JPH0486006A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To obtain a high common-mode rejection ratio (CMR) by extracting voltage changes respectively at the both terminals of a first resistor as the change of a current by current mirror circuits respectively connected to both the terminals of the first resistor. CONSTITUTION:At a current/voltage conversion circuit 16, a current signal from a voltage/current conversion circuit 15 is converted to a voltage signal and outputted by a feedback type operational amplifier OP1 connecting a feedback resistor RB. In this case, the potential at one terminal of the feedback resistor RB is made equal to a potential applied from a terminal TC. Therefore, an output terminal TOUT obtains an output spriously defining a potential applied from the terminal TC as zero potential. Thus, the high CMR can be obtained by applying the stable potential to the terminal TC regardless of the potentials of input terminals TA and TB or a power supply VCC.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an amplifier circuit using an operational amplifier.

Improved I to be able to obtain particularly high CMR
This invention relates to an amplifier circuit for C.

(Prior Art) An example of a simple amplifier circuit using an operational amplifier will be described with reference to FIG.

This amplifier circuit has a non-inverting input terminal 1 of an operational amplifier OP2.
Input terminals TA and T are connected to the inverting input terminal via resistors rARIF5, respectively, and a feedback resistor R9 is connected between the output terminal and the non-inverting input terminal. This circuit is
The differential voltage between two inputs is amplified with a constant amplification factor.

(Problem to be Solved by the Invention) In an IC amplifier circuit using such an operational amplifier, in order to obtain a 1 higher CMR (common mode rejection ratio), it is necessary to use resistors R8 to R4 with extremely high relative accuracy. A vessel is required.

In other words, in the amplifier circuit as shown in Fig. 1, the input terminal TA
, TB voltages are respectively VISA r VINB,
The voltage of the output terminal T0LIT is V. If it is UT.

out-V, NAIR4・(R1+R2)/(R3+R4
)・RoV +5B−R2/RI. In addition, R3-R4 are each resistor R1
~ represents the resistance value of R4.

Here, considering the conditions of R, -R,, R2-R, Vout-(VINA VINB) R2/R1.

When V INA" V INB, VOIJT becomes 0.

However, at the stage of manufacturing ICs for boat fishing.

This is insufficient to satisfy the above conditions, and there is a problem in that products that undergo a special manufacturing step to increase relative accuracy are extremely expensive.

Therefore, one object of the present invention is to provide an IC amplifier circuit that can obtain high CMR without being affected by the relative precision of resistors.

(Means for Solving the Problems) An amplifier circuit according to the present invention includes a voltage-current converter circuit that converts a voltage difference between two inputs into a current signal, and a current-voltage converter circuit that converts the current signal into a voltage signal and outputs the voltage signal. a conversion circuit, the voltage-current conversion circuit converts each voltage change across the first resistor connected between two transistors constituting the differential circuit into Current changes are extracted by current mirror circuits connected to both ends, respectively, and the current-to-voltage conversion circuit is characterized by comprising a negative feedback type amplifier circuit using an operational amplifier connected to a feedback resistor.

(Example) An embodiment of the present invention will be described with reference to FIG.

This circuit includes a bias circuit 13. having a bias terminal Vb+. Input circuit] 4. a first input terminal TA having a first input terminal TA;
input circuit] 1. A second input circuit 12 having a second input terminal TB. 1st. A voltage-current conversion circuit 15 for converting the voltage difference between the second input terminals TA and T into a current signal.
．． The current signal is converted into a voltage signal and output terminal T. ,1
It has a current-voltage conversion circuit 16 outputting from the current-voltage conversion circuit 16.

The first and second input circuits 11 and 12 are respectively.

PNP input transistor Q5. Q7, and transistors Qb and Qs for NPN input.

The operating status of these transistors is determined by the input switching terminal T.
It can be switched by changing the connection of s.

For example, regarding the first input circuit 11, when the input switching terminal T is connected to the earth GND line, in the input switching circuit 14, the first current mirror circuit 14-1 turns on the transistor Q6 through the diode D. , input via a PNP input stage is possible. On the other hand, when the input switching terminal T5 is opened, the input switching circuit 14
Then, the transistor Q is turned on through the diode D by the second current mirror circuit 14-2, and the NPN
Input via the input stage becomes possible. This also applies to the second input circuit 12.

In the voltage-current conversion circuit 15, the first. Second input terminal T
The differential voltage between A, T8 or transistor Q.

It occurs across resistor RA through Q2. For example, when a current I flows through the collector of the transistor Qz due to the differential voltage generated in the resistor RA, a current ■ also flows through one collector of the transistor QI2 constituting the current mirror circuit. A current I due to this voltage difference is generated by the transistor Q3. It is transmitted to the current-voltage conversion circuit 16 through the differential circuit formed by Q4. This is transistor QI3IQ+
The same applies to the current mirror circuit according to No. 4.

In the current-voltage conversion circuit 16, a feedback resistor R.

The current signal from the voltage-current conversion circuit 15 is converted into a voltage signal by a feedback-type operational amplifier OPl connected to the voltage-current conversion circuit 15, and outputted. Here, the potential at one end of the feedback resistor RB is the terminal T.

The potential is the same as that given by. Therefore, the output terminal T. At 8o, an output is obtained in which the potential applied from the terminal Tc is pseudo-zero potential. This means that an extremely high CMR can be obtained by providing the terminal Tc with a stable potential that is not affected by the potentials of the input terminals TA and TB or the power supply VCC.

Also, the amplification factor Av of the amplifier circuit is:

A v "" K is expressed as (resistor R8)/(resistance value of resistor RA), (K: current transfer function),
The matching accuracy between resistors RA and R6 is basically CMR.
Does not affect R. In addition, ■especially the voltage-current conversion circuit 1
Ic (collector current) of each transistor in 5
1 in VCE (collector-emitter voltage) characteristics
cUsing certain properties1. A cascode connection configuration is used in important locations.

(2) By configuring the current mirror circuit as a symmetrical circuit, the current transfer function K can be made to have less voltage dependence.

As a result, in a single circuit, the output voltage is V. L□, is VOIJ
T -AV-(VINA VINB
)-K・(VINA′-V+sa)・RB/RﾾWhen + VINA = VINB, the output voltage V
It is possible to make 0IJT extremely close to 0.

(Effects of the Invention) As explained below, according to the present invention, one resistor RA
By extracting the voltage difference between the two inputs across the resistors in the form of a current signal, the resistors RA, R,
It is possible to provide an amplifier circuit that can obtain a high CλIR without being affected by the relative accuracy of s.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention. FIG. 2 is a circuit diagram of a conventional I.
The figure which showed an example of the amplifier circuit for C. In the figure, 11. 1st input circuit, 12: 2nd input circuit,
13: Bias circuit, 14: Input switching circuit 1]]5:
Voltage-current conversion circuit, 16; current-voltage moxibustion conversion circuit.

Claims (1)

[Claims] (1) Voltage that converts the difference voltage between two inputs into a current signal -
The voltage-current conversion circuit includes a current conversion circuit and a current-voltage conversion circuit that converts the current signal into a voltage signal and outputs the voltage signal. Each voltage change at both ends of the first resistor is extracted as a change in current by a current mirror circuit connected to both ends of the first resistor, and the current-voltage conversion circuit connects a feedback resistor. An amplifier circuit comprising a negative feedback type amplifier circuit using a connected operational amplifier.