JPS5986316A - Switching circuit of differential amplifier pair - Google Patents

Abstract

PURPOSE:To attain the adoption of a band gap reference less in the temperature dependancy to a reference voltage of the differential pair by constituting the titled circuit that the two differential pairs are switched by a couple of transistors(TRs) turned on or off exclusively. CONSTITUTION:Switching signals C, inversion C' being opposite phase are applied to the base of TRsQ51, Q52. TRsQ41, Q42 act like a constant current source. When the input C is at L level and the TRQ51 turns off, the TRQ41 is turned on and a differential pair DF1 is selected. Since the inversion C' is at H level, the TRQ52 is turned on and the TRQ42 is turned off and a diffierential pair DF2 is inoperative. On the contrary, when the input C is at H and the inversion C' is at L, the differential pair DF2 is selected. Thus, the value of a reference voltage VR given in common to the differential pairs DF1, DF2 is the sum of a collector-emitter voltage for one stage's share of the TRQ41, Q42 and a base-emitter voltage of one stage's share of TRsQ41, Q42, and the band gap reference with less temperature dependancy is adopted.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a switching circuit for a pair of differential amplifiers, and in particular to a switching circuit for switching a pair of differential amplifiers, and in particular to a switching circuit that allows the pair of differential amplifiers to be driven at a low voltage.

Prior Art and Problems Some switching circuits that make only one of two differential pairs operable use a third differential pair DF3, as shown in FIG. This differential pair DF3 is a transistor Q3I
, Q32, the reference voltage VR2 is applied to the Q32 side, and the switching voltage Vc is applied to the Q31 side. And VC>V
If H2, the transistor Q31 is turned on and the first differential pair DF+ and the constant current source 11 are connected, and VC<
If it is VH2, the transistor Q32 is turned on, and the second differential pair DF2 and the constant current source 1 are connected. The first differential pair DF+ consists of transistors Q, , Q,2, with input vA connected to Qll and reference voltage VRI connected to Q,2. The second differential pair DF2 includes transistors Q211 Q2. , consists of Q2. The common reference voltage VR1 is applied to Q2□, and another input vB is applied to Q2□.

The disadvantages of this circuit configuration are the reference voltage ■R1, input voltage VA,
The point is that the differential pair DPI and DF2 do not operate unless VB is high. In other words, if the constant current source 1 is constructed with one stage of transistors, the potential difference from the ground potential to the emitter of the differential pair DF3 is 1VcEs (about 0. 4V). The emitter potential of the selected differential pair DF or DF2 is then VCESI of the switching transistor Q31 or Q32.
It's a step higher.

In addition to this, the i-transistor Q12 or Q2. The sum of the base-emitter voltage VBE (approximately 0.7V) becomes the lowest set potential of the reference voltage VRI, so VR+ > V
BE+ 2 VCES = 1.5 V ・−・−・
-(becomes 11.Input voltage VΔ, VB is above VRI,
I need to change down.

Generally, it is desirable to use a bandgap reference (BGR) with less temperature dependence as the reference voltage VRI, but the voltage obtained with this is 1.2 to 163.
Since V is the limit, it is impossible to satisfy the relationship expressed by the equation (]).

OBJECTS OF THE INVENTION The present invention attempts to solve the above-mentioned problems by devising a differential pair switching circuit.

Structure of the Invention The present invention provides two transistors each comprising a pair of transistors and a constant current source.
A switching circuit that enables one of a pair of differential amplifiers to operate, characterized in that a switching transistor is provided that exclusively turns on and off the transistor in response to the constant voltage of each differential amplifier pair. However, this will be explained in detail below with reference to the illustrated embodiment.

Embodiment of the Invention FIG. 2 shows an embodiment of the present invention, in which Q41 and Q4□ are constant current source transistors provided for each differential amplifier pair DPI and DF2, Q5. , Q is l transistor Q4.

This is a transistor that controls Q42 to turn on and off.

Constant current source '21 and diode D1 are 1-transistor Q,
.

is off when transistor Q4. The transistor is turned on by applying a constant voltage to the base of the transistor. Similarly, constant current source I22 and diode D2 apply a constant voltage to the base of transistor Q42 to turn it on when transistors Q and 2 are off.

