A multi-path chopper-stabilized capacitively coupled operational amplifier with 20V-input-common-mode range and 3µV offset

Abstract

Capacitively coupled chopper amplifiers are capable of handling common-mode voltages outside their supply rails, while also achieving high power efficiency and low offset [1-3]. However, a significant drawback of such amplifiers is a transfer-function notch around the chopping frequency (fchop). This is because their input choppers demodulate signals near fchop to DC, where they are blocked by the input capacitors. This problem is exacerbated by the use of a ripple-reduction loop (RRL) to suppress chopper ripple, which also creates a notch at fchop, and, moreover, can take up to 1ms to settle. The net result is an amplifier with a transfer-function notch and a step response that is accompanied by a slowly-decaying burst of chopper ripple [1]. To solve these problems, a multi-path capacitively-coupled chopper-stabilized operational amplifier (MCCOPA) is proposed. Implemented in a HV CMOS 0.7μm technology, it has a smooth transfer function and achieves a 20V common-mode voltage range (CMVR), 3μV offset and 148dB DC CMRR while drawing only 8μA from a 5V supply.