Fast settling, low noise, low offset operational amplifier and method

摘要

An amplifier ( 10 ) includes a first stage ( 4 ) including differentially coupled first (Q 1 ) and second (Q 2 ) input transistors and a controlled active load circuit ( 6 ). A second stage ( 8 ) includes differentially coupled third (Q 5 ) and fourth (Q 6 ) input transistors and a load circuit (Q 7,8 ). A first output ( 2 A) of the first stage ( 4 ) is coupled to a first input of the second stage ( 8 ), a second output ( 2 B) of the first stage ( 4 ) being coupled to a second input of the second stage ( 8 ). A common mode feedback amplifier ( 12 ) has an input coupled to receive a common mode signal ( 3 ) from the second stage ( 8 ) for producing an amplified common mode signal ( 9 ) on a control input of the controlled active load circuit ( 6 ) to provide fast settling of an output (Vout) of the second stage without substantially increasing amplifier noise.