Theory And Implementation Of Digital Radio Frequency Modulation

With the rapid development of communication technology,the internet and multimedia industry have achieved great progress.For example: the internet game,mobile terminal,social networks,video conferencing,remote control and other applications have been extensively applied.To satisfy the requirements of fast-growing users,faster data transfer rate is urgently needed in wireless communication system,which demands the improvement of power amplifier performance,so as to achieve higher output power in higher frequency bandwidth.Therefore,the study of high efficiency digital RF power amplifier becomes an inevitable choice for researchers.As the core of digital RF power amplifier,the modulator plays an important role in the analog/digital conversion.However,the modulator based on Sigma-Delta digital modulation technology has little distortion,high efficiency and low susceptibility to electromagnetic interference.The present work designed a digital modulation structure for driving digital power amplifier based on Sigma-Delta digital modulation technology.Firstly,the modulator structure model was established based on analyzing the working principle and different design theories of Sigma-Delta modulator.Then,the transfer function and the noise transfer function were deduced to determine the order of the modulator,the shape(cascade or single ring),stability and other corresponding performance indicators.Matlab Simulink software was used to design and simulate the modulator structure,and the output waveform of the modulator and the output spectrum of the modulator system could be achieved from analyzing the influence of different non-ideal factors on the performance of the modulator.Finally,a comprehensive RTL code could be achieved by using the Verilog language to describe the structure of modulator system.After the problems of system metastable and data synchronization being solved,the Modelsim,SignalTap and other tools were used to simulate,verify the modulator system and complete schematic layout.Then,the system could be implemented on the FPGA,and its physical performance could be tested on the oscilloscope,spectrum analyzer and other testing tools.After comparing the performance of the debugger designed with different methods,it indicated that the design of six order single loop and one bit bandpass Sigma-Delta modulator could achieved better performance.The simulation results demonstrated that when using the input bandwidth of 195 kHz and the frequency of 12.5MHz sine signal for simulation,under the condition of non-ideal,the signal to noise ratio could be up to 123.9dB and data valid digits could be up to 20.29 bits.After the realization in FPGA,under the condition of non-ideal,the signal to noise ratio can be up to 78 dB,which fully satisfies the design requirements.