Pull-down driver circuit for 3.3V I/O buffer using 1.9V fabrication process

摘要

A circuit for controlling a voltage provided to a switching transistor in a voltage conversion buffer which drives a high voltage output with low voltage transistors. The circuit has two elements to it. First, a pull-up circuit pulls the gate of the switching transistor to a high voltage level in response to a first state of a control logic signal. Second, a pull-down circuit pulls the gate of the switching transistor down to an intermediate voltage in response to a second state of the control logic signal. The intermediate voltage is set to be less than the high voltage by no more than approximately the low voltage amount. The pull-down circuit is a transistor connected to a low voltage source, which limits the pull-down voltage. Additional transistors are provided to turn on and off the pull-down transistor, with a circuit connected to a fail-safe low voltage source being used to protect these transistors.