Abstract: Chip-scale atomic clock (CSAC) is a type of miniaturized coherent population trapping (CPT) atomic clock with small scale and low-power.In this paper,we adopted the design of IIR filter to deal with output signal of CSAC.The design can help reduce the volume and improve short-term frequency stability of CSAC The experimental result shows  that resources IIR filter occupied is reduced by nearly 58% while compared with FIR filter.Besides,the short-term frequency stability of CSAC is improved by 1.4×10^-10τ^-1/2（τ=1s-100s）and the circuit size is reduced by 10% when compared with analog filter.

Key words: IIR filter, Chip-scale atomic clock, Digital filter, Cascaded