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Precise, low-jitter fractional divider using counter of rotating clock phases

  • US 5,970,110 A
  • Filed: 01/09/1998
  • Issued: 10/19/1999
  • Est. Priority Date: 01/09/1998
  • Status: Expired due to Term
First Claim
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1. A fractional divider comprising:

  • an input clock having an input period;

    a delay line, coupled to the input clock, having a plurality of output taps, successive output taps having successively larger phase shifts of the input clock;

    a phase mux, coupled to the plurality of output taps of the delay line, for outputting a selected clock in response to a control input;

    a rotational state machine having a plurality of states in a loop order, coupled to increment state to a next adjacent state in the loop order in response to the selected clock, the rotational state machine coupled to output a current state as the control input to the phase mux;

    wherein successive states in the loop order select successive output taps having successively larger phase shifts; and

    a counter, coupled to the selected clock, for pulsing an output clock after M pulses of the selected clock;

    wherein the rotational state machine increments to a next state, causing the phase mux to select an output tap having a larger phase shift, increasing a period of the selected clock for a first N periods of the selected clock;

    wherein the first N periods of the selected clock have an increased period while a remaining M-N periods have the input period of the input clock,whereby the output clock is pulsed after M.N periods of the input clock.

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