# Patent

## Title
Method and system for interference cancellation

## Abstract

Aspects of a method and system for interference cancellation substantially as shown in and/or described in connection with at least one of the figures, as set forth more completely in the claims. In this regard, a receiver may be operable to receive a differential signal via a differential channel, and to sense a common mode signal on the differential channel. A frequency range in which interference is present in the common mode signal may be determined. The differential signal and the common mode signal may be filtered to attenuate frequencies outside the determined frequency range. A phase and/or amplitude of the filtered common mode signal may be adjusted based on the filtered differential signal and the adjusted and filtered common mode signal may be subtracted from the received differential signal. The common mode signal may be sensed via a pair of resistors coupled to the differential channel.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE
This patent application makes reference to, claims priority to and claims benefit from U.S. Provisional Patent Application Ser. No. 61/243,987 filed on Sep. 18, 2009, and to U.S. Provisional Patent Application Ser. No. 61/362,012 filed on Jul. 7, 2010.


The above stated application is hereby incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
Certain embodiments of the invention relate to signal processing. More specifically, certain embodiments of the invention relate to a method and system for interference cancellation.
BACKGROUND OF THE INVENTION
In almost any communication system, interference, externally and/or internally generated, limits the performance of the communication system. Differential signaling is one technique that can be utilized for dealing with such interference. However, while differential signaling may reduce the effects of such interference, it does not eliminate them.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.
BRIEF SUMMARY OF THE INVENTION
A system and/or method is provided for interference cancellation, substantially as illustrated by and/or described in connection with at least one of the figures, as set forth more completely in the claims.
These and other advantages, aspects and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings.



BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
FIG. 1. is a diagram depicting two communication devices communicating over a plurality of communication channels, in accordance with an embodiment of the invention.
FIG. 2 is a diagram depicting an exemplary portion a communication device, which may be operable to provide interference cancellation, in accordance with an embodiment of the invention.
FIG. 3 is another diagram depicting an exemplary portion a communication device, which may be operable to provide interference cancellation, in accordance with an embodiment of the invention.
FIG. 4 is a diagram illustrating exemplary magnetics which may be operable to provide interference cancellation for a communication device, in accordance with an embodiment of the invention.
FIG. 5 is a flow chart illustrating exemplary steps for interference cancellation, in accordance with an embodiment of the invention.
FIG. 6 is another flow chart illustrating exemplary steps for interference cancellation, in accordance with an embodiment of the invention.



