PATENT DOCUMENT

Publication Number: US-9369219-B1
Application Number: US-201514635660-A
Country: US
Kind Code: B1

Title: Radio frequency systems and methods for controlling spurious emissions

Abstract:
Systems and method for improving performance of a radio frequency system are provided. One embodiment describes a radio frequency system, which includes an antenna that wirelessly transmits analog electrical signals at a desired transmission frequency; a feedback receiver that determines a feedback signal, which includes a portion of a transmitted analog electrical signal via a coupler; and a controller that determines location and magnitude of spurious emissions transmitted at frequencies other than the desired transmission frequency by comparing the feedback signal with a desired signal, in which the desired signal includes a digital electrical signal that does not contain noise introduced by the radio frequency system; and instructs the radio frequency system to adjust operational parameters used to transmit the analog electrical signals when the magnitude of the spurious emissions exceeds a spurious emissions limit at the determined location.

Claims:
What is claimed is: 
     
       1. A radio frequency system comprising:
 a transceiver configured to generate a first analog electrical signal based at least in part on a digital electrical signal using digital signal modulation, wherein the digital signal modulation introduces a first noise in the first analog electrical signal; 
 a power amplifier configured to generate a second analog electrical signal by amplifying the first analog electrical signal, wherein the power amplifier introduces a second noise in the second analog electrical signal; 
 an antenna configured to wirelessly transmit analog electrical signals at a desired transmission frequency; 
 a feedback receiver configured to determine a feedback signal comprising a portion of a transmitted analog electrical signal via a coupler; and 
 a controller configured to:
 determine location and magnitude of a spurious emission transmitted at a frequency other than the desired transmission frequency by comparing the feedback signal with a desired signal, wherein the desired signal comprises the digital electrical signal and does not contain noise introduced by the radio frequency system, the noise introduced by the radio frequency system comprises the first noise and the second noise, and the first noise and the second noise are configured to produce the spurious emission in the transmitted analog electrical signal; and 
 instruct the radio frequency system to adjust operational parameters used to transmit the analog electrical signals when the magnitude of the spurious emission exceeds a spurious emissions limit at the location. 
 
 
     
     
       2. The radio frequency system of  claim 1 , wherein the controller is configured to instruct the radio frequency system to use nominal operational parameters to transmit the analog electrical signals when the magnitude of the spurious emission does not exceed the spurious emissions limit at the location. 
     
     
       3. The radio frequency system of  claim 2 , wherein adjusting the operational parameters away from the nominal operational parameters reduces output power of the radio frequency system, efficiency of the radio frequency system, reliability of the radio frequency system, or any combination thereof. 
     
     
       4. The radio frequency system of  claim 1 , wherein the controller is configured to instruct the radio frequency system to the adjust operational parameters by adjusting filter rejection, decreasing amplification by the power amplifier, increasing linearity of the power amplifier, adjusting skew of the power amplifier, or any combination thereof. 
     
     
       5. The radio frequency system of  claim 1 , wherein the controller is configured to instruct the transceiver to generate the analog electrical signals such that the analog electrical signals include an inverse of the noise introduced by the radio frequency system. 
     
     
       6. The radio frequency system of  claim 1 , wherein the feedback receiver is configured to determine the feedback signal such that the feedback signal comprises the portion of the transmitted analog electrical signal at the desired transmission frequency;
 wherein the controller is configured to control output power of the radio frequency system based at least in part on the feedback signal. 
 
     
     
       7. The radio frequency system of  claim 1 , wherein the coupler is configured to determine the feedback signal such that the feedback signal comprises the portion of the transmitted analog electrical signal at a protected or restricted frequency. 
     
     
       8. A method, comprising:
 determining, using a controller in a radio frequency system, magnitude and location of a plurality of spurious emissions in a transmitted analog electrical signal; 
 determining, using the controller, number of spurious emissions in the plurality of spurious emissions; 
 determining, using the controller, type of each of the plurality of spurious emissions based at least in part on location of each of the plurality of spurious emissions; and 
 determining, using the controller, operational parameters used to transmit subsequent analog electrical signals by determining whether to adjust filter rejection of a filter, decrease amplification by a power amplifier, increase linearity of the power amplifier, adjust skew of the power amplifier, or any combination thereof based at least in part on number of spurious emissions in the plurality of spurious emissions and type, magnitude, and location of each of the plurality of spurious emissions, wherein:
 adjusting the filter rejection comprises tuning the filter to the location of one or more of the plurality of spurious emissions and adjusting aggressiveness of the filter to attenuate the subsequent analog electrical signals less than a set spurious emissions limit; 
 decreasing the amplification by the power amplifier comprises reducing output power used to transmit the subsequent analog electrical signals; 
 increasing the linearity of the power amplifier comprises increasing electrical power supplied to the power amplifier; and 
 adjusting the skew of the power amplifier comprises shifting one or more of the plurality of spurious emissions from a first frequency to a second frequency. 
 
 
     
     
       9. The method of  claim 8 , wherein determining magnitude, location, number, and type of the plurality of spurious emissions comprises comparing a portion of the transmitted analog electrical signal with a digital electrical signal, wherein the transmitted analog electrical signal is generated based at least in part on the digital electrical signal. 
     
     
       10. The method of  claim 8 , wherein determining magnitude, location, number, and type of the plurality of spurious emissions comprises:
 determining a model that describes spurious emissions based at least in part on operational parameters of the radio frequency system, wherein the operational parameters comprise ambient temperature, transmission frequency, output power, antenna load, or any combination thereof; 
 determining the operational parameters; and 
 inputting the operational parameters into the model. 
 
     
     
       11. An electronic device comprising: a radio frequency system configured to:
 control output power of a wirelessly transmitted analog electrical signal based at least in part on a feedback signal, wherein the feedback signal comprises a portion of the transmitted analog electrical signal at a transmission channel and adjacent channels to the transmission channel; 
 determine low order intermodulation spurious emissions of the transmitted analog electrical signal in the transmission channel and adjacent channels by comparing the feedback signal to a desired signal, wherein the desired signal does not contain noise introduced by the radio frequency system, the low order intermodulation spurious emissions comprise a 3rd order intermodulation spurious emission, and location of the 3rd order intermodulation spurious emission is in the adjacent channels; determine high order intermodulation spurious emissions of the transmitted analog electrical signal outside of the transmission channel and adjacent channels based at least in part on a relationship between magnitude and location of the low order intermodulation spurious emissions and the high order intermodulation spurious emissions, wherein the high order intermodulation spurious emissions comprise a 5th order intermodulation spurious emission and location of the 5th order intermodulation spurious emission is in a channel that is two channel bandwidths from the transmission channel; and 
 adjust operational parameters used to transmit subsequent analog electrical signals based at least in part on the low order intermodulation spurious emissions and the high order intermodulation spurious emissions. 
 
