Common-mode feedback bias generator for operational amplifiers

Details Common-mode feedback bias generator for operational amplifiers Common-mode feedback bias generator for operational amplifiers

1988-12-23

1990-06-12

Mottola, Steven

Amplifiers

With semiconductor amplifying device

Including differential amplifier

330253, H03F 345

Patent

active

049336444

ABSTRACT:
A common-mode feedback circuit comprises a reference generator (12) for generating a signal corresponding to a desired common-mode operating point connected to a common-mode bias circuit (14) for generating a second signal corresponding to the common-mode operating point of the outputs (V.sub.out.sup.+, V.sub.out.sup.-) of the fully differential operational amplifier. In the preferred embodiment, the common-mode bias circuit (14) includes a sensing circuit (58) comprising two MOS transistors (60, 62) having sources and drains connected together. The MOS transistors (60, 62) operate in the ohmic region to provide a variable load responsive to the output signals (V.sub.out.sup.+, V.sub.out.sup.-) connected to their gates.

REFERENCES:
patent: 4105942 (1978-08-01), Henry
patent: 4568885 (1986-02-01), McKenzie et al.
"High-Frequency CMOS Continuous-Time Filters," by Khorramabadi and Gray, IEEE Journal of Solid-State Circuits, vol. SC-19, No. 6, Dec. 1984, pp. 939-948.
"A High-Performance Micropower Switched-Capacitor Filter", by Castello and Gray, IEEE Journal of Solid-State Circuits, vol. SC-20, No. 6, Dec. 1985, pp. 1122-1132.
"A Family of Differential NMOS Analog Circuits for a PCM Codec Filter Chip," by Senderowicz et al., IEEE Journal of Solid-State Circuits, vol. SC-17, No. 6, Dec. 1982, pp. 1014-1023.

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