TELEPHONE LINE SWITCHING AND CONTROL CIRCUIT

摘要

PURPOSE:To attain the sure switching of a telephone line by confirming the incoming of a carrier of an outgoing data signal simultaneously when the average amplitude of the outgoing data signal is detected. CONSTITUTION:Since the average amplitude level of an output of a limiter amplifier circuit 37 is made higher than a preset level when the outgoing data signal is incoming normally to an information receiver 6, the output of logical 1 is obained at an amplitude detection circuit 38 and the output of logical 1 is obtained at a carrier detection circuit 40 because the carrier of the outgoing data signal is extracted from a band pass filter 39 at the same time. As a result, a switching operation signal is given to a line switch 4 from a drive circuit 43 as the output of a telephone line switching control circuit. If no outgoing data signal is incoming, even when the component of a comparatively large level due to noise is superposed, the output of the carrier detector does not go to logical 1 to cause no malfunction of changeover.