Gain-controlled broadband amplifier stage

Details Gain-controlled broadband amplifier stage Gain-controlled broadband amplifier stage

1990-12-12

1992-03-03

Laroche, Eugene R.

Amplifiers

With semiconductor amplifying device

Including gain control means

330277, H03G 330

Patent

active

050936310

ABSTRACT:
A broadband amplifier stage includes a field-effect transistor as an amplifying element whose gain is varied with the aid of the drain current at a fixed drain-source voltage U.sub.DS and requires higher-than-usual supply voltages to fulfill the condition U.sub.DS =constant. The DC gain of the amplifying element is not generally sufficient to keep the drain-source voltage constant at small currents. According to the invention, a high-gain operational amplifier is inserted into the feedback path to stabilize the drain-source voltage. The voltage source -U.sup.1 for adjusting the gate bias then drives a constant current through the voltage divider, thus maintaining the drain-source voltage U.sub.DS constant.

REFERENCES:
patent: 4420724 (1983-12-01), Owen
patent: 4943785 (1990-07-01), Benz et al.

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