Apparatus and method for incoming call detection and alarm circuitry for cellular telephones
US5638421A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jul 25, 1995 |
| Grant date | Jun 10, 1997 |
| Priority date | — |
| Expiry date | Jul 25, 2015 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M19/04
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
An apparatus and method for indicating an incoming call that generates a voltage signal with a value representative of the current drawn by operation of the device. A circuit monitors the voltage signal and generates a waiting for call state signal whenever the value of the voltage signal decreases from a first selected higher value to a first selected lower value for a first preselected period of time. An RF detection circuit monitors the status of the device's transmitter and generates a transmitter active status signal whenever RF appears for a selected period of time. An incoming call detection circuit generates an alarm start signal whenever the waiting for call state and transmitter active status signals are present and either the voltage signal increases from a second selected lower value to a second selected higher value and remains at or above the second selected higher value for a second preselected period of time, or the current goes from a lower preselected current value to a higher preselected current value and remains at or above the higher current value for a third preselected period of time. An alarm, operative upon receipt of the alarm start signal, indicates an in…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.