Transistor Q1. ．． Switching signals C and C having opposite phases to each other are applied to the base of Q.

In such a configuration, if transistors Q41 and Q4□, diodes D1 and D2, and current sources '21 and 122 are equal, transistors Q4 and Q4□ function as constant current sources that flow the same current, and the constant current source ■- in FIG. is equivalent to Then, when the input C is at the L (low) level, the transistor Q5. If is off, transistor Q, 1 is current source '2
The base current is supplied from 1 and turns on, and the differential pair DF
+ is selected. At this time, since υ is at H (high) level, transistor Q is turned on, so transistor Q4
The base current is cut off and the differential pair DF2 is turned off, and the differential pair DF2 does not operate. Conversely, if C=H and C=L, transistor Q is off, Q42 is on, and differential pair DF2 is selected.
I transistor Q,1 is on, Q41 is off, and differential pair DF+ is not selected.

Therefore, the function as a differential pair switching circuit is the same as in Fig. 1, but the reference voltage VRO value commonly applied to differential pairs DPI and DF2 is
ES and transistor Q, 2. It can be reduced to the sum of the VBEI stage of Q2.

VR＞VBE+VCES=1. IV
, , , , , , (2) Therefore, the reference voltage ■R is 1
．． 2-1.3 V bandgap reference (BG
R) can be adopted. Also, the signal Vc in FIG.
The amplitude of (VBE→-VCE) or more is required, but the amplitude of the signals C and C of the present invention is sufficient to be VBE.

FIG. 3 shows an example of application to a regulator. In the figure, D3 and transistor Q6. is the differential pair DF1. DF
Active load common to Q6. ,, Q63 is also a common output transistor. The operational amplifiers that drive the output transistors Q6° and Q63 are generally composed of only one differential pair, but the operational amplifier OP of this example is composed of two differential pairs DF1. It is configured including DF2. Series resistors R1 to R3 are connected between the output Vout of this regulator and ground, and RI.

The potential at the series connection point of R2 is negatively fed back to the inverting input of the differential pair DF+, and the potential at the series connection point of R2. The potential at the series connection point of R:l is the differential pair D
Negative feedback is provided to the inverting input of F2. Differential pair DPI, DF2
A reference voltage vR is applied to each non-inverting input of. This circuit operates so that the input voltages VΔ, vB are equal to the reference voltage vR, so the switching signal C is set to L and the differential pair DF+
When , is selected, and when the differential pair DF2 is selected with signal C set to L, then is. Since there is a relationship between the two equations (31 < (41), it is possible to generate a high/low binary DC output Vout. Note that Vin is generally the power supply voltage, but this value If it is low, the voltage specified by formula +31. +41 cannot be generated, so the voltage is set sufficiently higher than these.In the constant current source 12. + D + , Q4. and I22°D2.Q42, the current flowing through the diode D1. The currents flowing into the emitters of transistors Q4...Q42 have a constant ratio (area ratio of each junction) and operate as a current mirror.

Effects of the Invention As described above, in the present invention, a pair of transistors Q51. Since the constant current sources of the differential pairs DPI and DF2 are turned on and off by Q5□, and the two differential pairs are thereby switched, the reference voltage of the differential pair is reduced and the temperature dependence ('l This makes it possible to adopt a hunt gap reference with a small number of errors.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional differential amplifier pair switching circuit, FIG. 2 is a circuit diagram showing an embodiment of the present invention, and FIG. 3 is a circuit diagram showing an application example of the present invention. In the figure, DPl and DF2 are a differential amplifier pair, Q41°Q42
is a constant current source L transistor, (1), , jI, Q are switching transistors. Applicant Fujitsu Limited Representative Patent Attorney Minoru Aoyagi

Claims (1)

[Claims] In a switching circuit that enables operation of one of two differential amplifier pairs each comprising a pair of transistors and a constant current source, complementary switching signals are applied to the transistors forming the constant current source of each differential amplifier pair. 1. A switching circuit for a pair of differential amplifiers, comprising a switching transistor that exclusively turns on and off the transistor in response to a switching circuit.