JPH0355908A - Gain control amplifier circuit - Google Patents

Abstract

PURPOSE:To obtain a sufficiently large output amplitude even when power voltage is low by varying the current flowing to a load in response to the gain and decreasing a voltage drop caused in a load even when the gain is increased. CONSTITUTION:Bases of transistors(TRs) Q10, Q11 being components of a differential circuit connect to bases of TRs Q3, Q4 to detect the ratio of collector currents IC3, IC4 of the TRs Q3, Q4. The collector current of the TR Q10 results in a current (i) flowing to the collector of the Tr Q4 through TRs Q8, Q9 forming a current mirror circuit to decrease the voltage drop of a resistor R3. When currents I1, I4 of constant current sources 2, 5 are set to proper values by taking a power voltage and output amplitude into account, the output amplitude is increased.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a gain control amplifier circuit.

[Conventional technology]

Conventionally, a circuit shown in FIG. 2 has been known as this type of amplifier circuit. To explain the operation of FIG. 2, it is the output current of a differential circuit composed of transistors Ql and Q2. The gain of the output terminal 6 as seen from the input terminal 1 is changed by controlling the amount of 2 flowing through the load resistor R by a differential circuit of transistors Ql and Q4. To control the gain, the voltage difference between the power supplies 10 and 11 is controlled by resistors Rs and R. The power source 1
A change of 1 is treated as a change in gain.

[Problem to be solved by the invention]

In the conventional gain control amplifier circuit described above, when the gain is increased, the current Ic4 flowing through the load resistor R, increases;
As the voltage drop increases and the operating potential of the output signal decreases, when the power supply voltage is low, the collector-emitter voltage of transistor Q4 increases. ．． This has the disadvantage that the output signal cannot swing in the negative direction.

SUMMARY OF THE INVENTION An object of the present invention is to provide a gain control amplifier circuit that can provide a large output amplitude even when the gain is increased when the power supply voltage is low.

[Means to solve the problem]

The gain control amplifier circuit of the present invention includes first and second transistors connected in a differential manner, means for supplying an input signal current to the emitter junction of the first and second transistors, and the first transistor. a load for obtaining an output signal from the collector of the transistor; means for supplying a gain control voltage between the bases of the first and second transistors; means for generating a current exhibiting a change in phase with a change in collector current in the first transistor; and a current mirror circuit having an input terminal receiving the current from the means and having an output terminal connected to the collector of the first transistor. It is characterized by having the following.

〔Example〕 Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram for explaining one embodiment of the present invention, and the conventional example explained in FIG.
A current mirror circuit consisting of a transistor Q. ,Q
11 and a constant current width 5 are added.

As for the operation of the additional circuit, the transistor Q1. ,Qll
The base of the differential circuit composed of
By connecting to the base of 4, the collector current of transistors Q3 and Q4 is connected. 3y I. Detecting the ratio of 4, transistor Q1. By flowing current i into the collector of transistor Q4 through Q a and Q s forming a current mirror circuit, the voltage drop across R is reduced. Here, the current values II of constant current sources 2 and 5,
If I4 is set to an appropriate value that takes into account the power supply voltage and output amplitude, the output amplitude can be increased. [Effects of the Invention] As explained above, the present invention can reduce the voltage drop caused by the load even when the gain is increased by changing the current flowing through the load according to the gain, so even when the power supply voltage is low. , it becomes possible to obtain a sufficiently large output amplitude.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram for explaining an embodiment of the present invention, and FIG. 2 is a circuit diagram for explaining a conventional gain control amplifier circuit. 1...Input terminal, 2-5...Constant current source, 6...Output terminal, 7...High-level power supply terminal, 8...・Localization side power supply terminal, Q1~Ql1・
...Transistor, Rl to R6...Resistance.

Claims (1)

[Claims] first and second transistors connected in a differential manner, means for supplying an input signal current to the emitter junction of the first and second transistors, and obtaining an output signal from the collector of the first transistor; means for supplying a gain control voltage between the bases of the first and second transistors; and receiving the gain control voltage and varying a collector current in the first transistor in response to the gain control voltage. means for generating a current exhibiting a change in phase with
A gain control amplifier circuit comprising: a current mirror circuit whose input terminal receives the current from the means and whose output terminal is connected to the collector of the first transistor.