Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Reexamination Certificate
2002-07-12
2003-07-01
Lam, Tuan T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
C327S072000, C327S077000
Reexamination Certificate
active
06586984
ABSTRACT:
BACKGROUND
The present invention generally relates to methods and apparatuses for preventing damage to IO devices due to over voltage at pin, and more specifically relates to a method and apparatus for preventing damage to IO devices by band-limiting and source-following and using a comparator to signal a relatively small over-voltage condition on the pad.
Chips are often subject to over-voltage conditions at their input/outputs (IO's). A common method of protecting the IO's of a chip is to detect large over-voltage conditions, such as in the range of a thick-gate MOS device's Vt (i.e., 0.5-0.7 volt). Oftentimes, this amount of protection (i.e., being able to detect a 0.5-0.7 volt over-voltage condition) is not enough to adequately protect the IO's of the chip. It would be beneficial to be able to detect over-voltage conditions which are not quite as high, such as a 0.1 volt over-voltage condition at pin in order to more fully protect IO devices from being damaged as a result of an over voltage condition at pin.
OBJECTS AND SUMMARY
A general object of an embodiment of the present invention is to provide a method and apparatus for detecting a relatively small over-voltage condition at pin, such as a 0.1 volt over voltage, thereby preventing damage to IO devices due to over voltage at pin.
Another object of an embodiment of the present invention is to provide a method and apparatus where voltage levels are band-limited and source-followed, and a comparator is used to signal an over-voltage condition on the pin of an IO device.
Briefly, and in accordance with at least one of the foregoing objects, an embodiment of the present invention provides a method and circuit which provides that a source voltage and a pad voltage are band-limited and source-followed down in order to get them into the input range of a comparator, the output of which signals an over-voltage condition on the pad. The circuit provides the ability to provide the relationship between the source voltage and pad voltage to a comparator with a very small, tightly-controlled offset. This translates to the ability to detect very small over-voltage conditions on an IO. The circuit consumes little power, is highly accurate, and requires no special, expensive process options. The circuit can be used anywhere there is a desire to compare (with a small, accurate offset) two signals that are close to a source voltage, such as VDD. The circuit can also be used to compare signals close to VSS.
REFERENCES:
patent: 4524351 (1985-06-01), Kimura et al.
patent: 5378936 (1995-01-01), Kokubo et al.
patent: 5488324 (1996-01-01), Mizuta et al.
patent: 5942921 (1999-08-01), Talaga, Jr.
patent: 6008674 (1999-12-01), Wada et al.
patent: 6124732 (2000-09-01), Zilic et al.
Lam Tuan T.
LSI Logic Corporation
Trexler, Bushnell Giangiorgi, Blackstone & Marr, Ltd.
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