QUADRATURE BANDPASS DELTA-SIGMA MODULATION FOR DIGITAL RADIO

A quadrature bandpass Delta Sigma modulator IC facilitates monolithic digital-radio-receiver design by allowing straightforward ''complex A/ D conversion'' of an image-reject mixer's I and Q outputs, Quadrature bandpass BC modulators provide superior performance over pairs of real bandpass Delta Sigma modulators in the conversion of complex input si gnals, using complex filtering embedded in Delta Sigma loops to effici ently realize asymmetric noise-shaped spectra, The fourth-order protot ype IC, clocked at 10 MHz, converts narrowband 3,75-MHz I and Q inputs and attains a dynamic range of 67 dB in 200-kHz (GSM) bandwidth, incr easing to 71 and 77 dB in 100- and 30-kHz bandwidths, respectively, Ma ximum signal-to-noise plus distortion ratio (SNDR) in 200-kHz bandwidt h is 62 dB, Power consumption is 130 mW at 5 V, Die size in a 0.8-mu m CMOS process is 2.4 x 1.8 mm(2).