Patent Publication Number: US-2015064970-A1

Title: Systems, apparatus, and methods for an embedded emissions filter circuit in a power cable

Description:
CLAIM OF PRIORITY UNDER 35 U.S.C. §119 
     The present application for patent claims priority to Provisional Application No. 61/873,723 entitled “SYSTEMS, APPARATUS, AND METHODS FOR AN EMBEDDED EMISSIONS FILTER CIRCUIT IN A POWER CABLE” filed Sep. 4, 2013, and assigned to the assignee hereof. Provisional Application No. 61/873,723 is hereby expressly incorporated by reference herein. 
    
    
     FIELD 
     The present disclosure relates generally to a filter circuit for controlling emissions where the filter circuit is integrated within a power cable. 
     BACKGROUND 
     An increasing number and variety of electronic devices are portable and may be powered via cables. For example, a wireless power transmitter may be powered via a USB cable connected to a power supply. In some cases a device coupled to a cable may produce emissions in the cable that may be undesirable. 
     SUMMARY 
     Various implementations of systems, methods and devices within the scope of the appended claims each have several aspects, no single one of which is solely responsible for the desirable attributes described herein. Without limiting the scope of the appended claims, some prominent features are described herein. 
     Details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims. Note that the relative dimensions of the following figures may not be drawn to scale. 
     One aspect of the subject matter described in the disclosure provides a power cable apparatus. The apparatus includes a cable portion. The apparatus further includes a first connector portion coupled to a first end of the cable portion and configured to selectively couple to an electronic device. The apparatus further includes a second connector portion coupled to a second end of the cable portion opposite the first end. The apparatus further includes a filter circuit integrated within the second connector portion. The filter circuit is configured to attenuate emissions at an operating frequency of the electronic device. 
     Another aspect of the subject matter described in the disclosure provides an implementation of a method of filtering within a power cable apparatus. The method includes providing power to an electronic device via a first connector portion coupled to a first end of a cable portion of the power cable apparatus. The method further includes filtering emissions at an operating frequency of the electronic device via a filter circuit integrated within a second connector portion coupled to a second end of the cable portion opposite the first end of the cable portion of the power cable apparatus. 
     Yet another aspect of the subject matter described in the disclosure provides a DC power cable apparatus. The apparatus includes means for connecting to an electronic device for providing power. The apparatus includes means for connecting to a power supply. The apparatus includes means for attenuating emissions an operating frequency of the electronic device, the means for attenuating being integrated within the means for connecting to the power supply. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a functional block diagram of an exemplary wireless power transfer system, in accordance with exemplary embodiments of the invention. 
         FIG. 2  is a functional block diagram of exemplary components that may be used in the wireless power transfer system of  FIG. 1 , in accordance with various exemplary embodiments of the invention. 
         FIG. 3  is a schematic diagram of a portion of transmit circuitry or receive circuitry of  FIG. 2  including a transmit or receive antenna, in accordance with exemplary embodiments of the invention. 
         FIG. 4  is a functional block diagram of a transmitter that may be used in the wireless power transfer system of  FIG. 1 , in accordance with exemplary embodiments of the invention. 
         FIG. 5  is a functional block diagram of a receiver that may be used in the wireless power transfer system of  FIG. 1 , in accordance with exemplary embodiments of the invention. 
         FIG. 6  is a schematic diagram of a portion of transmit circuitry that may be used in the transmit circuitry of  FIG. 4 , in accordance with exemplary embodiments. 
         FIG. 7A  is a diagram of a power cable apparatus, in accordance with an exemplary embodiment. 
         FIG. 7B  is diagram of a portion of the cable of  FIG. 7A , in accordance with an embodiment. 
         FIG. 8  is a schematic diagram of a filter circuit that may be integrated within the cable of  FIGS. 7A and 7B , in accordance with an embodiment. 
         FIG. 9  is a flow chart of an exemplary method of filtering within a power cable apparatus, in accordance with an exemplary embodiment. 
         FIG. 10  is a functional block diagram of a power cable apparatus, in accordance with an exemplary embodiment. 
     
    
    
     The various features illustrated in the drawings may not be drawn to scale. Accordingly, the dimensions of the various features may be arbitrarily expanded or reduced for clarity. In addition, some of the drawings may not depict all of the components of a given system, method or device. Finally, like reference numerals may be used to denote like features throughout the specification and figures. 