DETAILED DESCRIPTION OF THE INVENTION
Certain embodiments of the invention may be found in a method and system for interference cancellation. In various embodiments of the invention, a receiver may be operable to receive a differential signal via a differential channel, and to sense a common mode signal on the differential channel. A frequency range in which interference is present in the common mode signal may be determined and the common mode signal and the differential signal may be filtered to attenuate frequencies outside the determined frequency range. A phase and/or amplitude of the filtered common mode signal may be adjusted based on the filtered differential signal and the adjusted and filtered common mode signal may be subtracted from the received differential signal. The common mode signal may be sensed via a pair of resistors coupled to the differential channel. A first terminal of a first one of the resistors may be coupled to a first wire of the differential channel, a first terminal of a second one of the resistors may be coupled to a second wire of the differential channel, a second terminal of the first one of the resistors may be coupled to a second terminal of the second one of the resistors, and the common mode signal may be present on the second terminals of the resistors. The second terminals of the resistors may be coupled to a first terminal of a primary winding of a transformer and a second terminal of the primary winding may be coupled to signal ground.
Either of an adaptive line enhancer and a filter may be selected for performing the filtering. A selection between the adaptive line enhancer and the filter may be based on signal levels output by the adaptive line enhancer and the filter. The filter may be selected in instances that the adaptive line enhancer is unable to converge on a frequency within the determined frequency range. A frequency response of the filter may be configured to select between a high-pass response and a low-pass response. The frequency range may be determined based on a pre-programmed or dynamically programmed value. The subtraction may be enabled and disabled based on signal levels of the common mode signal and/or signal levels of the filtered common mode signal. A phase and/or amplitude of the filtered common mode signal may be adjusted to minimize a difference between the filtered differential signal and the adjusted and filtered common mode signal.
FIG. 1 is a diagram depicting two communication devices communicating over a plurality of communication channels, in accordance with an embodiment of the invention. Referring to FIG. 1 there is shown a communication device 102a and a communication device 102b which communicate over a cable 108 that comprises communication channels 1061-106N, where N is an integer greater than or equal to 1.
Each of the communication devices 102a and 102b may comprise suitable logic, circuitry, interfaces, and/or code that may be operable to communicate, utilizing differential signaling, over one or more of the channels 1061-106N. Each communication channel 106n may comprise, for example a twisted-pair, where n is an integer between 1 and N inclusive. In this regard, each of the communication devices 102a and 102b may comprise one or both of a transmitter and a receiver. In various embodiments of the invention, the communication devices 102a and 102b may communicate over the cable 108 in accordance with IEEE 802.3 (Ethernet) standards. For example, for 10/100/1G/10GBASE-T the cable 108 may comprise twisted pairs 1061-1064, and the communication devices 102a and 102b may, depending on the particular 802.3 standard being utilized, may engage in simplex, half-duplex, and/or full-duplex communications over one or more of the twisted pairs 1061-1064.
In operation, interference signal 104 having frequency fint may be incident on the cable 108 and may appear on the channels 1061-106N as a common mode signal. Exemplary sources of the interference 104 comprise broadcast radio and/or television signals, cellular signals, and radiated electromagnetic interference (EMI) from other electronic devices or cables located near the cable 108. Degraded communications over the cable 108 resulting from the interference 104 may manifest itself in the form of, for example, increased receive error rates in the communication devices 102a and 102b. Accordingly, various aspects of the invention may enable, for each channel 106n, accurate estimation and/or reproduction of a common mode interference on the channel 106n, and subtracting the common mode interference from the differential signal received via the channel 106n. In an exemplary embodiment of the invention, the N common mode interference signals may be estimated or reproduced by detecting the common mode signal on only one of the channels 1061-106N. Accordingly, redundant detection circuitry may be reduced or eliminated. The common mode signals may be detected on any number of channels and utilized for reducing interference on any number of channels.
FIG. 2 is a diagram depicting an exemplary portion of a communication device, which may be operable to provide interference cancellation, in accordance with an embodiment of the invention. Referring to FIG. 2 the communication device 102 may comprise differential processing paths 2021-202N, common mode processing path 204, and control unit 208.
