Evaluation of different structures for loop filter on synthesizer specifications

In this paper, the effect of four architectures of loop filter (passive and active) on the performance of fractional-N frequency synthesizer at S-band is analyzed. Parameters of each loop filter is designed for a given phase margin and loop bandwidth. Then, phase noise and transient response of system, is simulated for comparison with another employed loop filter. The simulation is performed by using the practical program ADIsimPLL3.40.06. Furthermore, output spectrum of implemented circuit for two types of loop filter is shown.