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Apparatus and method for driving LED display

  • US 9,286,825 B2
  • Filed: 10/17/2013
  • Issued: 03/15/2016
  • Est. Priority Date: 10/17/2013
  • Status: Active Grant
First Claim
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1. An apparatus for driving LED display, comprising:

  • a system control unit comprising a synchronization signal generator configured to generate a synchronization start signal; and

    a plurality of phase locked loop circuits, each of the phase locked loop circuits comprising;

    a phase frequency detector configured to generate a phase difference signal according to a frequency divided signal and a reference frequency signal;

    a charge pump configured to receive the phase difference signal and to generate an output current according to the phase difference signal to adjust phase alignment;

    a loop filter configured to receive the output current and to convert the output current to a voltage controlled signal;

    a voltage controlled oscillator configured to receive the voltage controlled signal and to generate a voltage controlled output signal;

    a divider configured to receive the voltage controlled oscillator and a randomized number, and having a dividing ratio, wherein the dividing ratio is changing over a modulation period;

    a sigma delta modulator configured to generate the randomized number to the divider; and

    a spread spectrum modulation depth controller coupled to the sigma delta modulator and configured to receive the synchronization start signal from the synchronization signal generator, wherein upon receipt of the synchronization start signal the spread spectrum modulation depth controller starts a spread spectrum modulation,wherein the synchronization signal generator transmits the synchronization signal to the spread spectrum modulation depth controller after the system control unit changes a spread spectrum modulation depth of the spread spectrum modulation depth controller.

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