Phase-sensitive detector circuit with compensation for offset er

Details Phase-sensitive detector circuit with compensation for offset er Phase-sensitive detector circuit with compensation for offset er

1975-04-08

1977-03-01

Heyman, John S.

Amplifiers

With periodic switching input-output

307230, 307232, 307235K, 307237, 307297, H03F 102

Patent

active

040104249

ABSTRACT:
A phase-sensitive detector circuit comprises a pair of field-effect transistors switched in antiphase and connected at a switching point. The switching point is supplied with a signal to be detected through an a.c. coupling. One of the transistors is connected to the input of an operational amplifier having a feedback path designed to maintain its input as a virtual earth. A compensation circuit connected from the switching point to the input side of the a.c. coupling provides a compensation signal to cancel the effect of any offset voltage in the operational amplifier. The other switching transistor may be grounded or else may be connected to a second operational amplifier whose input is also maintained as a virtual earth by a feedback path. In the latter case the output from the circuit is taken differentially from the operational amplifier.
Alternatively, or in addition, a second pair of switching transistors supplied by a signal in antiphase to the signal supplied to the first-mentioned pair of transistors can be connected in a similar manner to supply the one or both operational amplifiers.

REFERENCES:
patent: 3237116 (1966-02-01), Skinner et al.
patent: 3473131 (1969-10-01), Perkins
patent: 3757241 (1973-09-01), Kime et al.
patent: 3828204 (1974-08-01), Farnsworth

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