A jitter suppression technique for a clock multiplier

This paper describes a jitter suppression technique for a clock multiplier IC that uses a phase-locked loop (PLL). It is shows that the jitter cutoff frequency of the jitter transfer function call be greatly improved by addin g a surface acoustic wave (SAW) filter whose center frequency equals the in put frequency. The jitter transfer function is mainly determined by the cha racteristics of the SAW filter. Therefore, the clock multiplier IC can be s et at a high loop gain to minimize the jitter generation without increasing the jitter cutoff frequency. The use of a clock multiplier IC that was fab ricated with Si bipolar technology and a SAW filter with the center frequen cy of 155.52 MHz and a quality (Q) factor of 1500 results in a very low jit ter generation of 3.5 mUI rms and an extremely low jitter cutoff frequency of about 50 kHz when the clock multiplier converts a clock frequency of 155 .52 MHz into a 2.48832-GHz signal.