The common mode path 204 may comprise suitable logic, circuitry, interfaces, and/or code that may be operable to sense a raw common mode signal present on the channel 1061, and to process the raw signal to output an enhanced common mode signal 206. The common mode path 204 may be operable to generate the common mode signal 206 by amplifying, filtering, and/or delaying the raw signal. The common mode signal 206 may be output to each of the differential paths 2021-202N.
Each differential path 202n may comprise suitable logic, circuitry, interfaces, and/or code that may be operable to adjust the phase and/or amplitude of the enhanced common mode signal 206 and subtract the resulting signal from the differential signal received via the channel 106n.
The control unit 208 may comprise suitable logic, circuitry, interfaces, and/or code that may be operable to configure the differential paths 2021-202N and/or the common mode path 204. For example, the control unit 208 may provide control signals to switching elements such as multiplexers, control gain of one or more amplifiers, control frequency of one or more filters, and/or control a delay introduced by one or more delay elements or components. In an exemplary embodiment of the invention, the control unit 208 may configure the differential paths 2021-202N and/or the common mode path 204 based on a signal strength of the raw common mode signal, the common mode signal 206, or some intermediate signal achieved while generating the common mode signal 206 from the raw common mode signal.
In operation, the signal 104 incident on the channels 1061-106N may result in a narrowband common mode interference signal at fint on each of the channels 1061-106N. Furthermore, due to length and/or impedance mismatches, for example, some of that common mode interference may get converted to narrowband interference at fint in the differential signal. To cancel or reduce such interference, the common mode interference on each channels 106n may be replicated or estimated and may be subtracted from the differential signal received via the channel 106n.
FIG. 3 is another diagram depicting an exemplary portion a communication device, which may be operable to provide interference cancellation, in accordance with an embodiment of the invention. Referring to FIG. 3 there is shown an exemplary differential path 202n, the common mode path 204, and the control unit 208. The differential path 202n comprises magnetics 302, hybrid 304, analog front end 306 (AFE), digital-to-analog converter (DAC) 308, analog-to-digital converter (ADC) 310, bandpass filter (BPF) 312, filter bank 314, multiplexers 316 and 325, adaptive filter 318, and combiners 320 and 324. Although FIG. 3 depicts only a single differential path, each of the differential paths 2021-202N may be treated and/or behave in a manner that is similar to that of the exemplary differential path 202n. The common mode path 204 comprises common mode sensor 326, variable gain amplifier (VGA) 328, ADC 330, adaptive line enhancer (ALE) 332, filter bank 334, multiplexers 336 and 338, delay block 340, and detector 342.
The magnetics 302 may comprise suitable logic, circuitry, interfaces, and/or code that may be operable to couple the channel 106n to the differential path 202n. In this regard, the magnetics 302 may provide noise and/or EMI suppression and/or may impedance match the channel 106n to the differential path 202n. In this regard, the magnetics 302 may comprise one or more transformers and/or one or more inductive chokes. In some instances, the magnetics 302 may also comprise other components such as resistors, capacitors, and/or inductors for achieving impedance matching, isolation, and/or noise and/or EMI suppression. In some embodiments of the invention, the magnetics 302 may comprise the common mode sensor 326, as described below with respect to FIG. 4. In various embodiments of the invention, the various components depicted in FIG. 3 may be interconnected via differential traces on and/or in printed circuit boards (PCBs) and/or integrated circuits (ICs) on and/or in which the components are fabricated. Such differential signal routing may reduce noise coupled into the signals within and/or on the PCBs and/or ICs.
The hybrid 304 may comprise suitable logic, circuitry, and/or code that may enable separation of the transmitted and received signals from the channel 106n and combining transmitted and received signals onto the channel 106n.
The analog front end (AFE) 306 may comprise suitable logic, circuitry, interfaces, and/or code that may be operable to perform processing of received signals and signals that are to be transmitted in the analog domain. Such processing may comprise, for example, amplification, filtering, modulation, and demodulation.
The DAC 308 may comprise suitable logic, circuitry, interface, and/or code that may be operable to convert a digital signal to an analog representation. That is, the digital signal 309 is converted to the analog signal 307.
Each of the ADCs 310 and 330 may comprise suitable logic, circuitry, interface, and/or code that may be operable to convert an analog signal to a digital representation. That is, the analog signal 307 is converted to the digital signal 311.
The BPF 312 may comprise suitable logic, circuitry, interfaces, and/or code having a frequency response such that frequencies within a selected band, the passband, are attenuated less than frequencies above and below the selected band. The frequency response of the BPF 312 may be controlled via the control signal 357 which may be generated by the ALE 332 and/or the control unit 208.
