Output driver circuit with body bias control for multiple power supply

Abstract

A push-pull output driver including two transistors in series, one transistor having its body bias controlled by logic circuitry commanded by the driver input. The driver has a pair of transistors in series, the transistor inputs being complementary to create a push-pull amplifier. A switching transistor is controlled by the inverse of the driver input signal and acts as a switch at the pull-up transistor well-tie. When the driver input is high, the switching transistor is off allowing the well-tie to the pull-up transistor to be connected to the driver output. When the input is low, the switching transistor turns on, switching the well-tie of the pull-up transistor to ground. By controlling the body bias of the pull-up transistor in this way, the switching speed of the output driver is significantly increased. When the output driver is in a disabled tri-state mode, the series transistors, and the switching transistor, are turned off. A first deselect transistor provides a high voltage at the drain of a load transistor to force it into cutoff. A select transistor is turned off to isolate the pull-up transistor well-tie from the output node, and a second deselect transistor is switched on to connect it to ground. This embodiment isolates the well-tie from the driver output while in tri-state to prevent latch-up initiated by multiple power supply operation.