A 200-MHz all-digital QAM modulator and demodulator in 1.2-μm CMOS for digital radio applications

A 200-MHz universal all-digital quadrature modulator and demodulator are presented for implementing the front-end signal processing functions for high-bit-rate digital radio applications. The modulator chip accepts a pair of 8-b in-phase and quadrature data streams and generates a band-limited IF digital output. The demodulator chip accepts a digitized IF input signal and generates a pair of filtered in-phase and quadrature baseband signals. The modulator and demodulator chips each incorporate matched 40-tap finite-impulse-response (FIR) square-root Nyquist filters and can accommodate symbol rates up to Mbd. The modulator chip can generate any arbitrary signal constellation within a rectangular grid of 256×256 points, thus resulting in a generic chip set suitable for a wide variety of high-bit-rate digital modem designs using various advanced multilevel modulation formats such as M-ary QAM. Both chips were fabricated in a 1.2-μm CMOS process