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

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 (f_chop). This is because their input choppers demodulate signals near f_chop 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 f_chop, 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.