Abstract:
A system for suppressing interference imposed on a victim communication signal by an aggressor communication signal including a circuit that comprises an input port, an output port, and a signal processing circuit connected between the input port and the output port, the signal processing circuit being operative to produce an interference compensation signal at the output port, for application to the victim communication signal, via processing a sample of the aggressor communication signal transmitted through the input port, and the input port being configured to connect to a sampling system that includes a first circuit trace running along a surface of a flex circuit of a portable wireless device that is dedicated to sensing the aggressor communication signal flowing on a second circuit trace running along the surface of the flex circuit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of and claims priority to U.S. patent application Ser. No. 12/380,654, filed Mar. 2, 2009 now U.S. Pat. No. 8,005,430, entitled “Method and System for Reducing Signal Interference,” which is a continuation of and claims priority to U.S. patent application Ser. No. 11/302,896, filed Dec. 14, 2005 now U.S. Pat. No. 7,522,883, entitled “Method and System for Reducing Signal Interference,” which claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 60/635,817, entitled “Electromagnetic Interference Wireless Canceller,” filed on Dec. 14, 2004, U.S. Provisional Patent Application Ser. No. 60/689,467, entitled “Automatic Gain and Phase Control for an Interference Cancellation Device,” filed on Jun. 10, 2005, U.S. Provisional Patent Application Ser. No. 60/696,905, entitled “Control Loop for Active Noise Canceller in Wireless Communication System,” filed on Jul. 6, 2005, U.S. Provisional Patent Application No. 60/719,055, entitled “Method and System for Embedded Detection of Electromagnetic Interference,” filed on Sep. 21, 2005, and U.S. Provisional Patent Application No. 60/720,324, entitled “Method and System for Reducing Power Consumption in an Interference Cancellation Device of a Wireless System,” filed on Sep. 23, 2005, the entire contents of each of which are hereby incorporated herein by reference in their entirety. 
    
    
     HELD OF THE INVENTION 
     The present invention relates to the field of communications, and more specifically to improving signal fidelity in a communication system by compensating for interference that occurs between two or more communication channels. 
     BACKGROUND 
     Electro-Magnetic Interference (“EMI”) is a major concern in wireless communication systems. These systems transmit and receive electro-magnetic (“EM”) signals to communicate data. Examples of such systems include mobile phones, wireless data networks (e.g. networks conforming to IEEE standards 802.11a/b/g/n), and global position systems/sensors (“GPSs”). EMI can become a problem when high-speed circuitry is routed in close proximity to a radio receiver. In particular, a high-speed signal can cause the emission of EMI, and when such a signal is routed in close proximity to a radio receiver, the receiver can undesirably receive the interference along with the intended received radio signal, termed the “victim” signal. The signal that imposes the interference can be termed the “aggressor” or “aggressing” signal. Thus, EMI often degrades the signal fidelity of the victim signal and impairs the quality of the radio reception. Exemplary sources of interference sources can include, among others, a high-speed bus carrying data from a processor to a high-resolution display and a high-speed bus carrying data from a camera imaging sensor to a processor. 
     As an example,  FIG. 1  illustrates the interference phenomenon in a mobile phone system  100  (along with a solution discussed below, in the form of an exemplary embodiment of the present invention), where a general/global system for mobile communications (“GSM”) radio receiver  105  can be aggressed by one or more interference sources. Specifically,  FIG. 1  illustrates two such exemplary EMI sources  110 ,  120 , each emitting and/or receiving interference  150 . One EMI source is a high-speed bus  120  carrying data from a digital signal processing (“DSP”) chip  135  to a high-resolution display  140 . The other EMI source is a high-speed bus  110  carrying data from a camera imaging sensor  145  to the DSP chip  135 . The camera imaging sensor  145  could comprise lenses coupled to a charge coupled device (“CCD”), for example. 
     Increasing the data rate or bandwidth of each lane, conductor, or channel of the display and camera busses  110 ,  120  is often desirable. This desire may be motivated by (i) a need to support higher display/camera resolution, which entails faster throughput commensurate with increasing the number of image pixels and/or (ii) a desire to reduce the number of data lanes in the bus  110 ,  120 , thereby involving an increase in the data rate on the remaining lanes to support the existing aggregate throughput. Thus, improvements in the display  140  or camera system  145  (e.g. higher resolution or condensed communication bus) can degrade the performance of the radio receiver  105  in the mobile phone system  100 . 
     Furthermore, it may be desired to improve the radio reception of mobile phones, such as cellular phones, with existing display/camera and bus technologies, i.e. to facilitate reception of weak radio signals. In other words, improving reception of low-power signals or noisy signals provides another motivation to reduce or to otherwise address interference  150  or crosstalk. A weak radio signal might have less intensity than the noise level of the EMI  150 , for example. Thus, it is desired to reduce the EMI  150  to facilitate reception of weaker radio signals or to enable operating a mobile phone or other radio in a noisy environment. 
     High-speed busses  110 ,  120  emitting, carrying, providing, imposing, and/or receiving interference can take multiple forms. For instance, in the mobile phone application described above, the bus  120  carrying the display data is often embodied as a “flex cable” which is sometimes referred to as a “flex circuit” or a “ribbon cable.” A flex cable typically comprises a plurality of conductive traces or channels (typically copper conductors) embedded, laminated, or printed on in a flexible molding structure such as a plastic or polymer film or some other dielectric or insulating material. 
       FIG. 2  illustrates several flex cables  200  any of which could comprise the data busses  110 ,  120  inside a mobile phone or another electronic device. (As discussed in more detail below, those flex cables  200  can be adapted to comprise an exemplary embodiment of the present invention.) The high-speed buses  110 ,  120  may also take the form of a plurality of conductive traces routed on a rigid dielectric substrate or material, such as circuit traces printed on, deposited on, embedded in, or adhering to a circuit board (“PCB”). 
