Phase lock loop charge pump with symmetrical charge and discharge currents
US5285114A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Aug 17, 1992 |
| Grant date | Feb 8, 1994 |
| Priority date | — |
| Expiry date | Aug 17, 2012 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03L7/093
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
A charge pump in a phase lock loop equalizes the charge and discharge currents flowing into the filter capacitor independent of the loop node voltage for providing a linear VCO output frequency. The potential at the output of the charge pump determines whether the charging/discharging current is decreased or increased. An active up control signal to increase VCO output frequency and a low level potential at the output of the charge pump limits the charging current to the loop filter while increasing the discharge current. An active down control signal to decrease the VCO output frequency and a high potential at the output of the charge pump limits the discharging current while increasing the charge current. The voltage change at the output of the charge pump in response to the up control signal is made equal to the voltage change during the down control signal for providing equal charge and discharge currents to the loop filter independent of the loop voltage.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.