The Design And Implementation Of High Dynamic Range Digital AGC Based On DPMR Protocol

In the field of wireless communication,the signal received by the receiver has a large peak-to-average power ratio,due to the impact of complex environmental factors such as long-distance transmission and obstacle occlusion reflection.If the signal amplitude exceeds the quantization range of ADC or is less than the precision of ADC,a great influence on subsequent digital processing such as demodulation and decoding will be generated.Therefore,an automatic gain control circuit is used to adjust the amplitude of the input signal during ADC sampling.In this paper,considering the complex application environment of dPMR digital two-way radio receiver,an automatic gain control circuit with large dynamic range,which can process constant envelope and non-constant envelope signals is designed.It is of great significance to improve the demodulation performance of the receiver and reduce the bit error rate of the system.In this paper,the advantages and disadvantages of different implementations and loop structures of automatic gain control circuits are studied and analyzed.Then the performance of key algorithms for automatic gain control loops is analyzed and compared.according to design requirements,the key algorithm and control flow of the feedback digital automatic gain control circuit are designed.For power estimation module,the IQ square and power estimation are used to obtain the average power of the input signal with average filtering.The logarithmic transformation module converts the power value to the logarithmic domain and directly adjusts the gain,which avoids follow-up index generation circuit,reduces the design complexity and obtains a high linearity.For the gain adjustment control module,the step-by-step adjustment method with multi-step values is used,which has a good balance between system convergence speed and adjustment precision.In the gain control flow,aiming at solving the problem of misjudgment during the DAGC processing of non-constant envelope signals,an optimized threshold detection algorithm is proposed.The final gain adjustment result is directly converted to digitally controlled signal to control the gain selections of front-end amplifiers which further reduces the design complexity.In this paper,the function of the DAGC circuit is verify by the Modelsim and the hardware circuit is implemented by the FPGA development board.The verification result shows that the digital automatic gain control circuit can correctly process the constant envelope and non-constant envelope signals,with a dynamic range of-65dBm(from-40 dBm to-105dBm),a convergence time of less than 16.7us and a sensitivity of-105 dBm.