RU1826121C - Synchronous demodulator - Google Patents

Abstract

The invention relates to radio engineering and can be used in instrumentation, in particular for constructing synchronous detectors. The goal is to increase accuracy by reducing common mode interference and switching error. The synchronous demodulator (LED) contains two operational amplifiers (op amps) 1 and 2, the outputs of which are the outputs of the LEDs, three voltage dividers made on two resistors connected in series, three switches to two positions, providing depending on the control reference signal connection to the serial connection by signal in the first half-period of the op-amp 1 and op-amp 2, and for the second half-period of the op-amp 2 and op-amp 1, thereby receiving two antiphase signals at the outputs of the synchronous demodulator. The gain is determined by the ratio of resistors in the voltage dividers. Accuracy is ensured by zero voltage on switches 8-10. 1 ill.

Description

With

with

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The invention relates to radio engineering and can be used in instrumentation, in particular for constructing synchronous detectors.

The purpose of the invention is to improve accuracy by reducing common mode noise and switching error.

The drawing shows a circuit diagram of a synchronous demodulator.

The synchronous demodulator contains the first and second operational amplifiers (op amps) 1 and 2, the first, second, third voltage dividers 3-5, each made on two resistors 6.7, the first, second, third switches 8-10 to two positions.

The synchronous demodulator operates as follows.

With the state of switches 8-10 indicated in the drawing, i.e. the fixed contact with is connected to the movable a, the signal supplied to the input of the device Bx through the divider 4 is fed to the second op-amp 2 and amplified by it. The gain is determined by the ratio of the resistances of the resistors 7 and 6 of the second divider 4. In this case, the voltage at the second output OUT2 will be equal to:

R4-7

and

Ovikh 2 - UB

(1)

JBXR where UBX is the voltage at the output of the device;

RA- &, R4-7 - resistance of resistors 6 and 7 of the second divider 4.

In the same way as the second op-amp 2 is connected to the input of the device, the first op-amp 1 is connected to the second output of Output 2 through the third divider 5 and the third switch 10. The voltage at the output of the first op-amp 1, i.e. at the first output of device OUT1, it will be equal to:

11out1 - out2 p „,, (2)

where Rs-e, Rs-7 are the resistances of resistors 6, 7 of the third divider 5.

Substituting the expression (1) in (2), we obtain:

IIit R5-6, very good

 R, (3)

In this mode, the first divider 3 is a resistive load connected between input Bx. and Output 1 of the device, and does not affect the state of the circuit.

When the state of the switches 8-10 is changed, the fixed contact is connected to the movable contact in the function of the op-amps 1, 2 and dividers 3, 4 are interchanged. In this case, the output voltages become equal to 1 R3-7 s-6

UeWxl - UBX -W

Uebtx2 - Uetdxl

10

fifteen

twenty

25

thirty

35

40

45

fifty

55

 . . R3-7 5 --- - Kg-bKz-6

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R (5)

where Нз-б, R3-7 are the resistances of resistors 6, 7 of the first divider 3.

Comparison of the expressions (1), (3), (4), (5) shows that when the ratios of the resistors R3-7 / R3-e Ri-7 / R4-6 of the first and second dividers 3 and 4 are equal and the resistors of the third divider are equal 5, the voltages at the outputs of the device Outputs 1 and 2 will be equal in magnitude and different in sign. In this case, the polarity of the output voltage relative to the input voltage is determined by the state of the switches 8-10 and changes synchronously with their switching. Thus, in synchronization with the reference control signal of the switches 8-10, the input signal is modulated or demodulated.

In addition to the conversion, the device provides signal amplification with a gain equal to the ratio of the resistances of the resistors of the first and second dividers 3 and 4. In this case, the output signal can be removed from any of the output terminals of Output 1, Output 2 or between these outputs, which increases the noise immunity for by doubling the magnitude of the signal, as well as the symmetry of the terminals, at which the useful signal is differential and the noise is in-phase. Since the movable contacts of the switches are connected to the common bus and to the inverting inputs of the op-amp 1 and op-amp 2, the non-inverting inputs of which are earthed, the switches in all modes are practically under zero voltage. This substantially reduces switching errors. In addition, such switches can be made on field effect transistors with an pn junction and p-type channel and controlled directly by TTL level signals without an additional control circuit, which greatly simplifies the implementation of the device, in particular in the form of a thin-film hybrid integrated circuit.

Claims (1)

The claims A synchronous demodulator containing the first and second operational amplifiers, the non-inverting inputs of which are connected to a common bus, the first, second, voltage dividers, each of which is made on series-connected resistors, as well as two resistors and a first two-position switch, which controls the input which is the input of the reference signal, while the first terminals of the first and second voltage dividers are connected to the outputs, respectively the first and second operational amplifiers, characterized in that, in order to increase accuracy by reducing the common mode noise and switching error, the second and third switches to two positions are introduced, the control inputs of which are combined with the control input of the first switch to two positions, two resistors are included sequentially and form a third voltage divider connected between the outputs of the first and second operational amplifiers, and the tap of which through the normally closed contacts of the third switch to two positions connected to the inverting input of the first operational amplifier, and through normally 5 closed contacts - with the inverting input of the second operational amplifier, and the second terminals of the first and second voltage dividers are connected and are the input of the synchronous demodulator, while the withdrawal of the first voltage divider through the normally closed contacts of the first switch to two positions is connected to the common bus, and through normally open - with the inverting input of the first operational amplifier, and the tap of the second voltage divider through the normally closed contacts of the second switch to two positions n to the inverting input of the second operational amplifier, and through normally open contacts - the common bus.