JPS5910013A - Gain control circuit - Google Patents

Abstract

PURPOSE:To ensure an optional and independent control for each differential amplifying circuit, by providing a variable current circuit in addition to a constant current circuit to each differential amplifying circuit to control the gain of each of these amplifying circuits. CONSTITUTION:An input signal ei added with a base bias V1 is applied to a differential amplifying circuit. A constant current decided by a fixed bias V2 is supplied to diodes D1 and D2 via transistors Q1 and Q2. The signal ei is amplified by the differential amplifying circuit and undergoes a current-voltage conversion by the diodes D1 and D2 to be outputted as an output Vout by TRQ7 and TRQ8. The gain of the differential amplifying circuit can be controlled by controlling the current flowing to the D1 and D2 since the current-voltage conversions of D1 and D2 have different gains due to their current values. This current control is carried out by a variable current circuit consisting of current control transistors Q4, Q5 and Q6. This variable current circuit applies the control signal voltage to a base bias V3 or V4 to control the current.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a pair of transistors having a differential configuration, each of which has a diode connected to its load, and a current flowing through the dimate.
The present invention relates to a gain control circuit that controls the gain of a differential amplifier circuit by changing the current flowing through the differential amplifier circuit.

[Technical background of the invention and its problems]

FIG. 1 shows a gain control circuit of a conventional differential amplifier circuit. Transistors Q,/, Q,2 forming a differential amplifier circuit
diodes D, ,D are installed as loads on the collectors of
2 is connected in the forward direction, and emitter resistors R5 and Ft4t are connected to the emitter terminal. Transistor Q3 and emitter resistor P.

The constant current flowing between the collector and emitter of this transistor Q constitutes a constant current source, and the constant current flowing between the collector and emitter of this transistor Q is equal to the control signal voltage e. controlled by The profit of this differential amplifier circuit is 1% i-t diode D,,D,! Depending on the current value flowing through diode D7. It will change according to the current-voltage characteristics of D and 2. Therefore, by changing the value of the constant current flowing through transistor Q, the gain of this differential amplifier circuit can be controlled.

However, in this conventional gain control circuit, the transistor Q
3 and an emitter resistance R, by changing the current source current 11^ itself, the diode D, , D, 2
Therefore, when the constant current source composed of the transistor Q and the emitter resistor n is used as a constant DC source for multiple differential amplifier circuits, each The drawback was that it was difficult to control the gain for each differential amplifier circuit.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a gain control circuit for a differential amplifier circuit that can control each differential amplifier circuit.

[Inplantation of invention]

To achieve this objective, the gain control circuit of the present invention includes:
A current control transistor is provided, the collector terminals of which are connected to the connection points of a differentially configured pair of transistors and a diode as their load, and a pair of current control transistors whose base terminals are commonly connected. The present invention is characterized in that a flow current in the diode is controlled by changing the pace terminal voltage.

The gain of the differential "ν1 width circuit according to an embodiment of the present invention is 1. )
]61111 times are shown in Figure 2. Similar to the conventional example ((transistors Q, , Q, 2 constitute a differential amplifier circuit [7, r1 tie to load]-domains D, D, are connected respectively,
Emitter resistors E J and R are connected to the cap. The transistor Q and the emitter resistor R form a constant 11L current source and supply a constant current to the differential amplifier circuit. In addition to this, in this embodiment, a current control transistor C:, 4t
, (→, O, Q, 6 are provided, and each diode D
,,I), variable 71 to control the circulation 11v: the current circuit is horizontally connected to the transistor Q7.
,! - is connected to emitter lJj.

Next, the operation of this embodiment will be explained. l'J in the differential amplifier circuit
: An input signal θ1 with a base bias of v is added. Emitter resistance F3 of transistor Q, , Q,2. Since it is connected to the collector of only 4t transistor Q, a constant current regulated by a fixed bias V,2 is supplied to the third diodes D, ,D,2 via transistors Ql,Q,2@. The input signal ei is amplified by this differential amplifier circuit, and the output signal - diode D,
D is converted into FE at W, 2, and is output as an output V.U by transistor Q7"J', which is a buffer. Diode D,
D, 2's first current-voltage conversion has a diode D because the gain differs depending on the current value due to its current-voltage characteristics.
, D, 2, the gain of the differential/dynamic amplifier circuit can be controlled. Current control transistors q and q'Qj control this current.
It is a variable current circuit composed of J.A common base bias ■Y is added to the freewheeling control transistors Q,...,Q, and this current side temperature 1 transistor Q, 'Q
A base bias v7 is applied to the current controlling transistor Q4 whose collector is connected to all the emitters of the transistors Q and T in common. When the side temperature 1 signal N1 pressure is high, the base bias v3 and the electric current f)1ε are controlled, and when the control signal - and the pressure are low, the base bias v7 and the current are controlled.

As described above, according to this embodiment, a variable current circuit is provided separately from the constant current circuit to control the current value of the load dimate, so that multiple differential amplifier circuits ( It is possible to control the gain of each of the six (not shown).

In the first embodiment, three current control transistors are used to make the variable I
An L-flow circuit was constructed, as shown in Figure 3! It may be configured with two current control transistors (1 transistor Q, , , Q, and 2 emitter resistors). It can be used for high control signal voltages.
3 is not used, the current flows to i′ simply by resistance, and the source is 41・
You can make one. Furthermore, can similar benefits be obtained by using p n p type transistors? W nil,l 141 circuits can be constructed.

〔Effect of the invention〕

As explained above, according to the present invention, each differential amplifier circuit is provided with a variable current circuit separately from its respective constant current circuit, and the gain thereof is divided by 1. , each differential amplifier circuit can be independently and arbitrarily controlled.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a dependent gain tli control circuit, and FIG. 3 is a circuit diagram of a gain control 14+ circuit according to an embodiment of the invention. FIG. 3 is a circuit diagram of a gain control circuit according to another embodiment of the present invention. R/IR+2. R31R4t, Rj, Rot, R7゜B,
i""9'R10"resistance,Q/"2"3'Q
,-,Q, ,...transistor, Q, ga, Q,,Q
, g... Current control transistor, D, , D,... Diode, θ1... Input signal, ■7. ■、! , ■3.
v4t base bias. Deru f1 agent boar crotch bay part 1 Figure l VcC

Claims (1)

[Claims] Diodes are connected as loads for a pair of differentially configured transistors, and violet 1 flows through the diodes.
In a gain control circuit that controls the gain of a differential amplifier circuit by changing the current, a collector terminal is connected to a connection point between the transistor and the diode, respectively,
Equipped with a pair of current control transistors whose base terminals are commonly connected. A gain control circuit characterized in that the current flowing through the diode is controlled by changing the base terminal voltage of these current control transistors.