Method and apparatus for detecting the connection status of an extension

Abstract

A detector circuit is provided for detecting the off-hook status of the extension telephone line. The detector is connected to tip and ring lines of the telephone line for determining a change in the voltage between the tip and ring lines. The detector includes a low pass filter for filtering noise and AC signals. The filtered signals are transmitted through a converter which converts a differential voltage between the signals into an absolute voltage relative to a ground. A pair of voltage peak detectors generate output signals in response to changes in the absolute voltage. A first peak detector provides a quickly varying output signal representing an instantaneous voltage. The second peak detector provides a slowly varying output response representative of an average voltage over a period of time. The average voltage is employed as a reference voltage against which the instantaneous voltage is compared. If a substantial difference between the instantaneous voltage and the average voltage is detected, a logic output signal is generated which indicates that an extension line is off-hook. In one embodiment, the detector circuit is employed as a component of a voice/data/fax modem. The modem responds to the detection of the off-hook extension line by deactivating a voice answering machine cycle. Further method and apparatus embodiments of the invention are described.