     EMI  150  can also become problematic when two or more radio services are operated on the same handset. In this situation, the transmitted signal for a first radio service may interfere with the received signal for a second radio service. Such interference can occur even when two or more services utilize different frequency bands as a result of (i) the transmitted power of the first signal being significantly larger than the received power of the second signal and/or (ii) limited or insufficient suppression of sidebands in practical radio implementations. Consequently, a small fraction of the first, transmitted signal can leak into the second, received signal as interference. 
     A third source of EMI  150  can be circuits or circuit elements located in close proximity to a victim channel or radio. Like the signals on the high-speed buses  110 ,  120 , signals flowing through a circuit or circuit component can emit EMI  150 . Representative examples of circuit elements that can emit a problematic level of EMI  150  include voltage controlled oscillators (“VCOs”), phased-lock loops (“PLLs”), amplifiers, and other active or passive circuit components (not an exhaustive list). 
     One technique for actively addressing signal interference involves sampling the aggressor signal and processing the acquired sample to generate an emulation of the interference, in the form of a simulated or emulated interference signal. A canceller circuit subtracts the emulated interference signal from the received victim signal (corrupted by the interference) to yield a compensated or corrected signal with reduced interference. 
     Conventional technologies for obtaining a representative sample of the aggressor signal, or of the interference itself, are frequently inadequate. Sampling distortion or error can lead to a diminished match between the interference and the emulation of the interference. One technique for obtaining a sample of the aggressor signal is to directly tap the aggressor line. However, the resulting loss of power on the transmitted aggressor line is detrimental in many applications, such as in handheld radios, cell phones, or handset applications. Directly tapping into the aggressor line can also adversely impact system modularity. 
     The interference sampling system should usually be situated in close proximity to the source or sources of interference. This configuration helps the sampling system sample the interference signals while avoiding sampling the radio signal. Inadvertent sampling of the radio signal could result in the canceller circuit removing the victim radio signal from the compensated signal, thereby degrading the compensated signal. In other words, conventional technologies for obtaining an interference sample often impose awkward or unwieldy constraints on the location of the sampling elements. 
     For handset applications, the sampling system should be compatible with the handset architecture and its compact configuration. Radio handsets, such as mobile phones, typically contain numerous components that design engineers may struggle to integrate together using conventional technologies. Strict placement requirements of conventional interference sampling systems frequently increase system design complexity. In other words, conventional interference sampling systems often fail to offer an adequate level of design flexibility as a result of positioning constraints. 
     Another shortcoming of most conventional technologies for active EMI cancellation involves inadequate management of power consumption. An active EMI cancellation system may consume an undesirably high level of electrical power that can shorten battery life in handset applications. That is, EMI cancellation technology, when applied in a cellular telephone or another portable device, often draws too much electricity from the battery or consumes too much energy from whatever source of energy that the portable device uses. Consumers typically view extended battery life as a desirable feature for a portable wireless communication product. Thus, reducing power consumption to extend usage time between battery recharges is often an engineering goal, mandate, or maxim. 
     To address these representative deficiencies in the art, what is needed is an improved capability for addressing, correcting, or canceling signal interference in communication systems. A need also exists for a compact system for sampling an aggressor signal and/or associated interference in a communication system, such as a cellular device. A further need exists for an interference sampling system that affords an engineer design modularity and/or flexibility. Yet another need exists for a system that reduces or suppresses signal interference while managing power consumption. A capability addressing one or more of these needs would support operating compact communication systems at high data rates and/or with improved signal fidelity. 
     SUMMARY OF THE INVENTION 
     The present invention supports compensating for signal interference, such as EMI or crosstalk, occurring between two or more communication channels or between two or more communication elements in a communication system. Compensating for interference can improve signal quality or enhance communication bandwidth or information carrying capability. 
     A communication signal transmitted on one communication channel can couple an unwanted interference signal onto a second communication channel and interfere with communication signals transmitting on that second channel. Either channel or each of the channels can comprise a transmission line, an electrical conductor or waveguide, a bus, a medium that provides a signal path, or an active or passive circuit element such as a filter, oscillator, diode, or amplifier (not an exhaustive list). Thus, a channel can be a GSM device, a processor, a detector, a source, a diode, a circuit trace, or a DSP chip, to name a few possibilities. 
     In addition to occurring between two channels, the interference effect can couple between and among three or more communication channels, with each channel imposing interference on two or more channels and receiving interference from two or more channels. A single physical medium, such as a single segment of wire, can provide a transmission medium for two or more channels, each communicating digital or analog information. Alternatively, each channel can have a dedicated transmission medium. For example, a circuit board or flex cable can have multiple conductors in the form of circuit traces, in which each trace provides a distinct communication channel. 
     In one aspect of the present invention, a sensor can be disposed in the proximity of one or both channels to obtain a sample or representation of the interference and/or the aggressor signal that produced, induced, generated, or, otherwise caused the interference. The sensor can comprise a sensing or sampling channel that obtains the sample. As an aggressor channel transmits communication signals, such as digital data or analog information, producing interference on a victim channel, the sensing channel can sample the aggressing communication signals and/or the interference. The sensing channel can be, for example, a conductor dedicated to obtaining a representation of the aggressing signal or the interference. Such a sensing conductor can be near a conductor carrying aggressing signals, near a conductor carrying victim signals, or in an EM field associated with the aggressing channel and/or the victim channel. The sensing conductor can be physically separated from the aggressing conductor while coupling to the aggressing conductor via an inductive field, a magnetic field, an electrical field, and/or an EM field. That is, the sensing conductor can obtain a sample of the aggressor signal without necessarily physically contacting or directly touching the aggressor conductor, for example. 