     DETAILED DESCRIPTION 
     The detailed description set forth below in connection with the appended drawings is intended as a description of exemplary embodiments of the invention and is not intended to represent the only embodiments in which the invention may be practiced. The term “exemplary” used throughout this description means “serving as an example, instance, or illustration,” and should not necessarily be construed as preferred or advantageous over other exemplary embodiments. The detailed description includes specific details for the purpose of providing a thorough understanding of the exemplary embodiments of the invention. In some instances, some devices are shown in block diagram form. 
     Wirelessly transferring power may refer to transferring any form of energy associated with electric fields, magnetic fields, electromagnetic fields, or otherwise from a transmitter to a receiver without the use of physical electrical conductors (e.g., power may be transferred through free space). The power output into a wireless field (e.g., a magnetic field) may be received, captured by, or coupled by a “receiving antenna” to achieve power transfer. 
       FIG. 1  is a functional block diagram of an exemplary wireless power transfer system  100 , in accordance with exemplary embodiments of the invention. Input power  102  may be provided to a transmitter  104  from a power source (not shown) for generating a field  105  for providing energy transfer. A receiver  108  may couple to the field  105  and generate output power  110  for storing or consumption by a device (not shown) coupled to the output power  110 . Both the transmitter  104  and the receiver  108  are separated by a distance  112 . In one exemplary embodiment, transmitter  104  and receiver  108  are configured according to a mutual resonant relationship. When the resonant frequency of receiver  108  and the resonant frequency of transmitter  104  are substantially the same or very close, transmission losses between the transmitter  104  and the receiver  108  are minimal. As such, wireless power transfer may be provided over larger distance in contrast to purely inductive solutions that may require large coils that require coils to be very close (e.g., mms). Resonant inductive coupling techniques may thus allow for improved efficiency and power transfer over various distances and with a variety of inductive coil configurations. 
     The receiver  108  may receive power when the receiver  108  is located in an energy field  105  produced by the transmitter  104 . The field  105  corresponds to a region where energy output by the transmitter  104  may be captured by a receiver  105 . In some cases, the field  105  may correspond to the “near-field” of the transmitter  104  as will be further described below. The transmitter  104  may include a transmit antenna  114  for outputting an energy transmission. The receiver  108  further includes a receive antenna  118  for receiving or capturing energy from the energy transmission. The near-field may correspond to a region in which there are strong reactive fields resulting from the currents and charges in the transmit antenna  114  that minimally radiate power away from the transmit antenna  114 . In some cases the near-field may correspond to a region that is within about one wavelength (or a fraction thereof) of the transmit antenna  114 . The transmit and receive antennas  114  and  118  are sized according to applications and devices to be associated therewith. As described above, efficient energy transfer may occur by coupling a large portion of the energy in a field  105  of the transmit antenna  114  to a receive antenna  118  rather than propagating most of the energy in an electromagnetic wave to the far field. When positioned within the field  105 , a “coupling mode” may be developed between the transmit antenna  114  and the receive antenna  118 . The area around the transmit and receive antennas  114  and  118  where this coupling may occur is referred to herein as a coupling-mode region. 
       FIG. 2  is a functional block diagram of exemplary components that may be used in the wireless power transfer system  100  of  FIG. 1 , in accordance with various exemplary embodiments of the invention. The transmitter  204  may include transmit circuitry  206  that may include an oscillator  222 , a driver circuit  224 , and a filter and matching circuit  226 . The oscillator  222  may be configured to generate a signal at a desired frequency, such as 468.75 KHz, 6.78 MHz or 13.56 MHz, that may be adjusted in response to a frequency control signal  223 . The oscillator signal may be provided to a driver circuit  224  configured to drive the transmit antenna  214  at, for example, a resonant frequency of the transmit antenna  214 . The driver circuit  224  may be a switching amplifier configured to receive a square wave from the oscillator  222  and output a sine wave. For example, the driver circuit  224  may be a class E amplifier. A filter and matching circuit  226  may be also included to filter out harmonics or other unwanted frequencies and match the impedance of the transmitter  204  to the transmit antenna  214 . As a result of driving the transmit antenna  214 , the transmitter  204  may wirelessly output power at a level sufficient for charging or power an electronic device. As one example, the power provided may be for example on the order of 300 milliWatts to 5 Watts to power or charge different devices with different power requirements. Higher or lower power levels may also be provided. 
