A 48–860 MHz CMOS Low-IF Direct-Conversion DTV Tuner

Abstract

A CMOS low-IF direct-conversion digital TV (DTV) tuner needs no off-chip harmonic rejection and image filters to receive both terrestrial and cable TV channels in the 48 to 860 MHz frequency range. Complex in-phase and quadrature (I/Q) poly-phase mixing together with coarse active RF filtering suppresses the third-harmonic mixing by 72 dB, and a digital LMS image correlation algorithm reduces the image leakage by 61 dB. A global AGC scheme keeps the signal level in the down-conver- sion mixer constant, and warrants the RF front-end linearity with strong blockers. Anti-aliasing and digital channel filters are made digitally programmable so that DTV standards with 6–8 MHz channel bandwidths can be supported. The measured system noise figure is 4–7 dB over the whole TV band. When measured at 500 MHz, the sensitivity is 86 dBm with ATSC-T 8-VSB signal, and the MER is 31.5 dB with actual J.83/B 256-QAM signal from a commercial CATV source. The chip implemented in 0.18 m CMOS occupies 5 5m m/50, and consumes 750 mW at 1.8 V.