Bandpass electromechanical sigma-delta modulator

Abstract

This thesis examines the design and implementation of electromechanical resonators and filters based continuous-time bandpass sigma-delta modulators (SDM). Compared with conventional active-RC, Gm-C and LC resonators based loop filters, the electromechanical resonator has the advantage of high Q factor and accurate resonant frequency without the need for automatic tuning. With the proposed anti-resonance cancellation and loop filter phase compensation techniques, both 2nd- and 4th-order SDMs are successfully implemented in a 0.35-um CMOS technology and tested with various electromechanical resonators. The measured peak SNDRs for the 47.3-MHz SAW resonator and 19.6-MHz MEMS resonator based 2nd-order SDMs are 54dB and 51dB, respectively, and the peak SNDR for the 4th-order 47.3-MHz SAW resonator based SDM is 66dB, all in 200-kHz bandwidth. A 4th-order electromechanical filter based wideband bandpass SDM with multi-feedback is also proposed and demonstrated in a 0.35-um SiGe BiCMOS, and achieves 60-dB SNDR and 65-dB DR in 1-MHz bandwidth when tested with a 110-MHz SAW filter.