Frequency multiplexed telephone system
US4706244A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jan 15, 1985 |
| Grant date | Nov 10, 1987 |
| Priority date | — |
| Expiry date | Jan 15, 2005 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M9/027
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A frequency multiplexed system for coupling a plurality of individual telephone sets to at least one subscriber telephone line. The system includes a line adapter unit for controlling use of subscriber lines and for assigning the use of frequency bands to the individual telephone sets. The system includes a two-conductor interconnection cable for coupling to each of the telephone sets and to the line adapter unit. The system has a power-down mode in which the loss of external power allows each of the individual telephone sets to use the subscriber line. The line adapter unit and each of the individual telephone sets employ transconductance amplifiers so that modulated current signals are produced on the interconnection cable, thus allowing a plurality of voice signals to be summed together by voltage addition for conferencing between the telephone sets and the subscriber lines. One embodiment of the invention includes the production of a pilot reference signal on the interconnection cable by the adapter unit so that synchronous modulation and demodulation by each of the telephone sets is made possible.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.