Physlock - an entry level lockin amplifier board

The design of a simple, entry-level low-cost, stand-alone lock-in amplifier is described. The instrument is useful for detecting and amplifying signals that are frequency synchronized with a reference signal. It is particularly important for detecting and measuring small signals in the presence of large noise. The design is based on a modulator/demodulator integrated circuit and uses a minimum number of components to accomplish input amplification, phase-sensitive detection, low-pass filtering, and dc amplification of the output signal.

Physlock is based on the integrated circuit AD630 and will be helpful in teaching students about low-level signal detection which is commonplace in numerous tasks in the experimental physics laboratory. It can also be used in the research laboratory (see specs below).

• Power 220 V, 50 Hz
• Reference signal amplitude > 1 V
• Dynamic Range 60 dB to 70 dB
• DC gains 1x or 10x
• AC input gains 1x, 50x, 100x, 500x, 1000x, 2000x, 5000x
• Low pass filter time constants 1 s, 0.1 s, 10 ms, 0.1 ms, 10 us
• Form of input signal Low frequency (< 1 kHz) periodic signal
  (square to sine converter is also provided).

The complete circuit diagram is given below. You are welcome to build this on your own.

Student details: Sultan Abdul Wadood (Final Year Project at EME, NUST)

Designed by Muhammad Shafique (Qosain Scientific) and Dr. Sabieh Anwar.

Testing and documentation by Shiraz Ahmad (MS Physics Student, LUMS)