JPS6210907A - Differential amplifier circuit - Google Patents

Abstract

PURPOSE:To improve the frequency characteristic by providing a resistor and a capacitor between both transistors (TRs) constituting a current mirror circuit. CONSTITUTION:A resistor R is connected between a common base of TRs Q3, Q4 and a collector of a TR Q1, a capacitor C1 is connected between the collector and emitter of the TR Q3 and a capacitor C2 is provided between the collector and emitter of the TR Q4, where the relation of C1=C2 exists. One bipolar TR in a couple of bipolar TRs constituting the current mirror circuit changes faster from turning-on to turning-off by using the resistor and the capacitor. Thus, the leading speed of the other bipolar TR being an output TR is quickened to improve the frequency characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a differential amplifier circuit with improved frequency characteristics.

2. Description of the Related Art A conventional differential amplifier circuit will be described with reference to FIGS. 4 and 5. In Figure 4, a PNP type transistor (Q
, )(Q, ) constitute a differential input amplifier circuit, and their common emitters are connected to a power supply Vcc via a constant current source 1.

The NPN type transistor (Q, ) (Q4) constitutes a current mirror circuit, whose common base is connected to the transistor (Q, ) (Q4).
3) is connected to the collector. Also, a transistor (Qa
) = the collector of the transistor (Ql) is the collector of the transistor (Q4), and the collector of the transistor (Q4) is the collector of the transistor (Q2)
A differential amplifier circuit is formed by connecting the collectors of the non-inverting input terminal 2 and the inverting input terminal f-
The non-inverting input and inverting input input from 3 are output terminal 4.
as a single output.

FIG. 5 shows another circuit example, in which an N P N transistor is used as the transistor (Q,) (Q2), and a P N transistor is used as the transistor (Q3) (Q,).
A P transistor is used. The operating principle is similar to the circuit shown in FIG.

Problems to be Solved by the Invention However, with such a conventional circuit configuration, when the above-mentioned differential amplifier circuit is used as an input stage amplifier circuit in an operational amplifier circuit, its phase frequency characteristics are not excellent, and the operational amplifier circuit The problem was that the closed loop gain was small.

The present invention solves the above-mentioned conventional problems.

It is an object of the present invention to provide a differential amplifier circuit that can control frequency characteristics.

Means for Solving the Problems In order to solve the problems, the differential amplifier circuit of the present invention has the following features:
Each of a pair of bipolar transistors having bases of the same conductivity type constituting a current mirror circuit is connected as a load for each of a pair of bipolar transistors having bases of a conductivity type opposite to the bases constituting a differential input amplifier circuit. , connecting the common base of the pair of bipolar transistors constituting the current mirror circuit and the collector of one of the bipolar transistors through a resistor,
Further, a container is provided between the collector and emitter of both transistors constituting the current mirror circuit.

Effects According to the above configuration, the resistance and capacitance increase the speed at which one of the pair of bipolar transistors constituting the current mirror circuit changes from on to off, and therefore the other bipolar transistor, which is the output transistor, Since the rising and falling speed of the transistor becomes faster, the frequency characteristics are improved.

Embodiments Hereinafter, embodiments of the present invention will be explained based on FIGS. 1 to 3.

□FIG. 1 is a circuit diagram of a differential amplifier circuit according to a first embodiment of the present invention, and the same components as those shown in FIG. 4 are given the same reference numerals and their explanations will be omitted. In FIG. 1, (R) is a transistor.

(Q3) The common base of (Q, ) and the transistor (Q8
), the resistor (C1) is the collector-emitter capacitance of the transistor (Q, ), (C
2) is the capacitance between the collector and emitter of the transistor (Q4). The capacity 1 (C□) (C2) is the collector
It may be the parasitic capacitance between the collector and emitter of each transistor (Q,) (Q,), which has a structure where the parasitic capacitance between the emitters becomes large, or the parasitic capacitance between each of the transistors (Q,) (Q,). It may be a composite capacitance of a capacitor forcibly attached externally between the collector and emitter and a parasitic capacitance between the collector and emitter. In this way, the differential amplifier circuit of this embodiment is different from the conventional circuit shown in FIG.
and capacitance (C, ) (C2) are used. However, it is assumed that C1=C. Note that parasitic capacitances between the collector and base and between the base and emitter of the transistor (Q,) (Q,) are omitted from illustration.

