Sensor circuit
US5424661A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Aug 12, 1993 |
| Grant date | Jun 13, 1995 |
| Priority date | — |
| Expiry date | Aug 12, 2013 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03K3/0307
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
A sensor circuit is disclosed for use with a clock circuit providing a periodic timing signal to a clock output, wherein a timing reference for the periodic timing signal is provided by a crystal connected between a crystal input and a crystal output of the clock circuit, or alternatively provided by an external periodic logic signal coupled to the crystal input. The sensor circuit provides a sensor output in a first state, thereby indicating the presence of an external periodic logic signal timing reference, in response to at least a given number of large-signal voltage transitions on the crystal input within a certain period of time, and otherwise provides a second state on the sensor output, typically to indicate the presence of a crystal timing reference. Also disclosed is a clock circuit including a sensor circuit, and further including means for disabling a feedback resistor necessary for crystal operation when the timing reference is determined to be provided by an external periodic logic signal.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.