In Electronics and Telecommunication systems, noise is ever present and limits the performance of the system. Noise can obscure a signal of interest, cause measurement errors or make a measurement all but impossible. Hence signal recovery instruments are in demand for experiments which are carried out with progressively smaller signals with weaker excitations. Lock-in amplifiers are used for signal recovery and precise measurement of weak signals. In the present work an attempt has been made to design and build a simple Lock-in amplifier system. The lock-up system includes a signal channel consisting of low noise amplifier, line frequency filters, auto-tracking band pass filter and a high gain ac amplifier. The reference, channel includes a discriminator, a phase locked loop (PLL) and phase shifter. The signal input and reference input are applied to a linear phase sensitive detector (PSD) whose output is suitable low pass filtered and amplified by a high gain amplifier, whose output is the desired recovered signal. The results of system performance tests are presented.
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