The invention relates generally to network communications. More particularly, the invention relates to methods and apparatuses for reducing electromagnetic interference in a received signal.
High-speed networks are continually evolving. The evolution includes a continuing advancement in the operational speed of the networks. The network implementation of choice that has emerged is Ethernet networks physically connected over unshielded twisted pair wiring. Ethernet in its 10/100BASE-T form is one of the most prevalent high speed LANs (local area network) for providing connectivity between personal computers, workstations and servers.
High-speed LAN technologies include 100BASE-T (Fast Ethernet) and 1000BASE-T (Gigabit Ethernet). Fast Ethernet technology has provided a smooth evolution from 10 Megabits per second (Mbps) performance of 10BASE-T to the 100 Mbps performance of 100BASE-T. Gigabit Ethernet provides 1 Gigabit per second (Gbps) bandwidth with essentially the simplicity of Ethernet. There is a desire to increase operating performance of Ethernet to even greater data rates.
The twisted copper wires can operate as antennas that are susceptible to receive electromagnetic interference (EMI). Generally, the EMI appears as a narrowband interference source to Ethernet receivers. Typically, Ethernet systems mostly rely on EMI protection that is provided by shielding, and by transmitting the information differentially to provide immunity against the common-mode characteristics of the EMI. Higher frequency EMI can be partially rejected by the filtering performed at the analog-front end (AFE) of the Ethernet receiver. Additionally, in the past, Ethernet systems had sufficient operating margin such that the EMI did not cause the link to fail.
However, the immunity of current Ethernet systems (higher frequency systems) to EMI is not sufficient, and the EMI can cause the link to fail, and be unable to transmit data. Suppression of EMI can be extremely challenging since the EMI usually appears at unknown times and with unknown frequency, bandwidth, power, modulation, duration, etc. Additionally, suppressing the EMI when the link is already transmitting data is extremely difficult since the EMI characteristics need to be determined very fast to be able to cancel the EMI before the link fails. Moreover, there is no training data to help detect and cancel the EMI since the link is transmitting real traffic.
It is desirable to have an apparatus and method for suppressing EMI of Ethernet systems to provide reliable link operation.
An embodiment includes a method of reducing electromagnetic interference of a received signal. A signal is received over at least two conductors. A common-mode signal is extracted from the at least two conductors. The common-mode signal is processed and summed with the received signal, thereby reducing electromagnetic interference of the received signal.
Another embodiment includes a transceiver. The transceiver includes a receive port operative to receive a signal over at least two conductors, means for extracting a common-mode signal from the at least two conductors, a processor operative to process the common-mode signal, and a canceller operative to sum the processed common-mode signal with the received signal to reduce electromagnetic interference of the received signal.
Another embodiment includes another method of reducing electromagnetic interference of a received signal. A signal is received over at least two conductors. A common-mode signal is extracted from the at least two conductors. Electromagnetic interference of the received signal is reduced using notch filtering, wherein the notch filtering is based at least in part on the processed common-mode signal.
Another embodiment includes another method of reducing electromagnetic interference of a received signal. A signal is received over at least two conductors. A common-mode signal is extracted from the at least two conductors. Electromagnetic interference of the received signal is reduced using slicer error feedback, wherein the slicer-error feedback filtering is based at least in part on the processed common-mode signal.
Other aspects and advantages of the described embodiments will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the described embodiments.
The described embodiments are readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which:
As shown in the drawings for purposes of illustration, the invention is embodied in an apparatus and methods for reducing electromagnetic interference of a received signal of a transceiver. The descriptions provided are generally focused on Ethernet transceivers, but the described embodiments can be used in other configurations of transceivers as well. It is to be understood that the electromagnetic signals can take different forms. That is the electromagnetic signals can couple into the receive signals wirelessly, through cables, through circuit boards, and/or through power supplies.
For this embodiment, a CM signal is generated by summing signals received from a pair of conductors (such as a pair of copper wires) at a summer 230. It should be noted that various methods can be used to extract the CM signal. For example, an embodiment includes tapping a center-tap of a transformer. Other methods can include extracting the CM signal before the transformer. The common mode signal is processed by processing circuitry 240. The differential mode signal is typically amplified by a programmable gain amplifier (PGA) 220. A summer (or canceller) 250 sums the received differential signal with the processed common mode signal to cancel at least a portion of the electromagnetic interference of the received differential signal. It is to be understood that EMI cancellation can be repeated for each of the N received signals, and that the CM signal processing can be different for each of the N received signals. Embodiments include converting the CM signal to a differential mode (DM) signal before, during or after the CM signal processing.
