Output buffer circuit with signal feed forward for reducing switching

Abstract

An output buffer circuit reduces switching induced noise in integrated circuit devices. A pulldown feed forward circuit is coupled between the input and the output pulldown transistor. The pulldown feed forward circuit bypasses at least some of the intermediate circuit elements of the output buffer circuit. The pulldown feed forward circuit initiates a relatively small sinking current through the output pulldown transistor in response to a first signal at the input before the intermediate circuit elements initiate relatively large sinking current through the output pulldown transistor means. A pullup feed forward circuit is coupled between the input and the output pullup transistor means. The pullup feed forward circuit bypasses at least some of the intermediate circuit elements of the output buffer circuit. The pullup feed forward circuit initiates a relatively small sourcing current through the output pullup transistor means in response to a second signal at the input before the intermediate circuit elements initiate the relatively large sinking current through the output pullup transistor. The output pulldown may include a relatively large current carrying capacity primary pulldown transistor element and a relatively small current carrying capacity secondary pulldown transistor element. The primary pulldown predriver is coupled to drive the primary pulldown transistor element, and the secondary pulldown predriver is coupled to drive the secondary pulldown transistor element. A similar circuit arrangement is provided for output pullup.