JP3049712B2 - Gain control amplifier circuit - Google Patents

Description

Description: TECHNICAL 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 kind of amplifier circuit. The operation of FIG. 2 will be described. The output current I _{C2 of the} differential circuit composed of the transistors Q ₁ and Q ₂ is the load resistance
And the amount flowing to R ₃ by changing the gain of the transistor Q _3, Q output terminal 6 which is controlled to viewed from the input terminal 1 in the differential circuit _4. The gain is controlled by converting the voltage difference between the power supplies 10 and 11 into current with the resistors R ₅ and R ₆ , and converting the current into voltage with the diodes D ₁ and D ₂ to form transistors Q ₃ and Q _By supplying the power to the base ₄ , the change of the power supply 11 is changed to the change of the gain.

[Problems to be solved by the invention]

In the conventional gain control amplifier circuit described above, when the gain is increased, the current I _C4 flowing through the load resistor R ₃ increases, so that the voltage drop of R ₃ increases and the operating potential of the output signal decreases, so that the power supply voltage is low. the collector-emitter voltage V _CE of the transistor Q ₄ is can not be secured, there is a disadvantage that the output signal can not swing in a negative direction.

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

[Means for solving the problem]

The gain control amplifier circuit according to the present invention includes a first and a second transistor connected in a differential manner, a circuit for supplying an input signal current to an emitter coupling point of the first and the second transistor, A load connected between the collector of the transistor and a power supply, a circuit for supplying a gain control voltage between the bases of the first and second transistors, and a current flowing through the load due to a change in the gain control voltage. A circuit for supplying a current corresponding to the gain control voltage to the collector of the first transistor when increasing the current, and increasing the current flowing to the collector of the first transistor.

〔Example〕

Next, the present invention will be described with reference to the drawings. First
The figure is a circuit diagram for explaining an embodiment of the present invention,
A current mirror circuit including transistors Q ₈ and Q ₉ , a differential circuit including transistors Q ₁₀ and Q ₁₁ and a constant current width 5 are added to the conventional example described with reference to FIG.

The operation of the additional circuitry, the transistors Q _10, based on the transistor Q of the differential circuit composed of Q _{11 3,} Q ₄ of the transistor Q ₃ by connecting to the base, Q ₄ of the collector current I
_C3, detects the ratio of I _C4, by pouring a current i to the collector of the transistor Q ₄ by Q _8, Q ₉ constituting the current mirror circuit the collector currents of the transistors Q _10, decreases the voltage drop across R ₃ ing. If the current values I ₁ and I ₄ of the constant current sources 2 and 5 are set to appropriate values in consideration of the power supply voltage and the output amplitude, the output amplitude can be increased.

〔The invention's effect〕

As described above, the present invention can reduce the voltage drop caused by the load even when the current flowing to the load is changed according to the gain to increase the gain, so that even when the power supply voltage is low, the output amplitude is sufficiently large. Can be obtained.

[Brief description of the 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 to 5 constant current source, 6 output terminal, 7 higher power supply terminal, 8 localization power supply terminal, Q ₁
QQ ₁₁ …… Transistor, R ₁ RR ₆ …… Resistance.

Claims (1)

(57) [Claims] A first and second transistor connected in a differential manner, a circuit for supplying an input signal current to an emitter junction of the first and second transistors,
A load connected between the collector of the transistor and a power supply, a circuit for supplying a gain control voltage between the bases of the first and second transistors, and a current flowing through the load due to a change in the gain control voltage. A circuit for supplying a current corresponding to the gain control voltage to the collector of the first transistor when increasing the current, and increasing the current flowing to the collector of the first transistor.