A circuit has an FET input stage with a first to a third FETs, two bipolar transistors in a push-pull circuit, controlled by the FET input stage, and a further FET connected to the collector of the second bipolar transistor and whose gate is in an active relationship with the input of the FET input stage, whereby the third FET is connected to the base of the second bipolar transistor. According to the invention, this circuit works as an FET TTL interface circuit, in which the other FET connected to the collector of the second bipolar transmitter operates as a clamping FET whose channel width lies within a specific range referred to that of the third FET.