Design of a Lock-in Amplifier

摘要

The lock-in amplifier is an instrument capable of measuring a periodic signal under adverse signal to noise conditions, i.e., RMS noise at least 20dB larger than the signal. A synchronous detector followed by a narrowband filter is used to give a dc voltage output which is proportional to the input signal amplitude. The design stresses simplicity. By using relatively inexpensive integrated circuits, preliminary testing indicated the performance could surpass existing standards. By using MOSFET chopper transistors in a series-shunt configuration the range of operating frequencies has been extended to 5 megahertz. The final unit is packaged in a 11 by 6 by 5 inch cabinet with a power supply. All operating conditions are met by using front panel controls and no external plug-in attachments are necessary. (Author)