| The parameters of the analog circuit of the underwater acoustic equipment will greatly affect the accuracy of the subsequent underwater acoustic signal processing results.For example: amplitude and phase consistency will affect the accuracy of beamforming calculation results;circuit noise affects the accuracy of almost all measurement items,and so on.Therefore,the parameters of the analog circuit must be measured and calibrated before the underwater acoustic equipment is used.With the increasing number of channels of underwater acoustic receiving equipment,the traditional measurement method of building a measurement platform by discrete instruments is time-consuming,labor-intensive and inefficient.Therefore,it is very necessary to develop a set of special multi-channel analog circuit parameter measurement system.At the same time,in order to adapt to the large amplification gain range of the signal conditioning circuit of the underwater acoustic receiving equipment,the analog circuit parameter measurement system is required to provide a weak test signal with a small amplitude.In view of the above requirements,this paper designs a set of hardware system for the measurement of analog circuit parameters,which can generate weak test signals,has multi-channel acquisition functions,and has self-checking functions.According to the overall design requirements of the system,the thesis divides the overall functional modules into four parts: test signal generation part,signal output part,digital control part,and signal acquisition part.The paper gives a detailed introduction to the specific functions and chip selection of these four parts of the circuit.The test signal generation part is responsible for generating the test signal for measurement.The design adopts STM32single-chip microcomputer to receive the command from the host computer and control the high-precision DAC chip AD5791 to generate the test signal.After the test signal passes through the attenuation network,it is output through the relay gate.The signal output part transfers the signal output by the test signal generation part for self-checking of the equipment and test of external equipment.The signal output part receives the command from the host computer through the STM32 single-chip microcomputer,and after parsing the command,it generates an output signal that meets the requirements by controlling the on-off of the analog switch and the relay.The digital control part is responsible for parsing the instructions of the upper computer,and controlling the signal acquisition part according to the instructions to complete the signal acquisition and data upload functions.The main control chip of the digital control part adopts FPGA(EP3C16Q240C8),and the communication interface between FPGA and host computer adopts USB(CY7C68013A)interface or network port(W5300).The signal acquisition part is responsible for completing the acquisition,buffering and transmission of the self-check input signal and the input signal of the external equipment.The signal acquisition part includes sixteen acquisition channels,the ADC(AD9244-40)chip is connected to the buffer RAM,and the data of different channels is finally uploaded in different channels through the control bus switch.After completing the writing and debugging of STM32 MCU and FPGA programs,the thesis conducts a comprehensive test on the relevant functions of each functional module,and measures the relevant circuit parameters of the analog signal conditioning circuit.Among them,the test signal generation module can generate a sinusoidal signal with an amplitude of1 m V～2V at the third octave point in the 1Hz～100k Hz frequency band,and can generate a weak sinusoidal signal with an amplitude as low as 100μV and a signal-to-noise ratio greater than 3d B in a 30 k Hz bandwidth.The amplitude consistency of the measurement system is0.102 d B in a 100 k Hz bandwidth,and the phase consistency is 0.255°.The circuit parameters meet the index requirements. |
