On-chip active RF tracking filter with 60dB 3rd-order harmonic rejection for digital TV tuners

Abstract

A new structure of RF tracking filter to solve the linearity and harmonic mixing problem in DTV (digital TV) tuner is proposed in this paper. The proposed structure composed of two filters: harmonic rejection tracking filter (HRTF) and RF tracking filter (RFTF). They are activated / deactivated by complementary digital control switches. HRTF works in the frequency range 48~287 MHz. It can reject not only 3 rd-order harmonic by more than 60 dB but also unwanted channel signal from 5 to 15 dB. The RFTF can reject unwanted signal from 287~860 MHz. The proposed structure can realize pre-band selection function in the tuner front-end and covers a wide frequency range from 48-860 MHz. The center frequency and the bandwidth of both filters can be tuned by adopting the proposed tuning method. Also, the proposed structure can be implemented without any off-chip component. Simulation results show the tunable ability of the center frequency from 48 to 860 MHz, and the bandwidth from 8~20 MHz. These features are obtained drawing 19.8 mA (7.2 mA from RFTF, 12.6 mA from HRTF) current from a 1.2-V supply in a standard 0.13 um CMOS technology.