Abstract: A ring detect circuit for detecting the ring signal on a telephone line and providing and electronic signal in response thereto, typically to initiate an automatic answer function. The circuit utilizes a differential amplifier with each of the differential inputs connected across one of the tip and ring lines so that an AC voltage between the tip and ring lines will provide a differential input to the amplifier. The amplifier is maintained nominally at midrange by an appropriate reference voltage, with the amplifier normally maintained within its linear range by effectively dividing down the relatively high AC ring signal. Also capacitive coupling is used to each of the tip and ring lines for DC isolation purposes. The output of the differential amplifier is peak detected and used to drive a delay circuit to eliminate undesired responses to line transients. Appropriate selection of the differential amplifier input impedance maximizes the common mode rejection thereof.