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Circuit For Preventing Chopper Feedback

IP.com Disclosure Number: IPCOM000098775D
Original Publication Date: 1959-Dec-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

French, WK: AUTHOR

Abstract

Additional components are included in the low frequency section LF of a chopper stabilized DC amplifier to establish an essentially constant impedance to an applied signal E(1). In this manner undesirable feedback usually imposed by a section LF of this kind on the signal E(1) is practically eliminated.

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Circuit For Preventing Chopper Feedback

Additional components are included in the low frequency section LF of a chopper stabilized DC amplifier to establish an essentially constant impedance to an applied signal E(1). In this manner undesirable feedback usually imposed by a section LF of this kind on the signal E(1) is practically eliminated.

High frequency components of the signal E(I) pass directly to an amplifier stage DC through a capacitor C(3). Low frequency components of the signal E(I) pass to the amplifier stage DC indirectly, through a junction J, an amplifier stage AC, a phase sensitive demodulator and a filter stage. Chopping of the signal E(I) is effected by actuation of a pair of mechanical contacts S(1) and S(2) which are rapidly opened and closed in a conventional manner. The rapid switching of the contacts S(1)-S(2) creates spurious and undesirable signal excursions or chopper feedback which may be imposed on the E(I) input, if not controlled. Minimization of chopper feedback is accomplished in the circuit by providing a compensating feedback loop in the LF stage which includes the resistor R3 and the capacitor C(2).

The amplifier AC has an infinite input impedance and is of -K gain. For illustrative purposes, it is assumed that the signal E(I) is positive. E(I) is normally directed simultaneously to the input of AC and to the chopper contacts S(1)-S(2) through the resistors R(1) and R(2). Whether or not the presence of the signal E(I) results in...