JPS5875909A - Operational amplifying circuit - Google Patents

Abstract

PURPOSE:To make an offset voltage hard to generate by using an NPN transistor (TR) which has a high common emitter current amplification factor, and thus making the influence of its base current hard to exert and the collector current ratio hard to vary. CONSTITUTION:When the base currents and output currents of TRs Q6 and Q8 are disregarded, emitter currents of the TRs Q6 and Q8 become equal to currents I2 and I3 of constant current sources respectively. Therefore, I2=I3, and if the emitter area of the TRQ6 is equal to that of the TRQ8, an input and an output voltage are equal. Those TRs Q6 and Q7 use NPNTRs having high hFE, so the influence of the base currents is hard to exert. The constant current sources use PNPTRs Q11 and Q12 and the emitter-collector voltages of the TRs Q11 and Q12 vary nearly similarly to a power voltage VCC, so that even if the power voltage varies, the ratio of the currents I2 and I3 is hard to vary. Consequently, the precision of the current ratio of the TRs Q6 and Q3 is high and an offset voltage is hard to generate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to obtain an operational amplifier circuit with a small offset voltage with a simple circuit configuration.

FIG. 1 is an example of a circuit using a typical conventional operational amplifier circuit as a voltage follower circuit.

In the figure, IN is the input terminal, OUT is the output terminal, and Q1
~Q6 is a transistor, 11 is a constant current source, Vc
c is the DC power supply voltage.

When making this circuit using an integrated circuit, generally the transistor Q
, , Since Q2 is composed of a PNP transistor with a lateral structure with low hFE, the transistor QuQ,
The current mirror circuit composed of Q2 is easily affected by the pace current, and the emitter-collector voltage of transistor Q is clamped by the pace-emitter voltage of transistor Q2.
By changing the emitter-collector voltage of transistors Q, , Q2 depending on the power supply voltage Vcc,
Due to the effect of the deviation in the collector current ratio of the transistors Q, Q, and Q, the collector current ratio of the transistors Q, , Q, and Q were shifted, resulting in a large offset voltage.

The present invention has been made to eliminate the above-mentioned drawbacks of the conventional ones, and an object of the present invention is to provide an operational amplifier circuit that is less likely to generate an offset voltage.

Embodiments of the present invention will be described below with reference to the drawings.

Figure 2 shows a circuit example of an operational amplifier circuit applied as a voltage follower circuit according to the first embodiment (corresponding to claim 1) of the first invention of the present application. , Vcc are the same as in Figure 1, Q6 is the first transistor whose input is the pace and the collector is connected to the first constant current source I2, and Q7 is the second transistor whose collector is connected to the pace of the first transistor Q. transistor, Qg is the third transistor with the emitter of the second transistor Q connected to the pace, the emitter of the first transistor Q6 connected to the collector, Q8 is the collector of the second constant current source ■3, and the emitter of A fourth transistor is connected to the emitter of the first transistor Qel, and its pace is connected to the collector, and the collector of the transistor Q8 is used as an output terminal OUT.

In this circuit configuration, transistors Qa, Q? If we ignore the base current and output current of transistor Q6
・The Qρ emitter current is equal to the current of the constant current source 4゜■. Therefore, if the emitter areas of transistors Q, ,Q, are equal, the input voltage and output voltage will be equal.

This circuit of FIG. 2 consists of transistors Qa, Q? is hF
Since it is composed of NPN (NPN) transistors with high E, it is less susceptible to the effects of base current. Also, constant current source I2.
I3 is a PNP) transistor Qo as shown in FIG.
+ Q10, but the emitter-collector voltage of the transistor Qlt ("2'I rule) is Vcc -2V BB, while the emitter-collector voltage of the transistor Q+t (Is side) The voltage is approximately Vcc-■in if the input voltage is V in, and it changes almost in the same way as the power supply voltage Vcc, and even if the power supply voltage fluctuates, the current ratio of I2 and I3 does not change easily. BL in Figure 6 is a bias line.

For these reasons, in the circuit shown in FIG. 2, the current ratio of the transistors Q, .

FIG. 3 is an example of an operational amplifier circuit according to the actual MfE of the first invention of the present application (corresponding to claim 2). This circuit uses the second transistor Q of the circuit shown in Figure 2.
, a Zener diode DI having a Zener voltage Z is provided as a voltage level shifting means between the emitter of the transistor Qo and the third transistor Qo.

