| 摘要 |
Disclosed is an improved ring trip circuit for a subscriber telephone, for detecting an on-hook state or an off-hook state of the telephone. The ring trip circuit can be formed in a small size and can be formed by an LSI. The ring trip circuit includes a voltage detecting circuit (2), for detecting a voltage difference ( DELTA V) between both ends of a ringer sending resistor, having a first circuit (S1, S2, A1 SIMILAR B3) converting the voltage difference to a current difference, and further having a second circuit (F) converting the current difference to a voltage, the voltage difference varying in response to an on-hook state or an off-hook state of the telephone, and a state detecting circuit (3) for detecting the on-book state or the off-hook state in response to a value of the voltage from the voltage detecting circuit. The voltage detecting circuit is formed by a plurality of current mirror circuits, each of which includes at least two transistors. The state detecting circuit includes a comparator circuit (CP1) formed by a plurality of transistors. |
