PATENT DOCUMENT

Publication Number: US-9537519-B2
Application Number: US-201414525077-A
Country: US
Kind Code: B2

Title: Systems and methods for performing power amplifier bias calibration

Abstract:
Wireless communications circuitry in an electronic device may include power amplifier circuitry that is powered using a bias voltage supplied by adjustable power supply circuitry. The power supply circuitry may include envelope tracking circuitry that continuously adjusts the bias voltage. The wireless communications circuitry may generate test signals and may generate performance metric data from the test signals. Processing circuitry may generate bias voltage calibration data based on the performance metric data and may provide the calibration data to the envelope tracking circuitry. After the calibration data has been generated, the envelope tracking circuitry may continuously select bias voltages to provide to the amplifier based on the magnitude of signals that are transmitted and the calibration data. By actively adjusting the bias voltage in this way, power consumption may be minimized without generating undesirable harmonics or other radio-frequency performance requirement violations.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 radio-frequency transmitter circuitry configured to transmit radio-frequency signals; 
 power amplifier circuitry configured to amplify the transmitted radio-frequency signals; 
 radio-frequency receiver circuitry coupled to an output of the power amplifier circuitry via a feedback path, wherein the radio-frequency receiver circuitry is configured to generate performance metric data based on the amplified radio-frequency signals; 
 processing circuitry configured to generate calibration data for the power amplifier circuitry based on the performance metric data generated by the radio-frequency receiver circuitry; and 
 circuitry that controls a gain provided by the power amplifier circuitry in amplifying the transmitted radio-frequency signals based on the calibration data, wherein the circuitry comprises storage circuitry that stores the calibration data, the calibration data comprises a data structure having a plurality of entries, and each entry of the plurality of entries has a corresponding output power level for the power amplifier circuitry and a corresponding bias voltage for the power amplifier circuitry. 
 
     
     
       2. The electronic device defined in  claim 1 , wherein the radio-frequency receiver circuitry is configured to generate a compression value associated with the power amplifier circuitry and wherein the processing circuitry is configured to generate the calibration data based on the compression value. 
     
     
       3. The electronic device defined in  claim 1 , wherein the radio-frequency transmitter circuitry and the radio-frequency receiver circuitry are formed on a common integrated circuit. 
     
     
       4. The electronic device defined in  claim 1 , further comprising:
 baseband processing circuitry that is coupled to the processing circuitry and that generates baseband data. 
 
     
     
       5. The electronic device defined in  claim 4 , further comprising:
 digital predistortion circuitry coupled between an output of the baseband processing circuitry and an input of the radio-frequency transmitter circuitry, wherein the digital predistortion circuitry performs digital predistortion operations on the baseband data based on a set of digital predistortion coefficients. 
 
     
     
       6. The electronic device defined in  claim 5 , further comprising:
 circuitry configured to generate the digital predistortion coefficients based on the calibration data and to provide the digital predistortion coefficients to the digital predistortion circuitry. 
 
     
     
       7. The electronic device defined in  claim 6 , wherein the circuitry is further configured to generate a power amplifier bias voltage based on the calibration data and to provide the generated power amplifier bias voltage to the power amplifier circuitry. 
     
     
       8. The electronic device defined in  claim 7 , wherein the circuitry is further configured to generate control signals based on the calibration data and to provide the control signals to the radio-frequency transmitter circuitry. 
     
     
       9. The electronic device defined in  claim 1 , further comprising:
 additional radio-frequency receiver circuitry; 
 radio-frequency front end circuitry coupled to the output of the power amplifier circuitry; and 
 a receive path coupled between the radio-frequency front end circuitry and the additional radio-frequency receiver circuitry. 
 
     
     
       10. The electronic device defined in  claim 9 , further comprising:
 an antenna coupled to an output of the radio-frequency front end circuitry. 
 
     
     
       11. An electronic device, comprising:
 radio-frequency transmitter circuitry configured to transmit radio-frequency signals; 
 power amplifier circuitry configured to amplify the transmitted radio-frequency signals; 
 radio-frequency receiver circuitry coupled to an output of the power amplifier circuitry via a feedback path, wherein the radio-frequency receiver circuitry is configured to generate performance metric data based on the amplified radio-frequency signals; 
 processing circuitry configured to generate calibration data for the power amplifier circuitry based on the performance metric data generated by the radio-frequency receiver circuitry, and the radio-frequency receiver circuitry comprises: 
 Fourier transform circuitry, wherein the Fourier transform circuitry is configured to generate a Fourier transform of the amplified radio-frequency signals and to generate a receive band noise floor value based on the generated Fourier transform, and the processing circuitry is configured to generate the calibration data for the power amplifier circuitry based on the generated receive band noise floor value. 
 
     
     
       12. A method for calibrating envelope tracking circuitry in an electronic device having wireless communications circuitry, wherein the wireless communications circuitry comprises power amplifier circuitry that is powered by the envelope tracking circuitry, the method comprising, with processing circuitry on the electronic device:
 instructing the wireless communications circuitry to transmit radio-frequency test signals; 
 retrieving performance metric data gathered in response to the transmitted radio-frequency test signals from the wireless communications circuitry; 
 processing the retrieved performance metric data to generate calibration data that identifies a plurality of bias voltages for powering the power amplifier circuitry, wherein the retrieved performance metric data comprises a performance metric data structure having a plurality of entries; 
 providing the calibration data to the envelope tracking circuitry; 
 with the processing circuitry, instructing a feedback receiver in the wireless communications circuitry to measure power amplifier compression values associated with the power amplifier circuitry based on the transmitted radio-frequency test signals, wherein each entry in the retrieved performance metric data structure includes a corresponding power amplifier compression value; 
 with the processing circuitry, selecting a power amplifier compression value; and 
 with the processing circuitry, filtering out entries from the performance metric data structure having power amplifier compression values that are different from the selected power amplifier compression value. 
 