Each of the filter banks 314 and 334 may comprise suitable logic, circuitry, interfaces, and/or code that may be configurable to have a high-pass and/or low-pass frequency response. The frequency response of each of the filter banks 314 and 334 may be controlled via the control signal 359 from the control unit 208. In an exemplary embodiment of the invention each of the filter banks may comprise a first order infinite impulse response (IIR) filter.
Each of the multiplexers 316, 325, 336, and 338 may comprise suitable logic, circuitry, interfaces, and/or code that may be operable to select one of a plurality of inputs for conveyance to an output. The signals 351, 351, 355, and 353 generated by the control unit may control, respectively, the multiplexers 316, 336, 325 and 338.
The adaptive filter 318 may comprise suitable logic, circuitry, interfaces, and/or code that may be operable to adjust an amplitude and/or phase of the signal 206 to minimize the error signal 321. In an exemplary embodiment of the invention, the adaptive filter 318 may comprise a two tap finite impulse response (FIR) filter. In various embodiments of the invention, a bandwidth and/or step size utilized in an adaptation algorithm performed by the adaptive filter 318 may be configured by the control unit 208. Such control may affect how long it takes the adaptive filter 318 to converge and/or the accuracy of the coefficients on which it converges.
The combiners 320 and 324 may each comprise suitable logic, circuitry, interfaces, and/or code that may be operable to combine digital signals. The combiners 320 and 324 may be operable to add and/or subtract two or more digital signals. The combiners 320 and 324 may be operable to weight the signals prior to addition or subtraction.
The common mode sensor 326 may comprise suitable logic, circuitry, interfaces, and/or code operable to detect a common mode signal on the channel 106n. The common mode sensor 326 may output a raw common mode signal 327. In an exemplary embodiment of the invention, the common mode sensor may comprise a pair of resistors and a transformer as described below with respect to FIG. 4. In another exemplary embodiment of the invention, the common mode sensor 326 may comprise a center tap of a transformer in the magnetics 302.
The variable gain amplifier (VGA) 328 may comprise suitable logic, circuitry, interfaces, and/or code that may be operable to amplify the raw common mode signal 327. The gain of the VGA 328 may be controlled via control signal 361 from the control unit.
The ALE 332 may comprise suitable logic, circuitry, interfaces, and/or code that may be operable to suppress wide-band noise component of the signal 331 while passing a narrow band component of the signal 331. In this regard, the ALE 332 may implement one or ore more algorithms to automatically seek and attempt to lock its passband to the frequency, fint, of the narrowband interference resulting from the interference signal 104 (FIG. 1). In an exemplary embodiment of the invention, the ALE 332 may comprise a second order Infinite Impulse Response (IIR) bandpass filter. In an exemplary embodiment of the invention, the ALE 332 may comprise a finite impulse response (FIR) filter. In various embodiments of the invention, a bandwidth and/or step size utilized in an adaptation algorithm performed by the ALE 332 may be configured by the control unit 208. Such control may affect how long it takes the ALE 332 to converge and/or the accuracy of the frequency on which it converges.
The delay block 340 may comprise suitable logic, circuitry, interfaces, and/or code that may be operable to delay the signal 337. That is, the signal 206 may be a delayed version of the signal 337. The delay introduced by the delay block 340 may be controlled by a control signal 363 from the control unit. The delay block 340 may compensate for the difference in delays between the differential path 202n and common mode path 204. The delay introduced by the delay block 340 may be fixed or programmable.
The detector 342 may comprise suitable logic, circuitry, interfaces, and/or code that may be operable to detect the levels of the signal 339 and compare the levels of the signal 339 to a threshold, Sth. The output 343 of the detector 342 may indicate whether the levels of the signal 342 is greater than or less than Sth.
The control unit 208 may be as described with respect to FIG. 2. The control unit 208 may be operable to generate the control signal 351 for controlling the multiplexers 316 and 336, the control signal 353 for controlling the multiplexer 338, the control signal 355 for controlling the multiplexer 325, the control signal 359 for configuring the filter banks 314 and 334, the control signal 361 for controlling the VGA 361, the control signal 363 for controlling the delay 363, and the threshold voltage Sth. In an exemplary embodiment of the invention, the control unit 208 may comprise a processor and memory.
In operation, the raw common mode signal 327 may be obtained from the sensor 326. The raw common mode signal 327 may be scaled by the VGA 328 resulting in the signal 329. Such scaling may be utilized to accommodate for the dynamic range of the ADC 330. The signal 329 may be digitized by the ADC 330 to generate the signal 331 which is input to ALE 332 and the filter bank 334.
The ALE 332 may attempt to detect and converge on the frequency, fint, of the narrowband interference present in the signal 331. After convergence, the bandpass filter portion of the ALE 332 may filter out wideband noise while passing a narrow range of frequencies around fint. In instances that the ALE 332 converges on fint, then the multiplexer 336 may select the signal 333 to be output as the signal 337.
