HYBRID INTERFACE CIRCUIT FOR OFFSETTING A SIDE TONE IN A KEYPHONE SYSTEM, PARTICULARLY SO AS TO OFFSET A SIDE TONE ACCORDING TO A LOOP IN THE HYBRID INTERFACE CIRCUIT USING A CENTER TAP PIN OF A TRANSFORMER

摘要

PURPOSE: A hybrid interface circuit for offsetting a side tone in a keyphone system is provided to minimize a side tone up to a long loop from a short loop in the hybrid interface circuit of an analog subscriber board using a transformer, thereby supplying a high-quality sound. CONSTITUTION: A transformer(T1) connects a local exchange(30) with a keyphone system(20). An impedance circuit(7) adds an increment of impedance in accordance with a loop by being connected with a center tap pin of the transformer(T1). A feedback circuit(8) offsets a side tone in connection with the impedance circuit(7). A receiving amplifier(6) offsets a side tone by a negative terminal being connected to the transformer(T1) and a positive terminal being connected to the feedback circuit(8).