Amplifiers – Signal feedback – Combined with control of bias voltage of signal amplifier
Patent
1976-05-03
1977-03-22
Rolinec, Rudolph V.
Amplifiers
Signal feedback
Combined with control of bias voltage of signal amplifier
330 22, 330 30D, H03G 330
Patent
active
040139727
ABSTRACT:
A gain controllable amplifier of the present invention comprises a first and a second differential amplifier. The first differential amplifier serves as an amplifier for an input signal to be impressed on emitters connected in common with each other, while the second differential amplifier serves as a base bias voltage control circuit of the first differential amplifier. The bias voltage derived from the second differential amplifier is changed by a D.C. bias voltage applied to the bases of the respective transistors in the second differential amplifier. The connected to the respective output terminals of the second differential amplifier are transistors whose bases receive a constant voltage. The gain of the first differential amplifier can be controlled by adjusting the D.C. bias voltage applied to the second differential amplifier. The present invention further comprises two current supply circuit each connected to the aforesaid respective output terminals of the second differential amplifier. When one of the transistors in the second differential amplifier is brought into a cut-off condition, the base bias voltage on the first differential amplifier is supplied directly through a current supply circuit. As a result, a variable range of the base voltage on the second differential amplifier is becomes wider, with a resulting increase in the gain control range of the first differential amplifier, thereby achieving increased attenuation of gain. The amplifier according to the present invention is suited for use as a gain control circuit especially for an audio circuit which requires attenuation to a great degree.
REFERENCES:
patent: 3641450 (1972-02-01), Lunn
patent: 3684974 (1972-08-01), Solomon et al.
Nishitoba Shigeo
Tokuda Kazuo
Dahl Lawrence J.
Nippon Electric Company Ltd.
Rolinec Rudolph V.
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