CMOS OPERATIONAL AMPLIFIER WITH IMPROVED COMMON-MODE REJECTION

摘要

- 9 -CMOS OPERATIONAL AMPLIFIER WITHIMPROVED COMMON-MODE REJECTIONAbstractA fully differential CMOS operationalamplifier (10) of the folded cascode type includes twosimilar signal current branches (32,34) connected inparallel between two supply voltage nodes (V+,V-). Eachbranch includes an N-type bias current transistor(42,54), a P-type cascode transistor (50,62), an N-typepull-down transistor (40,52), and a P-type currentsource transistor (48,60), all connected respectively inseries between the drain of an N-type common modesuppression feedback transistor (44,56) and the drain ofa P-type common mode suppression feedback transistor(46,58). The N-type feedback transistor has its sourceconnected to a negative supply voltage node. The P-typefeedback transistor has its source connected to apositive supply voltage node. The gates of the feedbacktransistors of each branch are connected to the outputnode (36,38) at the drain of the cascode transistor. Thegates of the other transistors are supplied withappropriate reference voltages (VB1,VB2,VB3,VB4).Second harmonic effects produced by the N-type and P-type feedback transistors of a branch cancel each otherat the output node. Also disclosed is a connection ofthe current source (20,22) of the differential inputstage (12) to the drains of the N-type feedbacktransistors for reducing noise and device mismatcheffects in the input stage.