Constant current line circuit
US4723280A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jun 24, 1985 |
| Grant date | Feb 2, 1988 |
| Priority date | — |
| Expiry date | Jun 24, 2005 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M19/005
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A constant current line circuit for connection to balanced tip and ring leads of a telephone line and unbalanced transmit and receive leads of a PABX. A differential amplifier receives and applies incoming audio signals carried by the tip and ring leads to the unbalanced transmit lead, and detects D.C. loop current flowing through the tip and ring leads and generates a D.C. signal in response thereto. A voltage controlled feed current supply, connected in a circuit to the differential amplifier, generates a constant current D.C. voltage to the tip and ring leads in response to receiving the D.C. signal, and an integrator circuit is connected in a feedback path from the output of the differential amplifier to a voltage control input of the supply, for filtering audio signals received by the differential amplifier and regulating the generated D.C. signal to a quiescent value of approximately zero volts. The line circuit provides simultaneous bidirectional signal translation and constant D.C. feed current generation in response to detecting the D.C. loop current and generating and regulating the D.C. signal.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.