     In another aspect of the present invention, a circuit that cancels, corrects, or compensates for or otherwise address communication interference can have at least two modes of operation. The interference compensation circuit could be coupled to the sensor, for example. In the first mode, the interference compensation circuit can generate, produce, or provide a signal that, when applied to a communication signal, reduces interference associated with that communication signal. In the second mode, the interference compensation circuit can refrain from producing or outputting the interference correction signal. The second mode can be viewed as a standby, idle, passive, sleep, or power-saving mode. Operating the interference compensation circuit in the second mode can offer a reduced level of power consumption. 
     The discussion of addressing interference presented in this summary is for illustrative purposes only. Various aspects of the present invention may be more clearly understood and appreciated from a review of the following detailed description of the disclosed embodiments and by reference to the drawings and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a functional block diagram of a communication system comprising an interference sensor coupled to an interference compensation circuit according to an exemplary embodiment of the present invention. 
         FIG. 2  illustrates flex circuits that can comprise an integral interference sensor according to an exemplary embodiment of the present invention. 
         FIG. 3  illustrates a functional block diagram of an interference compensation circuit according to an exemplary embodiment of the present invention. 
         FIG. 4  illustrates a frequency plot of an interference signal prior to interference compensation overlaid on a plot of the interference signal following interference compensation according to an exemplary embodiment of the present invention. 
         FIG. 5  illustrates a plot of an interference signal prior to application of interference compensation according to an exemplary embodiment of the present invention. 
         FIG. 6  illustrates a plot of an interference signal following application of interference compensation according to an exemplary embodiment of the present invention. 
         FIG. 7  illustrates an interference compensation circuit that can be coupled to an interference sensor according to an exemplary embodiment of the present invention. 
         FIG. 8  illustrates a flowchart of a process for operating an interference compensation circuit in a plurality of modes according to an exemplary embodiment of the present invention. 
     
    
    
     Many aspects of the invention can be better understood with reference to the above drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of exemplary embodiments of the present invention. Moreover, in the drawings, reference numerals designate corresponding, but not necessarily identical; parts throughout the different views. 
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The present invention supports canceling, correcting, addressing, or compensating for interference, EMI, or crosstalk associated with one or more communication paths in a communication system, such as a high-speed digital data communication system in a portable radio or a cellular telephone. An interference sensor can obtain a signal representation or a sample of a communication signal that imposes interference or of the interference. The interference sensor can be integrated into a structure, such as a flex circuit or a circuit board, that supports or comprises at least one conductor that imposes or receives the interference. In an exemplary embodiment, the interference sensor can be a dedicated conductor or circuit trace that is near an aggressor conductor, a victim conductor, or an EM field associated with the EMI. The sensor can be coupled to an interference compensation circuit. The interference compensation circuit can have at least two modes of operation. In the first mode, the circuit can actively generate or output a correction signal. In the second mode, the circuit can withhold generating or outputting the correction signal, thereby conserving power and/or avoiding inadvertently degrading the signal-to-noise ratio of the involved communication signals. 
     Turning to discuss each of the drawings presented in  FIGS. 1-8 , in which like numerals indicate like elements, an exemplary embodiment of the present invention will be described in detail. 
     Referring now to  FIGS. 1 and 2 ,  FIG. 1  illustrates a functional block diagram of a communication system  100  comprising an interference sensor  115 ,  125  coupled to an interference compensation circuit  130  according to an exemplary embodiment of the present invention.  FIG. 2  illustrates flex cables or flex circuits that can comprise one or both of the data buses  110 ,  120  illustrated in  FIG. 1  and that can be adapted in accordance with an exemplary embodiment of the present invention to comprise an interference sensor. In an exemplary embodiment, a cellular telephone or some other portable wireless device can comprise the communication system  100 . 
     A DSP chip  135  connects to a display  140  and a camera  145  via two data busses  110 ,  120  or channels. Digital data flowing on the data busses  110 ,  120  causes, induces, and/or is the recipient of interference  150 , such as EMI. Beyond the data busses  110 ,  120 , a channel receiving or causing interference can comprise the display  140 , and/or the radio system  105 . As will be appreciated by those skilled in the art, the victim radio system  105  handles communication signals in connection with transmission over a wireless network. 
     In an exemplary embodiment, a flex circuit  200 , as illustrated in  FIG. 2 , comprise the data busses  110 ,  120 . The flex circuit  200  typically comprises a polymer, plastic, or dielectric film that is flexible and further comprises conductive circuit traces deposited on or adhering to the film substrate. Conductors can be laminated between two pliable films, for example. The data buses  110 ,  120  can be embodied in one or more ribbon cables. 
     The communication system  100  comprises an interference compensation or correcting circuit  130 , depicted in the exemplary form of an integrated circuit  130 . The interference compensation circuit  130 , described in further detail below, delivers an interference compensation signal into or onto a channel that is a recipient of interference, to cancel or otherwise compensate for the received interference. The interference compensation signal is derived or produced from a sample of an aggressor communication signal that is propagating on another channel, generating the crosstalk. 
     The interference compensation circuit  100  can be coupled between the channel  110 ,  120  that generates the interference  150  and the device  105  that receives the interference  150 . In this configuration, the interference compensation circuit  130  can sample or receive a portion of the signal that is causing the interference and can compose the interference compensation signal for application to the victim device  105  that is impacted by the unwanted interference  150 . In other words, the interference compensation circuit  110 ,  120  can couple to the channel  110 ,  120  that is causing the interference  150 , can generate an interference compensation signal, and can apply the interference compensation signal to the recipient  105  of the interference to provide interference cancellation, compensation, or correction. 
