ABSTRACT
Digital integrated circuits require the implementation of special input, output, and interface circuits as well. Inputs must have protection circuitry to prevent ESD damage during handling as well as transmission gates for enable/disable operation. Output pins generally require high-current output drivers and tri-state operation to allow compatibility with busses. Interface circuits are needed for voltage level shifting between circuits operating with different voltages. Input pins to an integrated circuit may be subjected to electrostatic discharge from people, other components, or equipment carrying thousands of volts. All of these bipolar devices are relatively large, and this has led to the development of ESD protection networks that can be fabricated underneath the bonding pads to conserve die area. In fact, this design is not optimized with respect to either the silicon area or the overall delay. Generally, in an optimum design, all stages have roughly equal delays.
