Telephone line interface circuit without hookswitch relay
US6714645B1 · kind B1 · utility
Assignee
Inventors
Key dates
| Filing date | Jul 18, 2000 |
| Grant date | Mar 30, 2004 |
| Priority date | — |
| Expiry date | Jan 24, 2022 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M1/745
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A telephone line interface circuit which does not require a hookswitch relay is disclosed. An optoisolator is utilized to place a telephone line interface circuit on-hook and off-hook. In one embodiment, the optoisolator is controlled by an optoisolator control signal generated by a communications device such as a modem. An output of the optoisolator is coupled to an input of a DC control circuit. An output of the DC control circuit is coupled to a AC switch. When the optoisolator input control signal is activated, the optoisolator output enables voltage or current bias to the transistor, which places the telephone line interface circuit off-hook. When the optoisolator input control signal is deactivated, the optoisolator output disables voltage or current bias to the transistor, which places the telephone line interface circuit on-hook. In one embodiment, the DC control circuit is an electronic inductor comprising a pair of NPN transistors connected in a Darlington configuration. In one embodiment, the AC switch comprises a PNP transistor whose base is coupled to the output of the DC control circuit. In another embodiment the AC switch comprises an NPN transistor whose base is cou…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.