Telephone station set interface circuit
Interface circuit and method for telephone extension lines
Supply circuit for a subscriber's line circuit
Multifunction telephone with message information and control information circuits for connecting stations and common equipment in a telephone network
Telephone line circuit and system
Control of a key telephone system using a pulse width modulated signal
Apparatus for transmitting information via telephone lines
Data call transfer preindication
ApplicationNo. 06/616118 filed on 06/01/1984
US Classes:379/161, With exclusion or priority feature (e.g., lockout or privacy)379/166, Detail of line circuit or line card379/394, Impedance matching or line equalizing379/400For line length compensation
ExaminersPrimary: Brown, Thomas W.
Assistant: Vaas, R.
Attorney, Agent or Firm
International ClassesH04Q 11/04 (20060101)
H04M 9/00 (20060101)
AbstractAn interface circuit for interconnecting an analog telephone device with a digital telephone system includes an independent power supply (58) for driving the loop termination on an analog telephone device (22). An impedance matching circuit (54) and a summing network (42) are utilized to both couple the signal from the analog telephone device (22) to the analog input of a key service unit (10) and match the impedance therebetween. A switch, (46) is provided to disconnect the analog port of a digital telephone device (12) that is compatible with the key service unit (10). When the analog telephone device (22) is in the off-hook mode, a switch control (52) opens the switches (48) and (50) of switch (46). The digital telephone device (12) is under the control of a digital transmission line (20) to maintain an analog interconnection in the key service unit (10). The analog telephone device (22) operates on an independent loop termination with an independent loop current. The signal generated in the loop is summed with the analog port (18) of the key service unit (10) through the summing network (42). In this manner, an inexpensive analog telephone device (22) with a non-compatible termination requirement can be utilized on a digital telephone system such as a key service unit (10) or a PBX.