     
     
       13. The method defined in  claim 12 , further comprising:
 with the processing circuitry, instructing the wireless communications circuitry to measure output power levels of the transmitted radio-frequency test signals, wherein each entry in the retrieved performance metric data structure includes a corresponding output power level measured by the wireless communications circuitry; 
 with the processing circuitry, selecting an output power level; and 
 with the processing circuitry, filtering out entries from the performance metric data structure having output power levels that are different from the selected output power level. 
 
     
     
       14. The method defined in  claim 13 , further comprising:
 with the processing circuitry, instructing the wireless communications circuitry to measure adjacent channel leakage ratio values from the transmitted radio-frequency test signals, wherein each entry in the retrieved performance metric data structure includes a corresponding adjacent channel leakage ratio value measured by the wireless communications circuitry; 
 with the processing circuitry, comparing the retrieved performance metric data to a predetermined adjacent channel leakage ratio threshold level; and 
 with the processing circuitry, filtering out entries from the performance metric data structure having an adjacent channel leakage ratio value that is greater than the predetermined adjacent channel leakage ratio threshold level. 
 
     
     
       15. The method defined in  claim 14 , further comprising:
 with the processing circuitry, instructing the feedback receiver to measure receive band noise floor values based on the transmitted radio-frequency test signals, wherein each entry in the retrieved performance metric data structure includes a corresponding receive band noise floor value; 
 with the processing circuitry, comparing the retrieved performance metric data to a predetermined receive band noise floor threshold level; and 
 with the processing circuitry, filtering out entries from the performance metric data structure having a receive band noise floor value that is greater than the predetermined receive band noise floor threshold level. 
 
     
     
       16. The method defined in  claim 14 , wherein each entry in the retrieved performance metric data structure includes a corresponding bias voltage with which the radio-frequency test signals were transmitted, wherein the calibration data comprises a calibration data structure having a plurality of entries, the method further comprising:
 selecting a minimum bias voltage from the performance metric data structure and storing the minimum bias voltage as a given entry in the plurality of entries of the calibration data structure. 
 
     
     
       17. The method defined in  claim 12 , wherein instructing the wireless communications circuitry to transmit the radio-frequency test signals comprises:
 with the power amplifier circuitry, amplifying the radio-frequency test signals; and 
 with the power amplifier circuitry, sweeping through a plurality of different transmit voltage levels of the radio-frequency test signals while amplifying the radio-frequency test signals. 
 
     
     
       18. An electronic device, comprising:
 radio-frequency transmitter circuitry configured to transmit radio-frequency signals; 
 power amplifier circuitry configured to amplify the transmitted radio-frequency signals; 
 radio-frequency receiver circuitry coupled to an output of the power amplifier circuitry via a feedback path, wherein the radio-frequency receiver circuitry is configured to generate performance metric data based on the amplified radio-frequency signals; 
 processing circuitry configured to generate calibration data for the power amplifier circuitry based on the performance metric data generated by the radio-frequency receiver circuitry; 
 baseband processing circuitry that is coupled to the processing circuitry and that generates baseband data; 
 digital predistortion circuitry coupled between an output of the baseband processing circuitry and an input of the radio-frequency transmitter circuitry, wherein the digital predistortion circuitry performs digital predistortion operations on the baseband data based on a set of digital predistortion coefficients; and 
 circuitry configured to generate the digital predistortion coefficients based on the calibration data and to provide the digital predistortion coefficients to the digital predistortion circuitry, wherein the circuitry is further configured to generate radio-frequency gain index control signals based on the calibration data and to provide the radio-frequency gain index control signals to the radio-frequency transmitter circuitry to control a radio-frequency gain index provided to the transmitted radio-frequency signals by the radio-frequency transmitter circuitry. 
 
     
     
       19. An electronic device, comprising:
 radio-frequency transmitter circuitry configured to transmit radio-frequency signals; 
 power amplifier circuitry configured to amplify the transmitted radio-frequency signals; 
 radio-frequency receiver circuitry coupled to an output of the power amplifier circuitry via a feedback path, wherein the radio-frequency receiver circuitry is configured to generate performance metric data based on the amplified radio-frequency signals; 
 processing circuitry configured to generate calibration data for the power amplifier circuitry based on the performance metric data generated by the radio-frequency receiver circuitry; 
 baseband processing circuitry that is coupled to the processing circuitry and that generates baseband data; and 
 digital predistortion circuitry coupled between an output of the baseband processing circuitry and an input of the radio-frequency transmitter circuitry, wherein the digital predistortion circuitry performs digital predistortion operations on the baseband data based on a set of digital predistortion coefficients, and the digital predistortion circuitry is coupled to the output of the power amplifier circuitry via the feedback path.

