Electricity: electrical systems and devices – Safety and protection of systems and devices – Load shunting by fault responsive means
Reexamination Certificate
1998-12-10
2001-01-30
Leja, Ronald W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Load shunting by fault responsive means
Reexamination Certificate
active
06181540
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to electrostatic discharge protection arrangements for circuit devices and, more specifically, to a system and method for diverting the transmission of electrostatic discharges.
BACKGROUND OF THE INVENTION
It is well known to those skilled in the art that, during handling and testing of circuit devices, electrostatic charges can be applied to the contact pads of such a device. These charges may be subsequently discharged through the device, thereby causing damage. One solution known in the prior art for preventing damage from these electrostatic discharge (ESD) events is to connect protection devices, such as p-n junction diodes, between each contact pad and its corresponding operations circuit. Typically, one such diode leads to a voltage source V
CC
and another leads to ground. In the event a sufficient charge builds up on a contact pad, one of the two diodes will activate and direct the charge away from the operations circuit. Further, the activation of the diodes will be based on their threshold voltage (V
t
). For example, a positive charge will be diverted towards the voltage source V
CC
when the contact pad's potential exceeds one V
t
above V
CC
. Alternatively, a negative charge will be diverted toward ground when the contact pad's potential is one V
t
below ground.
Occasionally, it is desirable to drive an operations circuit at voltages beyond the one V
t
parameters. Those of ordinary skill in the art know that the trip point for shunting charges can be changed by adding diodes to the configuration described above. Nevertheless, based on prior art teachings, changing the trip point for several operations circuits would require adding diodes for each contact pad. Unfortunately, these diodes, as well as other ESD protection devices, require a significant amount of die space. Thus, it would be desirable to provide ESD protection, while at the same time allowing for the alteration of the trip point without the space requirements necessary in the prior art.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides for ESD protection and trip point alteration of a circuit device. Several embodiments of the present invention are designed to accommodate a circuit device having a plurality of terminals, each leading to a different operations circuit. In one preferred embodiment of the present invention, an ESD protection device is connected to each terminal. These ESD protection devices, in turn, are commonly coupled to a stack of additional ESD protection devices. The number of devices in this stack depends upon the particular trip point to be established. Thus, in addition to protecting the device from ESD, the shared stack in this preferred embodiment has the added advantage of reducing the number of ESD protection devices needed to safeguard the operations circuits. Further, this configuration allows for simultaneous trip point alteration for different operations circuits, once again reducing the number of ESD protection devices needed to do so. The present invention also encompasses various methods for achieving these advantages.
REFERENCES:
patent: 5293057 (1994-03-01), Ho
patent: 5315255 (1994-05-01), Bettinger
patent: 5654862 (1997-08-01), Worley
patent: 5721658 (1998-02-01), Ma
Input/Output Electrostatic Discharge Protection For Devices With Multiple Individual Power Groups Serial No. 08/961,341, filed Oct. 30, 1997, Docket No. 95-0863.01, Manny Ma (Continuation of Patent No. 5,721,658, issued Feb. 24, 1998, Serial No. 08/625,333, Docket No. 95-0863).
Schoenfeld Aaron M.
Wilson Alan J.
Brantley Charles
Leja Ronald W.
Micro)n Technology, Inc.
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