Amplifiers – With semiconductor amplifying device – Including gain control means
Patent
1988-11-02
1989-09-19
Mullins, James B.
Amplifiers
With semiconductor amplifying device
Including gain control means
330145, H03G 330
Patent
active
048685194
ABSTRACT:
An amplifier circuit having an FET connected in series with a resistor coupled to a constant voltage source, coupled between a pair of amplifiers, such as audio amplifiers in a two-stage amplifying circuit. The FET specifically and directly determines the amount of gain of the two-stage amplifier, or the like. R.sub.DS of the FET is continually monitored by its connection to one input of an amplifier serving as a comparator, with the other input thereof serving as a reference voltage derived from a modulated signal emanating from a microprocessor. Each of the signals V.sub.DS, and the reference from the microprocessor is filtered through a low pass filter to remove the audio, or other cyclical signals, and, in the latter case, in order to provide a substantially constant reference voltage to the input of the comparator. The output of the comparator is coupled to an RC circuit, the capacitor thereof being continually charged and discharged in response to the state of the output of the comparator. The output from the RC circuit is coupled to the FET to define the gate voltage of V.sub.GS thereof, which in turn determines the value of R.sub.DS , to thereby continually alter R.sub.DS, to thereby provide the gain so desired and specifically required in the amplifying circuitry. Such value is inherently defined by the modulated reference signal emanating from the microprocessor.
REFERENCES:
patent: 3631262 (1971-12-01), Jarrett
patent: 4013975 (1977-03-01), Kataoka et al.
patent: 4121183 (1978-10-01), Murphy
patent: 4468631 (1984-08-01), Goldberg
patent: 4766395 (1988-08-01), Dolby
"FETs As Voltage-Controlled Resistors", Siliconox, pp. 7-75 to 7-83.
"A Linear Multiple Gain-Controlled Amplifier", by Jim Sherwin, Aug. 1975.
Benn Marvin
DNIC Brokerage Company
Gerstein Milton S.
Mullins James B.
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