Analog Devices,inc.

Fred Weiss

Barrie Gilbert

Eberhard Brunner

Daryl Carbonari

A charge pump in a phase locked loop is enabled only when a loop filter needs to be updated, thereby reducing the power consumption of the charge pump. The charge pump is enabled or disabled in response to an enable signal which is generated by a latch. The enable signal is activated by look-ahead signals which are activated in advance of either a pulse from a reference signal or a pulse from a variable signal so as to allow the charge pump to stabilize before providing the charge current to update the loop filter. Logic signals from a programmable divider and reference signal generator are used to generate the look-ahead signals. The charge pump is disabled by a reset signal from a phase-frequency detector after the loop filter is updated. The charge pump includes a current switch for generating source and sink charge currents in response to pump-up and pump-down control signals. A bias cell provides two reference signals to the current switch. The reference signals are disabled in response to an enable signal, thereby disabling the current switch and reducing the power consumption of the charge pump.

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Newberg, OR, United States of America

Fred Weiss