The Research And Design Of Digital-Analog Integrated Tuner System

With the development of digital technology, the digitalization of global broadcast and TV industry has been a trend, the analog TV is being replaced by digital TV. The CES(Consumer Electronics Society) announced a series of technical specifications on the compatibility between new DTV receiver and digital cable system, which require the DTV receiver support the analog TV and digital TV services both.The paper uses the MC44S803 of Freescale Semiconductor to implement the digital-analog integrated tuner system in which the receiving, frequency reduction, amplification and output of both the analog NTSC and digital ATSC signals can be done. Firstly the development and standards of DTV is introduced and the meaning of this issue is indicated. Then the paper discusses the crucial technologies to implement the system, including the ATSC system structure and the ATSC receiver tuner circuit. It analyses the problem of channel forbidden and interference and the way to solve it. How to improve the receiving performance is also discussed. Then the paper designs the circuits in accordance with the signal processing procedure in the tuner system, including the RF input, two-level frequency conversion architecture, two-level intermediate frequency signal processing, VCO and PLL circuits, etc. The software controlling the tuner system includes the control of chip registers and communication of the chip. The paper focuses on the interference of combined frequency on IF signal and adopts the way of steping LO up or down, and by setting the software to step LO up or down,the needed channel is selected too. The communication platform of computer and tuner system is designed which uses the way of simulating I2C bus with PC parallel printer port. Finally the digital-analog integrated tuner system is tested and verified based on the platform, the test includes sensitivity, the range of received frequency, various parameters of the system, etc, and the frequency offset which is introduced by tuner step is observed and analyzed.The design of digital-analog integrated tuner system obtains satisfactory results based on the test and verification in practical application. The system is in accordance with CES specifications and can achieve the simplification of design and cost-down.