Patent
1991-03-05
1992-09-22
Lee, John D.
357 46, H01L 2702
Patent
active
051501872
ABSTRACT:
A shared protection circuit protects an MOS circuit, herein called a chip, from the destructive effects of electrostatic discharges conducted by any of the circuits input/output pins. The shared protection circuit is coupled to the high and low voltage source nodes used by the entire chip. In a preferred embodiment which protects against positive voltage electrostatic discharges, each input/output pin of the chip node is coupled by a diode to the high voltage source node so that a positive voltage transient on any input/output node will be transmitted to the high voltage source node. A Darlington pair of parasitic bipolar transistors conduct charge from the high voltage source node to the low voltage source node when turned on. A bias circuit turns on the Darlington pair of parasitic bipolar transistors when a positive voltage transient having at least a predefined magnitude occurs on the high voltage source node. As a result, the shared protection circuit will drain current from any input/output node, via the high voltage source node, when a positive voltage transient occurs thereon. The bias circuit also automatically turns off the Darlington pair of parasitic bipolar transistors after it has discharged excess voltage from the high voltage source node.
REFERENCES:
patent: 4947230 (1990-08-01), Kapoor
Lee John D.
VLSI Technology Inc.
Wise Robert E.
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