     A battery, not shown on  FIG. 1 , typically supplies energy or power to the interference compensation circuit  130  as well as the other components of the system  100 . As an alternative to a battery, a fuel cell or some other portable or small energy source can supply the system  100  with electricity. As discussed in more detail below, the system  100  and specifically the interference compensation circuit  130  can be operated in a manner that manages battery drain. 
     The interference compensation circuit  130  can generate the interference compensation signal via a model of the interference effect. The model can generate the interference compensation signal in the form of a signal that estimates, approximates, emulates, or resembles the interference signal. The interference compensation signal can have a waveform or shape that matches the actual interference signal. A setting or adjustment that adjusts the model, such as a set of modeling parameters, can define characteristics of this waveform. 
     The interference compensation circuit  130  receives the signal that is representative of the aggressor signal (or alternatively of the interference itself) from a sensor  115 ,  125  that is adjacent one or both of the data busses  110 ,  120 . In an exemplary embodiment, the sensor  115 ,  125  comprises a conductor, associated with one or both of the data bus channels  110 ,  120 , that is dedicated to obtaining a sample of the aggressor signal. For example, the data bus  110  can have a plurality of conductors that transmit data between the camera  145  and the DSP chip  135  and at least one other conductor that senses, sniffs, or samples the aggressor signal, or an associated EM or EMI field, rather carrying data for direct receipt. For example, one of the data bus conductors can function as a sensor during a time interval when that specific conductor is not conveying purposeful data. 
     In an exemplary embodiment, the sensor  115 ,  125  is integrated into a common structure to which the conductors of the data bus  110 ,  120  adhere or are attached: For example, the sensor  115 ,  125  can be attached to a flex cable  200 . In one exemplary embodiment, the sensor  115 ,  125  comprises a conductive trace deposited on the flex cable  200 . In one exemplary embodiment, the sensor  115 ,  125  couples to the communication signals propagating on the data bus  110 ,  120  via the EM field of those signals. For example, the coupling can be via induction rather than through a direct contact that could transmit direct current (“DC”) energy or signals below a threshold frequency. Thus, the sensors  115 ,  125  can be isolated from the aggressor channel below a threshold frequency and coupled to the aggressor channel above a threshold frequency. 
     The sensor  115 ,  125  can be formed into or integrated with the flex cable  200  at the time that the flex cable  200  is manufactured, for example as a step in a manufacturing process that involves lithography. The flex cable  200  can alternatively be adapted following its manufacture, for example by adhering the sensor to the flex cable  200 . That is, a conventional flex cable can be acquired from a commercial vendor and processed to attach the sensor  115 ,  125  to that cable. 
     In one exemplary embodiment of the present invention, the sensor  115 ,  125  comprises an interference sampler located in close proximity to an interference source. In another exemplary embodiment of the present invention, the interference compensation circuit  130  samples its reference signal from a conductor that is in the vicinity of a victim antenna. In yet another exemplary embodiment of the present invention, the interference sensor  115 ,  125  comprises a sampling mechanism embedded as a lane within the bus path  110 ,  120  of the interference source. For example, the sampling mechanism can comprise an additional conductive line running parallel to the other data lines in a flex cable, or in a rigid printed circuit board. Embedding the sampling mechanism can provide compact size, design flexibility, modularity, signal integrity, and minimal power draw from the sensed line, which are useful attributes for a successful sampling mechanism and EMI canceller or interference cancellation/compensation system. 
     Embedding or integrating the sensor  115 ,  125  or sampling mechanism in a unitary, monolithic, or integrated structure that comprises the bus path  110 ,  120  provides close proximity between the sensor  115 ,  125  and the interference source or sources. The resulting close proximity facilitates strong sampling of the interference relative to the radio signal. 
     Embedding or integrating the sensor  115 ,  125  with the bus path  110 ,  120  offers the system designer (and PCB board designer in particular) design flexibility. For example, the design engineer can be freed from the constraint of allocating board space near the interference source for the sampling mechanism, as would be required for an antenna implementation. The system designer can receive relief from the task of designing an antenna according to one or more specific reception requirements, such as a field pattern and a frequency range. 
     An integrated- or embedded-sensor solution based on dedicating a conductor  115 ,  125  of a multi-conductor bus  110 ,  120  to sensing can have an inherent capability to receive the EMI interference. The inherent receptivity can mirror the inherent emission properties of the other conductors that generate interference. In other words, since emission and reception are typically congruent phenomena, configuring the sensing conductor to have a form similar to the radiating conductor (aggressor) can provide inherent reception of the EMI frequencies of interest. 
     In one exemplary embodiment of the present invention, the embedded interference sensor  115 ,  125  can run, extend, or span the entire length of the data bus  110 ,  120  that has data lines emitting the aggressing EMI. 
     In one exemplary embodiment of the present invention, an interference sensing conductor  115  can extend a limited portion of the total span of the data bus  110 ,  120 , thereby helping the data bus  110 ,  120  maintain a compact width. Another exemplary embodiment which can minimize the width of the data bus has the sampling mechanism  115 ,  125  crossing over or under the data lines  110 ,  120 . The crossing can be a perpendicular crossing. The sensing conductor and the data conductors can form an obtuse angle or an acute angle, for example. 
     As illustrated in  FIG. 1 , the sensing conductor  115 ,  125  can be disposed at a terminal end of the data bus  110 ,  120 . For example, the sensing conductor  115  can comprise a conductive line near the electrical connection ports between the DSP chip  135  and a flex cable  200  that comprises the data bus  110 . Such a conductor can extend over, under, and/or around the bus, for example as a conductive band. 
