Dual-loop spread-spectrum clock generator with master PLL and slave voltage-modulation-locked loop
US5943382A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Dec 15, 1997 |
| Grant date | Aug 24, 1999 |
| Priority date | — |
| Expiry date | Dec 15, 2017 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG09G2330/06
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
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 i…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.