High-precision sensor front-end: Multi-path op-amp with chopping and nested miller compensation

We introduce a low-noise, dual-path op-amp for precision sensing. Chopping lifts. During the chopping process, the circuit translates the low-frequency offset and flicker (1/f) noise components out of baseband and repositions them around the chopping sidebands commonly referred to as the chop band. A dedicated feedback path commonly called the ripple-reduction loop (RRL) detects the periodic ripple and drives a corrective signal that cancels it, thereby strongly attenuating the ripple component. To prevent an RRL-induced notch in the transfer, the signal is steered through two tracks: a low-frequency path (LFP) and a high-frequency path (HFP). The LFP pairs chopping with the RRL to keep the low band clean, while the HFP terminates in a class-AB output stage for improved energy efficiency under dynamic loading. A nested Miller compensation scheme (NMC) couples the two paths, yielding an approximately first-order closed-loop response over the intended bandwidth.
The prototype is implemented in 180 nm 1P6M CMOS, operates from 1800 mV, dissipates 174 µW, and occupies 0.0118 cm² of active area. The measured UGBW is 3160 kHz.