Phase latched differential charge pump circuit and method
AssigneeAltera Corporation
InventorDavid Edward Jefferson
Life of this patent
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Abstract
A loop circuit such as a delay lock loop or a phase lock loop includes circuitry for changing the strength of the lock after lock has been achieved. Before lock is achieved, the strength of the charge pump circuitry that controls the charge in the low-pass filter in the loop may be relatively weak. After lock has been achieved, the strength of the charge pump circuit may be increased so that the circuit can maintain its locked condition in a noisy environment.
Claims8
In a loop circuit which attempts to match the phase of a reference clock signal and the phase of a feed-back clock signal which is at least partly controlled by the loop circuit, the loop circuit including a phase frequency detector for comparing the phases of the reference and feed-back clock signals and for producing a first or second output depending on whether the phase of the reference clock signal is ahead of or behind the phase of the feed-back clock signal, a low-pass filter having a charge storing component for producing an output voltage indicative of how much charge is stored on said charge storing component, said output voltage at least partly controlling the phase of the feed-back clock signal, and a charge pump circuit responsive to said first and second outputs for applying charge to or withdrawing charge from said charge storing component depending on which of said first and second outputs is active, improved charge pump circuitry comprising:
- phase lock detection circuitry for producing a phase lock output signal when the phase of the feed-back clock signal is approximately the same as the phase of the reference clock signal for at least a portion of a predetermined time interval;
- and
- charge pump amplifying circuitry responsive to said phase lock output signal for increasing the rate at which said charge pump circuit applies charge to or withdraws charge from said charge storing component in response to said first and second outputs.
The method of operating a loop circuit which attempts to match the phase of a reference clock signal and the phase of a feed-back clock signal which is at least partly controlled by the loop circuit, the loop circuit including a phase frequency detector for comparing the phases of the reference and feed-back clock signals and for producing a first or second output depending on whether the phase of the reference clock signal is ahead of or behind the phase of the feed-back clock signal, a low-pass filter having a charge storing component for producing an output voltage indicative of how much charge is stored on said charge storing component, said output voltage at least partly controlling the phase of the feed-back clock signal, and a charge pump circuit responsive to said first and second outputs for applying charge to or withdrawing charge from said charge storing component depending on whether said first or second output is active, said method comprising the steps of:
- detecting when the phase of the feed-back clock signal is approximately the same as the phase of the reference clock signal for at least a portion of a predetermined time interval in order to then produce a phase lock output indication;
- and
- increasing the rate at which said charge pump circuit applies charge to or withdraws charge from said charge storing component in response to said first and second outputs after said phase lock output indication has been produced.
Dependencies are inferred from the claim text.