A CMOS operational amplifier with chopper stabilization and a switched output

The input stage of a CMOS operational amplifier for use in a switched capacitor circuit is chopper stabilized by switches N13-N16 and N9-N12 so as to reduce the effect of flicker noise. Flicker noise (I/f noise) is normally reduced by using large area transistors which consume valuable IC area and which lower the amplifier bandwidth for a fixed supply current due to their parasitic capacitance. The dominant pole capacitances C1, C2 of the output stages act as low pass output filters for the chopper stabilized input stage. The switches N5,N7,N3,N8 allow the output stages to be switched into a high-impedance mode. This allows the elimination of a floating input switch (S1, figure 1) in switched capacitor circuits coupled to the amplifier output. It is difficult to drive floating switches effectively in circuits with low supply voltages.