     
     
       12. The electronic device of  claim 11 , wherein magnitude of the 5th order intermodulation spurious emission has a 5:1 ratio when magnitude of the 3rd order intermodulation spurious emission has a 3:1 ratio. 
     
     
       13. The electronic device of  claim 11 , wherein the electronic device comprises a portable phone, a media player, a personal data organizer, a handheld game platform, a tablet device, a computer, or any combination thereof.

Description:
BACKGROUND 
     The present disclosure relates generally to radio frequency systems and, more particularly, to controlling spurious emissions produced by a radio frequency system. 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     Many electronic devices may include a radio frequency system to facilitate wireless communication of data with other electronic devices and/or a network. The radio frequency system may include a transceiver that receives a digital representation of data as a digital electrical signal and generates an analog representation of the data as an analog electrical signal. A power amplifier may then amplify the analog electrical signal to a desired output power for wireless transmittance via an antenna at a desired radio frequency, such as an assigned resource block or channel. As used herein, a “channel” is intended to describe a range of frequencies and a “resource block” is intended to describe a range of frequencies within the channel. 
     Generally, regulations on wireless transmissions are set by regulatory bodies, such as the Federal Communications Commission (FCC) in the United States, Industry Canada (IC) in Canada, the Ministry of Internal Affairs and Communications (MIC) in Japan, and the European Telecommunications Standards Institute (ETSI) in Europe. More specifically, such regulatory bodies may set allowable spurious emissions limits for radio frequency systems, particularly in protected or restricted frequency bands. As used herein, a “frequency band” is intended to describe a range of radio frequencies including multiple channels and “spurious emissions” are intended to describe wireless signal transmission at frequencies other than a desired transmission frequency. 
     In some embodiments, spurious emissions may be the result of noise introduced into the analog electrical signal, for example, by the transceiver and/or the power amplifier. As a result, when the antenna transmits the analog electrical signal at a desired transmission frequency, spurious emissions may also be transmitted at other frequencies. More specifically, the magnitude and location (e.g., frequency) of the spurious emissions may be affected by operational parameters, such as ambient temperature, transmission frequency, output power, antenna load, and the like. In other words, even though the operational parameters may change, the radio frequency system should still operate to meet any spurious emissions limits. 
     SUMMARY 
     A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below. 
     The present disclosure generally relates to improving performance of a radio frequency system by controlling operation of the radio frequency system based at least in part on output spurious emissions. Generally, the radio frequency system may wirelessly communicate data with other electronic devices and/or a network by modulating radio waves at a desired transmission frequency based on an analog representation of the data (e.g., an analog electrical signal). However, the analog electrical signal may contain noise introduced by the components in the radio frequency system, which may cause the radio frequency system to transmit spurious emissions at other frequencies. 
     Although some amount of spurious emissions may be acceptable, the radio frequency system should still operate within set spurious emissions limits, particularly at protected or restricted frequency bands. However, the amount of spurious emissions transmitted by the radio frequency system may be dependent on the operational parameters, such as ambient temperature, transmission frequency, output power, antenna load, and the like. In other words, the amount of spurious emissions may be dynamic over operation of the radio frequency system. 
     Accordingly, the techniques described herein may improve operation of the radio frequency system by enabling dynamic control based at least in part on spurious emissions. In some embodiments, the radio frequency system may include a coupler that feeds back the analog electrical signal transmitted by an antenna to a feedback receiver. The feedback receiver may then compare the feedback signal with an ideal desired signal (e.g., a digital electrical signal). Based at least in part on the comparison, the radio frequency system may determine distortion (e.g., spurious emission) in the transmitted analog electrical signal introduced by the radio frequency system (e.g., a power amplifier and/or a transceiver). In some embodiments, the feedback receiver may be tuned to determine the spurious emissions at a particular out of band frequency (e.g., frequency outside of desired transmission frequency). In other embodiments, the feedback receiver may determine the spurious emissions at a range of frequencies around the transmission frequency, which may then be used to determine spurious emissions at other frequencies. 
     In this manner, the radio frequency system may determine the location (e.g., frequency) and/or magnitude of spurious emissions transmitted and adjust operational parameters of the radio frequency system when necessary. More specifically, the radio frequency system may operate using nominal operational parameters when the nominal operational parameters do not result in exceeding spurious emissions limits. However, when spurious emissions limits are exceeded, the radio frequency system may adjust operational parameters of the radio frequency system away from the nominal operational parameters. For example, in some embodiments, the radio frequency system may increase filter rejection, decrease amplification by a power amplifier, increase power amplifier linearity, adjust the skew of the power amplifier emissions (e.g., favor emissions on one side of the transmission frequency, which may land in a protected band, at the expense of emissions on the other side, which may have no emissions constraints), or any combination thereof. 
     However, adjustments of operational parameters away from the nominal operational parameters may affect performance of the radio frequency system, particularly power consumption, efficiency, and/or output power. As such, the techniques provided herein enable performance of the radio frequency system to be improved by predominantly using nominal operational parameters and dynamically adjusting the operational parameters of the radio frequency system based on spurious emissions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  is a block diagram of a electronic device with a radio frequency system, in accordance with an embodiment; 
         FIG. 2  is an example of the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 3  is an example of the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 4  is an example of the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 5  is block diagram of a portion of the radio frequency system of  FIG. 1 , in accordance with an embodiment; 
         FIG. 6A  is a plot of a first analog electrical signal transmitted by the radio frequency system of  FIG. 5 , in accordance with an embodiment; 
         FIG. 6B  is a plot of a first analog electrical signal transmitted by the radio frequency system of  FIG. 5 , in accordance with an embodiment; 
         FIG. 7  is a flow diagram describing a process for transmitting analog electrical signals using the radio frequency system of  FIG. 5 , in accordance with an embodiment; 
         FIG. 8  is a flow diagram describing a process for determining spurious emissions based on a feedback signal, in accordance with an embodiment; 
         FIG. 9  is a flow diagram describing a process for determining spurious emissions using a dedicated coupler, in accordance with an embodiment; 
         FIG. 10  is a flow diagram describing a process for determining spurious emissions using a shared coupler, in accordance with an embodiment; 
         FIG. 11  is a flow diagram describing a process for determining spurious emissions based on a model, in accordance with an embodiment; and 
         FIG. 12  is a flow diagram describing a process for determining adjustments to operational parameters of the radio frequency system of  FIG. 5 , in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments of the present disclosure will be described below. These described embodiments are only examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but may nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
