The lock in amplifier recovers and amplifies signals totally buried in noise
Essentially the lock in amplifier is a synchronous demodulator. It receives a noisy waveform in which the signal is buried on modulated carrier. At the receiver, the waveform is received along with a carrier that is synchronised with the signal’s carrier. Using the super-heterodyne principle the result is demodulated to reveal the buried signal. This technique is very powerful. The paper below details the mathematics of the technique. These days, implementations are almost exclusively digital, but having an analytic understanding helps with any lock in amplifier design process.
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