Electricity: electrical systems and devices – Safety and protection of systems and devices – Transient responsive
Reexamination Certificate
1999-09-02
2001-09-11
Huynh, Kim (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Transient responsive
C361S056000
Reexamination Certificate
active
06288885
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to electronic circuits and more particularly, to electrostatic discharge (“ESD”) protection circuits.
BACKGROUND OF THE INVENTION
It is well recognized in the electronics industry that electrostatic discharge (“ESD”) can severely damage integrated circuit devices. While electrical discharges as low as 30 volts can damage semiconductor integrated circuit (“IC”) devices, electrostatic discharges of several hundred volts can occur during the routine handling of printed circuit boards to which IC devices are attached.
In recognition of the potential for ESD voltages damaging sensitive semiconductor devices, many ICs are provided with on-chip ESD protection circuitry adapted to prevent ESD voltages from damaging other on-chip circuitry. Typically, such circuitry is provided for each individual pin of the integrated circuit. Those of ordinary skill in the art will be familiar with a great many different types and implementations of on-chip ESD protection circuitry. A common approach is to provide circuitry responsive to voltages above a certain threshold to divert such voltages directly to a ground terminal, thereby avoiding other circuitry on the IC. An example of this is proposed in U.S. Pat. No. 4,692,781.
Another common method of avoiding ESD damage to semiconductor devices is to add external (i.e., off-chip) ESD protection circuitry to the printed circuit boards upon which one or more ICs are disposed. Such external ESD protection circuitry is designed to divert any electrostatic discharge away from operational circuitry and toward a ground terminal. Such external ESD protection circuitry is typically made up of discrete components attached to the printed circuit board.
There are perceive disadvantages to the aforementioned methodology for avoiding ESD damage to ICs mounted on printed circuit boards. First, the discrete components that make up the ESD protection circuitry occupy space on the printed circuit board, thereby reducing the amount of space available for operational circuitry. Second, designing an ESD protection circuit for a printed circuit board increases the cost of designing that printed circuit board. Finally, such external ESD protection circuitry may not provide any ESD protection when the printed circuit board is not attached to a solid ground line. For example, a printed circuit board is not attached to a ground line when it is being shipped from the manufacturer to a customer, and is therefore vulnerable during shipping to ESD-related damage.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the foregoing perceived disadvantages.
SUMMARY OF THE INVENTION
The invention, in its various embodiments is a method and apparatus for electrostatic discharge protection. In accordance with one aspect of the present invention, an ESD protection device in the form of an integrated circuit and capable of providing electrostatic discharge protection to other operational circuitry on a printed circuit is provided. The ESD protection device includes an input coupled to a possible source of electrostatic discharge, for example, one or more of the conductive traces interconnecting the other operational components on the board. Further, the ESD protection device includes an output coupled to the operational circuitry on the printed circuit board, a capacitance structure between the input and the output, and a switch in series with the capacitance structure.
In accordance with another aspect of the invention, a method for protecting a printed circuit board from electrostatic discharge is provided. The method comprises switching the discharge to a capacitance structure for subsequent dissipation into the printed circuit board.
REFERENCES:
patent: 5287241 (1994-02-01), Puar
patent: 5369552 (1994-11-01), Barnes et al.
patent: 5784242 (1998-07-01), Watt
patent: 5959821 (1999-09-01), Voogel
patent: 5970321 (1999-10-01), Hively
patent: 5991135 (1999-11-01), Saleh
patent: 6060752 (2000-05-01), Williams
Jiang Tongbi
Kao David Y.
Huynh Kim
Kress Hugh R.
Micro)n Technology, Inc.
Winstead Sechrest & Minick
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