     As mentioned above, an electronic device may include a radio frequency system to facilitate wirelessly communicating data with another electronic device and/or a network. More specifically, the radio frequency system may modulate radio waves at a desired radio frequency, such as an assigned one or more resource block or channel, to enable the electronic device to communicate via a personal area network (e.g., Bluetooth network), a local area network (e.g., an 802.11x Wi-Fi network), and/or a wide area network (e.g., a 4G or LTE cellular network). In other words, the radio frequency systems may utilize various wireless communication protocols to facilitate communication of data. 
     Nevertheless, radio frequency systems may generally be operationally similar regardless of the wireless communication protocol used. For example, to transmit data, processing circuitry may generate a digital representation of the data as a digital electrical signal and a transceiver (e.g., a transmitter and/or a receiver) may then convert the digital electrical signal into one or more analog electrical signals. The analog electrical signal may then be amplified by a power amplifier, filtered by one or more filters, and transmitted by an antenna. 
     However, along with the data, the radio frequency system may also transmit spurious emissions. In some embodiments, the spurious emissions may be the result of noise introduced into the analog electrical signal by the transceiver and/or the power amplifier. For example, the transceiver may introduce noise as a result of digital signal modulation or analog impairments in the modulator, mixer, or driver amplifier and the power amplifier may introduce noise as a result of non-linearities. In some embodiments, adjacent channel leakage ratio (ACLR) may be used as a metric for spurious emissions levels outside the desired transmission frequency (e.g., allocated transmission channel). 
     In some instances, the spurious emissions may be transmitted at frequencies other than a desired transmission frequency. More specifically, spurious emissions may leak into frequencies surrounding the transmission frequency. For example, a radio frequency system transmitting a 10 MHz wide channel centered at 700 MHz (e.g., 695-705 MHz allocated bandwidth), may generate adjacent channel spurious emissions due to 3rd order products between 685-715 MHz, 5th order products between 675-725 MHZ, and so on with higher order products. Additionally, spurious emissions may occur at harmonics of the transmission frequency. For example, continuing with the above example, spurious emissions may occur at 1400 MHz (e.g., second harmonic), 2100 MHz (e.g., third harmonic), and so on. 
     However, regulatory bodies generally place a limit on amount of acceptable spurious emissions. In fact, some regulatory bodies may restrict wireless transmission at certain frequencies and only allow spurious emissions below a specified limit. For example, the FCC mandates that only spurious emissions are permitted at frequencies between 608-614 MHz. Moreover, the FCC mandates that the magnitude of the spurious emissions be less than 200 microvolts/meter. 
     As such, a radio frequency system should operate such that spurious emissions are lower than the set limits. Generally, spurious emissions vary based on operational parameters, such as ambient temperature, transmission frequency, output power, antenna load, and the like. For example, spurious emissions may increase as temperature increases. Additionally, spurious emissions are more likely to fall within protected frequencies when the transmission frequency is closer to the protected frequencies. Furthermore, magnitude of spurious emissions may increase as magnitude (e.g., output power) of the transmitted analog electrical signals is increased. In other words, the position (e.g., frequency) and magnitude of spurious emissions may dynamically vary over the course of operation of the radio frequency system. 
     Accordingly, as will be described in more detail below, performance of the radio frequency system may be improved by dynamically controlling operational parameters of the radio frequency system based at least in part on spurious emissions. In some embodiments, the radio frequency system may determine spurious emissions based at least in part on feedback of the analog electrical signal transmitted by the antenna. More specifically, the radio frequency system may determine location and/or magnitude of any spurious emissions by comparing the feedback signal (e.g., portion of the transmitted analog electrical signal) with a desired signal (e.g., ideal digital electrical signal), which does not include noise introduced by the radio frequency system. 
     Based on the determined spurious emissions, the radio frequency system may adjust operational parameters of the radio frequency system, particularly when the spurious emissions exceeded set limits. More specifically, when below spurious emissions limits, the radio frequency system may operate using nominal operational parameters. On the other hand, when limits are exceeded, the radio frequency system may adjust operational parameters of the radio frequency system. For example, the radio frequency system may increase filter rejection, decrease amplification by a power amplifier, increase power amplifier linearity, adjust the skew of the power amplifier emissions (e.g., favor emissions on one side of the transmission frequency, which may land in a protected band, at the expense of emissions on the other side, which may have no emissions constraints), or any combination thereof. 
     However, adjustments away from the nominal operational parameters may affect performance of the radio frequency system. For example, increasing filter rejection and/or output power may reduce reliability of transmissions by the radio frequency system. Additionally, increasing the filter rejection and/or increasing linearity of the power amplifier may increase power consumption, thereby decreasing efficiency (e.g., output power/DC power consumption). Furthermore, adjusting skew of the power amplifier may introduce spurious emissions at other frequencies. 
     In other words, the techniques may improve performance of a radio frequency system by predominantly using the nominal operational parameters and dynamically adjusting the operational parameters of the radio frequency system based on spurious emissions. To help illustrate, an electronic device  10  that may utilize a radio frequency system  12  is described in  FIG. 1 . As will be described in more detail below, the electronic device  10  may be any suitable electronic device, such as a handheld computing device, a tablet computing device, a notebook computer, and the like. 
     Accordingly, as depicted, the electronic device  10  includes the radio frequency system  12 , input structures  14 , memory  16 , one or more processor(s)  18 , one or more storage devices  20 , a power source  22 , input/output ports  24 , and an electronic display  26 . The various components described in  FIG. 1  may include hardware elements (including circuitry), software elements (including instructions stored on a non-transitory computer-readable medium), or a combination of both hardware and software elements. It should be noted that  FIG. 1  is merely one example of a particular implementation and is intended to illustrate the types of components that may be present in the electronic device  10 . Additionally, it should be noted that the various depicted components may be combined into fewer components or separated into additional components. For example, the memory  16  and a storage device  20  may be included in a single component. 
     As depicted, the processor  18  is operably coupled with memory  16  and the storage device  20 . More specifically, the processor  18  may execute instruction stored in memory  16  and/or the storage device  20  to perform operations in the electronic device  10 , such as instructing the radio frequency system  12  to communicate with another device. As such, the processor  18  may include one or more general purpose microprocessors, one or more application specific processors (ASICs), one or more field programmable logic arrays (FPGAs), or any combination thereof. Additionally, memory  16  and/or the storage device  20  may be a tangible, non-transitory, computer-readable medium that stores instructions executable by and data to be processed by the processor  18 . For example, the memory  16  may include random access memory (RAM) and the storage device  20  may include read only memory (ROM), rewritable flash memory, hard drives, optical discs, and the like. 
