Low noise readout circuit for THz measurements without using lock-in technique

The lock-in technique is commonly used for measurements of very small DC signals in the presence of overwhelming noise. However, phase sensitive detection has its own limitations and it cannot be always easily applied in every test setup configuration. This work deals with a low noise readout circuit intended to operate with FET-based THz detectors, which in fact can replace the lock-in equipment and eliminate the need of THz wave modulation. This circuit can be also successfully deployed for processing of small DC signals produced by other sensors or detectors.