Coded data generation or conversion – Analog to or from digital conversion – Digital to analog conversion
Reexamination Certificate
1998-02-26
2001-06-26
Williams, Howard L. (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Digital to analog conversion
Reexamination Certificate
active
06252532
ABSTRACT:
2. THE BACKGROUND OF THE INVENTION
a. The Field of the Invention
This invention relates to the field of network systems. In particular, the invention relates to a systems for reducing electromagnetic interference emissions in network interfaces.
b. Background Information
Ethernet is an industry standard (e.g., IEEE 802.3 specification) method of communicating between various devices and a local area network. For example, a computer includes a network interface card (NIC) that formats Ethernet data for transmission onto a network cable. The network cable carries the Ethernet formatted packets out to the rest of the network. The data signal is generated to comply with a particular specification for that type of Ethernet communications. For example, the Ethernet data signal might be generated to comply with the ANSI/IEEE standard 802.3 Ethernet voltage template. This voltage template applies to five and ten MHz frequency components of Ethernet data communications. Complying with the voltage template ensures that the NIC will not damage other devices connected to the cable, and ensures that other devices will be able to properly receive and decode the signals from the NIC.
One prior art NIC is shown in FIG.
1
. This NIC is available from 3COM Corporation, of Santa Clara, Calif. The NIC
100
is for generating the transmit signal
130
which corresponds to an Ethernet transmit signal. The transmit signal
130
is generated to support Manchester encoding of the Ethernet data. The transmit signal
130
is a combination of two other signals, a data signal and a pre-emphasis signal. The pre-emphasis signal adds a slight step to some of the waves in the transmit signal
130
.
The transmit signal
130
is created from four output signals from the Ethernet controller
101
. The Ethernet controller
101
is responsible for generating the pre-emphasis signal and the data signal. The combinations of these signals is eventually transmitted as the transmit data plus (TDP)
112
and the transmit data minus (TDM)
114
. Between the Ethernet controller
101
and the transformer
120
is a filter circuit that filters and combines the four output signals from the Ethernet controller
101
into the transformer
120
. (The transformer
120
is for electrical isolation and includes a seven pole filter.) The transformer
120
is available from Valor Corporation.
As part of the FCC's electromagnetic interference regulations, the NIC
100
must not emit an amount of electromagnetic radiation above a preset limit. The FCC and CISPR-B specifications, for example, limit the radiation from the NIC
100
. Importantly, any harmonic output above the fundamental frequency must be less than twenty-seven DB below the output at the fundamental frequency. Therefore, it is desirable to be able to reduce the amount of these high frequency components.
One problem with the NIC
100
is that the environment in which the NIC operates varies considerably (e.g., the temperature changes, the load on the wire changes, variations in the manufacturing processes, power supply variations). This variation can result in a change in the transmit signal
130
. For example, the temperature of the NIC
100
can significantly change the signal strength of the transmit signal
130
. The variation also arises as a result of manufacturing differences between different NICs
100
. This variation is undesirable in that it is difficult to meet the electromagnetic interference specification requirements while mataining the desired output levels for the transmit signal
130
. Therefore it is desirable to have some form of control over these output values.
Also, it is desirable to reduce the filtering requirements after the output of the Ethernet controller
101
. Reducing the filtering requirements can reduce the component count of the NIC
100
. This may significantly reduce the manufacturing costs of the NIC
100
.
3. A SUMMARY OF THE INVENTION
A system for reducing electromagnetic interference emissions is described. The system can include a network interface card with an Ethernet controller circuit. The Ethernet controller circuit uses a pair of programmable digital to analog converters to generate an Ethernet output signal that includes a pre-emphasis component and a data component. The Ethernet controller circuit monitors the Ethernet output signal and adjust the levels of the pre-emphasis component and the data component by adjusting the values to the digital to analog converters. By making these adjustments, the system reduces the electromagnetic interference caused by the network interface card but maintains valid Ethernet signals.
Although many details have been included in the description and the figures, the invention is defined by the scope of the claims. Only limitations found in those claims apply to the invention.
REFERENCES:
patent: 4032718 (1977-06-01), O'Neill
patent: 4063201 (1977-12-01), Komatsubara et al.
patent: 4103267 (1978-07-01), Olschewski
patent: 4193048 (1980-03-01), Nyhus
patent: 4342976 (1982-08-01), Ryser
patent: 4376274 (1983-03-01), Smart
patent: 4494109 (1985-01-01), Bernin
patent: 4689593 (1987-08-01), Richardson
patent: 4847986 (1989-07-01), Meinel
patent: 4975671 (1990-12-01), Dirks
patent: 4977491 (1990-12-01), Domenget et al.
patent: 5003622 (1991-03-01), Ma et al.
patent: 5126714 (1992-06-01), Johnson
patent: 5173671 (1992-12-01), Wendler et al.
patent: 5353001 (1994-10-01), Meinel et al.
patent: 5410535 (1995-04-01), Yang et al.
patent: 5430895 (1995-07-01), Huusko
patent: 5450490 (1995-09-01), Jensen et al.
patent: 5469334 (1995-11-01), Balakrishnan
patent: 5477204 (1995-12-01), Li
patent: 5497137 (1996-03-01), Fujiki
patent: 5541959 (1996-07-01), Myers
patent: 5570090 (1996-10-01), Cummins
patent: 5572511 (1996-11-01), Ouyang et al.
patent: 5629641 (1997-05-01), Cheng
patent: 5739780 (1998-04-01), Cheng et al.
patent: 5798723 (1998-08-01), Fong
patent: 5867557 (1999-02-01), D'Andrea et al.
patent: 5870049 (1999-02-01), Huang et al.
patent: 5926460 (1999-07-01), Jukl et al.
patent: 5987320 (1999-11-01), Bobick
patent: 5995555 (1999-11-01), Young
Stremler, Ferrel G., “Introduction to Communication Systems” Second Edition, Addison-Wesley Publishing, Reading, Massachusetts, (1977) Chapters 7 and 10, pp. 351-429, 571-633.
Fawal Marwan A.
Kwan George
Lo Burton B.
3Com Corporation
McDonnell & Boehnen Hulbert & Berghoff
Williams Howard L.
LandOfFree
Programmable compensation and frequency equalization for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Programmable compensation and frequency equalization for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Programmable compensation and frequency equalization for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2521761