In this differential amplifier circuit, transistor (Q3) (Q
If the current amplification factor in 4) is hFE and the angular frequency of the input signal is ω, then due to the existence of resistor R1 capacitance C=C2=C, the phase at output terminal 4 and the frequency characteristics of phase Q are as follows: This is greatly improved compared to the conventional differential amplifier circuit shown in the figure, and the effect becomes noticeable near the cutoff frequency of the differential amplifier circuit.

This is because the presence of resistance R and capacitance C increases the speed at which the transistor (Q3) changes from on to off, and therefore increases the rise speed of the output of the output transistor (Q4), and the degree of this improvement is The larger the CR product, the more noticeable it becomes, and it agrees with the result of the above equation (2) indicating the degree of phase improvement Q.

This principle will be explained in more detail using FIG. 3. Capacitance (CA) between the collector and emitter of N type transistor (Q□) that constitutes the current mirror circuit
), a capacitance (CO) is connected between the base and emitter, and a parallel circuit consisting of a capacitance (C) and a resistor (RA) is connected between the collector and base.
A power supply Vcc (Q = 0.7■) is connected between the emitters of a switch (S
I think that it is added by W). Then, consider how much the rate at which the base potential VBE falls when the switch (SW) is turned off depends on the capacitance (CA) and the resistance (RA).

When the switch (SW) is turned off, the capacitor (CA) begins to discharge, and most of the current becomes the collector current and the rest becomes the base current. At the same time, the capacity It(Go) also begins to discharge,
All of that current becomes a base current, and when the discharge is completed, the base potential becomes zero.

The base current is a part of the discharge current of the capacity (CA) and the capacity ((
': o), but if the resistance (RA) is not zero, the discharge current from the capacitor (CA) is equal to the capacitor (C
It contributes to the base current with a delay of time constant cc-R^ from the discharge current from n). In other words, the larger the time constant Cc-RA is, the faster the base potential falls and the transistor (Q3) is turned off.

From h, if the capacitance (CA) and resistance (RA) are large, the base potential will fall faster when the switch (SW) is turned off than in the case where they are not.

FIG. 2 is a circuit diagram of a differential amplifier circuit according to a second embodiment of the present invention. This embodiment corresponds to the conventional circuit shown in FIG. 5, and the operating principle is the same as that of the first embodiment. Therefore, the same effect can be obtained.

Effects of the Invention As described above, according to the present invention, the common base of a pair of bipolar transistors constituting a current mirror circuit and the collector of one of the bipolar transistors are connected via a resistor, and the current mirror circuit is further configured. Since a capacitor is provided between the collector and emitter of both transistors, the frequency characteristics of the phase Q at the output can be changed by the resistor and capacitor.

[Brief explanation of drawings]

FIG. 3 is a diagram explaining the principle of the differential amplifier circuit of the present invention, and FIGS. 4 and 5 are circuit diagrams of conventional differential amplifier circuits. (Q□) ~ (Q4)...Transistor, (R)...
Resistance, (C1) (C2)... Capacity agent Yoshihiro Morimoto Figure 1 Figure 2 W Figure 4

Claims (1)

[Claims] 1. Each of the bipolar transistors having a pair of bases of the same conductivity type constituting a current mirror circuit is replaced with a bipolar transistor having a base of a conductivity type opposite to the pair of bases constituting a differential input amplifier circuit. A common base of a pair of bipolar transistors constituting the current mirror circuit is connected as a load to each of the transistors, and a collector of one of the bipolar transistors is connected via a resistor, and both transistors constituting the current mirror circuit are connected as a load to each of the transistors. A differential amplifier circuit with a capacitance between the collector and emitter. 2. The differential amplifier circuit according to claim 1, wherein the parasitic capacitance between the collectors and emitters of both transistors is used as the capacitance between the collectors and emitters of both transistors constituting the current mirror circuit. 3. The combined capacitance of the parasitic capacitance between the collectors and emitters of both transistors and the capacitor connected between the collectors and emitters of both transistors was used as the capacitance between the collectors and emitters of both transistors that constitute the current mirror circuit. A differential amplifier circuit according to claim 1.