Ring-trip detector
US4447675A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Oct 29, 1982 |
| Grant date | May 8, 1984 |
| Priority date | — |
| Expiry date | Oct 29, 2002 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M19/026
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A ring-trip detector circuit is disclosed which detects a subscriber off-hook condition in the presence of a ringing signal. The ring-trip detector employs substantially all low-voltage components which enables it to be fabricated using integrated circuit techniques with the resultant cost and space-saving advantages inherent therein. The ringing signal is disabled upon detection of a DC component which is present in the telephone loop only when the subscriber goes off-hook. This circuit detects the DC voltage component across a resistor (20) in series with the ringing source (19) and the telephone loop (12, 13). The voltage across this resistor (20) is converted by resistance networks (23, 24) into two relatively small currents that are fed to low impedance points (25, 26). A difference current is formed therebetween, which is filtered (31, 45) to remove AC components, and compared with a threshold current (29, 46). Ring-trip occurs when the filtered difference current exceeds the threshold.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.