Research And Design Of RF Front-End For DMR Transmitter

DMR?Digital Mobile Radio?digital trunking communication standard has high spectrum efficiency and is fully compatible with analog trunking communication systems.It is widely recognized by the global communications industry.Transmitter RF front-end is the most important component of DMR communication system,and has been widely concerned by researchers in this field.At present,it is developing in the direction of high integration and low phase noise.This thesis analyzes the working principle of the transmitter structure.The frequency synthesizer,bandpass filter and power amplifier of RF front end of transmitter are designed respectively.The main contents are as follows:Firstly,the frequency synthesizer was studied and designed.Using the fractional frequency PLL frequency synthesis method,the characteristics of the noise source transfer function of the PLL frequency synthesizer are analyzed.By adjusting the loop filter bandwidth,phase margin and other related parameters,the system can obtain better phase noise and Spurious suppression.The simulation results show that when the loop bandwidth is 90kHz and the phase margin is49^o,the system is stable,and the phase noise is-98.21dBc/Hz@1kHz.Completed the design of the external circuit based on ADRF6755 frequency synthesizer and its internal register control circuit module,and the physical processing and testing are also carried out.The test result shows that the phase noise of the frequency synthesizer at the offset of 1 kHz is-98.21 dBc/Hz,and stray suppression is better than 50dBc.Secondly,the passive band-pass filter was studied and designed.According to the requirement of DMR transmitter RF front-end design index,an LC lumped parameter band-pass filter was designed.The filter has a simple structure and high selectivity.The simulation results show that the insertion loss in the passband is less than 1dB and the stopband attenuation is better than 30dB at 400MHz-470MHz.The layout design,physical processing and testing was carried out.The results show that the insertion loss of the bandpass filter in the passband is less than 2dB and the stopband attenuation is better than 24dB.Finally,the cascade power amplifier was studied and designed.In order to meet the requirements of transmitting power,the two level power amplifier HMC480 and HMC453 were used to simulate and design the bias network and matching network,and small signal analysis respectively.The layout design,physical processing and testing was carried out.The test results show that in the 400MHz-470MHz,the small-signal gain S₂₁of the cascaded power amplifier test is about 23.50dB,S₁₁ is better than 15dB.In summary,the feasibility of theory and design is verified by analyzing the simulation results and test results of the RF front-end modules of the transmitter.The measured results show that the performance of each module of the transmitter designed in this thesis can meet the design requirements of DMR transmitter system,which has certain practical value and application prospect.