Reduction of Current Mismatch in PLL Charge Pump

Low static phase offset is desired in Phase Locked Loops (PLL) employed in high speed I/O interfaces and frequency synthesizers. In this work, non idealities in phase frequency detector and charge pump contributing to static phase offset have been studied and their relative contributions analyzed in detail. A new charge pump architecture with reduced mismatch between Up and Dn current sources has been presented. It makes use of a single two stage amplifier for both current steering and reduction of mismatch. The efficacy of this architecture has been demonstrated with simulation results on a PLL running at an input reference frequency of 500 MHz in 65 nm CMOS technology.