| 摘要 |
<p>Switched body circuitry is provided to prevent a system I/O from being effected by the loss of power supply or ground to an MOS integrated circuit within the system. A semiconductor substrate of a first conductivity type has formed therein a well region of a second conductivity type opposite to that of the first conductivity type. First, second, third and fourth spaced-apart shallow diffusion regions of the first conductivity type are formed at the surface of the well region. The first and fourth of these regions are electrically connected to the well region through ohmic contacts. A first gate electrode, which overlies a first channel region between the second diffusion region and the third diffusion region, is connected to provide the proper logic function on the data line. This first gate electrode and the second and third diffusion regions combine to form an MOS transistor which is either an input pull up or pull down device or an output pull up or pull down driver of the MOS circuit. An I/O pad of the MOS circuit is connected to the second region and to a second gate electrode which overlies a second channel region between the third diffusion region and the fourth diffusion region. Thus, the second gate electrode and the third and fourth diffusion regions combine to define a first MOS switched body transistor. A power supply pad of the MOS circuit is connected to the third diffusion region and to a third gate electrode which overlies a third channel region between the first diffusion region and the second diffusion region. Thus, the third gate electrode and the first and second diffusion regions combine to define a second MOS switched body transistor. These two transistors control the potential of the I/O transistor's body (P-well or N-well) so as to keep the parasitic and ESD protection bipolar transistors and diode turned off during loss of power or ground to the chip.</p> |