     The receiver  208  may include receive circuitry  210  that may include a matching circuit  232  and a rectifier and switching circuit  234  to generate a DC power output from an AC power input to charge a battery  236  as shown in  FIG. 2  or to power a device (not shown) coupled to the receiver  108 . The matching circuit  232  may be included to match the impedance of the receive circuitry  210  to the receive antenna  218 . The receiver  208  and transmitter  204  may additionally communicate on a separate communication channel  219  (e.g., Bluetooth, zigbee, cellular, etc). The receiver  208  and transmitter  204  may alternatively communicate via in-band signaling using characteristics of the wireless field  206 . 
     As described more fully below, receiver  208 , that may initially have a selectively disablable associated load (e.g., battery  236 ), may be configured to determine whether an amount of power transmitted by transmitter  204  and receiver by receiver  208  is appropriate for charging a battery  236 . Further, receiver  208  may be configured to enable a load (e.g., battery  236 ) upon determining that the amount of power is appropriate. In some embodiments, a receiver  208  may be configured to directly utilize power received from a wireless power transfer field without charging of a battery  236 . For example, a communication device, such as a near-field communication (NFC) or radio-frequency identification device (RFID may be configured to receive power from a wireless power transfer field and communicate by interacting with the wireless power transfer field and/or utilize the received power to communicate with a transmitter  204  or other devices. 
       FIG. 3  is a schematic diagram of a portion of transmit circuitry  206  or receive circuitry  210  of  FIG. 2  including a transmit or receive antenna  352 , in accordance with exemplary embodiments of the invention. As illustrated in  FIG. 3 , transmit or receive circuitry  350  used in exemplary embodiments including those described below may include an antenna  352 . The antenna  352  may also be referred to or be configured as a “loop” antenna  352 . The antenna  352  may also be referred to herein or be configured as a “magnetic” antenna or an induction coil. The term “antenna” generally refers to a component that may wirelessly output or receive energy for coupling to another “antenna.” The antenna may also be referred to as a coil of a type that is configured to wirelessly output or receive power. As used herein, an antenna  352  is an example of a “power transfer component” of a type that is configured to wirelessly output and/or receive power. The antenna  352  may be configured to include an air core or a physical core such as a ferrite core (not shown). Air core loop antennas may be more tolerable to extraneous physical devices placed in the vicinity of the core. Furthermore, an air core loop antenna  352  allows the placement of other components within the core area. In addition, an air core loop may more readily enable placement of the receive antenna  218  ( FIG. 2 ) within a plane of the transmit antenna  214  ( FIG. 2 ) where the coupled-mode region of the transmit antenna  214  ( FIG. 2 ) may be more powerful. 
     As stated, efficient transfer of energy between the transmitter  104  and receiver  108  may occur during matched or nearly matched resonance between the transmitter  104  and the receiver  108 . However, even when resonance between the transmitter  104  and receiver  108  are not matched, energy may be transferred, although the efficiency may be affected. Transfer of energy occurs by coupling energy from the field  105  of the transmit antenna  214  coil to the receive antenna  218  residing in the neighborhood where this field  105  is established rather than propagating the energy from the transmit antenna  214  into free space. 
     The resonant frequency of the loop or magnetic antennas is based on the inductance and capacitance. Inductance may be simply the inductance created by the antenna  352 , whereas, capacitance may be added to the antenna&#39;s inductance to create a resonant structure at a desired resonant frequency. As a non-limiting example, capacitor  352  and capacitor  354  may be added to the transmit or receive circuitry  350  to create a resonant circuit that selects a signal  356  at a resonant frequency. Accordingly, for larger diameter antennas, the size of capacitance needed to sustain resonance may decrease as the diameter or inductance of the loop increases. Furthermore, as the diameter of the antenna increases, the efficient energy transfer area of the near-field may increase. Other resonant circuits formed using other components are also possible. As another non-limiting example, a capacitor may be placed in parallel between the two terminals of the antenna  350 . For transmit antennas, a signal  358  with a frequency that substantially corresponds to the resonant frequency of the antenna  352  may be an input to the antenna  352 . 
     In one embodiment, the transmitter  104  may be configured to output a time varying magnetic field with a frequency corresponding to the resonant frequency of the transmit antenna  114 . When the receiver is within the field  105 , the time varying magnetic field may induce a current in the receive antenna  118 . As described above, if the receive antenna  118  is configured to be resonant at the frequency of the transmit antenna  118 , energy may be efficiently transferred. The AC signal induced in the receive antenna  118  may be rectified as described above to produce a DC signal that may be provided to charge or to power a load. 