Description:
This application claims the benefit of provisional patent application No. 62/047,482, filed Sep. 8, 2014, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to wireless communications circuitry, and more particularly, to electronic devices having wireless communications circuitry. 
     Handheld electronic devices and other portable electronic devices are becoming increasingly popular. Examples of handheld devices include handheld computers, cellular telephones, media players, and hybrid devices that include the functionality of multiple devices of this type. Popular portable electronic devices that are somewhat larger than traditional handheld electronic devices include laptop computers and tablet computers. 
     Portable electronic devices are often provided with wireless communications capabilities. For example, handheld electronic devices may use cellular telephone communications standards to communicate with cellular networks. Handheld electronic devices typically have small battery with a limited battery capacity that is used for performing wireless communications. Unless care is taken to consume power wisely, an electronic device with a small battery may exhibit unacceptably short battery life. 
     Electronic devices with wireless communications capabilities typically include amplifying circuits that are used to amplify the power of radio-frequency signals prior to wireless transmission. For example, a radio-frequency power amplifier may receive input signals having an input power level and generate corresponding output signals having an output power level. The radio-frequency power amplifier receives a power supply voltage that powers the radio-frequency amplifier. 
     The power supply voltage (sometimes referred to as a bias voltage) provided to the radio-frequency power amplifier can be continuously adjusted based on the voltage magnitude of transmit signals that are amplified by the power amplifier in a process sometimes referred to as envelope tracking When performing envelope tracking, the power supply voltage is reduced at times when the transmit signals have a relatively low magnitude (i.e., a relatively low modulation envelope magnitude) and is increased at times when the transmit signals have a relatively high magnitude (i.e., a relatively high modulation envelope magnitude) so that overall power consumption is reduced in the device while transmitting radio-frequency signals. However, if care is not taken, reduced power supply voltages provided to the amplifier while performing envelope tracking operations can be insufficient to ensure satisfactory radio-frequency performance of the power amplifier. When provided with an insufficient power supply voltage, the power amplifier can generate spectral regrowth at harmonics of a transmit frequency that can undesirably interfere with a receive frequency of the device. 
     It would therefore be desirable to be able to provide wireless communications circuitry with improved power management capabilities. 
     SUMMARY 
     A method for operating an electronic device having wireless communications circuitry and processing circuitry is provided. The wireless communications circuitry may include power amplifier circuitry that is powered by a bias voltage supplied by adjustable bias voltage generation circuitry. The adjustable bias voltage generation circuitry may include envelope tracking circuitry that continuously adjusts the bias voltage based on the voltage magnitude of signals to be transmitted by the wireless communications circuitry and based on bias voltage calibration data stored on the device. 
     Processing circuitry on the device (e.g., calibration software running on the processing circuitry) may instruct baseband processing circuitry in the wireless communications circuitry to transmit radio-frequency test signals. The test signals may be transmitted by sweeping through a number of different voltage magnitudes and using a number of different bias voltages. The test signals may be conveyed to radio-frequency transceiver circuitry having transmitter circuitry and feedback receiver circuitry. The transmitter circuitry may feed radio-frequency test signals to the power amplifier circuitry and the power amplifier circuitry may amplify the test signals. The feedback receiver circuitry may receive the amplified test signals. 
     The processing circuitry may instruct the baseband processing circuitry and/or the feedback receiver circuitry to gather performance metric data from the transmitted radio-frequency test signals (e.g., adjacent channel leakage ratio values, receive band noise values, amplifier compression values, output power levels, etc.). The processing circuitry may retrieve the gathered performance metric data from the wireless communications circuitry and may process the performance metric data to generate calibration data for the envelope tracking circuitry. The device may generate calibration data for any desired combination of transmit signal voltage magnitudes and any desired device operating conditions. 
     After the calibration data has been generated, the baseband processing circuitry may provide transmit data signals that are different from the test signals to the envelope tracking circuitry and to the radio-frequency transmitter circuitry. The envelope tracking circuitry may continuously select bias voltages to provide to the power amplifier circuitry based on the transmit data signals (e.g., based on the voltage magnitude of the transmit data signals) and based on the received calibration data. For example, the calibration data may identify a bias voltage to use for a particular voltage magnitude of the transmit data signals and the envelope tracking circuitry may use the identified bias voltage to power the power amplifier circuitry for amplifying those transmit data signals. By actively adjusting the bias voltage based on the calibration data and the transmit signals, the wireless communications circuitry may reduce power consumption in the device relative to devices that provide constant bias voltages without generating undesirable radio-frequency harmonics, adjacent channel leakage violations, or other undesirable radio-frequency performance violations. 
     If desired, the calibration data may include a calibration data structure having multiple entries. Each entry may include a corresponding power amplifier bias voltage and transmit signal voltage magnitude. If desired, the each entry may include a corresponding output power level. The envelope tracking circuitry may identify a desired output power level and may select the bias voltage of the entry corresponding to that desired output power level to the power amplifier. 
     If desired, the processing circuitry may organize (e.g., store) the retrieved performance metric data in a performance metric data structure having multiple entries. Each entry may have a corresponding output power level measured by the baseband processing circuitry, amplifier compression value measured by the feedback receiver circuitry, adjacent channel leakage ratio value measured by the baseband processing circuitry, digital predistortion coefficient values; and receive band noise floor value measured by the feedback receiver circuitry. The processing circuitry may process the data structure to generate entries for the calibration data structure (e.g., to populate the calibration data structures with entries that may be used by the envelope tracking circuitry to provide a suitable bias voltage for any desired transmit signal under a wide range of operating constraints). 
