Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Unwanted signal suppression
Reexamination Certificate
1998-06-10
2002-06-11
Le, Dinh T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Unwanted signal suppression
C327S552000, C341S143000
Reexamination Certificate
active
06404276
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to computer systems and, more particularly, to an apparatus and method for tuning an on-chip filter used in transmitting signals, that meet government emission standards, from a computer system to a transmission medium.
2. Description of the Related Art
Many computer systems today are utilized in a networked configuration where each networked computer can transmit data to other computers on the same network. Various systems and related protocols have been developed over the years to implement such networks, such as Token Ring, Ethernet, and ATM. Depending upon which network is being used, certain requirements must be met, such as the types of hardware used and particular data characteristics.
The Ethernet local area network (LAN) is one of the most popular and widely used computer networks in the world. Since the beginnings of the Ethernet in the early 1970's, computer networking companies and engineering professionals have continually worked to improve Ethernet product versatility, reliability and transmission speeds. To ensure that new Ethernet products were compatible and reliable, the Institute of Electrical and Electronic Engineers (IEEE) formed a working group to define and promote industry LAN standards. Today, the IEEE has various Ethernet working groups that are responsible for standardizing the development of new Ethernet protocols and products under an internationally well known LAN standard called the “IEEE 802.3 standard.”
Currently, there are a wide variety of standard compliant Ethernet products used for receiving, processing and transmitting data over Ethernet networks. By way of example, these networking products are typically integrated into networked computers, network interface cards (NICs), routers, switching hubs, bridges and repeaters. Until recently, common data transmission speeds over Ethernet networks were 10 megabits per second (Mbps). However, to meet the demand for faster data transmission speeds, in May 1995 the IEEE 802.3 standards committee officially introduced another standard, the “IEEE 802.3u standard,” for a 100BASE-T system capable of performing data transmissions at up to about 100 Mbps. When operating with unshielded twisted pair (UTP) cable as a transmission medium, these networks are commonly referred to as 10BASE-T and 100BASE-T networks.
FIG. 1A
is a diagrammatic representation of two computers
102
,
104
, which are connected through a network
105
. The network
105
can include, for example, other computers, network hubs, network routers, servers or the like. Of course, a single cable connecting the computers
102
and
104
can alternatively be used. Each computer
102
and
104
includes systems to facilitate exchange of information to and from the computer. These systems are diagrammatically illustrated by an open systems interconnection (OSI) layered model
106
, that was developed by the International Organization for Standards (ISO) for describing the exchange of information between layers. The OSI layered model
106
is particularly useful for separating the technological functions of each layer, and thereby facilitating the modification or update of a given layer without detrimentally impacting the functions of neighboring layers.
Multiple layers (not shown) defined in the OSI model
106
are responsible for various functions, such as providing reliable transmission of data over a network; routing data between nodes in a network; and initiating, maintaining and terminating a communication link between users connected to the nodes. In addition, these layers are responsible for performing data transfers within a particular level of service quality; controlling when users are able to transmit and receive data depending on whether the user is capable of fall-duplex or half-duplex transmission; translating, converting, compressing and decompressing data being transmitted across a medium; and providing users with suitable interfaces for accessing and connecting to a network. Further, the lower portion of the OSI model
106
includes a media access control layer (MAC)
107
which generally schedules and controls the access of data to a physical layer (PHY)
108
.
At a lowermost layer of OSI model
106
, PHY layer
108
is responsible for encoding and decoding data into signals that are transmitted across a particular medium, such as a cable
110
. To enable transmission to a particular medium, the PHY layer
108
includes a physical connector which is configured and operable to receive the cable
110
. Also, the cable
110
can take various forms, including that of an unshielded twisted pair (UTP) cable.
When signals are passed through the cable
110
from the PHY layer
108
, the potential exists for portions of the signal to emit from the cable
110
when it is an unshielded type, such as a UTP cable. More specifically, the portions which may emit from the cable typically are high frequency components of the signal. Because such emissions can interfere with other electrical devices in the vicinity of the cable
110
, the U.S. government has developed stringent emission standards (commonly known as FCC Class A Requirements) to avoid such interference. To comply with such standards, in a the PHY layer the high frequency signal components are typically removed from the primary signal before transmission on the cable
110
. As is known in the art, this is commonly referred to as transmit pulse shaping that is followed by reconstruction filtering.
Ethernet transmitters have typically utilized a configuration such as that shown in
FIG. 1B
to remove high frequency components from the signal before transmission through cable
110
.
FIG. 1B
schematically depicts one PHY application of an Ethernet device, specifically an Ethernet card
150
. The Ethernet card
150
includes a PC board
152
on which a transmission system, formed by various components, is mounted. Included in these components is a packaged silicon chip
154
, a filter
156
, a transformer box
158
, and a connector
160
.
The packaged silicon chip
154
is configured to convert the input binary data from the host (e.g., a computer into which the Ethernet card
150
is mounted) to a signal that can be transmitted to the cable
110
. This typically is accomplished by a data converter such as a Manchester encoder
162
and a digital-to-analog converter (DAC)
164
that is integrated on the packaged silicon chip
154
. These devices alternatively can be located on separate semiconductor chips that are each mounted onto the PC board
152
.
The Manchester encoder
162
outputs a signal having voltage swings that correspond to the binary data. The DAC
164
then converts the digital signal voltage from the Manchester encoder
162
to an analog signal voltage utilizing a reference voltage, Vref
165
. Unfortunately, due to power supply or manufacturing process variations, the reference voltage level that is internally generated can vary by as much as about 20%, which can lead to inaccurate and inconsistent signals. In an Ethernet system, this would result in not matching an “Ethernet eye” template, which is a desired Ethernet transmission characteristic.
Electrically connected to the packaged silicon chip
154
, the filter
156
operates to remove the high frequency components from the signal passed from the silicon chip
154
. This is accomplished by tuning the filter, i.e., setting a cut-off frequency of the filter
156
, with frequencies below the cut-off frequency being passed by the filter
156
. More specifically, the cut-off frequency can be determined through characteristics of the components which form the filter. Unfortunately, the cut-off frequency will vary with variations in the filter component characteristics; thus large filter component variations can undesirably lead to large cut-off frequency variations. Alternatively, the cut-off frequency can be set by phase-locked loop (PLL) tuning that is well know to those skilled in the art. Unfortunately, though, PLL
Le Dinh T.
LSI Logic Corporation
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