       FIG. 4  is a functional block diagram of a transmitter  404  that may be used in the wireless power transfer system of  FIG. 1 , in accordance with exemplary embodiments of the invention. The transmitter  404  may include transmit circuitry  406  and a transmit antenna  414 . The transmit antenna  414  may be the antenna  352  as shown in  FIG. 3 . Transmit circuitry  406  may provide RF power to the transmit antenna  414  by providing an oscillating signal resulting in generation of energy (e.g., magnetic flux) about the transmit antenna  414 . Transmitter  404  may operate at any suitable frequency. By way of example, transmitter  404  may operate at the 6.78 MHz ISM band. 
     Transmit circuitry  406  may include a fixed impedance matching circuit  409  for matching the impedance of the transmit circuitry  406  (e.g., 50 ohms) to the transmit antenna  414  and a low pass filter (LPF)  408  configured to reduce harmonic emissions to levels to prevent self-jamming of devices coupled to receivers  108  ( FIG. 1 ). Other exemplary embodiments may include different filter topologies, including but not limited to, notch filters that attenuate specific frequencies while passing others and may include an adaptive impedance match, that may be varied based on measurable transmit metrics, such as output power to the antenna  414  or DC current drawn by the driver circuit  424 . Transmit circuitry  406  further includes a driver circuit  424  configured to drive an RF signal as determined by an oscillator  423 . The transmit circuitry  406  may be comprised of discrete devices or circuits, or alternately, may be comprised of an integrated assembly. An exemplary RF power output from transmit antenna  414  may be on the order of 2.5 Watts. 
     Transmit circuitry  406  may further include a controller  415  for selectively enabling the oscillator  423  during transmit phases (or duty cycles) for specific receivers, for adjusting the frequency or phase of the oscillator  423 , and for adjusting the output power level for implementing a communication protocol for interacting with neighboring devices through their attached receivers. It is noted that the controller  415  may also be referred to herein as processor  415 . Adjustment of oscillator phase and related circuitry in the transmission path may allow for reduction of out of band emissions, especially when transitioning from one frequency to another. 
     The transmit circuitry  406  may further include a load sensing circuit  416  for detecting the presence or absence of active receivers in the vicinity of the near-field generated by transmit antenna  414 . By way of example, a load sensing circuit  416  monitors the current flowing to the driver circuit  424 , that may be affected by the presence or absence of active receivers in the vicinity of the field generated by transmit antenna  414  as will be further described below. Detection of changes to the loading on the driver circuit  424  are monitored by controller  415  for use in determining whether to enable the oscillator  423  for transmitting energy and to communicate with an active receiver. As described more fully below, a current measured at the driver circuit  424  may be used to determine whether an invalid device is positioned within a wireless power transfer region of the transmitter  404 . 
     The transmit antenna  414  may be implemented with a Litz wire or as an antenna strip with the thickness, width and metal type selected to keep resistive losses low. In a one implementation, the transmit antenna  414  may generally be configured for association with a larger structure such as a table, mat, lamp or other less portable configuration. Accordingly, the transmit antenna  414  generally may not need “turns” in order to be of a practical dimension. An exemplary implementation of a transmit antenna  414  may be “electrically small” (i.e., fraction of the wavelength) and tuned to resonate at lower usable frequencies by using capacitors to define the resonant frequency. 
     The transmitter  404  may gather and track information about the whereabouts and status of receiver devices that may be associated with the transmitter  404 . Thus, the transmit circuitry  406  may include a presence detector  480 , an enclosed detector  460 , or a combination thereof, connected to the controller  415  (also referred to as a processor herein). The controller  415  may adjust an amount of power delivered by the driver circuit  424  in response to presence signals from the presence detector  480  and the enclosed detector  460 . The transmitter  404  may receive power through a number of power sources, such as, for example, an AC-DC converter (not shown) to convert conventional AC power present in a building, a DC-DC converter (not shown) to convert a conventional DC power source to a voltage suitable for the transmitter  404 , or directly from a conventional DC power source (not shown). 
     As a non-limiting example, the presence detector  480  may be a motion detector utilized to sense the initial presence of a device to be charged that is inserted into the coverage area of the transmitter  404 . After detection, the transmitter  404  may be turned on and the RF power received by the device may be used to toggle a switch on the Rx device in a pre-determined manner, which in turn results in changes to the driving point impedance of the transmitter  404 . 
