Ring trip circuit for subscriber telephone

Abstract From the Canadian patent

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, for detecting a voltage difference between both ends of a ringer sending resistor and having a circuit converting the voltage difference to a current difference, the voltage difference varying in response to an on-hook state or an off-hook state of the telephone, and a state detecting circuit for detecting the on-hook state or the off-hook state in response to a value of the voltage difference. The voltage …