Charge pump using switched capacitors for phase-locked loop control and method of operation

摘要

A charge pump for injecting a charging current onto a loop filter when a pump control signal is enabled. The charge pump comprises: i) MOS output transistors for injecting or removing the charge onto the loop filter; ii) pre-charge capacitors for storing pre-charge voltages at least equal to the desired gate-to-source voltages of the output transistors; and iii) switching circuitry for coupling the pre-charge capacitors to the gates of the output transistors when the Pump Up and/or Pump Down signals are enabled. The appropriate pre-charge voltage turns on the appropriate output transistor and the charging and/or discharging current is adjusted to a final level determined by the desired gate-to-source voltages and monitoring circuits.