     As another non-limiting example, the presence detector  480  may be a detector capable of detecting a human, for example, by infrared detection, motion detection, or other suitable means. In some exemplary embodiments, there may be regulations limiting the amount of power that a transmit antenna  414  may transmit at a specific frequency. In some cases, these regulations are meant to protect humans from electromagnetic radiation. However, there may be environments where a transmit antenna  414  is placed in areas not occupied by humans, or occupied infrequently by humans, such as, for example, garages, factory floors, shops, and the like. If these environments are free from humans, it may be permissible to increase the power output of the transmit antenna  414  above the normal power restrictions regulations. In other words, the controller  415  may adjust the power output of the transmit antenna  414  to a regulatory level or lower in response to human presence and adjust the power output of the transmit antenna  414  to a level above the regulatory level when a human is outside a regulatory distance from the electromagnetic field of the transmit antenna  414 . 
     As a non-limiting example, the enclosed detector  460  (may also be referred to herein as an enclosed compartment detector or an enclosed space detector) may be a device such as a sense switch for determining when an enclosure is in a closed or open state. When a transmitter is in an enclosure that is in an enclosed state, a power level of the transmitter may be increased. 
     In exemplary embodiments, a method by which the transmitter  404  does not remain on indefinitely may be used. In this case, the transmitter  404  may be programmed to shut off after a user-determined amount of time. This feature prevents the transmitter  404 , notably the driver circuit  424 , from running long after the wireless devices in its perimeter are fully charged. This event may be due to the failure of the circuit to detect the signal sent from either the repeater or the receive antenna  218  that a device is fully charged. To prevent the transmitter  404  from automatically shutting down if another device is placed in its perimeter, the transmitter  404  automatic shut off feature may be activated only after a set period of lack of motion detected in its perimeter. The user may be able to determine the inactivity time interval, and change it as desired. As a non-limiting example, the time interval may be longer than that needed to fully charge a specific type of wireless device under the assumption of the device being initially fully discharged. 
       FIG. 5  is a functional block diagram of a receiver  508  that may be used in the wireless power transfer system of  FIG. 1 , in accordance with exemplary embodiments of the invention. The receiver  508  includes receive circuitry  510  that may include a receive antenna  518 . Receiver  508  further couples to device  550  for providing received power thereto. It should be noted that receiver  508  is illustrated as being external to device  550  but may be integrated into device  550 . Energy may be propagated wirelessly to receive antenna  518  and then coupled through the rest of the receive circuitry  510  to device  550 . By way of example, the charging device may include devices such as mobile phones, portable music players, laptop computers, tablet computers, computer peripheral devices, communication devices (e.g., Bluetooth devices), digital cameras, hearing aids (and other medical devices), and the like. 
     Receive antenna  518  may be tuned to resonate at the same frequency, or within a specified range of frequencies, as transmit antenna  414  ( FIG. 4 ). Receive antenna  518  may be similarly dimensioned with transmit antenna  414  or may be differently sized based upon the dimensions of the associated device  550 . By way of example, device  550  may be a portable electronic device having diametric or length dimension smaller that the diameter of length of transmit antenna  414 . In such an example, receive antenna  518  may be implemented as a multi-turn coil in order to reduce the capacitance value of a tuning capacitor (not shown) and increase the receive coil&#39;s impedance. By way of example, receive antenna  518  may be placed around the substantial circumference of device  550  in order to maximize the antenna diameter and reduce the number of loop turns (i.e., windings) of the receive antenna  518  and the inter-winding capacitance. 
     Receive circuitry  510  may provide an impedance match to the receive antenna  518 . Receive circuitry  510  includes power conversion circuitry  506  for converting a received RF energy source into charging power for use by the device  550 . Power conversion circuitry  506  includes an RF-to-DC converter  520  and may also in include a DC-to-DC converter  522 . RF-to-DC converter  520  rectifies the RF energy signal received at receive antenna  518  into a non-alternating power with an output voltage represented by V rect . The DC-to-DC converter  522  (or other power regulator) converts the rectified RF energy signal into an energy potential (e.g., voltage) that is compatible with device  550  with an output voltage and output current represented by V out  and I out . Various RF-to-DC converters are contemplated, including partial and full rectifiers, regulators, bridges, doublers, as well as linear and switching converters. 
