Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Reexamination Certificate
2002-10-09
2003-09-23
Ton, My-Trang Nu (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
C327S376000
Reexamination Certificate
active
06624682
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to the field of input/output (I/O) circuitry for an integrated circuit (IC), and in particular to I/O circuitry for an IC that provides an adequate current path between an I/O pad and a source of potential, and guarantees a known state on the I/O pad, during times when the I/O voltage is floating.
Many ICs have I/O interface circuitry and pads that are supplied an I/O voltage, V
I/O
, while the core logic it interfaces to is supplied with a core voltage, V
core
. When such ICs are used in certain applications, the pad of the IC is required to be capable of sinking a specified amount of current while the I/O supply voltage is floating. Also during these times, it is advantageous to have a known state needed on the pad. Since the pad's driving and protection circuitry are controlled by the I/O voltage, there is no guaranteed that these circuits will provide an adequate current path between the pad and a source of potential (e.g., ground) when the I/O voltage is floating.
Thus, it would be advantageous to have a means of providing an adequate current path and known state for an IC's I/O pad during periods when the I/O voltage is floating.
SUMMARY OF THE INVENTION
In one aspect of the present invention, an integrated circuit is provided. The integrated circuit has an I/O pad and at least one I/O transistor coupled between the I/O pad and a source of potential. A combinatorial circuit is connected to the I/O transistor's gate to turn on the transistor during periods that an I/O voltage is likely to be floating. Turning the I/O transistor on pulls the pad to a known state and provides a current path between the pad and the source of potential.
In a particular embodiment, the combinatorial circuit has a first input coupled to an output signal of the integrated circuit and a second input coupled to an enable signal. A particular state of the output signal and the enable signal causes the combinatorial circuit to output a signal that turns the I/O transistor on.
Another aspect of the present invention provides a method of pulling an I/O pad to a known state and providing a current path between the pad and a source of potential during periods when an I/O voltage is likely to be floating. At least one I/O transistor coupled between the I/O pad and a source of potential is provided. Also provided is a combinatorial circuit connected to the I/O transistor and an enable signal such that the combinatorial circuit turns on the transistor in response to the enable signal being in a first state. The enable signal is switched into a first state during periods when an I/O voltage is likely to be floating.
REFERENCES:
patent: 4745305 (1988-05-01), Crafts
patent: 5973530 (1999-10-01), Morris et al.
patent: 6147510 (2000-11-01), Pappert
patent: 6300800 (2001-10-01), Schmitt et al.
patent: 6373282 (2002-04-01), Drapkin et al.
patent: 6400546 (2002-06-01), Drapkin et al.
Boutaud Frederic
FitzPatrick Sean M.
Krivacek Paul D.
Analog Devices Inc.
Nu Ton My-Trang
Samuels , Gauthier & Stevens, LLP
LandOfFree
Method and an apparatus to actively sink current in an... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and an apparatus to actively sink current in an..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and an apparatus to actively sink current in an... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3011316