Apparatus for interfacing analog telephone in isdn terminal adapter

Abstract

An apparatus for interfacing an analog telephone in an ISDN terminal adapter is able to independently perform call set-up regardless of a personal computer's operation, while being provided with ISDN audio service via an existing analog telephone. The apparatus includes a combocodec for converting a digital audio signal from the co-processor into an analog audio signal to supply it to a telephone, and for digitizing an analog audio signal from the telephone to supply it to the co-processor; a ring generator for generating a ring signal under the control of the co-processor; and a DC-voltage converter for generating a telephone driving voltage. A subscriber line interfacing circuit (SLIC) is connected to a telephone, a DC-voltage converter, and a combocodec, for supplying the telephone driving voltage to the telephone, interfacing the audio signals between the telephone and combocodec, and sensing the office line to determine the telephone's hook state. A relay is connected among the SLIC, ring generator, and the telephone, for supplying the ring signal from the ring generator to the telephone under the control of the SLIC. A tone decoder is provided for decoding a dual tone multi-frequency signal from among the audio signals from the SLIC to the combocodec, and transmitting the decoded signal to the co-processor.