Amplifiers – With semiconductor amplifying device – Including gain control means
Patent
1977-02-14
1978-04-11
Mullins, James B.
Amplifiers
With semiconductor amplifying device
Including gain control means
330 85, 330 86, 330110, 330293, H03G 330
Patent
active
040841294
ABSTRACT:
A voltage controlled variable gain circuit comprising: first, second, third and fourth same polarity transistors for dividing the output current of a first operational amplifier by dc gain control voltage and being connected with the output terminal of the first operational amplifier to which an input signal is applied; means for driving in inverse phase the respective pairs of a first and third transistors, and a second and fourth transistors; a first feedback circuit including a second operational amplifier with an inverting input terminal connected with the output terminal of the first transistor, a first resistor element and a first PN junction element connected in series between the input and output terminals of the second operational amplifier, and a second resistor element and a second PN junction element connected in series between the output of the second operational amplifier and the input terminal of the first operational amplifier, so as to negatively feedback the output current of the first transistor to the input terminal of the first operational amplifier: a second feedback circuit for negatively feeding back the output current of the second transistor to the input terminal of the first operational amplifier; and summing device for summing the output current of the third transistor inversed and the output current of the fourth transistor.
REFERENCES:
patent: 3502905 (1970-03-01), Bicking
patent: 3714462 (1973-01-01), Blackmer
Mullins James B.
Tokyo Shibaura Electric Co. Ltd.
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