     In one exemplary embodiment of the present invention, the embedded interference sensor  115  receives EMI interference not only from a primary element, such as its associated data bus  110 , but also from other sources on the handset, such as the display  140 , the camera  145 , the DSP  135 , etc. Thus, a single sensor  115  can sample multiple sources of interference to support correcting the interference from two or more sources via that single sensor and its associated interference compensation circuit  130 . 
     In one exemplary embodiment of the present invention, the interference compensation circuit  130  samples its reference signal (i.e. the aggressor source) from a conducting element  115 ,  125  that receives radiated EMI  150 . This sampling approach can sense the EMI  150  (or a filtered version thereof), or the aggressor signal in a non-intrusive manner. Specifically, the aggressor data line/source can remain essentially undisturbed physically. The data bus  110 ,  120  can function with little or no loss of power associated with the sensor  115 ,  125  inductively coupled thereto, typically without physical contact or direct electrical contact. That is, a dielectric material can separate the sensing conductor  115 ,  125  from the aggressor conductor, while providing inductive or EM coupling. 
     After sampling the reference signal, the interference compensation circuit  130  generates a compensation or cancellation signal which is adjusted in magnitude, phase, and delay such that it cancels a substantial portion of the interference signal coupled onto the victim antenna. In other words, the reference signal, which comprises the sample, is filtered and processed so it becomes a negative of the interference signal incurred by the received victim signal. The parameters of the magnitude, phase, and delay adjustment are variable and can be controlled to optimize-cancellation performance. 
     Turning now to  FIG. 3 , this figure illustrates a functional block diagram of an interference compensation circuit  130  according to an exemplary embodiment of the present invention. The interference compensation circuit  130  shown in  FIG. 3  can be embodied in a chip format as an integrated circuit (“IC”), as illustrated in  FIG. 1 , or as a hybrid circuit. Alternatively, the interference compensation circuit  130  can comprise discrete components mounted on or attached to a circuit board or similar substrate. Moreover, in one exemplary embodiment of the present invention, the system  100  that  FIG. 1  illustrates can comprise the system  300  of  FIG. 3 . 
     The interference compensation circuit  130  draws or obtains power or energy from the power supply  360 , and its associated battery  365 . As will be discussed in further detail below, the interference compensation circuit  130  can operate in a plurality of modes, each having a different level of consumption of battery energy. 
       FIG. 3  illustrates representative function blocks of the interference compensation circuit  130 , including a Variable Phase Adjuster  305 , a Variable Gain Amplifier (“VGA”)  310 , an emulation filter  315 , a Variable Delay Adjuster  320 , a Summation Node  325 , a power detector, and a controller  335 . 
     The interference sensor  115  obtains a sample of the aggressor signal via coupling of the interference field, as discussed above, from the receiving channel  110 . The sampled reference signal is fed through the compensation circuit  130  starting with the Variable Phase Adjuster  305 . The phase adjuster&#39;s role is to match, at the summation node  325 , the phase of the emulated compensation signal with the phase of the interfering signal coupled onto the victim antenna  340 . That is, the phase adjuster  305  places the phase of the compensation signal in phase with respect to the phase of the interference so that, when one is subtracted from the other, the compensation signal cancels the interference. The cancellation occurs at the summation node  325  by subtracting the coupled signal onto the victim antenna  340  from the emulated signal generated by the interference compensation circuit  130  using the sampled reference signal (from the sensor  115 ). 
     In an alternative embodiment of the compensation circuit  130 , the phase adjuster  305  can adjust the emulated signal phase to be 180 degree out of phase with the interfering coupled signal. In that case, the summation node  325  adds the two signals rather than performing a subtraction. 
     In one exemplary embodiment, the phase shifter  305  comprises quadrature hybrids, and four silicon hyper-abrupt junction varactor diodes, along with various resistors, inductors and capacitors for biasing, pull-up, and signal conditioning. In another exemplary embodiment, the phase shifter  305  comprises an active circuit. 
     The emulation filter  315  follows the variable phase shifter  305  in the cancellation path. The emulation filter  315  is typically a band pass (“BP”) filter that models the channel coupling and is also tunable in order to compensate for any drifts in channel center frequency. 
     In one exemplary embodiment, the emulation filter  325  comprises lumped elements and varactor diodes. The varactor diodes help change or control the center frequency of the emulation channel. 
     In one exemplary embodiment, the emulation filter  325  is a Finite Impulse Filter (“FIR”). The FIR can comprise taps and tap spacings that are extracted from or determined according to the coupling channel characteristics. In order to have robust cancellation for improved signal integrity of the communication system  100 , the emulation filter  325  typically should match, in trend, the coupling channel characteristics within the frequency band of interest. 
     The next component in the cancellation path is the controllable delay adjuster  320 , whose main role is to provide a match between the group delay of the coupled signal through the victim antenna  340  and the group delay of the emulated compensation signal at the summation node  325 . 
     The output of the delay adjuster  320  feeds into the VGA  310 . The VGA  310  matches the emulated signal&#39;s amplitude to the amplitude of the interference signal at the summation node  325 . Whereas the emulation filter  315  models the frequency characteristics (i.e. attenuation of frequencies relative to other frequencies) of the coupling channel, the VGA  310  applies a broadband gain, which is constant in magnitude across the frequency band of interest. Thus, the emulation filter  315  and the VGA  310  function collaboratively to match the magnitude of the channel&#39;s coupling response on an absolute scale, rather than merely a relative scale. 
     The VGA  310  feeds the interference compensation signal to the summation node  325 . In turn, the summation node  325  applies the compensation signal to the victim channel to negate, cancel, attenuate, or suppress the interference. 
