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Differential Amplifier With Zero Common Mode Gain

IP.com Disclosure Number: IPCOM000080620D
Original Publication Date: 1974-Jan-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Buhler, OR: AUTHOR

Abstract

This differential amplifier circuit includes output-to-input feedback which automatically adjusts the amplifier's input circuit, in a manner to achieve zero common-mode gain. This feedback dynamically maintains zero common-mode gain, and compensates for initial manufacturing tolerance variation, as well as temperature and long-term drift in the amplifier's circuit components.

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Differential Amplifier With Zero Common Mode Gain

This differential amplifier circuit includes output-to-input feedback which automatically adjusts the amplifier's input circuit, in a manner to achieve zero common-mode gain. This feedback dynamically maintains zero common-mode gain, and compensates for initial manufacturing tolerance variation, as well as temperature and long-term drift in the amplifier's circuit components.

Noninverting input terminal 11 of operational ampliiier 10 is connected to ground.potential 12, through fixed resistor 13 and variable resistor 14. The amplifier's inverting input terminal 15 is connected to the junction of resistors 16 and 17. The amplifier's output, e(0) appears at conductor 18.

Signal 19 represents the amplifier's input signal e(s). Signal 20 represents a common-mode signal. Primary winding 22 of transformer 21 is connected to the output of oscillator 23. The two transformer secondary windings 24 and 25 are connected to supply equal magnitude, in-phase signals to the amplifier's input terminals.

The oscillator introduces a known AC signal to the two amplifier input terminals. This signal is a common-mode signal. This common-mode signal is amplified by the common-mode gain of amplifier 10. The amplified common- mode signal is coupled to terminal 26 by way of narrow bandpass filter 27. The phase of the amplified common-mode signal at terminal 26 is compared to the phase of the oscillator output, at terminal 28, by synchronou...