Output driver circuit for high speed digital signal transmission

Abstract

An output driver circuit capable of driving its data output terminal to a digital logic level high, capable of driving its data output terminal to a digital logic level low, and capable of tristating its data output terminal has an output stage comprising a pullup transistor and a pulldown transistor. The two pullup and pull down transistors are coupled in series between two drive transistor circuits. In one aspect of the invention, the pullup and pulldown drive transistor circuits provide momentary low impedance connection of the pullup and pulldown transistors to the respective pullup and pulldown voltage sources during the initial switching waveforms of the digital signal. After the initial switching of the digital signal, the pullup and pulldown drive transistor circuits provide precise V.sub.OH and V.sub.OL voltage output levels and provide high impedance filtering of voltage supply line and ground line noise. In another aspect of the invention, the high frequency response of the output is enhanced by auxiliary pullup and pulldown drivers in parallel with the pullup and pulldown output transistors. These auxiliary pullup and pulldown drivers reduce the switching time of the digital signal output to provide increased frequency response even in a high capacitance loaded environment.