Jm. De La Rosa et al., A CMOS 0.8-mu m transistor-only 1.63-MHz switched-current bandpass Sigma Delta modulator for AM signal A/D conversion, IEEE J SOLI, 35(8), 2000, pp. 1220-1226
This paper presents a CMOS 0.8-mu m switched-current (SI) fourth-order band
pass Sigma Delta modulator (BP-Sigma Delta M) IC capable of handling signal
s up to 1.63 MHz with 10.5-bit resolution and 60-mW power consumption from
a 5-V supply voltage. This modulator is intended for direct A/D conversion
of narrowband signals within the commercial AM band, from 540 kHz to 1.6 MH
z. Its architecture is obtained by applying a lowpass-to-bandpass transform
ation (z(-1) --> -z(-2)) to a I-bit second-order low-pass Sigma Delta modul
ator (LP-Sigma Delta M). The design of basic building blocks is based upon
a detailed analysis of the influence of SI errors on the modulator performa
nce, followed by design optimization. Memory-cell errors have been identifi
ed as the dominant ones. In order to attenuate these errors, fully differen
tial regulated-folded cascode memory cells are employed. Measurements show
a best SNR peak of 65 dB for signals of 10-kHz bandwidth and an intermediat
e frequency (IF) of 1.63 MHz. A correct noise-shaping filtering is achieved
with a sampling frequency of up to 16 MHz.