Patent ID: 6747494
Filing Date: 2004-06-08
Classification: H03L

Abstract:
A charge pump for a phase locked loop arrangement, the charge pump comprising:a current source circuit having a predetermined slew rate and arranged for selectively providing charging current to the phase locked loop arrangement; a current sink circuit having a predetermined slew rate and arranged for selectively depleting charging current from the phase locked loop arrangement; and a constant current source which in locked mode is offset by current sink pulses of the current sink circuit; and wherein the current sink circuit comprises a current mirror comprising a first transistor and a second transistor with a gate of the first transistor coupled to a gate of the second transistor and a source of the first transistor coupled to a gate of the second transistor and the gate of the first transistor coupled to a drain of the first transistor, a bias current source coupled to the drain of the first transistor through a switch; and a leak current sink coupled to the sates of the first and second transistors; whereby when the switch is closed the current mirror is operable to mirror a differential between the bias current source and the leak current sink to the second transistor causing the current sink circuit to sink a current and the bias current source is operable to charge a parasitic capacitance of the current mirror and when the switch is open the leak current sink is operable to discharge the parasitic capacitance of the current mirror.