     Receive circuitry  510  may further include switching circuitry  512  for connecting receive antenna  518  to the power conversion circuitry  506  or alternatively for disconnecting the power conversion circuitry  506 . Disconnecting receive antenna  518  from power conversion circuitry  506  not only suspends charging of device  550 , but also changes the “load” as “seen” by the transmitter  404  ( FIG. 2 ). 
     As disclosed above, transmitter  404  includes load sensing circuit  416  that may detect fluctuations in the bias current provided to transmitter driver circuit  424 . Accordingly, transmitter  404  has a mechanism for determining when receivers are present in the transmitter&#39;s near-field. 
     When multiple receivers  508  are present in a transmitter&#39;s near-field, it may be desirable to time-multiplex the loading and unloading of one or more receivers to enable other receivers to more efficiently couple to the transmitter. A receiver  508  may also be cloaked in order to eliminate coupling to other nearby receivers or to reduce loading on nearby transmitters. This “unloading” of a receiver is also known herein as a “cloaking.” Furthermore, this switching between unloading and loading controlled by receiver  508  and detected by transmitter  404  may provide a communication mechanism from receiver  508  to transmitter  404  as is explained more fully below. Additionally, a protocol may be associated with the switching that enables the sending of a message from receiver  508  to transmitter  404 . By way of example, a switching speed may be on the order of 100 psec. 
     In an exemplary embodiment, communication between the transmitter  404  and the receiver  508  refers to a device sensing and charging control mechanism, rather than conventional two-way communication (i.e., in band signaling using the coupling field). In other words, the transmitter  404  may use on/off keying of the transmitted signal to adjust whether energy is available in the near-field. The receiver may interpret these changes in energy as a message from the transmitter  404 . From the receiver side, the receiver  508  may use tuning and de-tuning of the receive antenna  518  to adjust how much power is being accepted from the field. In some cases, the tuning and de-tuning may be accomplished via the switching circuitry  512 . The transmitter  404  may detect this difference in power used from the field and interpret these changes as a message from the receiver  508 . It is noted that other forms of modulation of the transmit power and the load behavior may be utilized. 
     Receive circuitry  510  may further include signaling detector and beacon circuitry  514  used to identify received energy fluctuations, that may correspond to informational signaling from the transmitter to the receiver. Furthermore, signaling and beacon circuitry  514  may also be used to detect the transmission of a reduced RF signal energy (i.e., a beacon signal) and to rectify the reduced RF signal energy into a nominal power for awakening either un-powered or power-depleted circuits within receive circuitry  510  in order to configure receive circuitry  510  for wireless charging. 
     Receive circuitry  510  further includes processor  516  for coordinating the processes of receiver  508  described herein including the control of switching circuitry  512  described herein. Cloaking of receiver  508  may also occur upon the occurrence of other events including detection of an external wired charging source (e.g., wall/USB power) providing charging power to device  550 . Processor  516 , in addition to controlling the cloaking of the receiver, may also monitor beacon circuitry  514  to determine a beacon state and extract messages sent from the transmitter  404 . Processor  516  may also adjust the DC-to-DC converter  522  for improved performance. 
       FIG. 6  is a schematic diagram of a portion of transmit circuitry  600  that may be used in the transmit circuitry  406  of  FIG. 4 . The transmit circuitry  600  may include a driver circuit  624  as described above in  FIG. 4 . The driver circuit  624  may be similar to the driver circuit  424  shown in  FIG. 4 . As described above, the driver circuit  624  may be a switching amplifier that may be configured to receive a square wave and output a sine wave to be provided to the transmit circuit  650 . In some cases the driver circuit  624  may be referred to as an amplifier circuit. The driver circuit  624  is shown as a class E amplifier, however, any suitable driver circuit  624  may be used in accordance with embodiments of the invention. The driver circuit  624  may be driven by an input signal  602  from an oscillator  423  as shown in  FIG. 4 . The driver circuit  624  may also be provided with a drive voltage V D  that is configured to control the maximum power that may be delivered through a transmit circuit  650 . To eliminate or reduce harmonics, the transmit circuitry  600  may include a filter circuit  626 . The filter circuit  626  may be a three pole (capacitor  634 , inductor  632 , and capacitor  636 ) low pass filter circuit  626 . 
     The signal output by the filter circuit  626  may be provided to a transmit circuit  650  comprising an antenna  614 . The transmit circuit  650  may include a series resonant circuit having a capacitance  620  and inductance (e.g., that may be due to the inductance or capacitance of the antenna or to an additional capacitor component) that may resonate at a frequency of the filtered signal provided by the driver circuit  624 . The load of the transmit circuit  650  may be represented by the variable resistor  622 . The load may be a function of a wireless power receiver  508  that is positioned to receive power from the transmit circuit  650 . 