In the circuit shown in Figure 2, the input applied voltage range is
3 VBE, which is relatively narrow, but the circuit rc in Figure 3
Oi”'ChaVBE ~3VBE +Vz (Vz i
7 Zener voltage of ener diode D1) and wide.

FIG. 4 shows an operational amplifier circuit according to the first embodiment of the second invention of the present application (corresponding to claim 3), in which the fourth transistor is A transistor Q+o is connected to the collector of Q8 as a current amplifying means, and its output is used as the output of this circuit.

FIG. 5 shows an operational amplifier circuit according to a second embodiment f (corresponding to claim 4) of the second invention of the present application, which is operated as a positive phase amplifier. R1 and R2 are connected in series between the emitter of the transistor Q+o in FIG. 4 and ground. The connecting point of the second resistor R, , It2 is connected to the base of the fourth transistor Q8.

In this circuit, the relationship between the input voltage Vin and the output voltage Vout is Vout-'9·Vin.

2 As described above, according to the present invention, the first transistor has the base as input and the collector connected to the first constant current source, the second transistor has the base connected to the collector of the first transistor, and the base a third transistor having the emitter of the second transistor connected to the collector and the emitter of the first transistor connected to the collector; and a fourth transistor having the emitter of the first transistor connected to the collector of the second constant current source. The operational amplifier circuit is constructed by outputting the collector of the fourth transistor either directly or through a current increasing means. NPN with high hFE in the second transistor)
By using a transistor, it can be made less susceptible to the influence of the base current, and the current ratio of the two constant current sources can be made less likely to change even if the power supply voltage fluctuates, making it possible to configure an operational amplifier circuit that is less prone to offset voltage. be.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional operational amplifier circuit, FIG. 2 is a circuit diagram of an operational amplifier circuit configured as a voltage follower circuit according to a first embodiment of the first invention of the present application, and FIG. 3 is a circuit diagram of a conventional operational amplifier circuit. FIG. 4 is a circuit diagram of an operational amplifier circuit configured as a voltage follower circuit according to the second embodiment of the invention of the present application, and FIG. 4 is a circuit diagram of an operational amplifier circuit configured as a voltage follower circuit according to the first embodiment of the second invention of the present application. Circuit diagram, 5th
The figure is a circuit diagram of an operational amplifier circuit configured as a positive phase amplifier by combining FIGS. 3 and 4 according to the second embodiment of the second invention, and FIG. 6 is a circuit diagram of an operational amplifier circuit configured as a positive phase amplifier. Constant current source I2. I is a specific circuit diagram of I. I2...first constant current source %'! ...Second constant current source, Q6...First resistor % Q7...Second
Transistor% Qll...Third transistor,
QB...Fourth transistor, DI...Voltage level shift means, Q. ...Current amplification means. In the drawings, the same reference numerals indicate the same or equivalent parts. Agent Shin Kuzuno - Figure 1 Figure 2 Figure 5 Figure 6

Claims (1)

[Claims] (1) A first transistor whose base is an input and whose collector is connected to a first constant current source; and a second transistor whose base is connected to the collector of the first transistor;
A third transistor whose base is connected to the emitter of the second transistor and whose collector is connected to the emitter of the first transistor.
and a fourth transistor whose collector is connected to a second constant current source and whose emitter is connected to the emitter of the first transistor, and the collector of the fourth transistor is used as an output. operational amplifier circuit. +21 The operational amplifier circuit according to claim 1, characterized in that voltage level shifting means is provided between the emitter of the second transistor and the base of the third transistor. (3) a first transistor whose base is input and whose collector is connected to a first constant current source; and a second transistor whose base is connected to the collector of the first transistor;
A third transistor whose base is connected to the emitter of the second transistor and whose collector is connected to the emitter of the first transistor.
a fourth transistor whose collector is connected to a second constant current source and whose emitter is connected to the emitter of the first transistor; and a current amplification means whose power is connected to the collector of the fourth transistor. An operational amplifier circuit characterized in that the output of the current amplifying means is used as the output. (4) The operational amplifier circuit according to item 3, characterized in that voltage level shifting means is provided between the emitter of the second transistor and the base of the third transistor.