equation (1), the above (
2) By substituting and transforming the equation, we can find the following.

Next, the DC voltage supplied to the control input terminal 22 is set to V c
1 and the voltage supplied to the base of the transistor 18 is Vo.

By substituting the expression, In this equation (5), the above (3) and (4) relationship is required.

If we rewrite this equation (6) as a common logarithm, we can obtain the common logarithm, and in this equation (7), log e=0
．． Substituting and transforming 4343 yields.

On the other hand, if the input voltage supplied to the input terminal 13 is El, and the output voltage obtained at the output terminal 16 is E2, the following relationship is obtained from the properties of an operational amplifier.

Therefore, when the gain Av2 of the circuit shown in FIG. 2 is calculated from the above equations (8) and (10), it becomes as follows.

That is, the gain of the gain control amplifier circuit shown in FIG. 2 is determined according to an exponential function of the DC voltage Vc1 applied to the control input terminal 22.

FIG. 3 is a circuit diagram showing the configuration of a gain control amplifier circuit according to another embodiment of the present invention, and in this figure, parts corresponding to those in FIG. 2 are given the same reference numerals.

In FIG. 3, the input terminal 13 is connected to the non-inverting input terminal of an amplifier 15 via a resistor 14, the inverting input terminal of this amplifier 15 is grounded, and the output terminal thereof is connected to an output terminal 16. ing.

This output terminal 16 is connected via a resistor 17 to the collector of a PNP transistor 26, the collector of an NPN transistor 27, and the inverting input terminal of an amplifier 19, whose non-inverting input terminal is grounded and whose output terminal is connected via a resistor 28. is connected to the common emitters of the P'NP transistors 26 and 29, and is also connected via a resistor 30 to the common emitters of the NPN l-transistors 27 and 31.

Then, the control input terminal 22 is connected to NPN1 via a resistor 23.
- a transistor 2γ connected to the base of a PNP transistor 29, the base of which is grounded via a resistor 24;
The base of the NPN transistor 31 and the base of the PNP transistor 26 are grounded, and the collector of the NPN transistor 31 and the collector of the PNP transistor 29 are both connected to the non-inverting input terminal of the amplifier 15.

In the gain control amplifier circuit having the above configuration, PNP I
- transistor 29 and NPN transistor 31 constitute a first circuit, and PNP transistor 26 and NPN transistor 27 constitute a second circuit.

The PNP transistor 29, the NPN transistor 31, the PNP transistor 26, and the NPNI-transistor 27 each have a complementary circuit configuration.

Therefore, whereas the circuit shown in FIG. 2 is defined only when the input voltage applied to the input terminal 13 is positive, the gain control amplifier circuit shown in FIG. 3 is defined only when the input voltage is positive or negative. It can be used in either case.

That is, when the input voltage applied to the input terminal 13 in FIG. 3 is positive, the NPN transistor 3L27 works as the transistor 21.18 in FIG.
PNP t-transistors 29 and 26 are reverse biased and do not operate at all.

Conversely, if the input voltage is negative, the PNP transistor 29
．． 26 acts as transistor 21.18 in FIG. 2, while NPN transistor 31.27 is reverse biased and does not operate at all.

That is, the gain control amplifier circuit shown in FIG. 3 has the same characteristics as the circuit shown in FIG. 2 regardless of whether the input voltage is positive or negative, and can be widely applied to gain control of AC signals.

As explained above, according to the present invention, a circuit including a resistor, a second amplifier, and first and second transistors is inserted in the feedback circuit of the first amplifier, and Since pressure is applied across the bases of the transistors, it is not necessary to particularly match the characteristics of the first amplifier and the second amplifier. Sufficiently excellent characteristics can be obtained without special consideration of the characteristics, and an inexpensive and high-performance gain control amplifier circuit can be provided.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional gain control term and @ circuit, and FIGS. 2 and 3 are circuit diagrams showing an embodiment of the present invention. 13... Input terminal, 15... First amplifier, 16... Output terminal, 17... Resistor, 18... Second transistor, 19...
...Second amplifier, 21...First transistor.

Claims (1)

[Claims] 1. Apply the input signal current obtained at the input terminal to the non-inverting input terminal of the first amplifier and the collector of the first transistor, supply the output signal of the first amplifier to the output terminal, and the inverting input of the second amplifier and the collector of the second transistor, and the output signal of the second amplifier is supplied to the inverting input of the first . the inverting input terminal of the first amplifier and the non-inverting input terminal of the second amplifier are respectively grounded;
．． A gain control amplifier circuit comprising a control voltage applied between each base of a second transistor, and a gain between the output terminal and the input terminal being determined according to an exponential function of the control voltage.