Method and apparatus for transmitting an electrical signal...

Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Slope control of leading or trailing edge of rectangular or...

Reexamination Certificate

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Details

C327S134000

Reexamination Certificate

active

06239637

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method and to an apparatus for processing an electrical signal to compress the leading and the trailing edges of pulses contained in the electrical signal. The invention finds practical applications in systems where electrical signals are transmitted at high data rates over printed circuit boards or connectors mounted to the printed circuit board. During the transmission, electrical signals are susceptible to attenuation, harmonic distortion and dispersion, among others, that cause inter-symbol interference. The method and the apparatus provided by the present invention compensate for the distortion allowing a reliable use of high data rate transmissions over electrical interconnects.
BACKGROUND OF THE INVENTION
Modern large-scale electronics such as telecommunication or computing systems are usually comprised of many interconnected shelves of processing, access and/or memory modules. The processing, access and memory functions are usually provided by modules that plug into a large printed circuit board (PCB) referred to as a backplane. (BP) or midplane (MP) located behind the modules. Duo to the huge quantities of data available for processing and storage there is a need for ever-increasing data rates on the modules and BPs. With the advent of synchronous optical networks (SONET), telecommunication and computer systems may be linked together by optical fibres that terminate on the module faceplates. Usually, in order to make use of the data carried by the optical fibre, the module must convert the signals to electrical pulses and demultiplex (demux) them to many slower speed data streams. The highest widely used optical data rate is 10 gigabits per second (OC192). Currently, such a data stream is often demuxed by a factor of 16 or even 64 to get 16 622 megabits per second or 64 155 megabits per second streams. This level of demuxing contributes greatly to the complexity of the electro-optic and processing/switching modules and the routing density on the PCBs. In addition, the power requirements of the demux and mux units can be significant.
The industry has recognized that it is desirable to allow electrical signals at a data rate exceeding 10 gigabits per second to be transmitted over standard copper interconnect. If this could be made possible, elctro-optic modules would not require a demux function at all since the electrical signal would also be at 10 gigabits per second. Furthermore, the routing and processing hardware would be made simpler since only a fraction of the currently existing I/Os and tracks would be needed.
The principal reason that commercially available 10 gigabits per second electrical interconnect does not already exist is that the standard BP and BP connectors possess too high a level of parasitic inductance, capacitance, resistance and conductance. These result in attenuation, harmonic distortion and dispersion (to name a few) to an extent that makes sufficiently error-free transmission of data virtually impossible.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides an electrical signal transmission device, comprising an input for receiving an input electrical signal containing a succession of pulses, each pulse including a leading edge and a trailing edge, The electrical signal transmission device includes a lossy transmission pathway for conveying the pulses in the input electrical signal, the lossy transmission pathway being susceptible to induce distortions in the pulses such that the leading edges and the trailing edges of the pulses elongate and become spread over respective time intervals. The lossy transmission pathway is coupled to a signal processing unit whose function is to process the pulses to reduce the time intervals over which the leading and the trailing edges of pulses are spread. The signal processing unit releases an output signal containing the pulses of the input signal.
The advantage of this signal transmission device resides in its ability to compensate for the pulse distortion particularly at the leading and at the trailing edges that occurs when electrical signals at high data rates are sent over conductors on a printed circuit board OL connectors mounted to printed circuit boards. Accordingly, this invention is particularly useful in the context of electrical signal transmission at high data rates, such as equal or in excess of 10 gigabits per second over copper interconnects. It should be noted, however, that the inventive principle is not limited to this context of utilization, as the invention may also find applications in other contexts or environments.
In a specific nonlimiting example of implementation, tile lossy transmission pathway comprises two signal channels implemented over a printed circuit board and including copper conductors and/or electrical connectors. The channels convey identical signals with the exception that one of the signals is DC shifted negatively by a magnitude that is approximately equal to the peak voltage level of the signal. The signal processing unit of the signal transmission device includes two functional units, namely a first functional unit and a second functional unit. One of the channels of the lossy transmission pathway is connected to the first functional unit while the other channel is connected to the second functional unit. The first functional unit is operative to compress the leading edge of pulses in the input signal by passing the signal through a non-linear signal transmission path. The non-linear signal transmission path is characterized by a signal propagation delay dependent upon an absolute value of the voltage level in the signal. The parts of the signal that are at a relatively high voltage are delayed less than the parts of the signal that are at a relatively low voltage. For example, the leading edge of a pulse has a relatively low voltage bottom segment that ramps-up to a relatively high voltage top segment. The high voltage top segment is transmitted faster through the non-linear signal transmission path than the low voltage bottom segment. This behavior compensates for spreading of the leading edge induced in the signal by the copper interconnects as a result of attenuation, harmonic distortion and dispersion, among others.
The second functional unit of the pulse edge compression device is responsible for compressing the trailing edge of the pulses in the signal that is DC negatively shifted. The purpose of the negative DC shifting of the signal is to transform the low voltage regions of the signal into high voltage regions (in absolute value terms) This has the effect of changing the behavior of the non-linear propagation path of the second functional unit comparatively to the first functional unit in that edge compression is effected on the trailing edge rather than on the leading edge.
Therefore, the output of the first functional unit is a signal containing a succession of pulses where the leading edges of those pulses have been compressed and the trailing edges of the pulses are expanded. The opposite signal structure is present at the output of the second functional unit. More particularly, the leading edges of the pulses are expanded while the trailing edges of the pulses arc compressed. The output signals of the functional units are passed through respective high pass filters that remove the low-frequency elements from the signals leaving only the high frequency elements. Since the compressed pulse edges are made up mostly of high frequency components, the signals released from the high pass filters include a succession of short pulses, where each short pulse corresponds to a leading edge or to a trailing edge of a pulse in the input signal. The output signals from the high pass filters are combined to reconstitute the pulses from the input signal. Specifically, the output signals are combined to produce a train of short positive and negative pulses, which correspond to the rising and falling edges of the input signal.
The invention also provides a method for transmitting an elec

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