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Wide Range Polarity Detector

IP.com Disclosure Number: IPCOM000090566D
Original Publication Date: 1969-May-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Hilliard, JJ: AUTHOR

Abstract

Digital signal processing systems often require an accurate signal polarity indication over input level ranges as large as 100 db. Current technology allows accurate polarity detection at levels of several millivolts with resultant dynamic ranges of from 50 to 60 db. To provide accurate polarity detection at levels in the order of tens of microvolts and dynamic ranges of 100 db or greater requires feedback techniques which cancel inherent semiconductor error and correct for change in error created by temperature variation. This circuit requires that the mean value of the input signal be zero. This is true of many signals subject to digital processing techniques.

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Wide Range Polarity Detector

Digital signal processing systems often require an accurate signal polarity indication over input level ranges as large as 100 db. Current technology allows accurate polarity detection at levels of several millivolts with resultant dynamic ranges of from 50 to 60 db. To provide accurate polarity detection at levels in the order of tens of microvolts and dynamic ranges of 100 db or greater requires feedback techniques which cancel inherent semiconductor error and correct for change in error created by temperature variation. This circuit requires that the mean value of the input signal be zero. This is true of many signals subject to digital processing techniques.

For low-level input signals, amplifier 1 operates in a linear manner with the feedback network composed of resistors 7...10 and capacitor 11. This feedback network provides DC feedback to correct offset errors while limiting feedback in the band of the input signal so that there is significant amplification of the input signal. The linear operation of the circuit extends from approximately -100 db to approximately i55db. It is at this point that the output of operational amplifier 1 saturates and nonlinear operation begins.

When the output of amplifier 1 saturates, it is possible for the correction applied to the offset input 14 to be in error if the positive and negative saturation voltages differ. This is because even in the case of perfect symmetry, there can be a DC voltag...