Weak magnetic detection signal detection based on digital lock-in amplifier

Optical pump magnetometer is a high-sensitivity and high-precision weak magnetic detection equipment commonly used in marine magnetic survey, which has a wide range of applications in marine geological research, resource exploration, magnetic target detection and so on. The lock-in amplifier is the key to determine the detection accuracy of weak magnetic signals in optical pump magnetometer. A fully digital lock-in amplifier based on the orthogonal phase-sensitive detection algorithm is proposed, which integrates the signal generator and phase-sensitive detector into a single field programmable gate array (FPGA) chip, and uses software programming instead of hardware circuit design. The system has the advantages of simple debugging, high integration. The direct digital synthesis(DDS) technology is used to generate the driving radio frequency coil signal and quadrature reference signal in the digital domain, which can reduce the phase-sensitive detection error. The frequency control word is used to generate the driving frequency, which can eliminate the frequency measurement error. The narrowband low-pass filter is implemented through multi-rate decimation technology, and the coordinate rotation digital computer(CORDIC) algorithm is used to implement the arctangent operation. The results show that the fully digital lock-in amplifier can accurately measure the phase of the signal to be measured in the full phase range of -180°~180°,and the absolute error is less than 0.0925°.