Front-end Design Of The Digital Down Converter Chip

Software Defined Radio is a new wireless communication system which based on the modem communication and digital signal processing theory. The basic idea is to build a programmable hardware platform which software can setting different parameter. Digital Down Converter(DDC) is one of the key technologies in the Software Defined Radio, DDC pick up useful narrowband signal from high-speed medium frequency digital signal and transform the signal to baseband, decrease the speed of the signal.Afterwrads,the low-speed baseband signal can be processed by DSP devices.Based on the research project, AM/FM receiver design,an in-depth study of the DDC technology is completed.The system architecture and algorithm of application specific DDC are improved, and increase programmability feature.The programmable and flexibility DDC chip is designed in this paper.After introducing basic theory and various key algorithms,the principle of quadrature digital mixing and digital filter design theory are described.The CORDIC, distributed(DA) algorithm and fold technology are focused on,the numerically controlled oscillator and mixer structure is improved using CORDIC algorithm, without lookup table and multiplier down conversion can be completed.Also,the structure of FIR filter is improved by using DA algorithm,which can save hardware resource.Then the digital down converter is modeled by Simulink, the feasibility and performance of algorithm is verified.Then focuses on the RTL implementation of DDC chip,detail analyse input and output module,mixer and digital filter. The last part of this paper complete logic synthesis base on 0.18μm process library of SMIC, also complete FPGA synthesis.Verification and logic synthesis result show that the DDC chip can meet the requirement, also have stable performance.