In instances that the fint is outside a range suitable for the bandpass filtering of the ALE 332, the output. That is, when the ALE 332 cannot converge on fint, the output the multiplexer 336 may select the output 335 of the filter bank 334 to be output as the signal 337. In this regard, in instances that fint is lower than the convergence range of the ALE 332, the filter bank 334 may be configured into a low-pass configuration. Similarly, in instances that fint is higher than the convergence range of the ALE 332, the filter bank 334 may be configured into a high-pass configuration.
The signal 337 may be communicatively coupled to the delay block 340. The amount of delay introduced by the delay block 340 may be controlled such that that the enhanced common mode signal 206 is roughly time aligned with the signal 317 in the differential path 202n.
The signal 337 is also coupled to the multiplexor 338. The multiplexor 338 may select between the signals 331 and the signals 337 for conveyance to the detector 342. In this regard, when the signal 331 is selected, the threshold Sth may be set to a first value and when the signal 337 is selected, the threshold Sth may be set to a second value. The detector 342 may measure levels of the signal 337 within a time period and compare the levels against the threshold Sth. The result 343 of the comparison may be input to the control unit 208 which may generate on or more control signals based on the result. In an exemplary embodiment of the invention, the multiplexer 338 and the detector 342 may be utilized to determine when to enable and when to disable interference cancellation. An example of enabling and disabling interference cancellation is described below with respect to FIG. 6.
In an exemplary embodiment of the invention, to select among the ALE 332 and the filter bank 334, the control unit 208 may alternate signal 351 between 0 and 1, thus alternating selection of the signal 333 and the signal 335, and determine which of the signals 333 and 335 to select based on the levels of the signals. For example, if the ALE 332 achieves convergence while it is selected, then the control unit 208 may stop alternating the signal 353 and stay on the value of the signal 353 that selects signal 333. If the ALE 332 does not converge, the signal 335 may be selected and signal levels may be checked for each of a high-pass and low-pass configuration of the filter bank 334. If either the high-pass or low-pass configuration results in signal 339 being above the threshold, then signal 335 may be selected and the signal 353 may stop alternating. Otherwise, the signal 333 may again be selected as the ALE 332 again attempts to converge on the narrowband interference, utilizing, for example, new parameters for bandwidth and/or adaptation step size. The process may repeat until the narrowband interference at fint is detected. In an exemplary embodiment of the invention, a low-pass configuration of the filter bank 334 may be selected when fint is on the low end of the frequency spectrum, a high-pass configuration of the filter bank 334 may be selected when fint is equal to half the sampling frequency or higher, and the ALE 332 may be selected for when fint is somewhere in between.
The signal 351 also controls the multiplexer 316. Accordingly, if the signal 333 is selected by the multiplexer 336, then the signal 313 is selected by the multiplexer 316. In instances that the ALE 332 has converged on fint, and the signal 333 has been selected by the multiplexer 336, the configuration of the ALE 332 may be copied to the BPF 312. That is, the signal 357 may configure the BPF 312 to have the same (within a tolerance) frequency response as the ALE 332. Similarly, in instances that the signal 335 is selected, the configuration of the filter bank 334 may be copied to the filter bank 314. That is, the signal 359 may configure the filter bank 314 to have the same, within a tolerance, frequency response as the filter bank 334.
The signals 317 and 206 may be input to the adaptive filter 318. The adaptive filter 318 may adjust the amplitude and/or phase of the signal 206 to generate the signal 319. In this regard, the adaptive filter 318 may adjust the phase and/or amplitude of the signal 206 to minimize the error signal 321. The signal 319 may correspond to an accurate replica of the interference in the signal 311 resulting from the interfering signal 104 (FIG. 1). Accordingly, once signal 319 is a stable representation of the narrowband interference at fint in the signal 311, the multiplexer 325 may be configured to output the signal 319 to the combiner 324 such that the signal 319 is subtracted from the signal 311. In this regard, when interference cancellation is disabled and/or the system is unable to detect or lock to the narrowband interference at fint, the multiplexer 325 may select the zero input which allows the signal 311 to pass through the combiner 324 unmodified.
FIG. 4 is a diagram illustrating exemplary magnetics, which may be operable to provide interference cancellation, for a communication device, in accordance with an embodiment of the invention. Referring to FIG. 4, the magnetics 302 may couple the channels 1061-106N to the differential signal traces 4061-406N. The magnetics 302 and may comprise chokes 4021-402N, transformers 4041-404N+1, and resistors 408a and 408b. In this regard, the common mode sensor 326 described with respect to FIG. 3 may comprise the resistors 408a and 408b and the transformer 404N+1.
The chokes 4021-402N may be operable to attenuate common mode signals while passing differential signals. In an exemplary embodiment of the invention, the chokes 4021-402N may comprise one or more inductors and/or ferrites.