     For example, the processing circuitry may selecting a desired output power level and may filter out entries from the performance metric data structure having output power levels that are different from the selected output power level. The processing circuitry may select a power amplifier compression value and may filter out entries from the performance metric data structure having power amplifier compression values that are different from the selected power amplifier compression value. The processing circuitry may compare the retrieved performance metric data to a predetermined adjacent channel leakage ratio threshold level and may filter out entries from the performance metric data structure having an adjacent channel leakage ratio value that is greater than the predetermined adjacent channel leakage ratio threshold level. The processing circuitry may compare the retrieved performance metric data to a predetermined receive band noise floor threshold level and may filter out entries from the performance metric data structure having a receive band noise floor value that is greater than the predetermined receive band noise floor threshold level. Each entry in the performance metric data structure may include a corresponding bias voltage with which the radio-frequency signals were transmitted. The processing circuitry may select a minimum bias voltage from the performance metric data structure after filtering the data structure and may store that minimum bias voltage level as a given entry in the plurality of entries of the calibration data structure. 
     During normal device operations, the baseband processing circuitry may provide a first transmit signal to the adjustable bias voltage generation circuitry and the radio-frequency power amplifier circuitry and may subsequently provide a second transmit signal having a second signal magnitude that is, for example, less than the first signal magnitude. The adjustable power supply circuitry may generate a first bias voltage based on the first transmit signal and the stored calibration data and may provide the first bias voltage to the power amplifier circuitry while the power amplifier circuitry amplifies the first transmit signal. The first bias voltage identified by the calibration data may have a magnitude that is greater than the first signal magnitude by a first voltage margin. The adjustable power supply circuitry may generate a second bias voltage based on the second transmit signal and the calibration data and may provide the second bias voltage to the power amplifier circuitry while the power amplifier circuitry amplifies the second transmit signal. The second bias voltage may have a magnitude that is greater than the second signal magnitude by a second voltage margin and that is less than first voltage margin (e.g., because greater voltage margins may be required for higher transmit power levels than for lower transmit power levels in order to ensure satisfactory radio-frequency performance). 
     This Summary is provided merely for purposes of summarizing some example embodiments so as to provide a basic understanding of some aspects of the subject matter described herein. Accordingly, it will be appreciated that the above-described features are merely examples and should not be construed to narrow the scope or spirit of the subject matter described herein in any way. Other features, aspects, and advantages of the subject matter described herein will become apparent from the following Detailed Description, Figures, and Claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an illustrative electronic device with wireless communications circuitry suitable for calibration in accordance with an embodiment of the present invention. 
         FIG. 2  is a circuit diagram of illustrative wireless communications circuitry having feedback receiver circuitry that may perform calibration operations for generating power amplifier bias voltage calibration data in accordance with an embodiment of the present invention. 
         FIG. 3  is an exemplary diagram plotting output power level versus input power level of a radio-frequency power amplifier in accordance with an embodiment. 
         FIG. 4  is an exemplary diagram plotting output power level versus input power level of digital predistortion circuitry in accordance with an embodiment. 
         FIG. 5  is an illustrative graph showing how power amplifier bias voltage may be continuously adjusted by different voltage margins relative to a transmit signal for different transmit signal magnitudes based on bias voltage calibration data to reduce power consumption even at relatively low transmit signal magnitudes while satisfying radio-frequency performance requirements in accordance with an embodiment of the present invention. 
         FIG. 6  is an illustrative graph showing how calibration software on an electronic device of the type shown in  FIG. 2  may select optimal power amplifier operation points for generating bias voltage calibration data in accordance with an embodiment of the present invention. 
         FIG. 7  is an illustrative graph showing how insufficient power amplifier bias voltages supplied to a power amplifier in wireless communications circuitry may cause the power amplifier to generate undesirable radio-frequency power at a receive frequency of the wireless communications circuitry in accordance with an embodiment of the present invention. 
         FIG. 8  is a flow chart of illustrative steps that may be performed by wireless communications circuitry for generating power amplifier bias voltage calibration data using radio-frequency test signals generated and measured by the wireless communications circuitry and for using the calibration data to perform wireless transmission in accordance with an embodiment of the present invention. 
         FIG. 9  is a graph of an illustrative sequence of radio-frequency test signals that may be produced by wireless communications circuitry at multiple transmit voltage levels with multiple amplifier bias voltage levels for generating bias voltage calibration data in accordance with an embodiment of the present invention. 
         FIG. 10  is a flow chart of illustrative steps that may be performed by wireless communications circuitry and/or external test equipment for generating radio-frequency performance metric data in response to radio-frequency test signals of the type shown in  FIG. 9  that can be used for generating bias voltage calibration data in accordance with an embodiment of the present invention. 
         FIG. 11  shows an illustrative radio-frequency performance metric data structure that may be generated by wireless communications circuitry using gathered radio-frequency performance metric data over a range of different test signal transmit magnitudes and bias voltages that may be processed to generate bias voltage calibration data in accordance with an embodiment of the present invention. 
         FIG. 12  is a flow chart of illustrative steps that may be performed by wireless communications circuitry for processing gathered radio-frequency performance metric data (e.g., a performance metric data structure such as that shown by  FIG. 11 ) for generating bias voltage calibration data that reduces overall power consumption in the wireless communications circuitry while satisfying radio-frequency performance requirements in accordance with an embodiment of the present invention. 
         FIG. 13  shows an illustrative table of bias voltage calibration data containing power amplifier voltage bias settings for a variety of different transmit signal powers that may be used by wireless communications circuitry for performing power amplifier envelope tracking to reduce overall power consumption without sacrificing radio-frequency performance in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     This relates to wireless communications, and more particularly, to calibrating and operating wireless electronic devices to enhance power consumption efficiency while satisfying performance constraints. 
     An illustrative wireless electronic device is shown in  FIG. 1 . Wireless electronic device  10  of  FIG. 1  may be a cellular telephone, a tablet computer, a laptop computer, a desktop computer, a personal computer, a portable media player, other miniature and portable devices, or other electronic equipment. 