Effectively, the embodiment of
As shown, an ADC (analog to digital converter) 310 samples the CM signal. A frequency estimator 320 estimates a frequency of at least one frequency component of the CM signal.
The frequency estimator 320 can employ multiple methods for EMI frequency estimation. Possible methods include time-domain methods, filter bank structures, linear prediction methods, frequency-domain interpolation methods, iterative detection and estimation, and many more methods.
The frequency estimate is used by a controller 340 to generate filter components (coefficients) of a band-pass filter 350. An embodiment of the band-pass filter includes an IIR (infinite impulse response) filter. For an embodiment, the band-pass filter 350 is tuned to have a pass-band that is centered at the estimated frequency of the electromagnetic interference. The controller 340 selects the filter components to define the center frequency and bandwidth of the band-pass filter 350.
For an embodiment, the band-pass filtered CM signal is additionally filtered by, for example, an FIR (finite impulse response) filter 360. The output of the filter 360 is summed with the received signal to cancel at least a portion of the electromagnetic interference.
The slicer makes decisions about the transmitted information, and can include channel decoding, multi-dimensional decoding, or just single dimensional symbol-by-symbol decoding. The slicer decision is used to generate an estimate of the other signals present in the received signal besides the transmitted information. As such, the EMI signal present in the received signal will be contained in the slicer error. This slicer error could then be processed, or filtered by the band-pass filter 520, to generate an estimate of the EMI signal. The EMI signal estimate based on the processed slicer error could then be subtracted from the received signal to cancel at least a portion of the EMI in the received signal.
For an embodiment, a frequency of the electromagnetic interference signal is estimated based on the common-mode signal. The above-described processing can utilize the frequency of the electromagnetic interference signal. More specifically, for an embodiment, the processing includes configuring a band-pass filter based upon the frequency of the electromagnetic interference signal, and wherein processing the common-mode signal comprises filtering the common mode signal with the band-pass filter. For a specific embodiment, the band-pass filter comprises an infinite impulse response filter. A center frequency, a bandwidth and a gain of the band-pass filter is based on the extracted common-mode signal. More specifically, the band-pass filter is configured based on the extracted common-mode signal by estimating at least one of a strength, a bandwidth, or noise level of the extracted common mode signal, or an estimate of an accuracy of the estimate of the frequency of the electromagnetic interference signal.
For an embodiment, the band-pass common mode signal is further processed by filtering the band-pass filtered common mode signal with N finite impulse response filters, generating a filtered output for each of N signals received over N of the at least two conductors (for example, twisted pairs of copper wire). Each of the N finite impulse response filters is adapted based on a corresponding differential signal of the received signal that includes the electromagnetic interference. Each of the N filtered outputs can be summed with a corresponding one of N signals received over N at least two conductors.
As previously described, an embodiment further includes notch filtering the receive signal, wherein a center frequency, bandwidth and/or gain of the notch filter is based on an estimate of a frequency of an electromagnetic interference signal. For an embodiment, the estimate of the frequency of the electromagnetic interference signal is based on the common-mode signal.
As previously described, an embodiment further includes determining an error of a slicer that decodes the receive signal and cancelling the electromagnetic interference based on the error. For a specific embodiment, the error is used to cancel the electromagnetic interference if the error is below a threshold. For embodiments, the presence of EMI, the frequency, the amplitude, and other EMI properties are determined based on the slicer error. The slicer makes decisions about the transmitted information, and thus the slicer error includes the other receive signals besides the transmitted information. The EMI signal present in the received differential signal is part of the slicer error, and processing the slicer error can therefore be used to detect the presence of the EMI signal, and determine its characteristics. The frequency of the EMI signal can be determined by determining strong frequency components in the slicer error using, for example, fast-Fourier-transform (FFT) processing to examine the frequency domain content of the slicer error signal.
As previously described, an embodiment further includes reducing a level of components of a transmit signal within the extracted common-mode signal. For a specific embodiment, reducing the level of components of the transmit signal within the extracted common-mode signal includes filtering the transmit signal and summing the filtered transmit signal with the common-mode signal.
The electromagnetic interference can include multiple sources of interference that include multiple interfering frequencies. An embodiment additionally includes estimating frequencies of multiple electromagnetic interference signals, and adapting band-pass filter configurations based at least in part on the frequencies.