     In one exemplary embodiment, the summation node  325  comprises a directional coupler. In an alternative exemplary embodiment, the summation node  325  comprises an active circuit such as a summer, which is typically a three-terminal device, or an output buffer, which is typically a two-terminal device. 
     For best performance, the summation node  325  should introduce essentially no mismatch to the victim antenna signal path. That is, the summation node  325  should ideally maintain the 50-ohm impedance characteristic of the system  130 . Nevertheless, in some situations, small or controlled levels of impedance mismatch can be tolerated. Avoiding impedance mismatch implies that the summation node  325  should have a high output impedance at the tap. Additionally, the summation node  325  should not add significant loss to the victim antenna receive path, as such loss can adversely affect receiver sensitivity. For illustrative purposes, this discussion of impedance matching references a system with a characteristic impedance of 50-ohms; however, exemplary embodiments of the present invention can be applied to systems with essentially any characteristic impedance. 
     While  FIG. 3  illustrates the components  305 ,  310 ,  315 ,  320  is a particular order, that order is exemplary and should not be considered as limiting. Moreover, the order of those components  305 ,  310 ,  315 ,  320  is usually not critical and can be changed, or the components  305 ,  310 ,  315 ,  320  can be rearranged, while maintaining acceptable performance of the interference compensation circuit  130 . 
     The interference compensation circuit  130 , which can be viewed as an EMI canceller, offers flexibility in that the cancellation or compensation parameters can be adjusted or controlled to optimize the match of the emulated coupling channel to the actual EMI coupling channel. More specifically, the controller  335  and its associated power detector  330  provide a feedback loop for dynamically adjusting the circuit elements  305 ,  310 ,  315 ,  320  in a manner that provides robust correction of interference. 
     Two methods for controlling these parameters are described in U.S. Provisional Patent Application Ser. No. 60/689,467, entitled “Automatic Gain and Phase Control for an Interference Cancellation Device” and filed on Jun. 10, 2005 in the name of Kim et al. and U.S. Provisional Patent Application Ser. No. 60/696,905, entitled “Control Loop for Active Noise Canceller in Wireless Communication System” and filed on Jul. 6, 2005 in the name of Schmukler et al. The entire contents of U.S. Provisional Patent Application Ser. Nos. 60/689,467 and 60/696,905 are hereby incorporated herein by reference. Thus, an exemplary embodiment of the present invention can comprise any of the technologies, teachings, systems, methods, processes, or disclosures of U.S. Provisional Patent Application Ser. Nos. 60/689,467 and 60/696,905. 
     Referring now to  FIG. 7 , this figure illustrates an interference compensation circuit  700  that can be coupled to an interference sensor  115 ,  125  according to an exemplary embodiment of the present invention. In other words, in one exemplary embodiment, the system  100  illustrated in  FIG. 1  and discussed above can comprise the circuit  700  rather that the circuit  130 . U.S. Provisional Patent Application Ser. No. 60/696,905, entitled “Control Loop for Active Noise Canceller in Wireless Communication System” and filed on Jul. 6, 2005 in the name of Schmukler et al. provides additional information about the circuit  700  to supporting using that circuit  700  in an exemplary embodiment of the present. The contents of U.S. Provisional Patent Application Ser. No. 60/696,905 are hereby included herein by reference. 
     Turning now to  FIG. 4 , this figure illustrates a frequency plot  410  of an interference signal prior to interference compensation overlaid upon a plot  420  of the interference signal following interference compensation according to an exemplary embodiment of the present invention. That is, the graph  400  illustrates laboratory test data collected before and after an application of interference compensation in accordance with an exemplary embodiment of the present invention. 
     More specifically,  FIG. 4  shows the coupling channel characteristics between a flex cable, similar to the flex cables  200  illustrated in  FIG. 2  and discussed above, and a 2.11 gigahertz (“(GHz”) antenna. The test data shows that, in laboratory testing, an exemplary embodiment of an interference compensation circuit  130  achieved a signal reduction greater than 25 dB in the frequency band between 2.1 GHz and 2.15 GHz. 
     Turning now to  FIGS. 5 and 6 , these figures respectively show spectral plots  500 ,  600  before and after applying interference compensation according to an exemplary embodiment of the present invention. More specifically, the traces  520 ,  620  of these plots  500 ,  600  illustrate data obtained in laboratory testing of an interference compensation system in accordance with an exemplary embodiment of the present invention. 
     The spectra  520 ,  620  characterize a 450 megabits-per-second (“Mbps”) (PRBS-31) interfering signal coupled onto a 2.1 GHz antenna that is in close proximity to a flex cable carrying the 450 Mbps signal. In the frequency band of interest  510 , the compensation achieved approximately 12 dB of interference suppression. 
     Referring now to  FIGS. 1 ,  2 , and  3 , the interference compensation circuit  130  can function or operate in at least two modes. In one mode, the circuit  130  can consume less power than in the other mode. That is, the interference compensation circuit  130  can transition from an active mode of relatively high power usage to an other mode of relatively low power usage. The other mode can be a standby mode, a power-saving mode, a passive mode, an idle mode, a sleep mode, or an off mode, to name a few possibilities. In that other mode, the interference compensation circuit can draw a reduced level of power, minimal power, essentially no power, or no power at all. Part or all of the interference compensation circuit illustrated in  FIG. 3  and discussed above can be disconnected from power in the other mode. An occurrence of one criterion or multiple criteria or conditions can trigger a transition from active compensation to a standby mode. Thus, the transition can occur automatically in response to an event other than a user turning off an appliance, such as a cell phone, that comprises the circuit  130 . 