     As shown in  FIG. 1 , device  10  may include storage and processing circuitry  12 . Storage and processing circuitry  12  may include one or more different types of storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory), volatile memory (e.g., static or dynamic random-access-memory), etc. Storage and processing circuitry  12  may be used in controlling the operation of device  10 . Processing circuitry in circuitry  12  may be based on processors such as microprocessors, microcontrollers, digital signal processors, dedicated processing circuits, power management circuits, audio and video chips, and other suitable integrated circuits. 
     Storage and processing circuitry  12  may be used to run software on device  10 , such as internet browsing applications, voice-over-internet-protocol (VOIP) telephone call applications, email applications, media playback applications, operating system functions, etc. Storage and processing circuitry  12  may be used in implementing suitable communications protocols. Communications protocols that may be implemented using storage and processing circuitry  12  include internet protocols, wireless local area network protocols (e.g., IEEE 802.11 protocols—sometimes referred to as WiFi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol, IEEE 802.16 (WiMax) protocols, cellular telephone protocols such as the “2G” Global System for Mobile Communications (GSM) protocol, the “2G” Code Division Multiple Access (CDMA) protocol, the “3G” Universal Mobile Telecommunications System (UMTS) protocol, the “4G” Long Term Evolution (LTE) protocol, MIMO (multiple input multiple output) protocols, antenna diversity protocols, etc. Wireless communications operations such as communications band selection operations may be controlled using software stored and running on device  10  (i.e., stored and running on storage and processing circuitry  12  and/or input-output circuitry  16 ). 
     Device  10  may have one or more batteries such as battery  14 . To minimize power consumption and thereby extend the life of battery  14 , storage and processing circuitry  12  may be used in implementing power management functions for device  10 . For example, storage and processing circuitry  12  may be used to adjust the power supply voltages that are used in powering the radio-frequency power amplifier circuitry. Whenever possible, these power amplifier bias voltages may be reduced to conserve power. If desired, storage and processing circuitry  12  may also be used to adjust the gain state of radio-frequency power amplifier circuitry on device  10  and may be used in adjusting the gain of a variable gain amplifier (VGA) that feeds output signals to the power amplifier circuitry. These adjustments may be made automatically in real time based on calibration data (sometimes referred to as calibration table data) stored on storage and processing circuitry  12  and control algorithms (software). For example, code may be stored in storage and processing circuitry  12  that configures storage and processing circuitry  36  to implement a control scheme in which operating settings are adjusted in accordance with calibration data to satisfy desired performance criteria such as desired transmit power levels, receive band noise levels, and adjacent channel leakage values while minimizing power consumption. 
     Input-output devices  16  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Examples of input-output devices  16  that may be used in device  10  include display screens such as touch screens (e.g., liquid crystal displays or organic light-emitting diode displays), buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers and other devices for creating sound, cameras, sensors, etc. A user can control the operation of device  10  by supplying commands through devices  16 . Devices  16  may also be used to convey visual or sonic information to the user of device  10 . Devices  16  may include connectors for forming data ports (e.g., for attaching external equipment such as computers, accessories, etc.). 
     Wireless communications devices  18  may include communications circuitry such as radio-frequency (RF) transceiver circuitry formed from one or more integrated circuits, power amplifier circuitry (e.g., power amplifier circuitry that is controlled by control signals from storage and processing circuitry  12  or other power supply circuitry to minimize power consumption while satisfying desired performance criteria), passive RF components, antennas, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications). 
     Device  10  can communicate with external devices such as accessories, computing equipment, and wireless networks over wired and wireless communications paths. For example, accessories such as wired or wireless headsets may communicate with device  10 . Device  10  may also be connected to audio-video equipment (e.g., wireless speakers, a game controller, or other equipment that receives and plays audio and video content), or a peripheral such as a wireless printer or camera. Device  10  may use a wired or wireless path to communicate with a personal computer or other computing equipment. The computing equipment may be, for example, a computer that has an associated wireless access point (router) or an internal or external wireless card that establishes a wireless connection with device  10 . The computer may be a server (e.g., an Internet server), a local area network computer with or without Internet access, a user&#39;s own personal computer, a peer device (e.g., another portable electronic device  10 ), or any other suitable computing equipment. Device  10  can also communicate with wireless network equipment such as cellular telephone base stations and associated cellular towers, etc. 
     In typical circuit architectures, a transceiver circuit in wireless communications circuitry  18  may supply radio-frequency signals to the input of a power amplifier for transmission through an antenna. The power at which the power amplifier outputs radio-frequency signals (i.e., the output of the power amplifier) establishes an output power level for the power amplifier. The power at which the transceiver circuit provides radio-frequency signals to the power amplifier establishes an input power level for the power amplifier. The input power level may correspond to a voltage magnitude (amplitude) of the transmitted signals at the input of the power amplifier. The output power level may correspond to a voltage magnitude of the transmitted signals at the output of the power amplifier. Adjustments to the power amplifier may be made to adjust the power of radio-frequency signals transmitted by device  10  (e.g., to ensure a suitable wireless link is established and maintained with external wireless communications devices at various distances with respect to device  10 ). 
     The antenna structures and wireless communications devices of device  10  may support communications over any suitable wireless communications bands. For example, wireless communications circuitry  18  may be used to cover communications frequency bands such as cellular telephone voice and data bands at 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, 2100 MHz, the Wi-Fi® (IEEE 802.11) bands at 2.4 GHz and 5.0 GHz (also sometimes referred to as wireless local area network or WLAN bands), the Bluetooth® band at 2.4 GHz, the global positioning system (GPS) band at 1575.42 MHz, etc. 
     Device  10  can cover these communications bands and other suitable communications bands with proper configuration of the antenna structures in wireless communications circuitry  18 . Any suitable antenna structures may be used in device  10 . For example, device  10  may have one antenna or may have multiple antennas. The antennas in device  10  may each be used to cover a single communications band or each antenna may cover multiple communications bands. If desired, one or more antennas may cover a single band while one or more additional antennas are each used to cover multiple bands. 