     Additionally, as depicted, the processor  18  is operably coupled to the power source  22 , which provides power to the various components in the electronic device  10 . As such, the power source  22  may includes any suitable source of energy, such as a rechargeable lithium polymer (Li-poly) battery and/or an alternating current (AC) power converter. Furthermore, as depicted, the processor  18  is operably coupled with I/O ports  24 , which may enable the electronic device  10  to interface with various other electronic devices, and input structures  14 , which may enable a user to interact with the electronic device  10 . Accordingly, the inputs structures  14  may include buttons, keyboards, mice, trackpads, and the like. Additionally, in some embodiments, the electronic display  26  may include touch sensitive components. 
     In addition to enabling user inputs, the electronic display  26  may display image frames, such as a graphical user interface (GUI) for an operating system, an application interface, a still image, or video content. As depicted, the display is operably coupled to the processor  18 . Accordingly, the image frames displayed by the electronic display  26  may be based on display image data received from the processor  18 . 
     As depicted, the processor  18  is also operably coupled with the radio frequency system  12 , which may facilitate communicatively coupling the electronic device  10  to one or more other electronic devices and/or networks. For example, the radio frequency system  12  may enable the electronic device  10  to communicatively couple to a personal area network (PAN), such as a Bluetooth network, a local area network (LAN), such as an 802.11x Wi-Fi network, and/or a wide area network (WAN), such as a 4G or LTE cellular network. As can be appreciated, the radio frequency system  12  may enable communication using various communication protocols. 
     Operational principles of the radio frequency system  12  may be similar for each of the communication protocols (e.g., Bluetooth, LTE, 802.11x Wi-Fi, etc). More specifically, as will be described in more detail below, the radio frequency system  12  may convert a digital electrical signal containing data desired to be transmitted into an analog electrical signal using a transceiver. The analog electrical signal may then be amplified using a power amplifier, filtered using a filter, and transmitted using an antenna. In other words, the techniques described herein may be applicable to any suitable radio frequency system  12  that operates in any suitable manner regardless of communication protocol used. 
     As described above, the electronic device  10  may be any suitable electronic device. To help illustrate, one example of a handheld device  10 A is described in  FIG. 2 , which may be a portable phone, a media player, a personal data organizer, a handheld game platform, or any combination of such devices. For example, the handheld device  10 A may be a smart phone, such as any iPhone® model available from Apple Inc. As depicted, the handheld device  10 A includes an enclosure  28 , which may protect interior components from physical damage and to shield them from electromagnetic interference. The enclosure  28  may surround the electronic display  26 , which, in the depicted embodiment, displays a graphical user interface (GUI)  30  having an array of icons  32 . By way of example, when an icon  32  is selected either by an input structure  14  or a touch sensing component of the electronic display  26 , an application program may launch. 
     Additionally, as depicted, input structures  14  may open through the enclosure (e.g., housing)  28 . As described above, the input structures  14  may enable a user to interact with the handheld device  10 A. For example, the input structures  14  may activate or deactivate the handheld device  10 A, navigate a user interface to a home screen, navigate a user interface to a user-configurable application screen, activate a voice-recognition feature, provide volume control, and toggle between vibrate and ring modes. Furthermore, as depicted, the I/O ports  24  open through the enclosure  28 . In some embodiments, the I/O ports  24  may include, for example, an audio jack to connect to external devices. Additionally, the radio frequency system  12  may also be enclosed within the enclosure  28  and internal to the handheld device  10 A. 
     To further illustrate a suitable electronic device  10 , a tablet device  10 B is described in  FIG. 3 , such as any iPad® model available from Apple Inc. Additionally, in other embodiments, the electronic device  10  may take the form of a computer  10 C as described in  FIG. 4 , such as any Macbook® or iMac® model available from Apple Inc. As depicted, the tablet device  10 B and the computer  10 C also include an electronic display  26 , input structures  14 , I/O ports  24 , and an enclosure  28 . Similar to the handheld device  10 A, the radio frequency system  12  may also be enclosed within the enclosure  28  and internal to the tablet device  10 B and/or the computer  10 C. 
     As described above, the radio frequency system  12  may facilitate communication with other electronic devices and/or a network by wirelessly communicating data. To help illustrate, a portion  34  of radio frequency system  12  is described in  FIG. 5 . As depicted, the portion  34  includes a digital signal generator  36 , a transceiver  38 , a power amplifier  40 , one or more filters  42 , a feedback coupler  39 , an antenna  44 , and a controller  41 . More specifically, the controller  41  may include one or more processor  43  and memory  45  to facilitate controlling operation of the radio frequency system  12 . For example, the controller  41  may instruct the transceiver  38 , the power amplifier  40 , the one or more filters, the coupler  39 , or any combination thereof to adjust operational parameters. Accordingly, in some embodiments, the controller processor  43  may be included in the processor  18  and/or separate processing circuitry and the memory  45  may be included in memory  16  and/or a separate tangible non-transitory computer-readable medium. 
     Additionally, the digital signal generator  36  may generate a digital representation of data desired to be transmitted from the electronic device  10  by outputting a digital electrical signal. Accordingly, in some embodiments, the digital signal generator  36  may include the processor  18  and/or a separate processing circuitry, such as a baseband processor or a modem in the radio frequency system  12 . 
     The transceiver  38  may then receive the digital electrical signal and generate an analog representation of the data. In some embodiments, the transceiver  38  uses digital signal modulation to generate an analog representation as an analog electrical signal. For example, when the digital electrical signal is high (e.g., “1”), the transceiver  38  may output an analog electrical signal with a positive voltage and, when the digital electrical signal is low (e.g., “0”), the transceiver  38  may output an analog electrical signal at zero volts. However, digital signal modulation used in the transceiver  38  may generally introduce some noise into the analog electrical signal. 
     Since the output power of the analog electrical signal may be small, the power amplifier  40  may receive and amplify the analog electrical signal by outputting an amplified analog electrical signal. More specifically, the power amplifier  40  may vary amplitude of the amplified analog electrical signal to enable the output power of the radio frequency system  12  to be adjusted. In fact, in some embodiments, the power amplifier  40  may mix noise/distortions introduced by the transceiver  38 , thereby introducing intermodulation spurious emissions. 
     Additionally, in some embodiments, the power amplifier  40  may include one or more transistors as electrical switches to amplify the analog electrical signal. Ideally, the power amplifier  40  should linearly adjust amplitude (e.g., output power) of the amplified analog electrical signals and maintain a constant phase shift between the input analog electrical signals and the output amplified analog electrical signals. However, transistors are generally not ideal (e.g., parasitic capacitance, memory effects, and/or a non-linear input to output transfer function), which may affect linearity and/or phase shift of the power amplifier  40 . For example, if amplitude modulation (AM) peaks exceed the drive capability of the power amplifier  40 , the power amplifier compression may result, thereby causing AM-AM (amplitude modulation to amplitude modulation) and/or AM-PM (amplitude modulation to phase modulation) distortion. This distortion may result in impairments, such as error vector magnitude (EVM), on the in-band portion of the transmitted analog electrical signal (e.g., at the desired transmission frequency), thereby degrading signal integrity. In other words, the effects on linearity and/or phase shift in the power amplifier  40  may generally introduce noise or distortion into the amplified analog electrical signal. 
