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We give design considerations for single-bit continuous-time Delta-Sigma modulators (CTDSMs) with FIR feedback DACs. These modulators have the low jitter sensitivity and high linearity properties characteristic of a multibit modulator, while using a simple one-bit quantizer, thereby combining the advantages of single-bit and multibit operation. We propose a method to compensate the loop for the delay introduced by the FIR-DAC. The efficacy of our architectural and circuit techniques is borne out by measurement results from a modulator that achieves about 71-dB SNDR in a 36-MHz bandwidth while consuming only 15 mW from a 1.2-V supply. Implemented in a 90-nm CMOS process and sampling at 3.6 GS/s, the CTDSM has a figure of merit (FoM) of 72.7 fJ/lvl, while occupying 0.12 mm2.
Date of Publication: Dec. 2012