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Multichannel-amplifier-with-gain-matching

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Multichannel amplifier with gain matching

Details

Inventors: Gingrich, Randal R.; Difiore, Nicholas L.;
Assignee: Ford Motor Company (Dearborn, MI)
Primary Examiner: Mullins; James B.
Assistant Examiner:
Attorney, Agent or Firm: Mollon; Mark, May; Roger L.

A multichannel amplifier employs field-effect transistors to vary the gain of operational amplifiers in each respective channel. Gain matching of the respective channels is obtained by providing each channel with a respective DC bias voltage which compensates for differences in pinch-off voltage of the field-effect transistors. The invention permits the use of inexpensive, unmatched JFETs in the amplifier. Close gain tracking achieves very accurate stereo imaging in an audio system.

DETAILED DESCRIPTION It is a principal object of the present invention to provide a multichannel amplifier with accurate gain tracking between channels It is another objection of the present invention to employ JFETs connected to respective operational amplifiers in a multichannel amplifier with compensation for variations in pinch-off voltages V.
sub.
p of the JFETs.
These and other objects are achieved in a multichannel amplification system having a plurality of channels, each channel comprising an amplifier and a field-effect transistor (FET).
External resistances including a respective FET are connected to each operational amplifier in a negative feedback arrangement for providing variable gain.
The drain of each FET is connected to the inverting input of each respective op amp.
The resistance provided by the FET is controlled by a control signal applied to the gate of the FET.
Negative feedback allows the voltage at the inverting and noninverting inputs of each op amp to be substantially equal.
Thus, bias voltages applied to the noninverting inputs of each respective op amp are offset in the present invention as necessary to compensate for differences in the pinch-off voltage of the FETs.

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