Bandpass Sigma–Delta Modulator Employing SAW Resonator as Loop Filter

摘要

Continuous-time bandpass (BP) sigma–delta modulators ($Sigma Delta$Ms) employing surface acoustic wave (SAW) resonators as loop filters are presented. Compared with the loop filters realized with $G_m$– $C$ and LC resonators, the SAW resonator has the advantage of high-$Q$ factor, wide resonant frequency range and accurate resonant frequency without the need for automatic tuning. With the proposed anti-resonance cancellation and loop filter phase compensation techniques, a second- and a fourth-order BP $Sigma Delta$Ms are demonstrated in a 0.35-$mu$m CMOS technology. Both modulators are tested with 47.3-MHz off-chip SAW resonators. The second-order modulator attains a dynamic range of 57 dB and peak signal-to-noise distortion ratio (SNDR) of 54 dB and the fourth-order one achieves a dynamic range of 69 dB and peak SNDR of 66 dB, both in a 200-kHz signal bandwidth. The fourth-order modulator is also measured in a 3.84-MHz signal bandwidth and achieves a dynamic range of 52.5 dB and peak SNDR of 50 dB, an effective 8-bit resolution.