     Operation of the wireless power transmitter  404  may result in undesired emissions in different parts of the system. For example, where a transmitter  404  and receiver  508  are loosely coupled (as compared to tightly coupled), the magnetic fields may not be well contained and may increase undesired emissions. A loosely coupled system may refer to a system as described herein with a coupling factor (k) indicative of an amount of flux penetrating a receiver coil  518  from a transmit coil  414  that is somewhere less than 0.5 (e.g., generally approximately or less than 0.2 or 0.1). A tightly coupled system may refer to a system with a coupling factor (k) greater than 0.5 (e.g., 0.8 or higher). As such, according to embodiments described herein, multiple different sources and paths for undesired emissions may be suppressed to meet emission limits. For example, harmonics from the receiver  508  may couple back into the transmitter  414 . These emissions, and emissions from the driver circuit  624  and/or other components, may further be reflected back into a DC line feeding the transmit circuitry. As such, undesired emissions may be produced in a DC cable by operation of the wireless power transmitter. 
     In accordance with aspects of certain embodiments, the DC cable may include a filter circuit. In one aspect, the DC cable may be a Universal Serial Bus (USB) cable, although other cables may be used in accordance with the principles described herein. The filter circuit may be configured to electrically isolate emissions. In one aspect, if the DC cable is configured to be connected to and to provide power to a wireless power transmitter, the DC cable may be configured to electrically isolate emissions from the driver circuit  624  and the transmit circuit  650  to the power source. For example, a filter circuit in the DC cable in accordance with embodiments may be configured to reject or attenuate emissions at a particular frequency or within a particular frequency range such as a range of frequencies including the operating frequency used for wireless power transmission. In an embodiment, the filter circuit may be configured to reject harmonic emissions below 30 MHz for conductive emissions. In an embodiment, the filter circuit may be configured to reduce/attenuate harmonic emissions below 30 MHz by substantially 15 dB. Other frequencies are also possible and the specific frequencies listed here are exemplary only. In one embodiment, the filter circuit may be implemented as a common mode choke circuit. In another embodiment, the filter circuit may include a common mode choke circuit and may include a further filter circuit (such as a differential filter circuit—e.g., a differential LC filter circuit). 
       FIG. 7A  is a diagram of a cable  700 , in accordance with an exemplary embodiment. The cable  700  may be configured to connect to any one of a number of different electronic devices and provide power and/or data. For example, the cable  700  may be configured to selectively couple and provide DC power to a wireless power transmitter  404 . The cable  700  may be configured as a USB cable. The cable includes a cable portion  704 , a first connector portion  703  and a second connector portion  702 . In one aspect, having to implement a filter circuit as described above in a power adapter or a ferrite bead on the power cable may be undesirable due to the need for either a custom power adaptor and/or reduced aesthetics that might result from a ferrite bead positioned on a cable. As such, in accordance with an embodiment, a filter circuit is hidden within the second connector portion  702  (e.g., in a USB cable on the USB A side). The A side of a USB cable may be configured for connection to the host device or the device supplying power to a device connected to the opposite side of the USB cable. Thus, where the cable  700  is a DC cable providing DC power to the wireless power transmitter circuitry, for example the driver circuit  624  and/or the transmit circuit  650  shown in  FIG. 6 , the filter circuit may be located in the second connector portion  702  located at a second end of the cable  700  opposite a first end, connected to or configured for connection to the wireless power transmitter circuitry. In this way, especially where the filter comprises a common mode choke, the filter may be located as far as possible from the primary source of electromagnetic emissions the filter circuit is intended to isolate from the DC power source. Moreover, the above-mentioned physical location of the filter circuit with respect to the wireless power transmitter circuitry may additionally apply where the DC cable is not a USB cable. 
       FIG. 7B  is diagram of a portion of the cable  700  of  FIG. 7B , in accordance with an embodiment. As shown in  FIG. 7B , a filter circuit  708  is hidden within the second connector portion  702 . The second connector portion may have a PCB  706 . The filter circuit  708  is positioned and/or integrated with the PCB  706 . The filter circuit  708  may be configured to be similar to and/or smaller in size than the second connector portion  702 . In this way, when the filter circuit  708  is integrated with the second connector portion  702 , the second connector portion  702  remains the same (e.g., form factor of the connector/entire cable is unaffected by the addition of the filter circuit  708 ). In this way the aesthetics of the cable is preserved while providing filtering capabilities. 
