The Optimization Design And Iplementation Of Digital Lock-in Amplifier

Lock-in Amplifier( LIA) is a precision instrument that used to detect and measure weak signals submerged in complicated noise,and the amplitude of the measured signal is typically much smaller than the amplitude of the noise signal value.In order to reduce hardware logic resources occupied of the Digital Signal Processing module of Digital Lock-in Amplifier.In this paper, in accordance with the characteristics that the orthogonal vector type duplex Digital Lock-in Amplifier's test results has nothing with the sampling frequency of the measured signal,the digital signal processing theory that multi-rate signal processing technology will be used to reduce the sampling frequency of measured signal and then processed under low sampling rate.(1)In view of the generated of the orthogonal reference signal, the principle of lookup table to be used in this paper, three-quarters of the storage space be saved.(2)The performance of digital narrowband low pass filter is the key of the digital Lock-in amplifier to realization of weak signal detection. A high performance digital narrowband low pass filter designed based upon the theory of multi-rate signal processing technology. The filter's passband cutoff frequency lowest 0.1 Hz, with high Q value, under 40 KHz sampling rate which achieving the requirements for the Digital Lock-in Amplifier to the filter. The implementation of the Cascade integral Comb filter used the theory of Hogenaur "cut off", not only can save a lot of hardware logic resources, and will be the minimum response time reduced from 7.53 ns to 6.519 ns, that the rate increased from 132.66 MHz to 153.40 MHz.Using the Interpolated second-order polynomials filter to compensate the pass band attenuation of CIC filter,to make it within the passband reduced to about 0.4 d B attenuation by 1.54 d B.By comparing the results by the system input value,modelsim simulation results and the simulink results showed that the digital signal processing module of the digital lock-in amplifier can be realized and measured the detected signal from noise signal.