Phase-locked loop having separate smoothing and loop filters
US4774480A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Feb 26, 1987 |
| Grant date | Sep 27, 1988 |
| Priority date | — |
| Expiry date | Feb 26, 2007 |
Classification
- Technology area (CPC Y)Emerging Cross-Sectional Technologies
- CPC primaryY10S331/02
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
A PLL comprising a phase comparator circuit for detecting the phase of a pulse signal based upon the input signal and the phase of a pulse signal based upon the output signal, a smoothing filter for smoothing the output of the phase comparator circuit, a loop filter for controlling the oscillation frequency on the basis of the smoothing filter, and a voltage controlled oscillator circuit for sending out the output signal having a frequency corresponding to the voltage based upon the output of the loop filter. Since the smoothing filter is separated from the loop filter, time constants of the smoothing filter and the loop filter can be set independently and with precision. If the time constant of the smoothing filter is chosen to be extremely small, for example, the time constant of the phase-locked loop is defined by the time constant of the loop filter. It is thus possible to define the time constant of the phase-locked loop by only selecting the time constant of the loop filter. Further it is possible to both suppress the jitter of the phase-locked loop and reduce the frequency ripple, for example.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.