Unbalanced ringing using a balanced ringing generator of a subscriber line interface circuit

摘要

A communication loop using a subscriber line interface circuit (SLIC) is modified such that it can operate in unbalanced ringing environments as well as balanced ringing environments. This is accomplished by grounding the tip lead of a telephone instrument and creating an open circuit at the tip lead of the SLIC. The ring lead of the telephone instrument and the ring lead of the SLIC are electrically connected, and an AC voltage applied to the ring lead by the SLIC is increased. A power supply is connected to the SLIC and biased to provide the increased AC voltage on the SLIC ring lead while the average voltage on the SLIC tip lead is maintained substantially at ground. The result of this circuitry is a trapezoidal signal meeting the amplitude, loading and crest factor requirements of Bellcore Technical Requirement Publications TA-NWT-000909 and TR-NWT-000057.