The invention relates generally to metal-oxide-semiconductor (MOS) integrated circuits and relates more particularly to an improved MOS output buffer in such a circuit.
Output buffers implemented in bipolar integrated circuit technology have sometimes included current responsive bipolar means and the like for limiting output currents from the buffers for selected purposes. However, MOS devices are characteristically high voltage, low current, voltage-responsive devices and MOS output buffers have not typically had to deal with currents of any substantial magnitude. It is now found that when MOS integrated circuits are adapted to meet certain high performance requirements under widely varying operating conditions in automotive vehicle control applications and the like, MOS transistors capable of providing desired output currents under certain worst case conditions tend to provide excessive currents under other conditions which might exceed the capacities of circuit busses it would be practical to provide on an MOS type of integrated circuit chip. In some applications, the excessive currents can occur briefly during normal operation and can result in poor circuit reliability over a suitable service life. In other cases, the excessive currents can occur through inadvertence by shorting during testing or troubleshooting or the like and can result in catastrophic failure of chip buss means.