Electromechanical resonator based bandpass sigma-delta modulator for wireless transceivers

Bandpass sigma-delta modulators commonly employ switch-capacitor (SC) or continuous-time (CT) loop filters. SC sigma-delta modulator can provide robust performance, but at low center frequencies. Its CT counterpart is able to operate at much high frequency, but its performance is often impaired by low-Q CT loop filters and the need of frequency tuning. In this paper, an alternative approach is introduced. Bandpass sigma-delta modulators employing electromechanical resonators as loop filter are described. As a proof-of-concept, a second- and fourth-order bandpass sigma-delta modulator are demonstrated in a 0.35-μm CMOS process using off-chip SAW resonators with a resonant frequency of 47.3 MHz. The dynamic ranges, measured in a 200-kHz signal bandwidth when sampled at 189.2 MHz, are 57 dB and 69 dB for the second- and fourth-order modulator, respectively. The chips operate under a 3.3-V single supply with a power dissipation of 30 and 45 mW, respectively.