AUTOMATIC SENSING METHOD AND CIRCUIT FOR TYPE OF TELEPHONE

摘要

The circuit for automatically detecting the kind of a subscriber telephone (100) when starting the dialing comprises a resistor (RP) for detecting a loop formation according to the on/off state of a hook switch (110), a differential amplifier (210) for amplifying the voltage detected by the RP, and a comparator (220) for comparing the amplified voltage with a reference voltage. The comparator provides the make/brake ratio pulse according to the value of the dialing digit in case of a mechanical telephone or provides the logical level signal of the hook-off state in case of a electronic telephone.