     In a handset application, operating the interference compensation circuit  130  in a power-saving mode can extend the operation time of a single battery charge, thereby enhancing the commercial attractiveness of the handset. Power reduction can be implemented or achieved without degrading interference compensation performance. 
     Conditions occur in wireless handset devices that provide an opportunity for reduced power consumption. In particular, many of the EMI sources are not always active and, therefore, are not always emitting interference. In situations in which the interference compensating circuit  130  and its associated controller  335  do not need to apply a compensation signal, the circuit  130  can transition to a sleep or stand-by mode of reduced power consumption. That is, rather than having one or more circuit elements receiving power while not producing an output or actively manipulating signals, power can be removed from those elements or from a selected set of circuit elements. 
     Thus, in one exemplary embodiment of the present patent invention, the system  100  experiences states in which operating certain components of the interference compensation circuit  130  is unnecessary. In such states, the controller  335  can place those components in a low-power or standby mode or can remove power entirely from those components. For example, when an EMI source is not active for a threshold amount of time, the interference compensation circuit  130  can transition to the standby mode. More specifically, when the bus  110  is not actively carrying data traffic, the interference compensation circuit  130  can switch to the standby mode to conserve battery power. 
     In one exemplary embodiment, the sensor  115  provides a signal that is indicative of whether the bus  110  is active. That is, the level, voltage, amplitude, or intensity of the signal that the sensor  115  output can provide an indication of whether the bus is actively transmitting aggressor signals. 
     When appropriate conditions are met, electrical power can be removed from the components  305 ,  310 ,  315 ;  320  that generate the emulated EMI signal. And, power can additionally or optionally be removed from some or all of the circuitry of the control module  335 . However, components used to store the emulation characteristics or parameters, i.e. the emulation channel settings that match the coupling channel, can be kept active so as to immediately or quickly restore the interference compensation circuit&#39;s emulation channel to its last known state when the EMI source (e.g. the aggressor channel  110 ) is reactivated. In other words, the memory system of the controller  335  can retain power access to avoid loss of the parametric values stored in memory. Keeping the parametric values in memory facilitates rapid restoration to active cancellation upon reactivation of the EMI source. Thus, recalling the operational settings of the phase adjuster  305 , the emulation filter  315 , the delay adjuster  320 , and the VGA  310  avoids the interference that would occur if the emulation was retrained from an arbitrary reset state following transition from standby mode to active mode. 
     Operating in the standby mode can comprise either full powering down one or more circuit components and/or operating in a state of reduced power usage. In some instances, the latter may be preferred in order to rapidly bring the component out of the standby state when the EMI source is reactivated. 
     In one exemplary embodiment of the present invention, a standby signal instructs or triggers the interference compensation circuit  130  to transition to its power-saving or standby state. The standby signal can also trigger the transition from the power-saving or standby state to an active state. A device transmitting the source of the EMI, or an associated power detector, can generate a signal indicating that it is actively transmitting data. For example, the DSP chip  135  that sends data to the display  140  in the mobile phone system  100  can output an binary signal or code to indicate that it not transmitting data and consequently emitting EMI. 
     As another example, the camera imaging sensor  145  that sends data to a the DSP chip  135  can output a binary signal or a digital code to indicate whether or not it is transmitting data that could produce EMI. As yet another example, a radio device that uses time-division multiplexing can provide the triggering standby signal. Such a radio device can be used in GSM or wideband code division multiple access (“W-CDMA”) applications, for example. In this situation, the radio may output a binary signal to mark the time divisions or intervals in which it is transmitting data. During those portions of the duplexing stage, the interference compensation should be active, as the transmitted signal can aggress a second radio device on a wireless handset. 
     In one exemplary embodiment of the present invention a power detector, such as the detector  330 , examines the sampled EMI signal and generates the standby signal based on properties of the sampled EMI signal. For example, a standby state can be set if the detector  330  determines that power of the sampled EMI signal is below a given or predetermined threshold. Conversely, the interference compensation circuit  130  can be activated when the detected power moves above the threshold. 
     In one exemplary embodiment of the present invention, the standby state can be declared if the time-localized peak amplitude of the sampled EMI signal falls below a given threshold. One advantage of this embodiment is that its implementation does not typically require an extra pin on the device package to be fed a dedicated standby signal. Instead, the standby signal could be derived from an available pin already used for EMI cancellation. 
     In one exemplary embodiment of the present invention, all the components  305 ,  310 ,  315 ,  320  of the emulation channel that are used to generate the emulated EMI signal from the sensor&#39;s sampled EMI source signal can be placed in the low-power standby state. In one exemplary embodiment of the present invention, one or more of the following components are placed in standby mode in response to an occurrence of a standby condition: the phase adjuster  305 , the EP channel emulation filter  315 , the delay adjuster  320 , and the VGA  310 . Reducing power consumption of those devices components  305 ,  310 ,  315 ,  320  facilitates significant power savings when the EMI source is inactive. 
     The controller  335 , which can also be referred to as a control module, can be inactive when the EMI source is inactive. With no source of EMI and an inactive controller  335 ; interference is not typically problematic. More specifically, no EMI occurs, and the emulation path is producing a zero emulation signal. In many circumstances, an improvement in interference performance can result from deactivating the emulation path when no source of EMI is active. If the emulation channel remains active when no EMI source is active, the emulation channel parameters may drift towards a set of values that poorly match the underlying EMI coupling channel. In this situation, activating the EMI source can result in poor tuning that causes the interference compensation circuit  130  to learn new, more effective parameters. In other words, when the interference compensation circuit  130  is inactive, an improperly tuned coupling channel can still produce a zero emulation signal since the sampled EMI source signal will be zero. 
