SU1001441A1 - Amplifier - Google Patents

Description

(i) AMPLIFIER

one

This invention relates to a measurement technique and is intended to amplify difference and attenuation in-phase signals.

A prior art amplifier comprising first, second and third operational headers, covered by first, second and third resistors through negative feedback, the non-inverting inputs of the first and second operational amplifiers are the differential input of the amplifier, and their inverting inputs are connected via a resistance divider. , the outputs of the first and second operational amplifiers through the fourth and fifth resistors are connected to the differential input of the third operational amplifier, non-inverted Its input is connected to the common bus through the sixth resistor, and the output is the output of the amplifier 1 3.

However, in the known amplifier, the common-mode component of the input signal is not well suppressed due to the spread of resistance values of the resistors in the feedback circuits.

The purpose of the invention is to increase the attenuation coefficient of in-phase signals at a lower class of accuracy of resistors in external feedback circuits.

The goal is achieved by connecting an element with negative resistance between the midpoint of the resistive divider and the common bus. In addition, an element with negative resistance is made on the fourth operational amplifier, covered by positive and negative feedbacks, respectively, through the seventh and eighth resistors, with the ninth resistor connected between its inverting input and the bus bar. 3lOO The diagram shows the electrical circuit of the proposed amplifier. The amplifier contains three operational amplifiers (OU) -OU, OU., OU with

differential input and unbalanced output, covered through resistors 1-3 respectively by negative feedback circuits, non-inverting inputs of OU and OU2 form the differential input of the measuring amplifier, their inverting inputs are interconnected through a resistive divider k, and outputs through resistors 5 and 6 connected to the differential input of an op-amp, the non-inverting input of which is connected via a resistor 7 to the case; an element with negative resistance is connected to the midpoint of the resistive divider 4, containing fourth OS swept through resistors 8 and 9, respectively chains positive and negative ..obratnoy communication with an inverting input OU4. through the resistor 10 is connected to the common point of the circuit. The amplifier works as follows. In the absence of an element with a negative resistance, the input OU and OU2 form a differential buffer cascade, the transfer coefficient of which for the common-mode signal is one. With the introduction of an element with negative resistance, the gain of the common-mode signal K is k.6.J. k) H K where Y is the conductivity of the corresponding resistor. Y - F is the average value of conductivities in the negative feedback circuit of the shelter and the shelter; The gain of the op amps covered by the negative feedback circuit characterizes the accuracy of the resistance adjustment in the load f.-f9f- Therefore, the coefficient of the attenuation of the common-mode noise of the input helmet and with the element on the opamp, Ko, / f ,.

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(2. erectise the accuracy of the resistor adjustment)

 For the entire amplifier, the common mode attenuation factor can be determined, to a first approximation, by the product

Spit Spit-COSO. eleven

Thus, the selection accuracy I + tl The output stage at the OS converts the differential signal into an unbalanced output, by analogy with the well-known circuit. Its coefficient of oscillation of the common-mode signal equal to the external resistors determines the magnitude of the scythe. If we assume that the resistors in the first stage, including the element with negative resistance, and in the second stage at the OS, are selected with the same accuracy, then in the proposed amplifier the Kose value is much higher than in the CTJHOM. For a given value of COEC, for example, selection of resistors in the proposed amplifier is required with an accuracy of 10, then in a known order, in order to provide the specified COCC, it is necessary to increase the accuracy of the resistor sub-system 3 times, and for E 1% OX for the specified spit should be 0 ,. The connection of an element with negative resistance requires the provision of stable operation conditions. The amplifier is stable when the positive feedback ratio does not exceed the negative feedback ratio. therefore, the condition must be met. The proposed device reduces the accuracy requirements of resistors. without degrading the COSO (for this case, the mismatch of resistors within 2. is permissible), which, at the end

Claims (2)

Claim N 1. An amplifier comprising first, second and third operational amplifiers, covered by respective first, second and third resistors the negative feedbacks, non-inverting inputs of the first and second operational amplifiers are differential input amplifier, and its inverting input through a resistive divider ²¹ connected between themselves, the outputs of the first and second operational amplifiers through the fourth and fifth resistors are connected to the differential input of the third operational amplifier, non-inverting 441 * whose input is connected to a common bus through a sixth resistor, and the output is an amplifier output, which means that, in order to increase the attenuation coefficient of common-mode signals, an element with negative -ι is connected between the midpoint of the resistive divider and the common bus resistance. 2. The amplifier according to claim 1, distinguished by the fact that the element with negative resistance is made on the fourth operational amplifier, covered by positive and negative feedbacks, respectively, through the seventh and eighth resistors, and between its non-inverting input and the common bus the ninth resistor is on.