     To facilitate reducing noise introduced by the transceiver  38  and/or the power amplifier  40 , one or more filters  42  may receive the amplified analog electrical signal and output a filtered analog electrical signal. More specifically, the one or more filters  42  may be tuned to attenuate portions of the amplified analog electrical signal at target frequencies, such as protected frequencies. However, since filters are generally not ideal, the one or more filters  42  may include a transition band that affects frequencies other than the target frequencies. In fact, when attenuating frequencies near the transmission frequency, the transition band may reduce the amplitude at the transmission frequency, thereby reducing output power of the radio frequency system  12 . 
     The filtered analog electrical signal may then be wirelessly transmitted to another electronic devices and/or a network via the antenna  44  at a transmission frequency as modulated radio waves. The transmitted analog electrical signal may also be fed back from the coupler  39  to a feedback receiver  47 , which may be used to facilitate controlling output power of the radio frequency system  12 . In some embodiments, the feedback receiver  47  may by tuned to the portion of the transmitted analog electrical signal at the transmission frequency and surrounding frequencies (e.g., frequencies in adjacent channels). Additionally or alternatively, the feedback receiver  47  may be tuned to portions of the transmitted analog electrical signal at particular target frequencies (e.g., protected frequencies). In this manner, as will be described in more detail below, the feedback of the transmitted analog electrical signal may also facilitate determining location (e.g., frequency) and/or magnitude of spurious emissions. 
     As described above, noise or distortion introduced by the radio frequency system  12  may result in spurious emissions at frequencies other than the desired transmission frequency. To help illustrate, examples of analog electrical signals  46  are described in  FIGS. 6A and 6B . More specifically,  FIG. 6A  describes a first analog electrical signal  46 A that is transmitted when the radio frequency system  12  is assigned fifty resource blocks (e.g., 10 MHz) and  FIG. 6B  describes a second electrical signal  46 B that is transmitted when the radio frequency system  12  is assigned one resource block. In the depicted embodiments, the radio frequencies are divided into channels with a bandwidth of 10 MHz. As such,  FIGS. 6A and 6B  describe the magnitude of the analog electrical signals  46  in a first channel  48  between 675-685 MHz, a second channel  50  between 685-695 MHz, a third channel  52  between 695-705 MHz, a fourth channel  54  between 705-715 MHz, and a fifth channel  56  between 715-725 MHz. It should be noted that the analog electrical signals  46  are merely intended to be illustrative and not limiting. 
     With regard to  FIG. 6A , since the radio frequency system  12  is assigned fifty resource blocks, the first analog electrical signal  46 A has a desired transmission bandwidth of 10 MHz. Thus, as depicted, the analog electrical signal  46 A includes a data portion  58 A at the frequencies between 695-705 MHz. More specifically, the data portion  58 A includes the analog representation of data desired to be wirelessly transmitted to another electronic device and/or a network. 
     However, the data portion  58 A may also include noise or distortion introduced, for example, by the transceiver  38 . As such, when the introduced noise or distortion is mixed in the power amplifier  40 , intermodulation spurious emissions may result. Generally odd order intermodulation spurious emissions occur near the transmission frequency. More specifically, 3rd order intermodulation spurious emissions may occur in channels directly adjacent to the transmission channel, 5th order intermodulation spurious emissions may occur at channels two channels away from the transmission channel, 7th order intermodulation spurious emissions may occur at channels three channels away from the transmission channel, and so on. For example, in the depicted embodiment, 3rd order intermodulation spurious emissions  60 A with a 10 MHz bandwidth occur in the second channel  50  and the fourth channel  54 . Additionally, 5th order intermodulation spurious emissions  62 A with a 10 MHz bandwidth occur in the first channel  48  and the fifth channel  56 . 
     With regard to  FIG. 6B , since the radio frequency system  12  is assigned one resource block, the second analog electrical signal  46 B has a desired transmission bandwidth of 0.2 MHz. In the depicted embodiment, the second analog electrical signal  46 B includes a data portion  58 B at frequencies around 695 MHz (e.g., edge of the third channel  52 ). More specifically, the data portion  58 B includes the analog representation of data desired to be wirelessly transmitted to another electronic device and/or a network. 
     However, in addition to the data portion  58 B, the analog electrical signal  46 B also includes a local oscillator (LO) spurious emission  63  at frequencies around 700 MHz and an in-phase quadrature (IQ) spurious emission  64  at frequencies around 705 MHz. In some embodiments, the local oscillator spurious emission  63  may be introduced by the transceiver  38  at the central frequencies of the channel (e.g., 700 MHz) since the transceiver  38  is generally tuned to the central frequencies. Additionally, the in-phase quadrature spurious emission  64  may also be introduced by imperfections of the transceiver  38  and occur at frequencies such that the local oscillator spurious emission  63  is between and equidistant from the data portion  58 B and the in-phase quadrature spurious emission  64 . 
     Additionally, when the data portion  58 B, the local oscillator spurious emissions  63 , and the in-phase quadrature spurious emission  64  are mixed in the power amplifier  40 , intermodulation spurious emissions may result. For example, in the depicted embodiment, 3rd order intermodulation spurious emissions  60 B occur in the second channel  50  at frequencies around 690 MHz (e.g., as a result of intermodulation between the data portion  58 B and local oscillator spurious emission  63 ) and at frequencies around 685 MHz (e.g., as a result of intermodulation between the data portion  58 B and the in-phase quadrature spurious emission  64 ). Similarly, 3rd order intermodulation spurious emission  60 B occur in the fourth channel  54  at frequencies around 710 MHz and 715 MHz. Additionally, 5th order intermodulation spurious emissions  62 A occur in the first channel  48  at frequencies around 675 MHz and 680 MHz and in the fifth channel  56  at frequencies around 720 MHz and 725 MHz. 
     However, as described above, regulatory bodies may place acceptable limits on spurious emissions (e.g., intermodulation spurious emissions  60  and  62 ), particularly at protected/restricted frequency ranges. For example, the FCC limits spurious emissions at frequencies between 608-614 MHz to 200 microvolts/meter. Thus, continuing with the above examples, it is possible that transmitting the analog electrical signals  46  may result in a higher order (e.g., 19th order) intermodulation spurious emission occurring in between 608-614 MHz. Moreover, if the analog electrical signals  46  use a lower transmission frequency (e.g., 615 MHz), it may be possible that lower order intermodulation spurious emissions (e.g.,  60  or  62 ) may occur between 608-614 MHz. 
     As such, the radio frequency system  12  may be operated such that spurious emissions meet set spurious emissions limits. To help illustrate, one embodiment of a process  66  for controlling operation of a radio frequency system  12  is described in  FIG. 7 . Generally, the process  66  includes determining spurious emissions limits (process block  68 ), determining transmitted spurious emissions (process block  70 ), determining whether spurious emissions are greater than the spurious emissions limits (decision block  72 ), and transmitting analog electrical signals using nominal operational parameters when the spurious emissions are not greater than the limits (process block  74 ). Additionally, when the spurious emissions are greater than the limits, the process  66  includes adjusting the operational parameters of the radio frequency system (process block  76 ) and transmitting the analog electrical signals using adjusted operational parameters (process block  78 ). Furthermore, the process  66  optionally includes offsetting the spurious emissions (process block  71 ). In some embodiments, the process  66  may be implemented using instructions stored in the memory  16 ,  45  and/or another suitable tangible non-transitory computer-readable medium and executable by the processor  18 ,  43 , and/or another suitable processing circuitry. 
