Method and circuit for failsafe switch-hook detection during fault in a telephone system
US5812658A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jan 30, 1995 |
| Grant date | Sep 22, 1998 |
| Priority date | — |
| Expiry date | Jan 30, 2015 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M19/026
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A circuit and method for maintaining switch-hook detection (SHD) in the presence of a fault in a telephone system may include a comparison of one of a tip current and a ring current to a reference current. A switch-hook detection indicates that a request for service has been made. The reference current may be a conventional switch-hook detection threshold current, I.sub.SHD, times a factor (G.sub.0 +1).sup.-1, where G.sub.0 is the predetermined operating gain of the amplifier in the telephone subscriber line interface circuit. The line current may be reduced in response to detection of a fault in the telephone system without affecting the determination whether a request for service has being made.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.