A 74.3 dB SNDR 3rd-Order VCO-Based DSM With Built-In Passive Low-Pass Filter in 65 nm CMOS

Abstract

This brief presents a voltage-controlled oscillator (VCO)-based continuous-time delta-sigma modulator (DSM) with 3^rd-order noise shaping capabilities, adopting only two active VCOs. To address the inherent nonlinearity in the VCO’s voltage-frequency characteristic, we propose the inclusion of a passive low-pass filter (LPF) within the DSM loop. This addition significantly reduces the input voltage range of the first VCO and facilitates an additional 20dB/decade noise shaping by setting the LPF’s pole to match the DSM’s signal bandwidth. Designed and fabricated in a 65 nm CMOS process, the prototype VCO-based DSM demonstrates a signal to noise and distortion ratio (SNDR) of 74.3 dB, a dynamic range (DR) of 81.2 dB, and consumes $318~\mu $ W with a signal bandwidth of 200 kHz, achieving a Schreier Figure of Merit (FoMs) of SNDR with 162.3 dB.