An embodiment includes utilization of common hardware in the implementation of the various band-pass (typically, IIR) and the FIR filtering. Specifically, this embodiment includes estimating a frequency of the electromagnetic interference signal based on the common-mode signal, notch filtering the receive signal, wherein a center frequency of the notch filter is based on the estimate of a frequency of an electromagnetic interference signal. Further, determining an error of a slicer that decodes the receive signal, filtering the error and cancelling the electromagnetic interference based on the filtered error. Further, configuring a band-pass filter based upon the estimate of the frequency of the electromagnetic interference signal, and wherein processing the common-mode signal comprises filtering the common mode signal with the band-pass filter, wherein the notch filter, error filtering and the band-pass filter share filtering circuit hardware. With different combinations of filtering in place and easy to reconfigure, an embodiment include a replica slicer generating a replica slicer error for testing different combinations of the notch filtering, the error filtering and the common mode filtering.
A Network of Devices
Although specific embodiments of the invention have been described and illustrated, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated. The invention is limited only by the appended claims.
Number | Name | Date | Kind |
---|---|---|---|
3506906 | Nestor | Apr 1970 | A |
3671859 | Miller | Jun 1972 | A |
4797902 | Nishiguchi et al. | Jan 1989 | A |
4870370 | Hedberg et al. | Sep 1989 | A |
5157690 | Buttle | Oct 1992 | A |
5283811 | Chennakeshu et al. | Feb 1994 | A |
5550924 | Helf et al. | Aug 1996 | A |
5777692 | Ghosh | Jul 1998 | A |
5832032 | Overbury | Nov 1998 | A |
5889511 | Ong et al. | Mar 1999 | A |
5910960 | Claydon et al. | Jun 1999 | A |
5995566 | Rickard et al. | Nov 1999 | A |
5995567 | Cioffi et al. | Nov 1999 | A |
6011508 | Perreault et al. | Jan 2000 | A |
6035360 | Doidge et al. | Mar 2000 | A |
6052420 | Yeap et al. | Apr 2000 | A |
6069917 | Werner et al. | May 2000 | A |
6285718 | Reuven | Sep 2001 | B1 |
6385315 | Viadella et al. | May 2002 | B1 |
6424234 | Stevenson | Jul 2002 | B1 |
6486746 | Gilbert | Nov 2002 | B1 |
6683913 | Kantschuk | Jan 2004 | B1 |
6690739 | Mui | Feb 2004 | B1 |
6711207 | Amrany et al. | Mar 2004 | B1 |
6734659 | Fortner | May 2004 | B1 |
6771720 | Yang et al. | Aug 2004 | B1 |
6924724 | Grilo et al. | Aug 2005 | B2 |
6934345 | Chu et al. | Aug 2005 | B2 |
6959056 | Yeap et al. | Oct 2005 | B2 |
6999504 | Amrany et al. | Feb 2006 | B1 |
7026730 | Marshall et al. | Apr 2006 | B1 |
7031402 | Takada | Apr 2006 | B2 |
7103013 | Kim et al. | Sep 2006 | B1 |
7123117 | Chen et al. | Oct 2006 | B2 |
7164764 | Zimmerman et al. | Jan 2007 | B2 |
7173992 | Frigon | Feb 2007 | B2 |
7180940 | Li et al. | Feb 2007 | B2 |
7200180 | Verbin et al. | Apr 2007 | B2 |
7315592 | Tsatsanis et al. | Jan 2008 | B2 |
7333603 | Sallaway et al. | Feb 2008 | B1 |
RE40149 | Vitenberg | Mar 2008 | E |
7440892 | Tamura | Oct 2008 | B2 |
7457386 | Phanse | Nov 2008 | B1 |
7459982 | Miao | Dec 2008 | B2 |
7492840 | Chan | Feb 2009 | B2 |
