05943382 is referenced by 44 patents and cites 18 patents.

A clock generator produces a frequency-modulated clock. A master phase-locked loop (PLL) includes a voltage summer that outputs a voltage to a voltage-controlled oscillator (VCO). The voltage to the VCO determines the frequency of the clock generated. A modulated voltage is subtracted by the voltage summer to produce voltage and thus frequency modulations. This modulated voltage is produced by a second loop that operates as a slave to the master PLL. The slave loop is a voltage-locked loop. The peak amplitude of the modulated voltage is locked to a control voltage of the master PLL. The control voltage is a stable voltage input to the voltage summer that is generated by phase comparisons of the output clock to a reference clock. To overcome the problem of locking to the modulating output clock, phase comparison is performed only at the same point in the modulation cycle, at the beginning of each modulation cycle. Thus modulations do not affect phase comparisons. The modulated voltage is generated by a waveform generator in the slave loop. The waveform generator is controlled by a feedback divider that also controls when phase comparison is performed. The amplitude of the waveform is adjusted to track the control voltage of the master PLL by comparing the control voltage to the modulated voltage, but only at the beginning of the modulation cycle. The modulation amplitude is kept constant over different supply voltages, ambient temperatures, and process corners.

Title
Dual-loop spread-spectrum clock generator with master PLL and slave voltage-modulation-locked loop
Application Number
701814
Publication Number
5943382
Application Date
December 15, 1997
Publication Date
August 24, 1999
Inventor
Mangesh S Pimpalkhare
Santa Clara
CA, US
Hung Sung Li
Santa Clara
CA, US
Agent
Stuart T Auvinen
Assignee
NeoMagic
CA, US
IPC
H03D 3/24
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