The transformers 4041-404N may be operable to inductively couple the differential outputs of the chokes 4021-402N to the differential signal traces 4061-406N. Each of the transformers 4041-404N may comprise a primary winding, a secondary winding, and a core.
In operation, common mode energy on the two conductors of channel 106N may sum through the resistors 408a and 408b and appear as a single-ended raw common mode signal at the primary winding 404N+1. The transformer 404N+1 may convert the single-ended raw common mode signal to a differential raw common mode signal on the differential trace 406N+1 
FIG. 5 is a flow chart illustrating exemplary steps for interference cancellation, in accordance with an embodiment of the invention. Referring to FIG. 5, the exemplary steps may begin with step 502 when a common mode sensor may sense a common mode signal on a differential channel and output a raw common mode signal. In step 504, the raw common mode signal may be enhanced by amplifying it, filtering it, and/or delaying it. The filtering may comprising automatically centering a pass band around a frequency, fint, of a narrowband interference signal present in the raw common mode signal, such that the narrow band interference signal is passed while wideband noise is filtered out.
In step 506, a phase and/or amplitude of the enhanced common mode signal may be adjusted such that the phase and amplitude of the enhanced common mode signal are approximately equal to the phase and amplitude of interference present on a received differential signal. That is, the same source of interference that generated the narrowband interference present in the common mode signal may also have created some interference on a received differential signal. That is, through imperfections in the channel and/or the received differential signal, some common mode to differential conversion may take place that results in interference in the received differential signal. Accordingly, adjusting the phase and/or amplitude of the enhanced common mode signal may result in a signal that accurately estimates the interference in the differential signal. In step 508, the interference estimate, that is, the phase and/or amplitude adjusted version of the enhanced common mode signal, may be subtracted from the received differential signal, thus resulting in a cleaner received signal.
FIG. 6 is another flow chart illustrating exemplary steps for interference cancellation, in accordance with an embodiment of the invention. Referring to FIG. 6, the exemplary steps may begin with start step 602 and proceed to step 604. In step 604, the communication device 102a may begin receiving signals via one or more of the differential channels 1061-106N. The communication device 102a may initially be configured such that interference cancellation is disabled.
In step 606, it may be determined whether signal 331 is greater than a first value of the threshold Sth. In this regard, while interference cancellation is disabled, the multiplexer 338 may be configured to select the signal 331 for conveyance to the detector 342. In instances that signal 331 is not greater than the threshold Sth, the steps may return to step 604. In instances that the signal 331 is greater than the threshold Sth, the exemplary steps may advance to step 608.
In step 608, it may be determined whether the frequency, fint, of the interference signal 104 (FIG. 1) is known. In an exemplary embodiment of the invention, a network administrator may be aware of a nearby radio tower or other source of interference and may program fint into the communication device 102a. In an exemplary embodiment of the invention, the location of the communication device 102a may be utilized to determine nearby sources of interference and the frequencies of the interference. For example, GPS may be utilized to map out the RF characteristics of an area and the GPS coordinates of the communication device 102a may be utilized to determine nearby sources of interference. In instances that fint is not known, the exemplary steps may proceed to step 612
In step 612, the communication device 102a may automatically detect the frequency, fint, of the narrowband interference. In this regard, fint may be detected by convergence of the ALE 332 and/or based on levels of the signals 333 and 335 measured by the detector 342. Once fint has been determined, corresponding filters 312 and/or 314 in the differential paths 1021-102N may be configured to pass the detected fint and filter out other frequencies. Subsequent to step 612, the exemplary steps may advance to step 614.
In step 614, the narrowband common mode signal output by the ALE 332 or the filter bank 334 may be delayed by delay block 340, resulting in the enhanced common mode signal 206. The signal 206 may then be phase and/or level adjusted by the adaptive filter 318. Upon the adaptive filter converging or stabilizing, the exemplary steps may proceed to step 616.
In step 616, the multiplexer 325 may be configured to select the signal 319 and the combiner 324 may subtract the signal 319 from the signal 311. Subsequent to step 616, the exemplary steps may proceed to step 618.
In step 618, if the levels of the narrowband signal 337 drops below a threshold then the exemplary steps may proceed to step 604 and interference cancellation may be disabled. This may happen, for example, when the signal 104 goes away or changes frequency. Conversely, while the level of the signal 337 remains above a threshold, interference cancellation may remain enabled.
