Study on Detection of Weak Signal by Phase Lock-in Amplification

In the scientific research and engineering practice, the detection of weak signal is often encountered. The traditional signal detection method can not accurately and effectively analyze the weak current. To this end, a phase-locked amplification was proposed to detect weak signal. According to the relevant theory of phase-locked amplifier, using the characteristic that the correlation between the reference signal and the signal to be measured was strong, the interdependency of the noise signal was weak, we detected the signal from a large amount of background noise for obtaining the amplitude and phase information of the signal to be measured under strong noise background. The weak signal was amplified and filtered. After amplifying, the signal went into the anti aliasing filter for filtering, which filtered out the interference of high frequency noise, and modulated the signal after the conversion. The experimental results show that the mathematical demodulation system based on FPGA, which has stable working performance and high detection precision to detect weak photoelectric signal. When the signal-to-noise ratio of RSNR is -26dB, the minimum detection accuracy can reach to 0.02pA, which has wide application value.