A 4TH-ORDER BANDPASS DELTA-SIGMA MODULATOR WITH REDUCED NUMBER OF OP AMPS

A switched-capacitor quadrature demodulation technique, which is insen sitive to first-order errors resulting from 90 degrees phase inaccurac y and path mismatch, is demonstrated to shift a band-pass spectrum dir ectly to de. A sampling rate of four times the passband center frequen cy facilitates the quadrature demodulation and removes the 90 degrees phase error. Furthermore, the path-mismatch error is canceled using th e same signal path repeatedly, thereby reducing the number of op amps. A fourth-order band-pass Delta-Sigma modulator, integrated in an area of 1 mm(2) using 2-mu m CMOS, consumes 0.8 mW with a single 3.3-V sup ply and exhibits an SNR of 56 dB within a 30-kHz bandwidth.