Optimization Design of Decimation Filter for the Phasemeter in the Space Gravitational Wave Detection

In space gravitational wave detection (SGWD), the cascaded integrator–comb (CIC) antialiasing filter is always utilized for the down-sampling of the phasemeter. However, the passband of the CIC filter is not flat, which means that the attenuation is not the same at different frequencies. Therefore, in fields that require high accuracy of phase true value, such as differential wavefront sensing (DWS), the traditional down-sampling method is not applicable. In this article, the filter of CIC-interpolated second-order polynomials (ISOP) architecture is developed for the compensation of the attenuation effect. A phasemeter is also developed for the experimental demonstration. The results show that the passband attenuation at 1 Hz reduces from 0.1076 to $3.86 \times 10^{-4} \; \text {dB}$ , significantly reducing the droop in the passband. The noise performance of the phasemeter is also tested, which can reach the level of $2\pi \; \mu \text {rad/Hz}^{1/2}$ .