Patent ID: 7221704
Filing Date: 2007-05-22
Classification: H03K,H03L,H04B

Abstract:
1. A digital circuit configured to spread the spectrum of a clock train comprising: a clock generator configured to generate the clock train; a variable divider configured to receive the clock train from the clock generator and divide the frequency of the clock train by a temporally-varying-divider value to modulate the clock train and generate a dithered clock train; a first accumulator configured to receive the dithered clock train from the variable divider and accumulate the dithered clock train to generate a frequency modulation waveform; a second accumulator configured to receive the frequency modulation waveform from the first accumulator and accumulate the frequency modulated waveform to generate a phase modulation signal; a phase-value calculator configured to receive the phase modulation signal from the second accumulator and calculate the temporally-varying divider value based on the phase modulation signal; and a closed-loop control circuit configured to receive the dithered clock train from the variable divider and track and filter the modulation of the dithered clock train to generate a second clock train that is the spread spectrum of the first mentioned clock train.