A fourth-order bandpass delta-sigma modulator with reduced numbers of op amps

A switched-capacitor quadrature demodulation technique, which is insensitive to first-order errors resulting from 90/spl deg/ phase inaccuracy and path mismatch, is demonstrated to shift a band-pass spectrum directly to dc. A sampling rate of four times the passband center frequency facilitates the quadrature demodulation and removes the 90/spl deg/ 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 /spl Delta/-/spl Sigma/ modulator, integrated in an area of 1 mm/sup 2/ using 2-/spl 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.