Pulse or digital communications – Systems using alternating or pulsating current – Antinoise or distortion
Reexamination Certificate
2002-07-26
2004-05-04
Corrielus, Jean B. (Department: 2631)
Pulse or digital communications
Systems using alternating or pulsating current
Antinoise or distortion
C375S224000
Reexamination Certificate
active
06731691
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to high speed networking transceivers and, more particularly to gigabit Ethernet transceivers having reduced power consumption, efficient clock domain partitioning and able to decode input symbols within a symbol period with a minimum of computational intensity.
DESCRIPTION OF THE RELATED ART
In recent years, local area network (LAN) applications have become more and more prevalent as a means for providing local interconnect between personal computer systems, work stations and servers. Because of the breadth of its installed base, the 10BASE-T implementation of Ethernet remains the most pervasive if not the dominant, network technology for LANs. However, as the need to exchange information becomes more and more imperative, and as the scope and size of the information being exchanged increases, higher and higher speeds (greater bandwidth) are required from network interconnect technologies. Among the highspeed LAN technologies currently available, fast Ethernet, commonly termed 100BASE-T, has emerged as the clear technological choice. Fast Ethernet technology provides a smooth, non-disruptive evolution from the 10 megabit per second (Mbps) performance of 10BASE-T applications to the 100 Mbps performance of 100BASE-T. The growing use of 100BASE-T interconnections between servers and desktops is creating a definite need for an even higher speed network technology at the backbone and server level.
One of the more suitable solutions to this need has been proposed in the IEEE 802.3ab standard for gigabit Ethernet, also termed 1000BASE-T. Gigabit Ethernet is defined as able to provide 1 gigabit per second (Gbps) bandwidth in combination with the simplicity of an Ethernet architecture, at a lower cost than other technologies of comparable speed. Moreover, gigabit Ethernet offers a smooth, seamless upgrade path for present 10BASE-T or 100BASE-T Ethernet installations.
In order to obtain the requisite gigabit performance levels, gigabit Ethernet transceivers are interconnected with a multi-pair transmission channel architecture. In particular, transceivers are interconnected using four separate pairs of twisted Category-5 copper wires. Gigabit communication, in practice, involves the simultaneous, parallel transmission of information signals, with each signal conveying information at a rate of 250 megabits per second (Mb/s). Simultaneous, parallel transmission of four information signals over four twisted wire pairs poses substantial challenges to bidirectional communication transceivers, even though the data rate on any one wire pair is “only” 250 Mbps.
In particular, the gigabit Ethernet standard requires that digital information being processed for transmission be symbolically represented in accordance with a five-level pulse amplitude modulation scheme (PAM-5) and encoded in accordance with an 8-state Trellis coding methodology. Coded information is then communicated over a multi-dimensional parallel transmission channel to a designated receiver, where the original information must be extracted (demodulated) from a multi-level signal. In gigabit Ethernet, it is important to note that it is the concatenation of signal samples received simultaneously on all four twisted pair lines of the channel that defines a symbol. Thus, demodulator/decoder architectures must be implemented with a degree of computational complexity that allows them to accommodate not only the “state width” of Trellis coded signals, but also the “dimensional depth” represented by the transmission channel.
Computational complexity is not the only challenge presented to modern gigabit capable communication devices. A perhaps greater challenge is that the complex computations required to process “deep” and “wide” signal representations must be performed in an almost vanishingly small period of time. For example, in gigabit applications, each of the four-dimensional signal samples, formed by the four signals received simultaneously over the four twisted wire pairs, must be efficiently decoded within a particular allocated symbol time window of about 8 nanoseconds.
Successfully accomplishing the multitude of sequential processing operations required to decode gigabit signal samples within an 8 nanosecond window requires that the switching capabilities of the integrated circuit technology from which the transceiver is constructed be pushed to almost its fundamental limits. If performed in conventional fashion, sequential signal processing operations necessary for signal decoding and demodulation would result in a propagation delay through the logic circuits that would exceed the clock period, rendering the transceiver circuit non-functional. Fundamentally, then, the challenge imposed by timing constraints must be addressed if gigabit Ethernet is to retain its viability and achieve the same reputation for accurate and robust operation enjoyed by its 10BASE-T and 100BASE-T siblings.
In addition to the challenges imposed by decoding and demodulating multilevel signal samples, transceiver systems must also be able to deal with intersymbol interference (ISI) introduced by transmission channel artifacts as well as by modulation and pulse shaping components in the transmission path of a remote transceiver system. During the demodulation and decoding process of Trellis coded information, ISI components are introduced by either means must also be considered and compensated, further expanding the computational complexity and thus, system latency of the transceiver system. Without a transceiver system capable of efficient, high-speed signal decoding as well as simultaneous ISI compensation, gigabit Ethernet would likely not remain a viable concept.
In a Gigabit Ethernet communication system that conforms to the 1000BASE-T standard, gigabit transceivers are connected via Category 5 twisted pairs of copper cables. Cable responses vary drastically among different cables. Thus, the computations, and hence power comsumption, required to compensate for noise (such as echo, near-end crosstalk, far-end crosstalk) will vary widely depending on the particular cable that is used.
In integrated circuit technology, power consumption is generally recognized as being a function of the switching (clock) speed of transistor elements making up the circuitry, as well as the number of component elements operating within a given time period. The more transistor elements operating at one time, and the higher the operational speed of the component circuitry, the higher the relative degree of power consumption for that circuit. This is particularly relevant in the case of Gigabit Ethernet, since all computational circuits are clocked at 125 Mhz (corresponding to 250 Mbps per twisted pair of cable), and the processing requirements of such circuits require rather large blocks of computational circuitry, particularly in the filter elements. Power consumption figures in the range of from about 4.5 Watts to about 6.0 Watts are not unreasonable when the speed and complexity of modern gigabit communication circuitry is considered.
Pertinent to an analysis of power consumption is the realization that power is dissipated, in integrated circuits, as heat. As power consumption increases, not only must the system be provided with a more robust power supply, but also with enhanced heat dissipation schemes, such as heat sinks (dissipation fins coupled to the IC package), cooling fans, increased interior volume for enhanced air flow, and the like. All of these dissipation schemes involve considerable additional manufacturing costs and an extended design cycle due to the need to plan for thermal considerations.
Prior high speed communication circuits have not adequately addressed these thermal considerations, because of the primary necessity of accommodating high data rates with a sufficient level of signal quality. Prior devices have, in effect, “hard wired” their processing capability, such that processing circuitry is always operative to maximize signal quality, whether that degree of processing is require
Abnous Arthur
Agazzi Oscar E.
Creigh John L.
Hatamian Mehdi
Kruse David E.
Broadcom Corp.
Corrielus Jean B.
McAndrews Held & Malloy Ltd.
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