A driver amplifier for a bus feeds single polarity signals of controlled slew rate to the bus. The slew rate control is effected by a feedback capacitor connected from the output to the input of the amplifier. A clamp is provided for selectively connecting the input of the amplifier through a low impedance path to a point of reference voltage so that when the amplifier is quiescent signals on the bus cannot be fed through the capacitor to turn on the amplifier. A current source and a switchable current sink are connected to the input of the amplifier to change the capacitor to produce the slew rate controlled transitions. Another driver amplifier of the same design but using components of the opposite conductivity type can be used to apply signals of the opposite polarity to the same bus.