Charge pump using switched capacitors for phase-locked loop control and method of operation
AssigneeNational Semiconductor Corporation
InventorRodney A. Hughes
Life of this patent
Estimating the term…
Abstract
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.
Claims23
A charge pump for injecting a charging current onto a loop filter coupled to an output of said charge pump when a Pump Up control signal received by said charge pump is enabled, said charge pump comprising:
- a P-channel output transistor for injecting said charging current onto said loop filter;
- a first pre-charge capacitor for storing a first pre-charge voltage at least equal to a first desired gate-to-source voltage of said P-channel output transistor;
- and
- first switching circuitry for coupling said first pre-charge capacitor to a gate of said P-channel output transistor when said Pump Up signal is enabled, such that said first pre-charge voltage turns on said P-channel output transistor and said charging current is adjusted to a final level determined by said first desired gate-to-source voltage.
An integrated circuit comprising:
- a system control section operating at a plurality of clock speeds;
- at least one of a phase-locked loop (PLL) and a delay-locked loop (DLL) providing at least one clock signal to said system control section, said at least one of a PLL and a DLL comprising a charge pump for injecting a charging current onto a loop filter coupled to an output of said charge pump when a Pump Up control signal received by said charge pump is enabled, said charge pump comprising:
- a P-channel output transistor for injecting said charging current onto said loop filter;
- a first pre-charge capacitor for storing a first pre-charge voltage at least equal to a first desired gate-to-source voltage of said P-channel output transistor;
- and
- first switching circuitry for coupling said first pre-charge capacitor to a gate of said P-channel output transistor when said Pump Up signal is enabled, such that said first pre-charge voltage turns on said P-channel output transistor and said charging current is adjusted to a final level determined by said first desired gate-to-source voltage.
A method of operating a charge pump comprising a P-channel output transistor for injecting a charging current onto a loop filter coupled to an output of the charge pump when a Pump Up control signal received by the charge pump is enabled, the method comprising the steps of:
- storing on a first pre-charge capacitor a first pre-charge voltage at least equal to a first desired gate-to-source voltage of the P-channel output transistor;
- and
- coupling the first pre-charge capacitor to a gate of the P-channel output transistor via a switch when the Pump Up signal is enabled, such that the first pre-charge voltage turns on the P-channel output transistor and the charging current is adjusted to a final level determined by the first desired gate-to-source voltage.
Dependencies are inferred from the claim text.