     Accordingly, the radio frequency system  12  may determine any set spurious emissions limits (process block  68 ). As described above, the spurious emissions limits regulating location (e.g., frequency) and/or magnitude of spurious emissions may be predetermined and set by regulatory bodies. Thus, in some embodiments, a manufacturer may store any such spurious emissions limits in memory (e.g.,  16  or  45 ) upon manufacture. Thus, upon powering on, the radio frequency system  12  may poll the memory to determine spurious emissions limits. Additionally or alternatively, to facilitate operating under jurisdictions of various regulating bodies, the radio frequency system  12  may receive spurious emissions limits for a particular jurisdiction from a network upon powering up. 
     Additionally, the radio frequency system  12  may determine the location (e.g., frequency) and/or magnitude of spurious emissions transmitted (process block  70 ). As described above, the spurious emissions may vary based on operational parameters, such as ambient temperature, transmission frequency, output power, antenna load, and the like. Accordingly, in some embodiments, as will be described in more detail below, the radio frequency system  12  may determine the operational parameters and supply the operational parameters to a model, which relates the operational parameters to spurious emissions. 
     Additionally or alternatively, as described above, the radio frequency system  12  may determine the spurious emissions based at least in part on a feedback signal received from the coupler  39 . To help illustrate, one embodiment of a process  80  for determining spurious emissions based on the feedback signal is described in  FIG. 8 . Generally, the process  80  includes determining a desired (e.g., ideal) signal (process block  82 ), determining a feedback signal (process block  84 ), and comparing the desired signal and the feedback signal (process block  86 ). In some embodiments, the process  80  may be implemented using instructions stored in the memory  16 ,  45  and/or another suitable tangible non-transitory computer-readable medium and executable by the processor  18 ,  43 , and/or another suitable processing circuitry. 
     Accordingly, the radio frequency system  12  may determine the desired signal (process block  82 ). More specifically, the desired signal represents the data to be transmitted without any noise or distortion. As such, the desired signal may be the digital electrical signal received from the digital signal generator  36  because the digital electrical signal does not include noise or distortion introduced by the transceiver  38  and/or the power amplifier  40 . 
     Additionally, the radio frequency system  12 , and more particularly the feedback receiver  47 , may determine the feedback signal from the coupler  39  (process block  84 ). As described above, the feedback receiver  47  may determine portions of the transmitted analog electrical signal at frequencies surrounding the transmission frequency to facilitate controlling output power of the radio frequency system  12 . Accordingly, in some embodiments, the feedback receiver  47  may be shared and tuned to the portion of the transmitted analog electrical signal at frequencies surrounding the transmissions frequency. Additionally or alternatively, the feedback receiver  47  may be dedicated and tuned to portions of the transmitted analog electrical signal at specific frequencies. 
     In either embodiment, the radio frequency system  12  may determine location (e.g., frequency) and/or magnitude by comparing the desired signal with the feedback signal (process block  88 ). More specifically, the radio frequency system  12  may determine location of spurious emissions based on frequencies at which the desired signal and the feedback signal differ. Additionally, the radio frequency system  12  may determine magnitude of the spurious emission based on difference between the desired signal and the feedback signal at those locations. 
     To help illustrate, one embodiment of a process  90  for determining spurious emissions using a dedicated feedback receiver  47  is described in  FIG. 9 . Generally, the process  90  includes determining a target frequency (process block  92 ), setting a feedback receiver to the target frequency (process block  94 ), determining feedback signal at the target frequency (process block  96 ), and determining spurious emissions at the target frequency (process block  98 ). In some embodiments, the process  90  may be implemented using instructions stored in the memory  16 ,  45  and/or another suitable tangible non-transitory computer-readable medium and executable by the processor  18 ,  43 , and/or another suitable processing circuitry. 
     Accordingly, the radio frequency system  12  may determine the target frequency (process block  92 ) and set the feedback receiver  47  accordingly (process block  94 ). In some embodiments, the target frequency may be set to protected/restricted frequencies that are likely to contain spurious emissions above a set limit. The feedback receiver  47  may then be tuned to determine portions of the analog electrical signal  46  at the target frequency and possibly surrounding frequencies. 
     In this manner, the radio frequency system  12  may determine any spurious emissions at the target frequency by comparing the desired signal at the target frequency and the feedback signal at the target frequency (process block  98 ). More specifically, the radio frequency system  12  may determine that spurious emissions occur at the target frequency when the desired signal and the feedback signal differ. Additionally, the radio frequency system  12  may determine magnitude of the spurious emissions at the target frequency based on amount of difference between the desired signal and the feedback signal at the target frequency. 
     In other words, the use of a dedicated feedback receiver  47  enables explicitly determining location and/or magnitude of spurious emissions at one or more target frequencies. However, to reduce components and/or cost of the radio frequency system  12 , a shared feedback receiver  47  may still be used to determine location and/or magnitude by calculating spurious emissions based on feedback of the portion of the transmitted analog electrical signal at frequencies surrounding the transmission frequency (e.g., transmission channel and adjacent channels). 
     To help illustrate, one embodiment of a process  100  for determining spurious emissions using a shared feedback receiver  47  is described in  FIG. 10 . Generally, the process  100  includes determining feedback signal at a transmission channel (process block  102 ), determining feedback signal at adjacent channels (process block  104 ), and determining spurious emissions at other frequencies (process block  106 ). Additionally, process  100  may optionally include adjusting a relationship between the intermodulation spurious emissions (process block  108 ). In some embodiments, the process  100  may be implemented using instructions stored in the memory  16 ,  45  and/or another suitable tangible non-transitory computer-readable medium and executable by the processor  18 ,  43 , and/or another suitable processing circuitry. 
     As described above, a shared feedback receiver  47  may be used to facilitate controlling output power by determining the portion of the transmitted analog electrical signal at the transmission frequency. Since the feedback receiver  47  may have a bandwidth of multiple channels, the feedback signal may include the portion of the transmitted analog electrical signal in the transmission channel, which includes the transmission frequency (process block  102 ), as well as the portion of the transmitted analog electrical signal in channels adjacent to the transmission channel (process block  104 ). As such, the radio frequency system  12  may explicitly determine location and/or magnitude of spurious emissions in the transmission channel and the adjacent channels by comparing the feedback signal with the desired signal. 
     More specifically, lower order intermodulation spurious emissions (e.g.,  60  and/or  62 ) generally occur in frequencies surrounding the transmission frequency and, thus, may be explicitly determined. However, since higher order intermodulation spurious emissions may occur multiple channels away, they may be outside of the feedback receiver  47  bandwidth. Nevertheless, the radio frequency system  12  may still determine (e.g., infer) location and/or magnitude of such intermodulation spurious emissions based on the signal integrity of the in-band feedback signal. 
     As discussed above, an odd order intermodulation emission (e.g.,  60  or  62 ) generally occurs at each channel on either side of the transmission channel. As such, the radio frequency system  12  may determine the location (e.g., channel) of the intermodulation spurious emissions based at least in part on this relationship. For example, as discussed in  FIGS. 6A and 6B , since the transmission channel is the third channel  52 , the 3rd order intermodulation spurious emissions  60  occur in the second channel  50  and the fourth channel  54  and the 5th order intermodulation spurious emissions  62  occur in the first channel  48  and the fifth channel  56 . 
