Abstract: In order to detect weak signal，a phase sensitive detector based on voltage frequency conversion is
proposed． The voltage to be measured is converted into frequency through the voltage frequency conversion
circuit，and the frequency signal is counted and digital filtered by the single-chip microcomputer according to the
reference signal，so as to realize weak signal detection． The related detection principle is analyzed，the hardware
and software design and implementation of the system are completed，the verification experiment and error
analysis are carried out，and the correctness and feasibility of the scheme are verified． The system is simple in
principle，low in cost，reliable，convenient and practical，and has a broad application prospect in weak signal
detection．

Key words: phase sensitive detection, voltage frequency conversion, weak signal detection, filter