A fourth-order bandpass delta-sigma modulator with reduced number of Op amps

A switched-capacitor quadrature demodulation technique, which is insensitive to first-order errors resulting from 90 degrees phase inaccuracy and path mismatch, is demonstrated to shift a band-pass spectrum directly to de. A sampling rate of four times the passband center frequency facilitates the quadrature demodulation and removes the 90 degrees phase error. Furthermore, the path-mismatch error is canceled using the 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 supply and exhibits an SNR of 56 dB within a 30-kHz bandwidth.