JPH07154163A - Differential amplifier circuit - Google Patents

Abstract

PURPOSE:To make an output DC current constant even when an amplification factor is changed by applying a current change just reverse to a current change in an operating current source to a differential amplifier circuit. CONSTITUTION:An emitter area ratio of transistors(TRs) 19, 11, 13 be 1:2:1 and resistance of resistors 21-23 be set to be 2:1:2, then when a current I1 is supplied to a resistor 18, a current 2I1 flows to a collector of the TR 11 and a current I1 flows to a collector of the TR 13. When the resistance of the resistor 18 is changed to change the amplification factor, a current change of I1 being a half of the current 2I1 is produced. A change in the collector current of the TR 13 changes a collector current I2 of the TR 24. The emitter area and the emitter resistance of TRs 15-17 are set equal to each other and the collector current of each TR is I2. On the other hand, a current I1 flows to the TRs 4, 3. Thus, a current I2+I1=-I0-I1+I1=I0=constant flows to output terminals 6, 7. Thus, the DC current of the output terminals 6, 7 is made constant independently of the gain of the differential amplifier circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable gain type differential amplifier circuit, and more particularly to a differential amplifier circuit which can be directly connected to a circuit in the next stage even if the gain is changed.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional differential amplifier circuit in which a signal from an input terminal (1) is applied to a base of a second transistor (3) via a DC blocking capacitor (2). It Then, the signal is amplified by the differential amplifier (5) composed of the first and second transistors (4) and (3) and is led to the first and second output terminals (6) and (7), It is transmitted to the circuit (8) in the next stage.

In order to change the gain of the differential amplifier (5),
This is performed by changing the current value of the operating current source (9) and changing the impedances on the emitter side of the first and second transistors (4) and (3).

[0004]

However, when the current value of the operating current source (9) in FIG. 2 changes, the DC levels of the first and second output terminals (6) and (7) change, There is a problem that the circuit in the next stage cannot be directly connected to the first and second output terminals (6) and (7).

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and includes a differential amplifier having first and second transistors whose emitters are commonly connected, and the first and second differential amplifiers.
An operating current transistor that supplies an operating current to a common emitter of the transistor, a third transistor whose base is commonly connected to the base of the operating current transistor, a constant current source, and a fourth transistor. A shunt circuit for shunting the constant current of the third current collector circuit according to the current flowing in the collector-emitter paths of the third and fourth transistors;
A fifth and sixth transistor connected in a current mirror relationship with the transistor and having collectors connected to the collectors of the first and second transistors.

[0006]

According to the present invention, the current value change of the operating current source of the differential amplifier is exactly opposite to the current value change generated by the shunt circuit, and the output current of the shunt circuit is applied to the collectors of the first and second transistors. We are supplying.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing a case where the differential amplifier circuit of the present invention is integrated into an IC, and (10) shows first and second transistors (4) and (3) whose emitters are commonly connected. A differential amplifier having: an operating current transistor for supplying an operating current to a common emitter of the first and second transistors (4) and (3); and a base for the operating current transistor (11). Third commonly connected to the base
It has a transistor (13), a constant current source (14), and a fourth transistor (15), and a constant current I ₀ of the constant current source (14) is supplied to the third and fourth transistors (13) and ( A shunt circuit (16) and (17) for shunting the current flowing in the collector-emitter path of 15) is connected in current mirror relation with the fourth transistor (15), and has a collector in the first and second transistors (4). And fifth and sixth transistors connected to the collectors of (3), (1
Reference numeral 8) is a variable resistor for setting the current flowing through the current mirror circuit (20) composed of the operating current transistor (11), the third transistor (13) and the seventh transistor (19).

The emitter area ratio of the seventh transistor (19), the operating current transistor (11), and the third transistor (13) of FIG. 1 is set to 1: 2: 1, and the resistance of the resistors (21) to (23) is set. Set the value to 2: 1: 2. And
Assuming that the current flowing through the variable resistor (18) is I ₁ , the collector of the operating current transistor (11) receives the current 2I ₁ .
A current I ₁ flows through the collector of the third transistor (13). That is, if the resistance value of the variable resistor (18) is changed to change the amplification factor, the current 2I ₁ changes, and a half of the current change occurs in I ₁ .

Collector current of the third transistor (13)
Changes the emitter voltage of the PNP transistor (24)
Of the PNP transistor (24)
Current I₂Change. The current I₂Is I₂= I₀-I
₁It is expressed as (1). Fourth to fifth transistors
(15) to (17) all have the same emitter area,
Since the emitter resistances are set equal (= R),
Collection of the fifth and sixth transistors (16) and (17)
Current is I₂Becomes Meanwhile, the first and second transitions
The currents I are applied to the collectors of the stars (4) and (3) ₁Flow
Therefore, the first and second output terminals (6) and (7) are connected to
Current I₂＋ I₁= I₀-I₁＋ I₁= I₀= Constant ... (2) flows
Be done.

Therefore, according to the circuit of FIG. 1, the first and second
The DC current at the output terminals (6) and (7) can be constant regardless of the gain of the differential amplifier.

[0011]

As described above, according to the present invention, it is possible to provide a differential amplifier circuit which can be directly connected to the circuit of the next stage even if the gain of the differential amplifier is changed.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a differential amplifier circuit of the present invention.

FIG. 2 is a circuit diagram showing a conventional differential amplifier circuit.

[Explanation of symbols]

 (10) Differential amplifier (11) Operating current transistor (12) Shunt circuit

Claims (1)

[Claims] 1. A first and a second emitter whose emitters are commonly connected.
A differential amplifier having a transistor, an operating current transistor that supplies an operating current to a common emitter of the first and second transistors, a third transistor whose base is commonly connected to the base of the operating current transistor, and a constant current source And a fourth transistor, and a shunt circuit that generates a current obtained by subtracting a current flowing through the third transistor from the constant current of the constant current source from the fourth transistor, and a current mirror relationship with the fourth transistor. A fifth and sixth transistor connected to each other and having collectors connected to collectors of the first and second transistors, respectively.