     Additionally, the magnitudes of the odd order intermodulation spurious emissions are generally related. For example, in some embodiments, magnitudes of the odd order intermodulation spurious emissions may be related such that magnitude of the 3rd order intermodulation spurious emission has a 3:1 ratio, magnitude of the 5th order intermodulation spurious emission has a 5:1 ratio, magnitude of the 7th order intermodulation spurious emission has a 7:1 ratio, and so on. Accordingly, since the 3rd intermodulation spurious emission  60  and/or the 5th intermodulation spurious emission  62  generally occurs in an adjacent channels and are fed back, the radio frequency system  12  may determine the magnitude of the higher order intermodulation spurious emissions based on the relationship between the magnitudes. 
     In some embodiments, the relationship between the magnitudes of the odd order intermodulation spurious emissions may be predetermined by a manufacturer and stored in memory (e.g.,  16  or  45 ) as a look-up-table (LUT) or a model. Moreover, since spurious emissions may vary based on operational parameters, the relationship between magnitudes of the odd order intermodulation spurious emissions may be updated over the course of operation of the radio frequency system  12  (process block  108 ). For example, if the feedback receiver  47  has bandwidth capable of measuring multiple odd order intermodulation spurious emissions, the radio frequency system  12  may determine whether the measured magnitudes are consistent with the determined relationship and adjust the relationship (e.g., model or LUT) accordingly. 
     Additionally, since the spurious emissions may vary based on operational parameters, a model describing relationship between spurious emissions and various operational parameters may be used to determine spurious emissions. To help illustrate, one embodiment of a process  110  for determining spurious emissions using a model is described in  FIG. 11 . Generally, the process  110  includes determining a model of spurious emissions (process block  112 ), determining operational parameters (process block  114 ), and determining spurious emissions (process block  116 ). Additionally, the process  110  optionally includes adjusting the model of spurious emissions (process block  118 ). In some embodiments, the process  110  may be implemented using instructions stored in the memory  16 ,  45  and/or another suitable tangible non-transitory computer-readable medium and executable by the processor  18 ,  43 , and/or another suitable processing circuitry. 
     Accordingly, the radio frequency system  12  may determine the model describing relationship between spurious emissions and operational parameters (process block  112 ). In some embodiments, the model may be determined by a manufacturer and stored in memory (e.g.,  16  or  45 ). More specifically, the manufacturer may run a testing or training sequence to determine how sets of operational parameters affect spurious emissions. For example, the manufacturer may determine the location and magnitude of spurious emissions at varying ambient temperatures, transmission frequencies, output powers, and antenna loads. 
     The radio frequency system  12  may then determine the operational parameters that are inputs to the model (process block  114 ). In some embodiments, this may include polling various sensors (e.g., temperature sensors) and/or the memory to determine various operational parameters. For example, the radio frequency system  12  may poll a temperature sensor to determine ambient temperature. Additionally, the radio frequency system  12  may poll memory to determine a desired transmission frequency, a desired output power, current antenna load, or any combination thereof. 
     In this manner, the radio frequency system  12  may determine location and/or magnitude of spurious emissions by inputting the operational parameters into the model (process block  116 ). Moreover, since the radio frequency system  12  may still include a shared feedback receiver  47  to facilitate controlling output power, the radio frequency system  12  may determine portions of the transmitted analog electrical signal at the transmission channel and adjacent channels, thereby enabling the radio frequency system  12  to determine spurious emissions in the transmission channel and adjacent channels. As such, the radio frequency system  12  may determine whether the measured magnitudes are consistent with the model and adjust the model accordingly. 
     Returning to  FIG. 7 , once the spurious emissions are determined, the radio frequency system  12  may optionally offset the spurious emissions (process block  71 ). As described above, the spurious emissions may be a result of noise introduced by the transceiver  38  and/or the power amplifier  40 . Accordingly, to offset the spurious emissions, the transceiver  38  may generate the analog electrical signal such that it includes an inverse of the noise introduced by the transceiver  38  and/or the power amplifier  40 . In this manner, the noise introduced by the transceiver  38  and/or the power amplifier  40  may be canceled out, thereby reducing spurious emissions. 
     Additionally, the radio frequency system  12  may determine whether the spurious emissions are greater than set limits (decision block  72 ). When not greater than the limits, the radio frequency system may transmit the analog electrical signals using nominal operational parameters (process block  74 ). More specifically, the nominal operational parameters may be a set of operational parameters that balance ability of the radio frequency system  12  to meet spurious emissions limits, efficiency (e.g., output power/DC power consumption), and reliability of transmission. 
     On the other hand, when greater than the limits, the radio frequency may adjust the operational parameters away from the nominal operational parameters to reduce spurious emissions below the limits (process block  76 ). For example, adjusting the operational parameters may include adjusting filter rejection (process block  120 ), decreasing amplification by the power amplifier (process block  122 ), increasing power amplifier linearity (process block  124 ), adjusting skew of power amplifier (process block  126 ), or any combination thereof. 
     In some embodiments, the radio frequency system  12  may adjust the one or more filters  42  to control frequencies targeted by the filters  42  and/or aggressiveness of the filtering (process block  120 ). More specifically, the radio frequency system  12  may tune the filters  42  to target particular frequencies at which to reduce spurious emissions. As such, the filters  42  may be tuned to particular frequencies where spurious emissions are exceeding limits. Additionally, the aggressiveness the filters  42  may be adjusted to control amount the spurious emissions are attenuated (e.g., reduced) at the target frequencies. 
     However, as described above, the filters  42  generally include a transition band and, thus, may affect frequencies other than the target frequencies. For example, when the filters  42  are tuned to a frequency near the transmission frequency, the transition band of the filters  42  may also attenuate the transmitted analog electrical signal at the transmissions frequency. Moreover, as the aggressiveness increases, the frequencies affected by the transition band may increase as well as the magnitude of the attenuation at the affected frequencies. 
     In other words, the tuning and/or aggressiveness of the filters  42  may affect the output power of the transmitted analog electrical signals. To compensate, the radio frequency system  12  may increase the amplification by the power amplifier  40 . However, increasing amplification may consume a greater amount of electrical power to achieve the same output power, thereby decreasing efficiency (e.g., output power/DC power consumption) of the radio frequency system  12 . In fact, to improve efficiency, under nominal operational parameters, the radio frequency system  12  may utilize less aggressive filtering or even bypass the filters  42  entirely. As such, adjusting the filter rejection away from the nominal operational parameters may affect performance of the radio frequency system  12 , for example, by decreasing output power and/or decreasing efficiency. 
     Additionally, in some embodiments, the radio frequency system  12  may decrease amplification by the power amplifier  40  to reduce magnitude of spurious emissions over the spectrum of the transmitted analog electrical signals (process block  122 ). More specifically, the magnitude of intermodulation spurious emissions (e.g.,  60  or  62 ) may be directly related to the output power of the transmitted analog electrical signal. In other words, by decreasing output power of the transmitted analog electrical signal as a whole via reduction in amplification by the power amplifier  40 , the magnitude of the spurious emissions may also be decreased. 
