Research On Delta-sigma Modulator For Short-wave Digital Power Amplifier

Short-wave communication is one of the most commonly used long-distance communication methods.Due to the superior invulnerability of the ionospheric channel,short-wave communication is widely used in special scenes such as national defense and military,navigation and aviation,and disaster relief.Short-wave power amplifiers are one of the key components in short-wave communication system transmitters.Their power consumption and efficiency have a huge impact on the performance of communication systems,including battery life,system cooling,and device size.Compared with traditional short-wave power amplifiers,digital power amplifiers have higher efficiency and lower power consumption,which can effectively reduce the heat generation of power devices and the size of equipment to meet the requirements of portable mobility and battery durability of short-wave communication equipment.At the same time,the digital power amplifier can be driven by digital signals,reducing the use of data conversion devices such as DACs,and can be used to implement full digital transmitter front-end systems for software radio.Frequency hopping technology is an important anti-interference technology,which can select a suitable frequency point to establish a communication link according to the communication environment to achieve optimal communication transmission.In order to realize the application of digital power amplifiers on short-wave,this thesis designs a digital modulator that can generate digital drive signals and can be applied to short-wave adaptive frequency hopping communication.Comparing the characteristics of different digital modulation techniques,this thesis selects Delta-Sigma modulation technology to study digital modulators for short-wave digital power amplifiers.According to the principle of Delta-Sigma modulator,this thesis analyzes the performance,advantages and disadvantages of Delta-Sigma modulators with different modulation orders,quantization steps and loop structure,and adopts the third-order single-loop single-bit quantization structure to design the structure of the modulator.The low-pass prototype DeltaSigma modulator is modeled by appropriate topology,and the band-pass Delta-Sigma modulator is modeled by frequency mapping theory.The CORDIC algorithm is used to solve the parameters that include the modulation information in the frequency mapping structure to module the frequency-adaptive Delta-Sigma modulator.The parameters of the Delta-Sigma modulator are designed and optimized by MATLAB,and the desired modulator model is built and simulated in Simulink.The similarities and differences between the band-pass modulator and the low-pass modulator are analyzed according to the simulation results,and the feasibility of the frequency mapping is verified.The digital circuit of the modulator module is designed by Verilog and used to build a band-pass Delta-Sigma modulator system.The BIT configuration file is generated by Synthesizing and Implementing in ISE 13.4,and finally downloaded to the FPGA to complete the hardware circuit implementation.The design has an oversampling rate of 32 and a system clock of 120 MHz.For the sake of general discussion,the 16 MHz and 26 MHz frequency points are used for verification.The simulation results in Simulink show that the modulation bandwidth is about 2 MHz,and the signalto-noise distortion ratio is 79.2 dB and 78.2 dB,the effective number of bits are 12.87 bits and 12.69 bits respectively.After the implementation of the FPGA hardware circuit,the signal analyzer is used to test its performance.The signal modulation bandwidth is about 2 MHz,the signal-tonoise ratio can reach 60 dB,and the effective number of bits is 9.67 bits,which is still extended comparing to the 9 bits of the input signal.The feasibility of using a band-pass Delta-Sigma modulator for short-wave digital power amplifiers is verified.