JPS6373707A - voltage follower circuit - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to voltage follower circuits with reduced offset current.

BACKGROUND OF THE INVENTION FIG. 2 is a diagram showing a conventional voltage follower circuit constructed using transistors. In FIG. 2, vl is an input terminal, vOUT is an output terminal, and vcc is a power supply voltage terminal.

Transistor Q8. Q9 constitutes a current mirror. Transistor Q10゜Qll and constant current source. constitutes a differential amplifier. Transistor Q12 and constant current source I4 constitute an emitter follower that takes out the output of the differential amplifier. Capacitor C2 and resistor R4 are
This is for phase compensation. The resistor R3 is for compensating the offset current generated by the resistor R4 and the base current of the transistor Q11.

The operation of the conventional voltage follower circuit configured as above will be explained. Input signal v1 is transmitted through transistors 08 and 09
Current mirror and transistor Q
10. It is converted into a current signal IC1° by a differential amplifier composed of Qll, constant current Riko 3, and resistor R3. This current signal I is applied to the transistor Q12 and the constant current source C1. An output voltage signal vQUT is generated by an emitter follower configured with . Further, the output voltage signal vOUT is applied to the transistor Q1 which constitutes the differential amplifier via the resistor R4.
The zero-order voltage applied as an input to the base of the conventional voltage 7-year lower circuit (off cell) El will be explained. The base currents of transistors Q8 and Q9 are increased by 8.
9 and the current amplification factors are hFEPs and hFEP9, the collector current IC8°"Cs is as follows.

Next, reduce the base current of transistor Q12 by 1°, and reduce the base current of transistor Q10. Assuming that the collector current of Qll is C10''C11, the following equation is obtained from the first equation.

In this second equation, hFEP8”hFEP9=hFK
If P.''B8=IB9=IB, the second equation becomes as follows.

Then, the offset current Δ is the difference between IC11 and IC1°. fh becomes as follows.

Δ”off1=Ic11-IC10=2×IB+lB1
2"""(') As is clear from the fourth equation, in the conventional voltage 7-year lower circuit shown in Fig. 2, the base current of transistor QB, 09, which constitutes the current mirror, is based on the base current of transistor Q12. Transistor Q10
．． The difference in the collector current of Qll, that is, ΔI, occurs as an offset current. Therefore, it was not possible to realize a voltage follower circuit with sufficient circuit performance.

An object of the present invention is to provide a voltage follower circuit that reduces offset current by adding a circuit function that can compensate for base current.

Means for Solving the Problems The structure of the voltage 7-year lower circuit of the present invention capable of achieving the above object is as follows: a first current mirror composed of first and second transistors; a differential amplifier configured with third and fourth transistors having respective collectors connected to and having opposite polarities to the first and second transistors, and a base connected to the collector of the third transistor, a sixth transistor with a polarity opposite to that of the third transistor; a sixth transistor connected to the collector of the sixth transistor; a sixth transistor with a polarity opposite to that of the third transistor; a second current mirror configured with a seventh transistor in which is selected to be an integral multiple of the sixth transistor, and a common connection point between the emitters of the third and fourth transistors and the sixth and seventh transistors; A signal input terminal is provided at the base of the third transistor, and a signal output terminal is provided at the connection point between the second current mirror and the second current source. It is attached.

Function: According to this configuration, the circuit function of compensating the base current of the transistor constituting the current mirror is exhibited.

Example FIG. 1 shows an embodiment of the voltage follower circuit of the present invention.

In Figure 1, vl is an input terminal, voUd is an output terminal, and vc
c is a power supply voltage terminal. Transistors Q1 and Q02 constitute a first current mirror. Transistor Q3
, 04 and Constant Current Rikou.

constitutes a differential amplifier. Capacitor C1 and resistor R2 are for phase compensation. The resistor R1 is a resistor provided to compensate for the offset caused by the base current of the resistor R2 and the transistor Q4, and Q5 is a transistor for correcting the base current.

Transistor Q6. Q7 constitutes a second current mirror. Constant current source! 2 is the output current.

In the voltage 7-year lower circuit of the present invention configured as described above, the offset will be described.

Transistor Q1. The base current of Q2 is
・If “B2” and the current amplification factors are hFEPl and hFEP2, the collector currents IC4 and Ic2 are as follows.

Next, the base current of transistor Q5 is set to 6 Ω, and transistor Q3. The collector current of Q4 is Ic3, respectively.
．． Assuming Ic4, the following equation is obtained from the sixth equation.

Engineering C4=hFEP2xIB2+lB2+IB1 This 6th
In the formula hFEP1=hFEP2=hFEP・IB1
If ="B2="B2, then the sixth equation becomes as follows.

Then, the offset current Δk, which is obtained as the difference between C4 and Ic3, is as follows.

ff2 Δ”off2=Ic4 IC3=2XIB -E
j +++−+−(8) As is clear from this equation, the transistors Q1 and 02 that constitute the first current mirror
The difference between the collector currents of transistors Q3 and 04 based on the base current of , that is, Δ"off2, is generated as an offset current. By the way, in the voltage 7-year lower circuit of the present invention, the offset current of the eighth equation is set to zero ff2. Therefore, transistor Q6 is added, and “BP=”B
By establishing the relationship s, the difference in collector current due to the base current is compensated for.

