Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Reexamination Certificate
2000-01-31
2001-10-09
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
C327S312000, C327S313000, C361S090000
Reexamination Certificate
active
06300815
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to dampening circuits, and more particularly to a voltage reference overshoot protection circuit to dampen residual device, e.g. backplane, energy during switching operations.
2. Description of the Prior Art
Dampening circuits are well known in the art. The type of dampening circuit used is dependent upon the particular application. One application of dampening circuits is associated with unwanted ringing in a backplane. Recent advancements in backplane technology have made higher switching speeds possible. Modern trends indicate that improvements in switching speeds associated with backplanes will not only be desirable, but necessary, in order to accommodate the higher CPU speeds utilized in state of the art computers and related peripherals, among other devices.
One source of ringing in backplanes is associated with a low to high switching transition of a backplane driver voltage. Those skilled in the art of backplane technology have generally used edge rate control techniques to minimize the ringing in a backplane during a backplane driver output signal low to high switching transition. Edge rate control techniques are used to increase the rise and fall times of the backplane driver output signal. Although these known techniques have proven adequate in the past, such techniques are not able to accommodate the high speeds necessary to provide backplanes that are functional with higher speed computers, peripherals and other digital devices presently being designed and produced. These known edge rate control dampening techniques are problematic in that they reduce the bandwidth necessary to accommodate the higher data transmission rates and shorter propagation delay times generally associated with modern communication devices and protocols.
In view of the foregoing, a need exists for a dampening circuit capable of eliminating or substantially reducing unwanted ringing in devices such as backplanes, among other like devices. The bandwidth capabilities of such devices can then be optimized to accommodate higher data transmission speeds than that achievable using conventional edge rate control techniques generally known in the art.
SUMMARY OF THE INVENTION
The present invention is directed to a dampening circuit architecture capable of substantially reducing the ringing voltage injected into a driven device, e.g. backplane, associated with a driver circuit such as a backplane driver. One preferred embodiment of the present invention is a voltage reference overshoot protection circuit that reduces the unwanted ringing in a backplane. This is achieved without the aid of an internally controlled bias generator.
A simple open drain output driver is used to help summarize the present invention. In one embodiment, an open drain output driver is coupled to a supply voltage V
TT
via a pull-up resistor connected to a backplane. Thus, when the open drain output driver is turned off, it will be pulled to a “high” state via the supply voltage V
TT
. If this low to high transition has a fast edge rate, unwanted ringing can occur in the backplane.
The present invention substantially reduces the unwanted ringing in the backplane as follows. One preferred embodiment of the present invention comprises a p-channel transistor having a gate voltage V
REF
, provided by an external voltage source. When the voltage provided by the open drain output driver rises above the gate voltage V
REF
, plus the voltage threshold of the p-channel transistor, the p-channel transistor will start to turn “on” and supply a gate voltage to an n-channel dampening transistor. As the ringing gets higher, more gate voltage is supplied to the n-channel dampening transistor, thereby pulling the open drain output driver voltage down and counteracting the undesirable ringing in the backplane caused by the open drain output driver overshoot.
In view of the foregoing descriptions, another preferred embodiment of the present voltage reference overshoot dampening circuit comprises:
a first transistor capable of receiving a reference voltage signal and configured to receive an oscillating voltage signal such that the first transistor can pass a current proportional to the oscillating voltage signal there through when the oscillating voltage signal exceeds a level determined by the reference voltage signal and a turn-on voltage signal associated with the first transistor; and
a second transistor configured to receive the oscillating voltage signal and the current passed by the first transistor such that the second transistor is capable of reducing the oscillating voltage signal in proportion to a current received from the first transistor.
Another preferred embodiment of the present voltage reference overshoot dampening circuit comprises:
a first transistor configured to receive a reference voltage and further configured to receive a ringing voltage such that the first transistor can generate a control voltage when the ringing voltage exceeds a level determined by the reference voltage and a turn-on voltage associated with the first transistor; and
a second transistor configured to receive the control voltage generated by the first transistor such that the second transistor is capable of reducing the ringing voltage received by the first transistor.
Yet another preferred embodiment of the present voltage reference overshoot dampening circuit comprises:
a p-channel transistor having a drain, a gate configured to receive a reference voltage and a source configured to receive a ringing voltage such that the first transistor can generate a variable drain voltage when the ringing voltage exceeds a level determined by the reference voltage and the p-channel transistor turn-on voltage; and
a first n-channel transistor having a gate configured to receive the variable drain voltage generated by the p-channel transistor and further having a source configured to receive the ringing voltage such that the first n-channel transistor is capable of changing the ringing voltage received by the p-channel transistor in response to a change in the variable drain voltage generated by the p-channel transistor.
Still another preferred embodiment of the present invention comprises:
means for receiving a ringing voltage and generating a variable control voltage when the ringing voltage exceeds a predetermined level such that the variable control voltage amplitude at a particular moment in time is dependent on the ringing voltage amplitude at the particular moment in time; and
means for receiving the variable control voltage and changing the ringing voltage amplitude at the particular moment in time in response thereto.
Yet another preferred embodiment of the present invention comprises:
a first transistor configured to receive a reference voltage and a ringing voltage such that the first transistor can generate a control current having a value dependent upon the ringing voltage amplitude when the ringing voltage amplitude exceeds a level determined by the reference voltage and a turn-on voltage associated with the first transistor; and
a second transistor configured to receive the ringing voltage and the control current generated by the first transistor such that the second transistor is capable of changing the ringing voltage amplitude in response to the control current received from the first transistor.
Thus, in one aspect of the invention, an overshoot protection circuit substantially reduces unwanted ringing in a device such as a backplane without the aid of an internally controlled bias generator.
In still another aspect of the invention, an overshoot protection circuit substantially reduces unwanted ringing in a device without impairment of “off” state current specifications.
REFERENCES:
patent: 3867649 (1975-02-01), Cochran
patent: 5066875 (1991-11-01), Ueno et al.
patent: 5534811 (1996-07-01), Gist et al.
patent: 5793241 (1998-08-01), Sanzo et al.
patent: 6018202 (2000-01-01), Meinders
Eyck Timothy A. Ten
Hinterscher Eugene B.
Brady III Wade James
Cunningham Terry D.
Holmbo Dwight N.
Luu An T.
Telecky , Jr. Frederick J.
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