JPH06112744A - Gain control amplifier - Google Patents

Abstract

PURPOSE:To provide a gain control amplifier which can facilitate the control with high gain and also can reduce the component area of the amplifier. CONSTITUTION:1st and 2nd transistors TR Q1 and Q2 have the bases connected to the signal input terminals and the collectors connected to the signal output terminals respectively. The resistances R3 and R4 are connected to the emitters of both TR Q1 and Q2, and the bidirectional TR Q3 and Q4 are connected to between the emitters of the TR Q1 and Q2. Both TR Q3 and Q4 consist of a pair of TRs having their collectors and emitters connected opposite and parallel to each other. These collectors and emitters are connected to the emitters of the TR Q1 and Q2, and the bases of both TRs are connected in common to a current source I.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to amplifiers, and more particularly to high frequency gain controlled amplifiers in integrated circuits.

[0002]

2. Description of the Related Art An example of a conventional gain control amplifier of this type is shown in FIG. In the figure, the bases of the first and second transistors Q1 and Q2 are respectively connected to input terminals IN1 and IN.
2 and each collector is connected to the high potential terminal VCC through the resistors R1 and R1 and the output terminals OUT1 and OUT.
2 are connected. Further, transistors Q3 and Q4 forming a bidirectional transistor are connected in series between both collectors. That is, the transistors Q3 and Q4 have their bases and collectors connected to each other, and each emitter has a first and second emitter.
Connected to each collector of the transistors Q1 and Q2. Further, the commonly connected bases are connected to the high potential terminal VCC via the current source I. In addition, each transistor Q1, Q2
The emitter of is connected to the low potential terminal VEE via resistors R3 and R4, and the resistor R and the capacitor C are connected between both emitters.

In this gain control amplifier, the bidirectional transistors Q3 and Q are changed by changing the current of the current source I.
The saturation resistance of No. 4 changes, and the signals input from the input terminals IN1 and IN2 receive the load resistance including resistances R1 and R2 and the saturation resistance of the bidirectional transistors Q3 and Q4, and the resistance R3.
It is amplified by a gain determined by the ratio of R4, R and the feedback impedance of the capacitor C, and the output end OU
It is output to T1 and OUT2. Further, the capacitor C causes peaking in this output to improve the wide band characteristic.

[0004]

In this conventional gain control amplifier, when high gain control is performed in an integrated circuit, resistors R1 and R2 and bidirectional transistors Q1 and Q2 are used.
It is necessary to increase the load resistance formed by the saturation resistance of the above or to reduce the feedback resistance R. However, if the former load resistance is increased to control the high gain, the first and second transistors Q1 , Q2 must be prevented from reversing the collector potential and the base potential, which poses a problem that high gain control is limited. Further, if the resistance R of the latter feedback resistor is reduced to control a high gain, the area of the resistor must be increased in order to guarantee the characteristics of the resistor, so that the area formed by the gain control amplifier becomes large. There is a problem. An object of the present invention is to provide a gain control amplifier which can easily control a high gain and has a small area.

[0005]

According to the present invention, there are provided first and second transistors each having a base connected to a signal input terminal and each collector connected to a signal output terminal, and the first and second transistors. A resistor connected to each emitter of the transistor and a bidirectional transistor connected between these emitters. The bidirectional transistor is composed of a pair of transistors whose collector and emitter are connected in parallel in opposite directions. The collectors and emitters of these transistors are connected to the emitters of the first and second transistors, and the bases of both transistors are commonly connected to a current source that provides a constant current.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 (a) shows a circuit diagram of an embodiment of the present invention. The first and second transistors Q1 and Q2 have their bases as input terminals IN1 and IN2, and their collectors have resistors R1 and R2 respectively. It is connected to the high potential terminal VCC through the output terminals OUT1 and OUT2. Also,
The emitters of the first and second transistors Q1 and Q2 are connected to the low potential terminal VEE via the resistors R3 and R4, and third and fourth transistors Q3 and Q4 that form a bidirectional transistor between the emitters of the first and second transistors Q1 and Q2. A capacitor C is connected to (a transistor whose bases are commonly connected). That is, the common bases of these bidirectional transistors Q1 and Q2 are connected to the high potential terminal VCC through the current source I, and the collector of the third transistor Q3 and the emitter of the fourth transistor Q4 are respectively connected to the first transistor Q.
The emitter of the third transistor Q3 and the collector of the fourth transistor Q4 are connected to the emitter of the second transistor Q2, respectively.

According to this circuit, the input terminals IN1 and IN2 are
The amplification degree of the input signal is determined by the ratio of the resistors R3 and R4, the saturation resistance of the bidirectional transistors Q3 and Q4, the feedback impedance of the capacitor C, and the load resistance of the resistors R1 and R2. In order to perform control at high gain, it is sufficient to reduce the saturation resistance of the bidirectional transistors Q3 and Q4.
Since 3 and Q4 are connected in parallel, the minimum resistance value can be reduced to about 1/4 of the saturation resistance of the bidirectional transistor connected in series as shown in FIG. In addition, the feedback resistance of the amplifier is set to the bidirectional transistors Q3 and Q4.
Since it is configured as described above, it is not necessary to configure the integrated circuit with a small resistance, and the area configuring the amplifier can be reduced.

Further, when the bidirectional transistors Q3 and Q4 are connected in parallel, they are generated between the base and collector and between the base and emitter of the transistor Q3, as shown in the equivalent circuit of FIG. 1 (b). Parasitic capacitance C
1, C2, and the parasitic capacitance C generated between the base-emitter and the base-collector of the transistor Q4, respectively.
The capacitors C3 and C4 are connected in parallel with the capacitor C between the emitters of the first and second transistors Q1 and Q2 as a combined capacitor, and the capacitance value of the capacitor C can be reduced by that amount, thereby further reducing the amplifier. The constituting area can be reduced.

FIG. 2 shows a second embodiment of the present invention,
The same parts as those in the above embodiment are designated by the same reference numerals. Here, when the capacitance of the capacitor C in FIG. 1 is smaller than the combined parasitic capacitance generated by the bidirectional transistors Q3 and Q4, the capacitor C is omitted. Also in this circuit, it is possible to obtain substantially the same effect as in the first embodiment,
Moreover, since no capacitor is used, integration can be facilitated.

[0010]

As described above, according to the present invention, the bidirectional transistor connected between the emitters of the first and second transistors, the emitter and the collector are connected in parallel in the opposite direction, and the current source is connected to the common base. Since the configuration is connected, the saturation resistance can be reduced, the feedback resistance can be reduced or omitted, control of wide band high gain can be facilitated, and the area configured by the amplifier in the integrated circuit can be reduced. Is obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention and a diagram showing a capacitance parasitic on a bidirectional transistor.

FIG. 2 is a circuit diagram of a second embodiment of the present invention.

FIG. 3 is a circuit diagram of an example of a conventional amplifier.

[Explanation of symbols]

 Q1 1st transistor Q2 2nd transistor Q3, Q4 Bidirectional transistor R1-R4 Resistor C Capacitor I Current source

Claims (1)

[Claims] 1. A first and a second transistor having respective bases connected to a signal input terminal and respective collectors connected to a signal output terminal, and respectively connected to respective emitters of the first and second transistors. And a bidirectional transistor connected between these emitters,
The bidirectional transistor is composed of a pair of transistors whose collector and emitter are connected in parallel in opposite directions. The collector and emitter of these transistors are connected to the emitters of the first and second transistors, and the bases of both transistors are A gain control amplifier, which is commonly connected to a current source for providing a constant current.