     However, reducing output power of the radio frequency system  12  may affect reliability of communication with the other electronic device and/or the network. For example, a lower output power may increase the risk of data packets being dropped. In some embodiments, this may cause the radio frequency system  12  to resend the dropped data packets, which consumes additional electrical power, or simply proceed without the dropped packets, which may affect communication (e.g., call) quality. In fact, under nominal operational parameters, the radio frequency system  12  may utilize amplification in the power amplifier  40  that balances efficiency and communication reliability. As such, adjusting amplification away from the nominal operational parameters may affect performance of the radio frequency system  12 , for example, by decreasing efficiency and/or decreasing communication reliability. 
     Furthermore, in some embodiments, the radio frequency system  12  may increase linearity of the power amplifier  40  to reduce noise introduced by the power amplifier  40  (process block  124 ). As described above, the power amplifier  40  may introduce noise due to a non-linear relationship between amplitude of the input and output analog electrical signals and/or an inconsistent phase shift between the input and output analog electrical signals, which vary based on output power. Thus, improving linearity of the power amplifier  40  may decrease amount of noise introduced, thereby reducing spurious emissions. 
     Generally, linearity may be improved by increasing electrical power supplied to the power amplifier  40 . As such, increasing linearity to achieve the same output power may decrease efficiency (e.g., output power/DC power consumption) of the radio frequency system  12 . In fact, under nominal operational parameters, the radio frequency system  12  may utilize a linearity of the power amplifier  40  that balances efficiency and introduced noise. As such, adjusting amplification away from the nominal operational parameters may affect performance of the radio frequency system  12 , for example, by decreasing efficiency. 
     Moreover, in some embodiments, the radio frequency system  12  may adjust the skew of the power amplifier  40  to adjust location (e.g., frequency) of the spurious emissions (process block  126 ). For example, when the power amplifier  40  utilizes envelope tracking, the skew of the power amplifier  40  may be adjusted to shift spurious emissions from one side of the transmission frequency to the other. In other words, spurious emissions at some frequencies may be improved at the expense of others. This may be particularly useful when protected/restricted frequencies occur closer on one side of the transmission frequency. 
     However, since the location of protected/restricted frequencies may vary based on jurisdiction, under nominal operational parameters, the radio frequency system  12  may utilize a skew that evenly spreads the spurious emissions on either side of the transmission frequency. As such, adjusting skew of the power amplifier  40  away from the nominal operational parameters may affect performance of the radio frequency system  12 , for example, by introducing spurious emissions at other frequencies. 
     Once the operational parameters of the radio frequency system  12  are adjusted using any combination of the techniques described above, the radio frequency system  12  may transmit subsequent analog electrical signals using the adjusted operational parameters while meeting any spurious emissions limits (process block  78 ). As described above, each of the techniques that may be employed to adjust the operational parameters introduce different tradeoffs. Accordingly, it may be desirable to employ techniques based at least in part on type, location, magnitude, and/or number of the spurious emissions. 
     To help illustrate, one embodiment of a process  128  for determining the adjustments to the operational parameters is described in  FIG. 12 . Generally, the process  128  includes determining magnitude, location, number, and type of spurious emissions that exceed limits (process block  130 ) and determining adjustments on operational parameters (process block  132 ). In some embodiments, the process  128  may be implemented using instructions stored in the memory  16 ,  45  and/or another suitable tangible non-transitory computer-readable medium and executable by the processor  18 ,  43 , and/or another suitable processing circuitry. 
     Accordingly, as described above, the radio frequency system  12  may determine magnitude and location of spurious emissions, for example, using a feedback signal and/or a model of spurious emissions. Additionally, the radio frequency system  12  may determine number of spurious emissions based at least in part on number of instances the feedback signal differs from a desired signal. Furthermore, the radio frequency system  12  may determine the type of each spurious emission based on location of the spurious emission. For example, when the spurious emissions are in set intervals from the transmission channel, the radio frequency system  12  may determine that the spurious emissions are intermodulation spurious emissions (e.g.,  60  or  62 ). Spurious emissions at integer multiples of the desired transmission frequency may be identified as harmonics. Emissions type and location may also be known to the controller  41  in advance based on the type of signal being transmitted. 
     Based at least in part on the magnitude, location, type, and number of the spurious emissions, the radio frequency system  12  may then determine what techniques to employ when adjusting the operational parameters (process block  132 ). For example, when spurious emissions exceed limits at a large number of frequencies, the radio frequency system  12  may determine that reducing amplification by the power amplifier  40  should be used to enable decreasing spurious emissions across the spectrum of the transmitted analog electrical signal. Additionally, when power consumption is not a concern (e.g., when electronic device  10  connected to a wall outlet), the radio frequency system  12  utilize adjusting filter rejection and/or increasing power amplifier  40  linearity. Furthermore, when intermodulation spurious emissions exceed limits, the radio frequency system  12  may determine to increase power amplifier  40  linearity to reduce noise introduced by the power amplifier  40  that cause the intermodulation spurious emissions (e.g.,  60  or  62 ). Moreover, when spurious emission (e.g.,  60  or  62 ) exceed limits on one side of the transmission frequency but not the other, the radio frequency system  12  may determine to adjust skew of the power amplifier  40  to shift location of leakage spurious emissions. 
     Accordingly, the technical effects of the present disclosure include improving performance of a radio frequency system by adjusting operation based at least in part on spurious emissions. More specifically, the radio frequency system may predominantly operate using nominal operational parameters, which may strike a balance between efficiency (e.g., output power/DC power consumption) and reliability. However, since occurrence of spurious emissions may vary over operation, the radio frequency system may adjust the operational parameters away from the nominal operational parameters so that spurious emissions limits are not exceeded. In this manner, the nominal operational parameters may be set more aggressively, thereby improving efficiency and/or reliability, since the operational parameters may be dynamically adjusted when spurious emissions exceed set limits. 
     The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure.

Metadata:
Filing Date: 20150302
Publication Date: 20160614
Grant Date: 20160614
Priority Date: 20150302
Inventors: GOEDKEN RYAN JOSEPH
Assignee: APPLE INC
CPC Classifications: [{"code": "H04B1/0475", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/14", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B17/14", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B17/0085", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B2001/0416", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F3/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B2001/0416", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F3/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/0085", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B2001/0408", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B1/0475", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B1/0475", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/14", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 56100691