     The radio-frequency performance of wireless communications circuitry  18  in device  10  may be characterized by one or more wireless (radio-frequency) performance metrics. Device  10  (e.g., baseband processor circuitry in device  10 , storage and processing circuitry  12 , or calibration software running on device  10 ) may obtain data associated with wireless performance metrics (e.g., device  10  may generate performance metric data or may receive performance metric data measured for device  10  by external circuitry). For example, device  10  may obtain performance metric data associated with performance metrics such as received power, receiver sensitivity, receive band noise (e.g., a receive band noise floor voltage level), frame error rate, bit error rate, channel quality measurements based on received signal strength indicator (RSSI) information, adjacent channel leakage ratio (ACLR) information (e.g., ACLR information in one or more downlink frequency channels), channel quality measurements based on received signal code power (RSCP) information, channel quality measurements based on reference symbol received power (RSRP) information, channel quality measurements based on signal-to-interference ratio (SINR) and signal-to-noise ratio (SNR) information, channel quality measurements based on signal quality data such as Ec/Io or Ec/No data, information on whether responses (acknowledgements) are being received from a cellular telephone tower corresponding to requests from the electronic device, information on whether a network access procedure has succeeded, information about how many re-transmissions are being requested over a cellular link between the electronic device and a cellular tower, information on whether a loss of signaling message has been received, information on whether paging signals have been successfully received, any desired combination of these performance metrics, and other information that is reflective of the performance of wireless circuitry  18  in device  10 . 
     Other examples of radio-frequency performance metric data that may be obtained by device  10  include radio-frequency performance metric data associated with radio-frequency uplink (transmit) test signals that are transmitted by device  10  such as Error Vector Magnitude (EVM), output power, spectral parameters, Adjacent Channel Leakage Ratio (ACLR), performance metrics associated with radio-frequency power amplifier circuitry on device  10  such as amplifier compression and efficiency, etc. If desired, device  10  may obtain radio-frequency performance metric information associated with power amplifier circuitry in wireless circuitry  18  such as power amplifier compression information, power amplifier efficiency information, etc. Radio-frequency performance metrics associated with signals transmitted by device  10  may be generated by external wireless circuitry (e.g., an external test station) or by circuitry on device  10  that receives the transmitted signals via a wired feedback path coupled to the output of power amplifier circuitry in the device. In general, performance metric data may include data associated with any desired performance metric for the transmission or reception of radio-frequency signals by wireless communications circuitry  18 . Performance metric data may, for example, include performance metric values measured for a given performance metric (e.g., measured error rate values, measured power level values, measured SNR values, measured ACLR values, measured receive band noise floor level values, measured RSSI values, etc.). 
     Illustrative wireless communications circuitry that may be used in circuitry  18  of  FIG. 1  is shown in  FIG. 2 . Device  10  may perform radio-frequency test and calibration operations to characterize and calibrate the radio-frequency performance of wireless communications circuitry  18  (e.g., using one or more radio-frequency performance metrics). Device  10  may perform calibration operations by gathering test data (e.g., radio-frequency performance metric data) associated with the wireless performance of device  10  and generating calibration data based on the gathered test data for use during normal device operation (e.g., calibration data such as one or more calibration values used by device  10  during normal operation of device  10  by an end user). A device  10  having wireless communications circuitry  18  on which radio-frequency calibration is being performed may sometimes be referred to herein as device under test (DUT)  10 ′. DUT  10 ′ may, for example, be a fully assembled electronic device that is enclosed within a form factor or device housing or a partially assembled electronic device (e.g., DUT  10 ′ may include some or all of wireless circuitry  18  prior to completion of manufacturing of device  10 ). 
     As shown in  FIG. 2 , DUT  10 ′ may be calibrated in a calibration system  20 . Calibration system  20  may include optional external test and calibration computing equipment such as test host  22  and test equipment  24 . Test host  22  may include computing equipment such as a personal computer, laptop computer, handheld or portable computer, or any other desired computing equipment and may be coupled to DUT  10 ′ via path  26  (e.g., a wired or wireless communications path). Test host  22  may be coupled to test equipment  24  via path  28  and may convey test/calibration commands to test equipment  24  via path  28 . Test equipment  24  may pass test data and other information to test host  22  via path  28 . 
     Test equipment  24  may include equipment for receiving and analyzing radio-frequency signals transmitted by DUT  10 ′ via communications link  30  such as signal analyzer equipment, vector network analyzer (VNA) equipment, radio-frequency tester equipment, etc. For example, DUT  10 ′ may transmit radio-frequency test signals in an uplink direction to test equipment  24  via link  30  and equipment  24  may process the received test signals to characterize and/or calibrate the transmit performance of DUT  10 ′ (e.g., by generating one or more sets of performance metric data and using the performance metric data to generate corresponding radio-frequency calibration data). Test equipment  24  may provide the performance metric data to test host  22 . Test host  22  and/or software running on DUT  10 ′ may generate corresponding calibration data based on the test data. Communications link  30  may be a wired communications path (e.g., one or more radio-frequency transmission lines or cables) or a wireless communications path (e.g., maintained using one or more wireless communications protocols). If desired, external test host  22  and test equipment  24  may be omitted from calibration system  20 . In this scenario, DUT  10 ′ may transmit radio-frequency test signals and may use the transmitted radio-frequency test signals to characterize and/or calibrate the radio-frequency performance of wireless circuitry  18  without expensive external test and calibration equipment. Such calibration without the use of test equipment such as test equipment  24  and test host  22  may, if desired, be performed during normal device operation (e.g., by an end user after manufacturing and assembly of device  10 ). As an example, device  10 ′ may be calibrated using test host  22  and test equipment  24  during manufacture of device  10  (e.g., prior to use of device  10  by an end user) and may be re-calibrated after manufacture of device  10  during normal device operation by an end user (e.g., to update calibration data stored on device  10 ). 
     As shown in  FIG. 2 , wireless communications circuitry  18  in device  10 ′ may include one or more antennas such as antennas  60 . Antennas  60  may be formed using any suitable antenna types. For example, antennas  60  may include antennas with resonating elements that are formed from loop antenna structures, patch antenna structures, inverted-F antenna structures, slot antenna structures, planar inverted-F antenna structures, helical antenna structures, hybrids of these designs, etc. Different types of antennas may be used for different bands and combinations of bands. For example, one type of antenna may be used in forming a local wireless link antenna and another type of antenna may be used in forming a remote wireless link antenna. 