       FIG. 8  is a schematic diagram of a filter circuit  808  in accordance with an embodiment. In  FIG. 8 , the filter circuit  808  is configured as a common mode choke. As described above, the filter circuit  808  may further include a differential filter circuit in addition to the common mode choke circuit shown. However, other filter circuits may be used in accordance with the embodiments described herein. While portions of the disclosure with regards to the power cable have been described in relation to a wireless power transfer system, it is noted that the power cable and filter circuit may be used in any one of a number of systems where further filtering may be desirable. As such, the cable  700  in accordance with embodiments is not limited to being used with a wireless power transfer system. 
       FIG. 9  is a flow chart of an exemplary method  900  of filtering within a power cable apparatus, in accordance with an exemplary embodiment. Block  902  may include providing power to an electronic device via a first connector portion coupled to a first end of a cable portion of the power cable apparatus. The method may continue with block  904 , which may include attenuating emissions at an operating frequency of the electronic device via a filter circuit integrated within a second connector portion coupled to a second end of the cable portion opposite the first end of the cable portion of the power cable apparatus. In some implementations, the filter circuit may be configured to be smaller than the second connector portion. In some other implementations, the filter circuit may comprise a common mode choke circuit, such as that previously described in connection with  FIG. 8 . In another implementation, the filter circuit may comprise the common mode choke circuit and a differential filter circuit. In some implementations, the power cable apparatus may comprise a USB power cable and the second connector portion may comprise an A side connector of the USB power cable. In some implementations, emissions of a wireless power transmitter into a power supply coupled to the second connector may be reduced utilizing the filter circuit. 
       FIG. 10  is a functional block diagram of a power cable apparatus  1000 , in accordance with an exemplary embodiment of the invention. Those skilled in the art will appreciate that the apparatus may have more components than illustrated in  FIG. 10 . The apparatus  1000  includes only those components useful for describing some prominent features of implementations within the scope of the claims. In one implementation, the apparatus  1000  is configured to perform the method  900  shown above in  FIG. 9 . The apparatus  1000  may comprise the power cable apparatus  700  shown in  FIG. 7A , for example, which may be shown in more detail in one or more of  FIGS. 6 ,  7 B and  8 . 
     The apparatus  1000  comprises means  1002  for connecting to an electronic device for providing power. In some implementations, the means  1002  can be configured to perform one or more of the functions described above with respect to block  902  of  FIG. 9 . As previously described in connection with  FIG. 7A , the means  1002  may comprise the first connector portion  703  shown in  FIG. 7A , for example. 
     The apparatus  1000  may further include means  1004  for connecting to a power supply. In some implementations, the means  1004  can be configured to perform one or more of the functions described above with respect to block  902  of  FIG. 9 . The means  1004  may comprise the second connector portion  702  shown in  FIG. 7 , for example. 
     The apparatus  1000  may further include means  1006  for attenuating emissions at an operating frequency of the electronic device, the means for attenuating being integrated within the means for connecting to the power supply. In some implementations, the means  1006  may be configured to be smaller than the means for connecting to the power supply. In some implementations, the means  1006  can be configured to perform one or more of the functions described above with respect to block  904  of  FIG. 9 . The means  1006  may comprise the filter circuit  708  shown in  FIG. 7B , for example. 
     The various operations of methods described above may be performed by any suitable means capable of performing the operations, such as various hardware and/or software component(s), circuits, and/or module(s). Generally, any operations illustrated in the Figures may be performed by corresponding functional means capable of performing the operations. For example, a means for selectively allowing current in response to a control voltage may comprise a first transistor. In addition, means for limiting an amount of the control voltage comprising means for selectively providing an open circuit may comprise a second transistor. 
     Information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. 
     The various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. The described functionality may be implemented in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the embodiments of the invention. 
     The various illustrative blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     The steps of a method or algorithm and functions described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a tangible, non-transitory computer-readable medium. A software module may reside in Random Access Memory (RAM), flash memory, Read Only Memory (ROM), Electrically Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), registers, hard disk, a removable disk, a CD ROM, or any other form of storage medium known in the art. A storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer readable media. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal. 
     For purposes of summarizing the disclosure, certain aspects, advantages and novel features of the inventions have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. 
     Various modifications of the above described embodiments will be readily apparent, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.