| Tuner system is a very important part of the television receiver because its performance decides almost 90 percent parameters of the whole receiver. The TV's selectivity, sensitivity and anti-interference are almost decided by the tuner system. With the rapid development of TV, the requirement of tuner performance and integration becomes stricter and stricter. The market of Electronic tuner is fastly growing accordingly.The research of tuner system is expatiated in this paper. It composes of expatiation of system structure and performance indices, comparison between mechanical tuning and electronic tuning, characteristic analysis of voltage-based channel control and PLL-based channel control, and the design of PLL system for channel control. The complete system solution is also given. Electronic tuning is used in tuning circuit and PLL channel control is used in mixing circuit. The above design realizes more accurate tuning and integrates IF demodulation module into the IF circuit.The amplification and demodulation of IF signal are achieved. The design gets the output of CVBS and audio signal at last. Accordingly it achives efficient electromagnetism shield. And the application of microtrip theory in microwave circit is studied. The circuit composed of lumped element and distributed elment is designed based on the microtrip theory. The total scheme for this tuner system is given. The suitable chips are chosen for the system and hardware model is constructed according to the system design. The key circuit of the hardware is particularly analyzed and the product is optimized.The product designed in this paper applies I2C for the channel control and can recive Off-air channels and full band cable channels. It can work in multi-mode including PAL B/G, I, D/K, NTSC M/N, SECAM L. According to the test result, this product can realize precise tuning and runs stably. The performance of the tuner has met the expected requirement of system design and can be applied in PC multimedia card, TV tuner, and etc. |
