Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Reexamination Certificate
1999-10-08
2001-06-05
Le, Dinh T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
C327S099000, C327S141000, C327S165000, C327S168000
Reexamination Certificate
active
06242961
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to methods and circuits for restoring a drooped DC signal, and, in particular, methods and circuits for restoring a drooped DC signal using both asynchronous and synchronous methods.
2. Description of the Prior Art
A DC signal may have both positive and negative amplitudes. As a DC signal travels from a transmitter to a receiver via a long medium (such as a cable), if the DC signal is not balanced, the signal will droop as it travels through a transformer. This situation is also know as base-line wander. For example, referring to
FIG. 1
a,
a transmitter
10
is connected to a transformer
15
and out to a cable
14
. On the other end of the cable
14
, there is another transformer
17
connected to a receiver. Drooping occurs after both transformers. At node A
16
, a point near the transmitter
10
, as is illustrated by
FIG. 1
b,
there is almost no drooping. After passing through the transformers,
15
and
17
, at a point near the receiver
12
, node B
18
, there may be significant dropping as is illustrated by
FIG. 1
c.
Note that the illustrated signal waveforms are MLT3 signals used in network protocols. The present invention as is disclosed below is not limited to MLT3 signals.
In a drooping situation, both the positive amplitude and the negative amplitude drifts toward zero volt. In order to properly process the received signal, a receiver should restore the signal before further processing the signal. Otherwise, the equalizer cannot generate the correct results. Therefore, it is desirable to have methods and circuit for restoration of a drooped signal.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide methods and circuits for restoring a drooped signal.
It is another object of the present invention to provide methods and circuits asynchronous restoration of a drooped signal.
It is yet another object of the present invention to provide methods and circuits synchronous restoration of a drooped signal.
It is still another object of the present invention to provide methods and circuits for restoration of a drooped signal using both asynchronous and synchronous methods.
Briefly, the present invention in one embodiment discloses a circuit for the restoration of a drooped signal. In the asynchronous mode, the drooped signal can be restored by detecting the peak of the received signal and the peak of the inverted received signal and take the difference between the two peaks. This difference signal is fed back the equalizer. In the synchronous mode, the drooped signal is sliced and passed to a regeneration circuit. The regenerated signal is compared with the equalized signal to generate a difference signal, again fed back to the equalizer. The sliced signal is also fed to a clock recovery circuit which recovers the clock signal embedded in the received signal. The two modes can be combined to provide an optimal method for the restoration of a drooped signal.
An advantage of the present invention is that it provides methods and circuits for restoring a drooped signal.
Another advantage of the present invention is that it provides methods and circuits asynchronous restoration of a drooped signal.
Yet another advantage of the present invention is that it provides methods and circuits synchronous restoration of a drooped signal.
Still another advantage of the present invention is that it provides methods and circuits for restoration of a drooped signal using both asynchronous and synchronous methods.
These and other features and advantages of the present invention will become well understood upon examining the figures and reading the following detailed description of the invention.
REFERENCES:
patent: 5122677 (1992-06-01), Sato
Fang Wen
Liu James
Wu Wen-Chung
Altima Communication, Inc.
Arent Fox Kintner & Plotkin & Kahn, PLLC
Le Dinh T.
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