CMOS operational amplifier with improved common-mode rejection

Details CMOS operational amplifier with improved common-mode rejection CMOS operational amplifier with improved common-mode rejection

1985-12-27

1987-04-07

Mullins, James B.

Amplifiers

With semiconductor amplifying device

Including differential amplifier

330258, 330311, H03F 345

Patent

active

046564373

ABSTRACT:
A fully differential CMOS operational amplifier (10) of the folded cascode type includes two similar signal current branches (32,34) connected in parallel between two supply voltage nodes (V+,V-). Each branch includes an N-type bias current transistor (42,54), a P-type cascode transistor (50,62), an N-type pull-down transistor (40,52), and a P-type current source transistor (48,60), all connected respectively in series between the drain of an N-type common mode suppression feedback transistor (44,56) and the drain of a P-type common mode suppression feedback transistor (46,58). The N-type feedback transistor has its source connected to a negative supply voltage node. The P-type feedback transistor has its source connected to a positive supply voltage node. The gates of the feedback transistors of each branch are connected to the output node (36,38) at the drain of the cascode transistor. The gates of the other transistors are supplied with appropriate reference voltages (V.sub.B1, V.sub.B2, V.sub.B3, V.sub.B4). Second harmonic effects produced by the N-type and P-type feedback transistors of a branch cancel each other at the output node. Also disclosed is a connection of the current source (20,22) of the differential input stage (12) to the drains of the N-type feedback transistors for reducing noise and device mismatch effects in the input stage.

REFERENCES:
patent: 4533876 (1985-08-01), Haque et al.
IBM Technical Disclosure Bulletin: "Complementary FET Differential Amplifier" W. Cordaro, vol. 16, No. 10, Mar., 1976.
IEEE Journal of Solid-State Circuits: "Power-Supply Rejection in Differential Switched-Capacitor Filters" Alejandro De LaPlaza and Patrick Morlon, vol. sc-19, No. 6, Dec. 1984.

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