Returning to step 608, in instances that fint is known, the exemplary steps may proceed to step 610. In step 610, in instances that fint is within a lock range of the ALE 332, then the ALE 332 may be configured such that it will quickly lock to fint and the passband of the corresponding BPFs 312 in the differential paths 2021-202N may be set to fint. Alternatively, in instances that fint is outside a lock range of the ALE 332, then the filter bank 334 may be configured to pass fint and the corresponding filter banks 314 in the differential paths 2021-202N may be configured to pass fint. Subsequent to step 610, the exemplary steps may advance to step 614.
Various embodiments of a method and system for interference cancellation are provided. In an exemplary embodiment of the invention, one or more circuits and/or processors of a communication device 102a (FIGS. 1-3) may be operable to receive a differential signal 311 (FIG. 3) via a differential channel 106n (FIGS. 1-3), and to sense a common mode signal 327 (FIG. 3) on the differential channel 106n. A frequency range in which interference is present in the common mode signal 327 may be determined and the differential signal 311 and the common mode signal 327, or signal 331, an amplified and/or digitized version of signal 327, may be filtered to attenuate frequencies outside the determined frequency range. A phase and/or amplitude of the filtered common mode signal 337, or the signal 206, a delayed version of signal 337, may be adjusted based on the filtered differential signal 317 and the adjusted and filtered common mode signal 319 may be subtracted from the received differential signal 311.
The common mode signal 327 may be sensed via a pair of resistors 408a and 408b (FIG. 4) coupled to the differential channel 106n. A first terminal of the resistors 408a may be coupled to a first wire of the differential channel 106n, a first terminal of the resistors 408b may be coupled to a second wire of the differential channel 106n, a second terminal of the resistor 408a may be coupled to a second terminal of the resistor 408b, and the common mode signal 327 may be present on the second terminals of the resistors. The second terminals of the resistors 408a and 408b may be coupled to a first terminal of a primary winding of a transformer 404N+1 and a second terminal of the primary winding may be coupled to signal ground.
Either of an adaptive line enhancer 332 and a filter 334 may be selected for performing the filtering. A selection between the adaptive line enhancer 332 and the filter 334 may be based on signal levels output by the adaptive line enhancer 332 and the filter 334. The filter 334 may be selected in instances that the adaptive line enhancer 332 is unable to converge on a frequency within the determined frequency range. A frequency response of the filter 334 may be configured to select between a high-pass response and a low-pass response. The frequency range may be determined based on a programmed value which may be pre-programmed or determined dynamically. The subtraction may be enabled and disabled based on signal levels of the common mode signal 327, or signal 331, an amplified and/or digitized version of signal 327, and/or signal levels of the filtered common mode signal 337. A phase and/or amplitude of the filtered common mode signal 337, or signal 206, a delayed version of signal 337, may be adjusted to minimize a difference between the filtered differential signal 317 and the adjusted and filtered common mode signal 319.
Other embodiments of the invention may provide a non-transitory computer readable medium and/or storage medium, and/or a non-transitory machine readable medium and/or storage medium, having stored thereon, a machine code and/or a computer program having at least one code section executable by a machine and/or a computer, thereby causing the machine and/or computer to perform the steps as described herein for interference cancellation.
Accordingly, the present invention may be realized in hardware, software, or a combination of hardware and software. The present invention may be realized in a centralized fashion in at least one computer system, or in a distributed fashion where different elements are spread across several interconnected computer systems. Any kind of computer system or other apparatus adapted for carrying out the methods described herein is suited. A typical combination of hardware and software may be a general-purpose computer system with a computer program that, when being loaded and executed, controls the computer system such that it carries out the methods described herein.
The present invention may also be embedded in a computer program product, which comprises all the features enabling the implementation of the methods described herein, and which when loaded in a computer system is able to carry out these methods. Computer program in the present context means any expression, in any language, code or notation, of a set of instructions intended to cause a system having an information processing capability to perform a particular function either directly or after either or both of the following: a) conversion to another language, code or notation; b) reproduction in a different material form.
While the present invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present invention without departing from its scope. Therefore, it is intended that the present invention not be limited to the particular embodiment disclosed, but that the present invention will include all embodiments falling within the scope of the appended claims.

