Charge pump circuit with symmetrical current output for phase-controlled loop system

A current source circuit for use in a phase-controlled loop system having a filter, said current source circuit comprising:

• an output node coupled to the filter so as to provide a control voltage thereto;
• a charge pump having means for sourcing a positive current to the output node and means for sourcing a negative current from the output node, said positive current and said negative current each having an amplitude dependent upon the control voltage at the output node;
• and
• feedback means for continuously sensing an amplitude difference between the amplitude of the positive current and the amplitude of the negative current when the phase-controlled system is in a phase-locked condition and for compensating at the output node for said amplitude difference so that the amplitude difference between the positive current and the negative current supplied by the charge pump is canceled at the output node when the phase-controlled loop system is in phase-locked condition.

A phase-locked loop (PLL) system for providing an output signal in phase with a received reference signal, said PLL system comprising:

• a phase comparator having a first input and a second input, said first input being coupled to receive the reference signal and said second input being coupled to receive as feedback the output signal, said phase comparator including means for comparing the phases of the reference signal and the output signal and for selectively providing one of a charge increase command and a charge decrease command;
• a filter having a filter node;
• a voltage controlled oscillator coupled to said filter for providing the output signal in response to a control voltage applied to the filter node;
• and
• a charge pump coupled between said phase comparator and said filter for applying the control voltage to the filter and having an output node connected to the filter node, and means for sourcing a positive current to the output node in response to a charge increase command and means for sourcing a negative current from the output node in response to a charge decrease command, said charge pump further including feedback means for continuously sensing an amplitude difference between the amplitude of the positive current and the amplitude of the negative current when the PLL system is in a phase-locked condition and for compensating at the output node for said amplitude difference such that positive and negative currents of equal amplitude appear at the output node of said charge pump when the PLL system is in said phase-locked condition.