     In one embodiment of the present invention, all of the components, or essentially all of the active components, of the control module can be placed in the standby state when the standby signal is asserted, thereby providing a high level of power savings. 
     In one exemplary alternative embodiment of the present invention, the register or memory elements used to store the controllable parameters in the emulation channel are fully powered, while the rest of the control module  335  is deactivated. This embodiment facilitates rapidly or immediately returning the emulation channel to its pre-standby state when the system exits the standby mode. In other words, once the system leaves standby mode, the interference compensation circuit  130  can resume cancellation from a previously-known and accurate channel model, rather than starting the cancellation from an arbitrary reset state. Resuming operation of the interference compensation circuit  130  from an arbitrary set of parameters may take an undesirably long period of time prior to convergence to an accurate channel model. During this learning time, EMI cancellation performance may be insufficient or inadequate. 
     Referring now to  FIG. 7 , the interference compensation circuit  700  can operate in two or more modes, one of which offers reduced power consumption relative to the other. In other words, in one exemplary embodiment of the present invention, the circuit  700  transitions to a power-saving mode upon occurrence of a trigger event. In that mode, power can be removed from one or more of the power detector  220 , the switching device  230 , the sample and hold circuits  240   a  and  240   b , and the comparator  250 . The power detector  220  and comparator  250  are two leading contributors to power consumption, thus disconnecting their power supply can achieve significant power savings. The control and timing circuit  260  typically comprises low-speed digital logic that consumes negligible power. Nonetheless, most of this circuit  260  can be deactivated with the exception of the registers, which store the values of the emulation channel  270  parameters. 
     Turning now to  FIG. 8 , this figure illustrates a flowchart of a process  800  for operating an interference compensation circuit  130  in a plurality of modes in accordance with an exemplary embodiment of the present invention. The Process  800 , which is entitled Operate Interference Compensation Circuit, can be viewed as a process for managing power consumption of an interference compensation circuit  130 . 
     At Step  805 , a data transmitter, such as the camera  145  or the DSP chip  135  issues a standby signal that can comprise a digital code. The code carries the status of the transmitter, for example whether the transmitter is actively transmitting data or is in a passive state between two time periods of data transmission. In one embodiment, the code specifies whether the transmitter is preparing to actively transmit data or to change between operational states. 
     At Step  810 , the controller  335  receives the standby signal and determines whether the transmitter is in an active state of transmitting data or a passive state. Decision Step  815  branches the flow of Process  800  to Step  825  if the standby signal indicates that the transmitter is active. If, on the other hand, the standby signal indicates that the transmitter is passive, then decision Step  820  follows Step  820 . 
     At decision Step  820 , the controller  335  determines whether the interference compensation circuit  130  is in an active mode or is otherwise in a passive mode, If the interference compensation circuit  130  is in an active mode, then Step  830  follows Step  820 . 
     At Step  830 , the controller  335  stores the current or present compensation parameters in memory and removes power from the emulation channel components  305 ,  310 ,  315 ,  320 . This action places the interference compensation circuit  130  in a standby or power-saving mode. The stored compensation parameters typically comprise the settings of each of the adjustable components  305 ,  310 ,  315 ,  320  of the emulation channel. 
     If at decision Step  820 , the controller  335  determines that the interference compensation circuit  130  is in the standby mode rather than the active mode, then Step  840  follows Step  820 . At Step  840 , the interference compensation circuit  130  remains in the standby mode. 
     If decision step  815  branches the flow of Process  800  to Step  825  rather than Step  820  (based on the standby signal indicating active data transmission), then at decision Step  825 , the controller  335  determines whether the interference compensation circuit  130  is in active mode or standby mode. 
     If the interference compensation circuit  130  is in active mode, then Step  845  follows Step  825 . At Step  845 , the interference compensation circuit  130  remains in active mode. 
     If the controller  335  determines at decision Step  825  that the interference compensation circuit  130  is in standby mode rather than active mode, then Step  835  follows Step  825 . At Step  835 , the controller  335  recalls the current or last-used compensation parameters from memory and restores power to the powered-down components. Restoring power typically comprises initializing each of the adjustable components  305 ,  310 ,  315 ,  320  of the emulation channel with the parametric settings recalled from memory. 
     Step  850  follows execution of either of Steps  835  and  845 . At Step  850 , the interference compensation circuit  130  generates an estimate of the interference based on processing the aggressor sample, which the sensor  115  obtained. As discussed above with reference to  FIG. 3 , the emulation channel components  305 ,  310 ,  315 ,  320  process the sample to output the interference estimate. 
     At Step  855 , the interference compensation circuit  130  applies the interference estimate to the victim channel to cancel, suppress, or correct the interference occurring thereon. 
     Following execution of any of Steps  830 ,  840 , and  855 , Process  800  loops back to and executes Step  805  as discussed above. Execution of Process  800  continues following the loop iteration. 
     In summary, a system in accordance with an exemplary embodiment of the present invention can comprise a sensor that obtains a representative interference sample or a sample of an interfering signal. A system in accordance with an exemplary embodiment of the present invention can alternatively, or also, comprise a circuit that operates in two or more modes to cancel, correct, or compensate for interference imposed on one communication signal by another signal. The system can be applied to wireless communication devices, such as cell phones, personal data assistants (“PDAs”), etc. However, those skilled in the art will appreciate that the present invention is not limited to the described applications and that the embodiments discussed herein are illustrative and not restrictive. Furthermore, it should be understood that various other alternatives, to the embodiments of the invention described here may be recognized by those skilled in the art upon review of this text and the appended figures. Such embodiments may be employed in practicing the invention. Thus, the scope of the present invention is intended to be limited only by the claims below.