VARIABLE DRIVER FOR REDUCING OVERSHOOT, UNDERSHOOT, AND NOISE IN OUTPUT BUFFER

摘要

PURPOSE: A variable drive output buffer is provided to reduce undershoot, overshoot, and switching noise logic signal transitions. CONSTITUTION: A variable drive output buffer(10) includes a first driver stage(70) and a second driver stage(80), each coupled between an input node and an output node. The second driver stage includes a standard pull-up(M2) and pulldown(M1) transistor pair. The first output driver stage of the circuit is designed to propagate a substantial portion of the signal change before the pull-up or pulldown transistor of the second driver stage is turned on. The first output driver stage charges or discharges a substantial portion of the current associated with the output node so that there is little hard drive left by the time either of the pull-up or pulldown transistor is turned on by the signal change. The first driver stage preferably includes a first transition device(20) in parallel with the pulldown transistor and a second transition device(30) in parallel with the pull-up transistor. A delay stage(40) of the first driver stage propagates the input signal faster than a delay stage(50) of the second driver stage propagates that signal to the pull-up and pulldown transistors.