Lock-In amplifiers are a unique device that is typically not well understood and how it can be used to solve some rather complex reference issues. Sometimes called Clean-Up amplifiers, in it’s simplest form, a lock-in amplifier can be likened to a PLL. An OCXO of some desired level of performance is locked to an external timing signal. The phase noise of the resulting locked signal is dominated by the OCXO and its characteristics. Depending upon the design, the quality of the reference signal used to discipline the OCXO can be rather poor. The signal can be a reference of the same frequency, an optical signal or even a PPS or some defined frequency with a mathematical relationship to the OCXO.

Why consider a lock-in amplifier? A common use is in larger reference systems where a single master reference must be distributed across a wide area. Cable losses and induced noise can render a reference unacceptable. Fiber optic systems will typically degrade phase noise. This is where a Lock-In amplifier excels. A lock-In amplifier can restore a reference to the required performance level and maintain timing synchronization with the master source