Quadrature Bandpass Modulation for Digital Radio

A quadrature bandpass 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 modulators provide superior performance over pairs of real bandpass modulators in the conversion of complex input signals, using complex filtering embedded in loops to efficiently realize asymmetric noise-shaped spectra. The fourth-order prototype 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, increasing to 71 and 77 dB in 100and 30-kHz bandwidths, respectively. Maximum signal-to-noise plus distortion ratio (SNDR) in 200-kHz bandwidth is 62 dB. Power consumption is 130 mW at 5 V. Die size in a 0.8m CMOS process is 2.4 1.8 mm2.