## Claims

1. A method for communications, the method comprising:
receiving a differential signal via a differential channel;
sensing a common mode signal on said differential channel;
determining a frequency range in which interference is present in said common mode signal;
configuring a frequency response of a filter according to said determined frequency range in which interference is present in said common mode signal and filtering, by said filter, said differential signal;
adjusting, by an adaptive filter circuit, at least one of a phase and an amplitude of said common mode signal based on said filtered differential signal; and
updating said received differential signal based on said adjusted common mode signal.

2. The method according to claim 1, further comprising selecting between an adaptive line enhancer and a filter bank.

3. The method according to claim 2, further comprising selecting between said adaptive line enhancer and said filter bank based on signal levels output by said adaptive line enhancer and said filter bank.

4. The method according to claim 2, further comprising selecting said filter bank when said adaptive line enhancer is unable to converge on a frequency within said determined frequency range.

5. The method according to claim 2, further comprising selecting between a high-pass response and a low-pass response of said filter bank.

6. The method according to claim 1, wherein said determining a frequency range in which interference is present in said common mode signal comprises automatically seeking and locking to a narrowband interference frequency of said common mode signal.

7. The method according to claim 2, further comprising enabling and disabling subtraction of said adjusted and filtered common mode signal from said received differential signal.

8. The method according to claim 1, wherein said adjusting at least one of a phase and an amplitude of said common mode signal further comprises reducing a difference between said filtered differential signal and said adjusted common mode signal.

9. The method according to claim 1, further comprising filtering said common mode signal by attenuating frequencies outside said determined frequency range in which interference is present in said common mode signal.

10. A method for communications, the method comprising:
in a communication device:
receiving a differential signal via a differential channel;
sensing a common mode signal on said differential channel;
determining a frequency range in which interference is present in said common mode signal;
filtering said common mode signal and said differential signal;
adjusting at least one of a phase and an amplitude of said filtered common mode signal based on said filtered differential signal;
subtracting said adjusted and filtered common mode signal from said received differential signal; and
sensing said common mode signal via a pair of resistors coupled to said differential channel, wherein
a first terminal of a first one of said resistors is coupled to a first wire of said differential channel;
a first terminal of a second one of said resistors is coupled to a second wire of said differential channel;
a second terminal of said first one of said resistors is coupled to a second terminal of said second one of said resistors;
said second terminals of said resistors are coupled to a first terminal of a primary winding of a transformer and a second terminal of said primary winding is coupled to signal ground; and
said common mode signal is present on said second terminals of said resistors.

11. The method according to claim 10, wherein said adjusting at least one of a phase and an amplitude of said common mode signal further comprises reducing a difference between said filtered differential signal and said filtered common mode signal.

12. The method according to claim 10, wherein said determining a frequency range in which interference is present in said common mode signal comprises automatically seeking and locking to a narrowband interference frequency of said common mode signal.

13. A system for communications, the system comprising:
a receiver that receives a differential signal via a differential channel;
a common mode sensor that senses a common mode signal on said differential channel;
an adaptive line enhancer that determines a frequency range in which interference is present in said common mode signal;
a filter having a frequency response configured according to said determined frequency range in which interference is present in said common mode signal that filters said differential signal;
an adaptive filter circuit that adjusts at least one of a phase and an amplitude of said filtered common mode signal based on said filtered differential signal; and
a combiner that updates said received differential signal based on said adjusted and filtered common mode signal.

14. The system according to claim 13, further comprising a filter bank and a multiplexer that selects between said adaptive line enhancer and said filter bank.

15. The system according to claim 14, wherein said multiplexer selects between said adaptive line enhancer and said filter bank based on signal levels output by said adaptive line enhancer and said filter bank.

16. The system according to claim 14, wherein said multiplexer selects said filter bank when said adaptive line enhancer is unable to converge on a frequency within said determined frequency range.

17. The system according to claim 14, further comprising a control unit that selects between a high-pass response and a low-pass response of said filter bank.

18. The system according to claim 13, wherein said adaptive line enhancer automatically seeks and locks to a narrowband interference frequency of said common mode signal.

19. The system according to claim 14, further comprising a control unit that disables and enables subtraction of said adjusted and filtered common mode signal from said received differential signal.

20. The system according to claim 13, wherein said adaptive filter circuit further reduces a difference between said filtered differential signal and said adjusted common mode signal.

21. The system according to claim 13, further comprising a common mode filter that attenuates frequencies outside said determined frequency range in which interference is present in said common mode signal.

22. A system for communications, the system comprising:
at least one processing circuit operable to:
receive a differential signal via a differential channel;
sense a common mode signal on said differential channel;
determine a frequency range in which interference is present in said common mode signal;
filter said common mode signal and said differential signal;
adjust at least one of a phase and an amplitude of said filtered common mode signal based on said filtered differential signal; and
subtract said adjusted and filtered common mode signal from said received differential signal; and

a transformer and a pair of resistors coupled to said differential channel, wherein
a first terminal of a first one of said resistors is coupled to a first wire of said differential channel;
a first terminal of a second one of said resistors is coupled to a second wire of said differential channel;
a second terminal of said first one of said resistors is coupled to a second terminal of said second one of said resistors;
said second terminal of said first one of said resistors and said second terminal of said second one of said resistors are coupled to a first terminal of a primary winding of said transformer;
a second terminal of said primary winding is coupled to signal ground; and
said common mode signal is present on said second terminals of said resistors.

23. The system according to claim 22, wherein said at least one processing circuit is further operable reduce a difference between said filtered differential signal and said filtered common mode signal.

24. The system according to claim 22, wherein said at least one processing circuit is further operable to automatically seek and lock to a narrowband interference frequency of said common mode signal.