A CMOS TV tuner/demodulator IC with digital image rejection

Superheterodyne TV tuners have been implemented in discrete forms using tunable RF and SAW IF filters. Integrating TV tuners in CMOS technology without them is a challenging task to cope with technical issues such as harmonic mixing and image. The image rejection in low- or zero-IF systems has been limited to 30-40 dB by analog imperfections such as I/Q path gain and phase mismatches. A single-chip low-IF TV tuner solution is proposed so that the image can be suppressed digitally using an image cancellation technique based on a complex one-tap LMS signal decorrelation algorithm. Programmable digital filtering and video/sound demodulation make a multistandard TV tuner feasible in the 48-860 MHz VHF/UHF band. The chip has a maximum gain of 63 dB and an input automatic gain control (AGC) range from -15 to 25 dB with 0.85-dB steps. It achieves an image and IF rejection of 60 dB, a peak carrier-to-noise ratio (CNR) of 55 dB, and a peak sound signal-to-noise ratio (SNR) of 44 dB without frequency modulation (FM) de-emphasis. The prototype occupies 6/spl times/6 mm/sup 2/ in 0.25-/spl mu/m CMOS and consumes 1 W at 2.5 V.

I. Introduction

Various analog/digital TV standards exist today throughout the world [1]. The standard terrestrial and cable TV band covers a wide frequency range spanning from 48 to 860 MHz. The broadband TV tuner design involves some of the challenging technical issues such as harmonic mixing, image, dynamic range, and linearity. Unlike narrowband RF receivers, the harmonics of the local oscillator fall in the same TV band when receiving lower band channels. This causes higher band channels to alias into the IF signal band in the down-conversion mixing process. An effort to avoid this harmonic mixing contributes greatly to the complexity of the RF front-end design. Traditionally, superheterodyne TV tuners have been implemented using passive tuning elements in shielded cans for high- RF tracking filters and relying heavily on a high level of manufacturing technology. Several TV tuner architectures have been proposed in the past to replace bulky tuners by monolithic silicon chips. Those approaches either do not provide truly integrated solutions as they still rely on external surface acoustic wave (SAW) filter [2] [3] [4] or suffer from the stringent matching requirement [5] to achieve the desired performance.