Sri International

Floyd A Brown, Jr

Dilip G Saraf

A differential amplifying system is disclosed which includes a first section having a pair of amplifying channels comprising a pair of operational amplifiers having low noise characteristics, each of which amplifiers has an inverting input, a noninverting input, and an output terminal. Input capacitors are provided for differentially connecting an input signal to be amplified to the noninverting inputs of said pair of amplifiers. Balanced negative feedback resistance circuits are provided for connecting the output terminals of the amplifiers to their own inverting inputs. The noninverting amplifier inputs are connected to ground through a balanced pair of tapped resistance networks. Balanced positive feedback circuits, each including a resistor, connect the amplifier output terminals to the taps on the associated resistance networks for positive feedback to said noninverting amplifier inputs thereby increasing the effective input resistance of said amplifying channels. The output terminals of said pair of amplifiers are resistance coupled to the inverting and noninverting inputs of a third operational amplifier having an output proportional to the difference of the two input signals supplied thereto from said pair of amplifiers. A fourth operational amplifier capacitance coupled to the output signal from the third operational amplifier provides the system with the desired voltage gain.

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Palo Alto, CA, United States of America

Floyd A Brown, Jr