Abstract: An electronic circuit is disclosed which passes current to an output node when the rate of change of voltage on an input node exceeds a predetermined value. A differentiating network is serially disposed between a voltage-driven source and a normally cut off common base amplifier to monitor the rate of change of the voltage signal. The common base amplifier is prebiased to conduct when the output of the differentiator exceeds the threshold value. The circuit may include temperature compensation means and adjustable prebiasing means. When a pair of such circuits are utilized in a differential or push-pull mode, the displacement current in the pair of capacitors has a serial conduction path for rates of change of input voltage below the threshold value, and a parallel conduction path above the threshold value.