The Research Of Digital Lock-In Technology

With the high-speed development of the photoelectrical technology and sensor technology, it is often met that we need to measure the weak signal has been drowned in strong background nois.The lock-in amplifier can measure weak volume that can not be measured with traditional methods.The principle is the noise is not correlated with reference signal,while the signal we attempt to measure ,which was submerged in the strong nois ,has a high correlation with reference signal. According to the phase-sensitive detector in different ways, the lock-in amplifier can be classified as anolog lock-in amplifier and digital lock-in amplifier, the latter has greater flexibility and higher accuracy than the former.The wide-band digital lock-in amplifier we study is divided by function into the analog signal preprocessing module, AD module, DSP digital signal processing module and the host computer communication module. Analog signal goes through the program-controlled filter, program-controlled amplifier into the AD chips, and transformed into digital signals .Then it goes with reference signal to the relevant demodulator as input signals, the digtal signals which have been processed are uploaded to the host computer through asynchronous serial and displayed. In this subject , TI's TMS320VC5416 is selected as the core processor, the main chip to complete the external control and digital signal correlated demodulator. AD976A is selected to transform anolog signal to digital signal.The sampling frequency is controlled by the DSP internal timer, and the common DSP I / O pins to enable AD transformation.The subject developed a wide-band digital lock-in amplifier.It can be filtered and amplified automatically ,and the longest integral time is 100 second.As a result,it is a suitable way of weak signal detection for the signal whose frequency is from 10 Hz to 10 kHz, and whose amplitude is from 100 nV to 100 mV. Experimental results show that, when the sampling points N is greater than 8192, the result is the closest to the theoretical value.Digital lock-in amplifier is the equipment which is used for detecting the weak signal submerged in strong background noise.Some related products are also available in the market.While,the equipment which the subject designed can measure weak signal in nV class.Further more,it has higher accuracy, the more flexible approach.I am sure that this product is once available,it will have a profound theoretical significance and huge market potential.