A Micropower Chopper—CDS Operational Amplifier

A low-power spur-free precision amplifier, which uses input chopping and correlated double sampling for demodulation, is presented. This circuit employs an AC coupling between the first and the second stage that removes the first stage offset without causing ripple. The input rail-to-rail circuit, fabricated in a mixed 0.18-0.5 μm CMOS technology, operates with supply ranging from 1.8 V to 5 V. The circuit achieves a simulated 168-dB DC gain with an overall current consumption of 14.4 μA. The measured offset voltage over the available samples results in a distribution with 2-μV standard deviation. The obtained input noise density at low-frequency equal to 37 nV/√Hz gives a 5.5 noise efficiency factor.

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