A 1.3-mW 73.3-dB DR 10-MHz Bandwidth CT Delta-Sigma Modulator with a Charge-Recycled SC DAC and 52.7-dB Alias Rejection

Abstract

A multi-level DAC with high intrinsic linearity and low power consumption enables a greater design space for wide-band continuous-time (CT) Delta-Sigma modulators (DSMs). This manuscript introduces an intrinsically highly linear 5-level switched-capacitor (SC) DAC with a power-saving charge recycling technique for wideband CT DSMs. We also adopt a distinct modulator architecture that places a large low-pass filter (LPF) capacitor at the input of the first amplifier. This architecture substantially enhances the modulator’s power efficiency and restores the modulator’s alias rejection ratio (AR) in the presence of an SC type of DAC. To validate the proposed techniques, a DSM prototype with a 10-MHz bandwidth and 800 MHz sampling rate ($f_s$) is fabricated in a 65-nm CMOS technology. Consuming 1.3 mW from a 1.2-V supply, the prototype achieves a peak signal-to-noise-plus-distortion ratio of 72.3 dB and a dynamic range of 73.3 dB in experiments. The corresponding Warden’s and Schreier’s figures of merits are 19.3 fJ/conv-step and 171.2 dB, respectively. The measured ARs are 52.7 dB and 54.3 dB at $f_s$ and $2f_s$, respectively. The DSM further tolerates an rms clock jitter of 11 ps.