An active substrate driver for mixed-voltage SOI systems on a chip

High-voltage transistors in SOI that coexist with traditional low-voltage transistors enable the development of mixed-voltage (high-voltage and low-voltage) systems-on-a-chip. The parasitic back-channel transistor, however, is a critical issue in these mixed-voltage single-chip systems. The presence of high-voltage can create a situation in which the parasitic back-channel device turns on and "shorts-out" the top device inducing functional failure of the system. An active substrate driver has been designed that automatically adjusts the substrate bias voltage to a level ensuring the back-channel devices remain off. The active substrate driver should also help compensate for shifts in back-channel transistor threshold voltages induced by temperature, aging, and irradiation effects.