| 摘要 |
PCT No. PCT/JP88/00607 Sec. 371 Date Feb. 21, 1989 Sec. 102(e) Date Feb. 21, 1989 PCT Filed Jun. 18, 1988 PCT Pub. No. WO88/10542 PCT Pub. Date Dec. 29, 1988.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 a 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 DIFFERENCE 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 the on-hook state or the off-hook state of the telephone, and a state detecting circuit (3) for detecting the on-hook 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.
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