Ring trip circuit for subscriber telephone
US4995111A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Feb 21, 1989 |
| Grant date | Feb 19, 1991 |
| Priority date | — |
| Expiry date | Feb 21, 2009 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M19/026
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
An improved ring trip circuit for a subscriber telephone, for detecting an on-hook state or an off-hook state of the telephone. The ring trip circuit can be formed in a small size and can be formed by a LSI. The ring trip circuit includes a voltage detecting circuit (2), for detecting a voltage difference (.DELTA.V) between both ends of a ringer sending resistor, having a first circuit (S1, S2, A1.about.B3) converting the voltage difference to a current difference, and further having a second circuit (F) converting the current difference to a voltage, the voltage difference varying in response to the on-hook state or the off-hook state of the telephone, and a state detecting circuit (3) for detecting the on-hook state or the off-hook state in response to a value of the voltage from the voltage detecting circuit. The voltage detecting circuit is formed by a plurality of current mirror circuits, each of which includes at least two transistors. The state detecting circuit includes a comparator circuit (CP1) formed by a plurality of transistors.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.