Embedded Lab

Lock-in amplifiers are used to detect and measure very small AC signals which are buried in an overwhelming noise. For example, consider a case where you want to single out a 5 mV sine wave from a white noise signal with 2 V amplitude. A lock-in amplifier makes this measurement possible. It uses a technique called phase-sensitive detection, which uses a specific frequency reference to extract the component of the signal at the reference frequency and phase. Noise signals, at frequencies other than the reference frequency, are then rejected and do not affect the measurement. This instructable describes how to construct a very simple lock-in amplifier using Anlog Devices’ AD630 high precision balanced modulator. The overall cost of this lock-in counter is around $60.

DIY lock-in amplifier