     Digital data signals that are to be transmitted by device  10  may be provided to baseband processor  34  using path  36  (e.g., from storage and processing circuitry  12  of  FIG. 1 ). Circuit  34  may modulate these signals in accordance with a desired communications protocol (e.g., a desired cellular telephone standard and modulation scheme) and may provide corresponding output signals for transmission to transceiver circuitry  48  via path  38  (e.g., to one or more transmitters  58  in transceiver circuitry  48 ). Transceiver circuitry  48  may include mixer circuitry that up-converts the output signals to a radio-frequency and that transmits the radio-frequency signals to radio-frequency power amplifier circuitry  46 . If desired, digital predistortion (DPD) circuitry  50  may be interposed on path  38 . DPD circuitry  50  may provide digital predistortion to the data received from baseband processor  34  for mitigating power amplifier compression associated with amplifier circuitry  46 . For example, DPD circuitry  50  may perform gain expansion on the transmit signals using selected digital predistortion coefficients. 
     Digital predistortion circuitry  50  may, for example, receive IQ samples from baseband processor  34  and optionally convert the IQ samples from the I-Q coordinate plane into an equivalent representation in the polar coordinate plane. Once the IQ samples have been converted into the polar coordinate system in which the magnitude of the signals corresponds to the amplitude of the signal to be transmitted and in which the angle of the signals corresponds to the phase of the signal to be transmitted, circuitry  50  may predistort the converted signals according to a predetermined set of predistortion coefficients. In the example of  FIG. 2 , the amplitude of the transmitted signals may be altered according to an amplitude modulation predistortion coefficient value (sometimes referred to as the “AMAM” value), whereas the phase of the transmitted signals may be altered according to a phase modulation predistortion coefficient value (sometimes referred to as the “AMPM” value). 
     Digital-to-analog converter circuitry (not shown) may be interposed on path  38  between DPD circuitry  50  and transceiver circuitry  48  for converting digital data signals to analog data signals for transmission. Circuitry  34  may be implemented using a single integrated circuit (e.g., a baseband processor integrated circuit) or using multiple circuits (e.g., some or all of circuitry  34  may be formed as a part of storage and processing circuitry  12  of  FIG. 1 ). Baseband processor circuitry  34  may include control circuitry for controlling one or more portions of wireless communications circuitry  18 . 
     Control circuitry in baseband processing circuitry  34  may be used to issue control signals on path  40  that adjust the level of voltage Vcc (e.g., sometimes referred to herein as power supply voltage Vcc or power amplifier bias voltage Vcc) that is produced by adjustable power supply circuitry  42  on line  44 . Bias voltage Vcc may be used as a power supply voltage for one or more active power amplifier stages in power amplifier circuitry  46 . 
     If desired, signals that are to be transmitted over antennas  60  may be amplified by transmitter circuitry such as transmitters  58  in transceiver circuitry  48  (e.g., using one or more variable gain amplifiers). The output of transceiver circuitry  48  may be coupled to the input of power amplifier circuitry  46  via path  52 . Transceiver circuitry  48  may provide signals to be transmitted to the input of power amplifier circuitry  46  (e.g., transmit signals having a corresponding voltage magnitude Vin). Power amplifier circuitry  46  (sometimes referred to as a power amplifier circuit or power amplifier) may contain one or more individual power amplifiers (sometimes referred to herein as amplifier stages or gain stages). During data transmission, power amplifier circuitry  46  may boost the output power of transmitted signals TX to a sufficiently high level to ensure adequate signal transmission. For example, power amplifier circuitry  46  may receive transmit signals from transceiver circuitry  48  having a voltage level Vin and a corresponding input power level Pin and may output amplified transmit signals TX having an output power level Pout (and a corresponding output voltage magnitude Vout). The gain provided by power amplifier circuitry  46  may be defined as the ratio of output power level Pout to input power level Pin. 
     Radio-frequency (RF) front end circuitry  54  may be coupled to the output of power amplifier circuitry  46 . Front end circuitry  54  may include radio-frequency switching circuitry (e.g., multiplexing circuits), passive elements such filtering circuitry (e.g., as duplexers and diplexers), impedance matching circuitry including networks of passive components such as resistors, inductors, and capacitors that ensures that antennas  60  are impedance matched to the rest of circuitry  18 , and/or any other desired radio-frequency front end circuitry. If desired, filtering circuitry in front end  54  may be used to route input (receive) and output (transmit) signals based on their frequency. For example, filtering circuitry in front end  54  may transmit (uplink) signals TX from the output of amplifier  46  to antennas  60  and may route receive (downlink) signals RX that have been received by antennas  60  onto receive path  56 . If desired, low noise amplifier circuitry (not shown) may be interposed on receive path  56 , may amplify received signals RX on path  56 , and may provide these signals to transceiver  48  (e.g., to one or more receiver circuits  62  in transceiver circuitry  48 ). Transceiver circuitry  48  may provide signals received over path  56  to baseband circuitry  34  via path  61  (e.g., after down-converting the signals to a baseband frequency using mixer circuitry). 
     The output of power amplifier circuitry  46  may be coupled to a feedback path  64  via coupling circuitry such as radio-frequency coupler  66 . Feedback path  64  may convey radio-frequency transmit signals TX amplified by power amplifier circuitry  46  to one or more feedback receiver circuits  68  in transceiver circuitry  48 . If desired, feedback receiver circuits  68  may process the transmit signals received over feedback path  64  to characterize the radio-frequency performance of transmitters  58  and/or power amplifier circuitry  46 . Feedback receiver  68  may generate baseband data corresponding to the signals received over feedback path  64  (e.g., by down-converting the received transmit signals to a baseband frequency using mixer circuitry) and may provide the data to baseband processor circuitry  34  via path  61 . Baseband processor circuitry  34  may process the data received from feedback receivers  68  to characterize the radio-frequency performance of wireless circuitry  18  and/or to generate calibration data for wireless circuitry  18  based on the received data. If desired, transmit signals TX may be provided to DPD circuitry  50  via feedback path  64  and DPD circuitry  50  may perform digital predistortion operations on transmit signals received from baseband processor  34  based on the transmit signals TX received over feedback path  64 . 
