A digital lock-in technique for small signal detection with square wave reference over a wide frequency range

We discuss an approach to design of a digital lock-in amplifier with full utilization of advantages of a high precision sigma-delta analog to digital converter with configurable output filter. The particular attention is paid to the hardware simplification including the input anti-alias filter and digital signal processing. We show that the configurable oversampling together with the use of square wave reference allows one to obtain a simple and precise digital lock-in amplifier with frequency range of more than 10 decades and input dynamic reserve exceeding 120dB.