A 44-μW, 91.3-dB SNDR DT Δ Σ Modulator With Second-Order Noise-Shaping SAR Quantizer

This article presents a single-loop third-order discrete-time delta-sigma modulator (DTDSM) with a 4-bit second-order noise shaping successive approximation register (NS SAR) quantizer. To realize an aggressive noise transfer function (NTF), a novel Finite Impulse Response (FIR) filter is embedded in the NS SAR. As employing a flipped voltage follower (FVF), which offers unity gain instead of an open loop dynamic amplifier, the proposed FIR filter is sharp and insensitive to process, voltage, and temperature (PVT) variation. Fabricated in a 65-nm 1P9M CMOS technology, the prototype DTDSM consumes
$44 \mu \text{W}$
when operating at a 1.2-V supply voltage and a sampling rate of 2.4 MS/s. It achieves a peak Schreier figure of merit (FoM) of 177.9 dB with a signal-to-noise and distortion-ratio (SNDR) of 91.3 dB at an oversampling ratio (OSR) of 64.