Next, we will discuss the output current. The input signal v1 is converted into a current signal IC3 by a first current mirror made up of transistors Q1 and 02, a differential amplifier made up of transistors 03 and 04, a constant current source I, and a resistor R1. The base current IBs is then transmitted to the transistor Q6. transistor Q
The relationship between base current IB6 and collector current Ic5 of transistor Q5 is as follows, assuming that the current amplification factor of transistor Q5 is hFEPs.

IC5”hFEP5×IBs ・=−−・=(
9) Here, from condition 2 for compensating the influence of offset current, P=5 is applied to equation 9, and h
==31 =h FEPI FEP2 When FEPes=hFEP, the ninth equation becomes as follows.

I = 2
・・・－・・・・・・・・・・・・・・・(10) By the way,
Collector current Ic3. of transistors Q3 and Q4 forming the differential amplifier. The relationship between Ic4 and constant current is as follows when the base current is sufficiently small.

Work 1 = Work C3”C4・・・・・・・・・・・・・・・
(11) Therefore, from the above equations 7 and 11 and 2, from the relationship P=IB6, the equation becomes as follows.

I 1=2XhFHpX I B p +4X I B
p −·= −−(12) Also, from the 10th equation and the 12th equation, Ic5 is as follows.

Furthermore, the relationship between the second current mirror constituted by the transistors Q6 and Q07, the constant current source 12, and the collector current Ic6 of the transistor Q5 is as follows, assuming that the base current of the transistor Q7 is 7 and the current amplification factor is hFEN. become that way.

Here, n is the transistor size of the transistor Q7 based on the transistor size of the transistor Q6.

Rearranging the 14th formula, I B7X (hFEN+ 1) +nXIB7(h
FEN+1) = I2IB7((hFEN+1
)+n(hFEN+1))=I2 Therefore, the collector current lCe5 is calculated from 7+IB7(hFE+1)=7(n
+(hFEN+1)), and IB7 of this formula
By substituting Equation 16 into , the following relational expression is obtained.

Further, the relationship between the constant current source 11 and the voltage can be expressed as follows from equations 13 and 14.

In the 16th equation, the current amplification factor hFEN,! :hFEP
Assuming that is sufficiently large, Equation 17 becomes as follows.

I, = T-x I, ・・・・・・・・・
・・・・・・・・・・・・・・・(18) As is clear from the 18th equation, if the current amplification factor of the transistor is sufficiently controlled, the constant current source 11 should be 1/n+
It can be set to 1.

In other words, if the relationship of Equation 18 is established by adding the second current mirror, even if the value of constant current source ■2 is increased,
The influence on constant current science and technology can be reduced. Since the differential amplifier constituted by transistors Q3 and Q4 is well balanced, offset current due to variations in transistors can be reduced.

Effects of the Invention In the voltage follower circuit of the present invention, offset current can be reduced by providing a circuit for compensating base current. Furthermore, by providing a current mirror in the output section, even if the current of the constant current circuit for output is increased, the offset current generated by this can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a voltage follower circuit of the present invention, and FIG. 2 is a diagram showing a conventional voltage follower circuit. Ql, 02. Q8. Q9...Transistor forming a current mirror, Q3. Q4. Q10. Qll・
...Transistor constituting a differential amplifier, 11.
I3... Constant current source for differential amplifier, C1, C2
・・・・・・Phase compensation capacitor, R2, R4...
...Resistor for phase compensation, R1, R3...Resistor for base current compensation, Q5...Transistor for base current compensation, Qe. Q7...Transistor forming a current mirror, Ql2...Emitter follower transistor, I2゜engineering.・・・・・・Constant current source for output. Name of agent: Patent attorney Toshio Nakao and one other QI
Q2061; 17 --- Current mirror transistor Q3Q4 -- Ichinohezuke Rikibo tile quick-fighting transistor house -- 1-be Kuden Te U self 1st prize transistor R1 ~ -- ° <- S xun poor moxibustion Snoring Shichito 5LR2 --- 4 Standing 4 Rone Playing F
Figure 1 Figure 2 Figure 6 Contents of amendment Procedural amendment (voluntary) December 2r, 1985

Claims (1)

[Claims] a first current mirror made up of first and second transistors, and third and fourth transistors each having a collector connected to the current mirror and having a polarity opposite to that of the first and second transistors. The configured differential amplifier has a base connected to the collector of the third transistor, a fifth transistor whose polarity is opposite to that of the third transistor, and a base connected to the collector of the fifth transistor, and a base connected to the collector of the third transistor. a second current mirror configured of a sixth transistor having opposite polarity and a seventh transistor having the same polarity as the sixth transistor and whose transistor size is an integral multiple of the sixth transistor; The first and second current sources are connected to a common connection point between the emitters of the third and fourth transistors and the sixth and seventh transistors, and a signal input terminal is attached to the base of the third transistor. , A voltage follower circuit characterized in that a signal output terminal is attached to a connection point between the second current mirror and the second current source.