A micropower chopper-stabilized operational amplifier using a SC notch filter with synchronous integration inside the continuous-time signal path

A micropower chopper stabilized opamp is presented. The new topology incorporates a switched capacitor filter with synchronous integration inside the continuous, time signal path virtually eliminating chopping noise. A three-stage amplifier with multipath nested Miller compensation is modified to incorporate chopping of the input stage, sinc filtering to notch any chopping ripple, and a compensation scheme to maintain an undistorted high-speed signal path. Characteristics of the amplifier presented include rail to rail input and output operating on supplies of 1.8 to 5.5 V over -40 degrees C to 125 degrees C. Quiescent supply current is 17 mu A, input offset is 3 mu V, input offset drift is 0.02 mu V/degrees C, GBW is 350 kHz, and the chopping frequency is 125 kHz. Die area is 0.7 mm(2) using a precision analog mixed-signal CMOS process combining low-noise 0.6-mu m analog transistors with 0.3-mu m digital CMOS capability.