Design of PLL frequency synthesizer based on the fourth-order active filter

The fourth-order active loop filter is employed to design the PLL frequency synthesizer at S-band in this paper. By using ADIsimPLL3.1 the transfer function and the phase noise are simulated. The testing results of the real circuits performance parameters coincide with the simulated results very well. And it is verified that the high order loop filter can improve the phase-noise of the PLL frequency synthesizer.