Design Of AGC System Based On PID Algorithm

The communication system is affected by external environment,causing the fluctuating signal to be received by the receiver.In order to complete the correct demodulation of the baseband signal,it is necessary to add an automatic gain control circuit(AGC)in the receiver to achieve the purpose of stable signal output through the way of gain compensation.This paper proposes a design about the analog-digital hybrid AGC system.The structure is used to complete the design of the digital processing module in FPGA.The control voltage converted by the analog-to-digital converter is fed back to the variable gain amplifier(VGA),and the output power is adjusted by controlling the gain of the VGA.The main contents of this paper are concluded as follows.(1)This article describes the hardware structure block diagram of the analog-digital hybrid AGC system,and selects the appropriate device type according to the design specifications.Use the form of multi-stage VGA cascaded low noise amplifier to realize the design of RF gain link,and the switch is used to control the fixed gain amplifier,which provides multiple possibilities for testing.Choose logarithmic detector with high linearity and large dynamic range,a single-channel ADC converter with high sampling rate,FPGA chip of Spartan6 series and a DAC converter with single-channel input/dual-channel output in the control voltage feedback link.Complete the design of the entire circuit according to the system block diagram and device manual,draw the PCB layout board,and complete the processing of the hardware.(2)This thesis realizes the function of gain automatic compensation in the digital processing unit.Using Verilog HDL language to encode the PID gain control algorithm,and completing the output deviation compensation in the FPGA chip.The digital design in FPGA adopts the top-down approach.First,the SPI serial port protocol is used to configure the internal registers of the AD9233.The ADC converts the output level of detector into the corresponding offset binary code.Then calculating the error between the average value of the ADC sampled data and the target output power by proportional-integral-derivative calculation in the PID gain control module.Finally,the DAC bus control module is used to drive the digital-to-analog converter AD5322,and the converted analog output is used as the control voltage of the VGA chip.The Modelsim software is used to realize the functional timing simulation of each module,the ISE tool is used to perform the timing constraints and placement and routing,and the bit scream file of design code is loaded to the Flash of FPGA chip through the JTAG interface,complete the design of the system's digital control processing unit.(3)This article builds a test platform for the analog-digital hybrid AGC system,verifies and analyzes the actual working conditions of the variable gain amplifier ADL5246 and the logarithmic detector ADL5513.The test results show that the operating frequency of the system is 1.9GHz,the gain of the system is adjusted by changing the control voltage of the VGA,and the output power is stable at about-15 dBm.