A Direct Sensor Readout Circuit Using VCO-Driven Chopping with 42dB SNR at 800µVpp Input

Abstract

This work presents a new voltage-controlled-oscillator (VCO)-based sensor readout chip for sub-millivolt signal sensing applications. The proposed sensor front-end utilizes a new multi-path chopping topology driven by VCO output phases that reduces the modulation noise magnitude by spreading the noise power over a relatively large frequency range. It removes the need for extra filters required by the conventional chopping technique, reducing the front-end area and complexity. A linearization technique for the VCO is developed to improve the linear operating range. The prototype was implemented in a 65nm process. It processes an 800µVpp input signal and achieves 42dB SNR with 1KHz bandwidth while consuming 1.84µW.