Design And Realization Of Head-end Modulator For Digital Cable Television

When stepping into the digital era, the information exchange among people became more and more popular. As a high band-efficiency digital modulation scheme, QAM (Quadrature Amplitude Modulation) Modulator is widely adopted in the wide-band communication era, such as Digital Video broadcasting, Fixed Broadband Wireless Access, Satellite Communication, Digital Microwave Transmission and so on.Paper research mainly embodies in the following aspects: Firstly,by compareing the development of international digital television and the standard of international digital TV broadcasting,analyse the structure of digital TV broadcasting and the basic principle of demodulation QAM modulation, come up with the way of making FPGA to be core,controlling BCM3034 to realize QAM demodulation hardware system resolution.The content include system interface to handle modules, TS stream, channel code modulation, RF module, and for each module has a hardware circuit design. Secondly, by researching digital TV changing fluence,and then accord system structure to do power,RF power design.Thirdly, according the request and description of DVB-C, by using number and spectrum analyser vector analyzer, net analyzer, code stream player to analyse the designed circuit,including DVB-C demodulation tesing,MPEC-2 code stream tesing,modulation error rate testing.In recent years, with the great progress made in the field of IC and digital communication, FPGA become more and more popular in Electronic Industry, as it features high integration, convenience, code portability and so on. This paper studies the implementation of QAM modulation on the FPGA and BCM3034, source process and base band I/Q signal output from channel coding are implemented on FPGA, IF signal output by modulating I/Q signal are implemented on BCM3034. The frequency is 36MHz and the bandwidth is 8MHz. Through used up-converter, the IF signal are up-converted,filtered and amplified. The RF signal are outputted, which's frequency is 110MHz～870MHz. The RF signal's frequency is adjustable with 100 KHz step. The output signal power range from -7dBm to 3dBm, which is adjustable with 1dBm step. The main contribution of this paper can be concluded as following:1. Current situation of International and Domestic digital TV development and general situation of International standards of digital TV are introduced. The composition of Community Antenna Television and significance of the paper are described in detail.2. The basic principle of QAM modulation and demodulation are studied, and QAM modulator system design is elaborated. The solution based on FPGA is offered and is divided into four modules which are the system interface module, the TS stream processing module, the channel coding and modulation module, the RF modulator module. Then each module is introduced one by one.3. Circuit Design Based on FPGA and BCM3034 is studied, including the introduction of the BCM3034 chip and FPGA model selection. The BCM3034 circuits are detailed study. The product is demonstrated.4. Digital TV up-converter circuit is studied. Based on digital television up-converter working principle, the paper describes the design of the local oscillator, the design of filter, the design of power adjustable attenuation circuit, the design of the selectable filter circuit and the design of RF power attenuator circuit. The product is demonstrated.5. Testing and experimental results are introduced. Three aspects mainly are elaborated, which are DVB-C standard index's demand and description, circuit test and index test. Overall test results meet requirements. The test results indicate that DVB-C modulator based on FPGA and BCM3034 has met the national standards.