Contents I. Introduction
The charge pump is one of the core modules of the phase-locked loop. It converts the voltage pulse signal with phase difference information output from the PFD into a current that charges and discharges the loop filter to change the control voltage of the VCO. Charge pump suffers from non-ideal effects such as charge injection, clock feedthrough, and current mismatch [1]. These effects will degrade the PLL reference spur and phase noise [2]. Typical charge pumps are drain-switched charge pump, source-switched charge pump and gate-switched charge pump, as shown in Fig. 1. The drain-switched charge pump has a fast turn-on response, but suffers from charge sharing, charge injection, and clock feedthrough. The source-switched charge pump has a small current mismatch and weak charge injection effect, but affected by clock feedthrough. Gate-switched charge pump reduces charge injection, charge sharing, and clock feedthrough, but has current mismatch problem.
