Design Of Filter For Cmmb Tuner

China Mobile Multimedia Broadcasting (CMMB) is a mobile multimedia standard specified in China mainland by the State Administration of Radio, Film, and Television (SARFT). CMMB uses S-band (2635MHz-2660MHz) for satellite broadcast and UHF-band (470MHz-798MHz) for terrestrial broadcast. And the channel bandwidth can be either 2MHz or 8 MHz. CMMB specifications demand CMMB tuner has high linearity and low noise. Further more, CMMB UHF-band frequency distribution is very complicated, and the adjacent channel interference can be 35dB-43dB higher than wanted QPSK signal. These make the design of baseband analog filter very difficult.In this thesis, the application of CMMB is introduced briefly in Chapter 1. And then the CMMB standard specifications for CMMB tuner and baseband filter design considerations are presented in Chapter 2. Chapter 3 introduces the principle of analog filter design. Chapter 4 gives the detailed circuit implementation. Chapter 5 presents the layout of the proposed filter and the simulation results.A 6th order Active RC low pass filter (LPF) for direct conversion architecture for CMMB tuner is presented in this thesis. The proposed low pass filter is based on the prototype of Chebyshev filter, and with a notch added in the transition band for better frequency selectivity. The proposed filter is implemented in biquad topology; it has automatic frequency tuning and Q enhancement calibration circuit. It has tunable bandwidth from 800kHz to 3.756MHz, depending on the channel bandwidth in use. The proposed filter provides tunable gain from OdB to 39dB, with 3dB per step. Simulation results show that the proposed filter has a sharp transition band and the rejection of strong adjacent channel interference at 5.25MHz is about 50dB. It achieves high linearity and low noise. Its inband (5kHz-3.756MHz) average input noise is less than 22nV/sqrt Hz. The proposed LPF circuit is implemented in a 0.18μm CMOS process, and occupies a die area of 850×760μm2 (bothⅠand Q channel). The filter dissipates 8.1mA current with 1.8V supply voltage.