Abstract:

Because of large size and high price, the commercially available lockin amplifier or virtue lock-in amplifier cannot be integrated into portable devices. By using signal correlation detection principle, a portable quadrature lock-in amplifier is designed and developed based on ARM7 processor, which consists of two PSD(Phase Sensitive Detectors) with quadrature reference signals. Hardware modules are welded and debugged, including reference signal generator, analogue multiplicator, lowpass filter, etc. In order to prove the function of each module, output waveforms are measured and taken. Using the output sine-wave signal from a commercially available signal generator as the signal to be detected, the relations between input and output of the two PSDs are calibrated. The characteristics involving measurement scale, mean error, frequency selective property and detection limit are intensively tested and characterized. Experimental results show that, the detection limit on signal amplitude is less than 5 mV, the measuring scale is 5~3 000 mV, the absolute mean error is less than 10 mV, the mean error relative to the measuring scale is smaller than 1%, the allowed bandwidth of the detected signal is 0~50 kHz, and the 3 dB bandwidth is less than 1 Hz. Because of good frequency selectivity and high accuracy, the proposed portable lockin amplifier exhibits potential applications in weak signal detection, industrial control and instrumental devices.

Key words: weak signal detection, lock-in amplifier, correlation detection, frequency-selective property