A Practical Design of Phase-Locked Amplifier

In order to extract weak sensing signal, a practical lock-in amplifier circuit is designed. By generating two orthogonal reference signals multiplied by the measured signal after lowing noise amplifier and anti-aliasing filter, then through the low pass filter and mean square root calculation for weak signal extraction. A kind of square wave multiplier based on changes is also applied to achieving multiply operation of wide dynamic range, DC drift of small and high linearity and making the extraction of signal with higher accuracy. The test results indicate that the design not only improves the accuracy of the signal and makes the circuit structure simple, but also reduces the requirements of element consistency and the problems of the general amplifier which needs to be predictive that measured signal and the reference signals are different have been overcome.