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

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-conversion 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 mum CMOS occupies 5times5mm², and consumes 750 mW at 1.8 V.