7522928 | O'Mahony | Apr 2009 | B2 |
7542528 | Cheong | Jun 2009 | B1 |
7634032 | Chu et al. | Dec 2009 | B2 |
7656956 | King | Feb 2010 | B2 |
7706434 | Farjadrad | Apr 2010 | B1 |
7708595 | Chow et al. | May 2010 | B2 |
8094546 | Schenk | Jan 2012 | B2 |
8139602 | Meier | Mar 2012 | B2 |
8284007 | Langner et al. | Oct 2012 | B1 |
8320411 | Sedarat et al. | Nov 2012 | B1 |
8331508 | Dabiri | Dec 2012 | B2 |
8472532 | Schley-May et al. | Jun 2013 | B2 |
8625704 | Sedarat et al. | Jan 2014 | B1 |
20030186591 | Jensen et al. | Oct 2003 | A1 |
20030223488 | Li et al. | Dec 2003 | A1 |
20030223505 | Verbin et al. | Dec 2003 | A1 |
20040010203 | Bibian et al. | Jan 2004 | A1 |
20040023631 | Deutsch et al. | Feb 2004 | A1 |
20040164619 | Parker et al. | Aug 2004 | A1 |
20040213366 | Ono | Oct 2004 | A1 |
20040239465 | Chen et al. | Dec 2004 | A1 |
20040252755 | Jaffe et al. | Dec 2004 | A1 |
20040257743 | Chen et al. | Dec 2004 | A1 |
20050018777 | Azadet | Jan 2005 | A1 |
20050025266 | Chan | Feb 2005 | A1 |
20050053229 | Tsatsanis et al. | Mar 2005 | A1 |
20050097218 | Sultenfuss et al. | May 2005 | A1 |
20050123081 | Shirani | Jun 2005 | A1 |
20050135489 | Ho et al. | Jun 2005 | A1 |
20050203744 | Tamura | Sep 2005 | A1 |
20050243483 | Chen et al. | Nov 2005 | A1 |
20060018388 | Chan | Jan 2006 | A1 |
20060056503 | Keshab et al. | Mar 2006 | A1 |
20060159186 | King | Jul 2006 | A1 |
20060182014 | Lusky et al. | Aug 2006 | A1 |
20060256880 | Frisch | Nov 2006 | A1 |
20070014378 | Parhi et al. | Jan 2007 | A1 |
20070081475 | Telado et al. | Apr 2007 | A1 |
20070146011 | O'Mahony et al. | Jun 2007 | A1 |
20070192505 | Dalmia | Aug 2007 | A1 |
20070258517 | Rollings et al. | Nov 2007 | A1 |
20070280388 | Torre et al. | Dec 2007 | A1 |
20080089433 | Cho et al. | Apr 2008 | A1 |
20080095283 | Shoor | Apr 2008 | A1 |
20080107167 | Tung et al. | May 2008 | A1 |
20080160915 | Sommer et al. | Jul 2008 | A1 |
20080198909 | Tsatsanis et al. | Aug 2008 | A1 |
20080267212 | Crawley et al. | Oct 2008 | A1 |
20090061808 | Higgins | Mar 2009 | A1 |
20090097401 | Diab | Apr 2009 | A1 |
20090097539 | Furman et al. | Apr 2009 | A1 |
20090154455 | Diab | Jun 2009 | A1 |
20090161781 | Kolze | Jun 2009 | A1 |
20100046543 | Parnaby | Feb 2010 | A1 |
20100073072 | Ullen et al. | Mar 2010 | A1 |
20100074310 | Roo et al. | Mar 2010 | A1 |
20100086019 | Agazzi et al. | Apr 2010 | A1 |
20100111202 | Schley-May et al. | May 2010 | A1 |
20100159866 | Fudge et al. | Jun 2010 | A1 |
20110032048 | Wu et al. | Feb 2011 | A1 |
20110069794 | Tavassoli Kilani et al. | Mar 2011 | A1 |
20110106459 | Chris et al. | May 2011 | A1 |
20110212692 | Hahn | Sep 2011 | A1 |
20110256857 | Chen et al. | Oct 2011 | A1 |
20110293041 | Luo et al. | Dec 2011 | A1 |
20110296267 | Malkin et al. | Dec 2011 | A1 |
Number | Date | Country |
---|---|---|
WO 9740587 | Oct 1997 | WO |
WO2011056970 | May 2011 | WO |
Entry |
---|
U.S. Appl. No. 12/563,938, filed Sep. 21, 2009, Sedarat. |
U.S. Appl. No. 12/604,323, filed Oct. 22, 2009, Sedarat et al. |
U.S. Appl. No. 12/604,434, filed Oct. 22, 2009, Farjadrad et al. |
U.S. Appl. No. 12/604,351, filed Oct. 22, 2009, Sedarat et al. |
Number | Date | Country | |
---|---|---|---|
20110296267 A1 | Dec 2011 | US |