Research And Design Of Digital Up Converter Based On Delta-Sigma Modulation

The software defined radio(SDR) is a rapidly evolving technology whose requirement is as much as possible to digitize the analog signal, simplify the analog front end of the transmitter, get the A/D conversion closer to the antenna. And the SDR processes the digitized signal using the software to realize the system function and meet the appropriate specifications in the whole transmitter system as possible as it can. With the digital radio system gradually replacing the analog radio system, the SDR is getting people’s attention and has been widely used in various fields of military, civilian and commercial. Meanwhile, the technology of programmable logic device develops rapidly. It is increasely important to build an open-architecture radio system based on SDR by using these programble hardware modules. The technology of digital up conversion is not only a key component of software defined radio but also a technical difficulty needing to be resolved urgently.In this paper we chose the digital up conversion technology as the research project. We do a deep research on the basic principles of digital up converter. Then, starting from the research status of digital up conversion, we survey the existing realization scheme of digital up converter in detail and carefully analyze the advantages and disadvantages of the various implementation of digital up converter. And based on it, we propose a new design scheme of digital up converter. The digital up converter consists of various functional modules, including:FIR filter, CIC filter, Delta-Sigma modulator, word generation module and high-speed serial transmission module. All the processes of the digital up converter are in the digital domain. The digital up converter is able to perform a direct up-conversion of a baseband signal to the desired REFirstly, according to the proposed design scheme of digital up converter, we build the simulation model for each functional module in the Matlab/Simulink platform and do the algorithm simulation for each module separately and system-level simulation to verify the correctness of the algorithm. Then we write the Verilog HDL code to do a hardware implementation for each module in the Quartus II software development platform. Finally the successfully compiled code runs on the Arria V GX Starter Kit. And hardware-level measured results are obtained using Tekronix’s MDO4054-6 Mixed Domain Oscilloscope. The results show that the algorithm and hardware implementation of the digital up converter design scheme proposed in this paper are entirely feasible and the stopband attenuation of the RF signal after up-conversion is not less than 30dB. As well as the up-conversion output frequency can be flexibly and conveniently reconfigured by modifying the corresponding system parameters.