Time corrected, continuously updated clock
US4582434A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Apr 23, 1984 |
| Grant date | Apr 15, 1986 |
| Priority date | — |
| Expiry date | Apr 23, 2004 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG04R40/00
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
Time referenced RF signals are periodically received and processed for updating a microprocessor-controlled clock. The clock automatically scans several frequencies at which the coded RF timing signals are transmitted, selecting the strongest received signal for synchronization therewith and causes a capture LED to be illuminated upon detection of a sufficiently strong signal at the beginning of a minute tone at one of the received frequencies. The microprocessor periodically determines the timing difference between an internal timer and the received RF timing signals. A time difference correction is provided to a digital-to-analog converter which provides an appropriate voltage to a varactor diode in a crystal oscillator circuit for adjusting the microprocessor's operating frequency until it can no longer resolve a difference between the received RF timing signals and its internal timer. This permits highly accurate clock operation in between the periodic reference time updates and eliminates cumulative time error. Manual switches are provided for correcting for received signal propagation delay and for selecting the appropriate time zone as well as for allowing for daylight savin…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.