Abstract: A demodulation circuit that cascading the synchronous integrator and the phase sensitive detector and its application in the Coherent Population Trapping (CPT) atomic frequency standard is introduced. By theoretical calculation and the advanced design system software simulation, it is found that the demodulation circuit has high Q value and a good noise suppression capability and can be applied to CPT atomic frequency standard. By testing of the circuit, it’s confirmed that the circuit can demodulate the light detection signal and provide high-performance differential curve of the Doppler absorption spectrum used to lock the laser frequency and the differential curve of the CPT spectrum used to lock the microwave.

Key words: Atomic frequency standard, Demodulation circuit, Synchronous integrator, Phase-sensitive detector