Low cost lock-in amplifier solutions

The analog part of the lock-in amplifier consists in three units: the measuring channel, the synchronization channel and one or two PSD (phase sensitive detector) circuits. For low frequency applications, the PSD circuit can be build with ordinary operational amplifiers and CMOS multiplexers. The paper presents a study of the proposed PSD circuit and two examples: a conditioner for the LVDT (linear variable differential transformer) sensor, and an device which together with a laboratory DDT (direct digital synthesis) signal generator can measure the gain-frequency and phase-frequency diagrams (Bode diagrams) of an electric circuit.