Digital and analog phase detector for a frequency synthesizer
US4490688A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Apr 6, 1981 |
| Grant date | Dec 25, 1984 |
| Priority date | — |
| Expiry date | Apr 6, 2001 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04B1/405
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
A sample and hold phase detector for a phase locked loop includes a digital detector for detecting the frequency and phase difference between the reference signal and the voltage controlled oscillator (VCO) signal. In a first mode of operation, the digital detector generates a first signal relating the difference in frequency and in a second mode of operation generates a second signal relating the difference in phase. A capacitor stores the first or second signal depending on the operational mode of the digital detector. The capacitor is selectively discharged in response to a discharge signal produced by the digital detector when either the VCO frequency is higher than the reference frequency or following each detection of a phase difference. A first amplifier is used to bypass a portion of the loop filter to effect rapid changes in VCO frequency in the first mode while a second amplifier couples the control voltage to the VCO via the loop filter to maintain proper VCO frequency in the second mode.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.