The Design Of Weak Signal Vector Detection System

Weak signal detected system is designed to specially detect weak physical techniques. It is the key subject that uses the electronic testing technology and signal processing methods to separate the useful signal from the large number of the noise. With the further research of micro-sensors application, when the traditional methods can't detect the signal, we not only want to get the amplitude of the signal, but also obtain phase of the signal. In the felid of weak signal detection, the Locked-in-amplifier is used widely because of the advantages of stable center frequency, narrow pass-band, high quality factor.Based on the theory of correlation in phase-sensitive detection, the technology of Locked-in-amplifier and low noise amplifier, we designed the weak current signal detection system because the current micro-sensor signal is small, high frequency and difficult to be measured. The system can pick up the weak current signal amplitude and phase, and make the analog-digital Locked-in-amplifier become small size, easy to operate, intelligent to control.Based on ZnO nanowire sensor of high resistant,high frequency and weak current, we design AC current source. It can simulate the sensor to generate current signal with the frequency of 30KHz, range of 1.7nA-86.9nA. The system includes current-voltage conversion circuit, the combination of filter circuit, two-phase--sensitive circuit, phase shift circuit, microcontroller circuits and computer display interface. The system can get the weak signal from the noise and real-time displaying on Computer. Comparing the result between the calibration of SR7265 and the measurement of the signal detection system,we can get the performance parameters: The current accuracy is 0.24nA and the phase accuracy is1.79°.It can meet the test requirements of a weak current sensor.