     Transceiver circuitry  48  may, if desired, be formed on a single integrated circuit or on multiple integrated circuits. For example, transmitter  58 , feedback receiver  68 , and receiver  62  may be formed on a single shared integrated circuit (chip). In another suitable arrangement, transmitter  58  and feedback receiver  68  are formed on a single shared integrated circuit whereas receivers  62  are formed on one or more separate integrated circuits. In yet another suitable arrangement, feedback receiver  68  and receivers  62  are formed on a single common integrated circuit whereas transmitter  58  is formed on a separate integrated circuit. In another suitable arrangement, transmitters  58  and receivers  62  are formed on a first integrated circuit whereas feedback receiver  68  is formed on a second integrated circuit. In yet another suitable arrangement, transmitter  58 , feedback receiver  68 , and receivers  62  are each formed on different respective integrated circuits. If desired, additional transmitters may be formed on transceiver circuitry  58  (e.g., on a shared integrated circuit with circuitry  58 ,  68 , and  62 ). 
     As device  10  is operated in a cellular network or other wireless communications network, the amount of power that is transmitted by wireless circuitry  18  (e.g., output power level Pout of signals TX) is typically adjusted up and down in real time. For example, if a user is in the vicinity of a cellular tower, the cellular tower may issue a command that instructs device  10  to reduce its transmitted power level (output power level). If a user travels farther away from the tower, the tower may issue a TPC command that requests an increase in transmitted power. 
     The gain of power amplifier circuitry  46  may be adjusted to conserve power while ensuring that required amounts of output power can be satisfactorily produced. For example, when transmitted power requirements are modest, a lower bias voltage Vcc may be provided to amplifier circuitry  46  by adjustable power supply circuitry  42  to conserve power. However, the magnitude of Vcc can affect power amplifier linearity (e.g., particularly in scenarios where input voltage Vin is relatively high). Nonlinearities can result in signal distortion and adverse effects such as increases in adjacent channel leakage or generation of signal power at harmonic frequencies of the transmit frequency with which transmit signals TX are transmitted by transceiver  48 . For example, an amplifier will generally exhibit more adjacent channel leakage (sometimes referred to as adjacent channel leakage ratio or adjacent channel power) at a given output power when operated at a relatively low bias voltage than when operated at relatively high bias voltage. Nevertheless, maximum Vcc levels are generally only required when it is desired to maximize power amplifier linearity. When less power amplifier linearity is tolerable, the magnitude of Vcc can be reduced. Because operation with lowered Vcc settings can reduce power consumption (thereby conserving power for battery  14 ), device  10  preferably reduces Vcc from its nominal maximum level whenever possible. 
     When controlling the operation of wireless circuitry  18  in this way to conserve power, care should be taken that relevant operating criteria are being satisfied. For example, a wireless carrier or other entity may require that a cellular telephone meet certain minimum standards when operating in the network of the wireless carrier. A carrier may, for example, establish required limits on adjacent channel leakage. Devices that allow too much adjacent channel leakage will not be permitted to operate in the carrier&#39;s network. In addition, non-linearities in power amplifier circuitry  46  may generate harmonic frequency contributions to the transmit signal TX. The harmonic frequency contributions can often overlap with a receive frequency of device  10 ′. In this scenario, the harmonic contribution of the transmit signal can leak onto receive line  56  of device  10 ′ and can cause errors or distortions in the signals received by receiver  62 . Power can be conserved by backing Vcc off from its nominal maximum value, but only so long as this decrease in power amplifier bias does not cause adjacent channel leakage violations, generate undesirable harmonics, or cause other performance criteria to be violated. In general, higher bias voltages Vcc may be required to amplify transmit signals at higher input voltages Vin than transmit signals at lower input voltages Vin in order to ensure suitably low harmonic contributions generated by amplifier  46  for both the higher and lower input voltages. 
     If desired, adjustable power supply circuitry  42  may (continuously) adjust the bias voltage Vcc that is provided to power amplifier circuitry  46  in real time using a so-called “envelope tracking” process. By performing envelope tracking, adjustable power supply circuitry  42  may continuously adjust the power supply voltage Vcc provided to amplifier  46  up and down based on the voltage level Vin (e.g., based on the voltage level of an modulation envelope of the transmit signal) of the data that is being transmitted by baseband processor  34  (e.g., to help to ensure that amplifier  46  operates at a peak efficiency for the power required to transmit a given signal). For example, adjustable power supply circuitry  42  may include envelope tracking circuitry  68  that generates a bias voltage Vcc corresponding to a particular voltage level Vin that is being transmitted (e.g., so that lower bias voltages Vcc may be used when the transmit signals have a relatively low voltage level Vin and higher bias voltages Vcc may be used when the transmit signals have a relatively high voltage level Vin in order to reduce power consumption while still providing signals with a desired output power level). 
     Baseband processor circuitry  34  may simultaneously provide transmit data to transceiver circuitry  48  via path  38  and envelope tracking circuitry  68  via path  40 . Envelope tracking circuitry  68  process the transmit data received from baseband  34  to determine a corresponding bias voltage Vcc to provide to amplifier  46  for amplifying the radio-frequency signal associated with the transmit data. In some scenarios, baseband processor  70  may generate in-phase and quadrature-phase (I/Q) data associated with the transmit data and may provide the I/Q data to envelope tracking circuitry  68 . Envelope tracking circuitry  68  may include magnitude generation circuitry (e.g., circuitry that generates test data magnitude values Vin as the square root of the sum of I 2  and Q 2 ) and may include amplifier circuitry that generates bias voltage Vcc based on the generated test data magnitude. 
     If desired, calibration data  70  may be stored on adjustable power supply circuitry  42 . Envelope tracking circuitry  68  may determine a bias voltage Vcc to provide to amplifier  46  based on the transmit data received from baseband processor  34  and based on calibration data  70 . For example, calibration data  70  may identify a particular bias voltage Vcc to use for a given voltage Vin of the transmitted data under a variety of operating constraints imposed on wireless circuitry  18  (e.g., so that an appropriate value Vcc may be used for transmit signals having different voltages Vin under any desired operating conditions). The operating constraints may be used in generating calibration data  70  so that supply circuitry  42  selects an appropriate bias voltage Vcc given the desired operating constraints. Operating constraints on wireless circuitry  18  that may be used in generating calibration data  70  may include, for example, power amplifier efficiency constraints associated with amplifier  46 , receive band noise constraints, ACLR constraints, etc. (e.g., so that a satisfactory link may be established with an external base station). Tracking circuitry  68  may use the appropriate bias value Vcc identified by the calibration data to bias power amplifier  48  in real time. 
     Calibration data  70  may be generated by device  10 ′ (e.g., in calibration system  20 ). For example, calibration software such as calibration software  72  (sometimes be referred to herein as test software) loaded onto DUT  10 ′ may direct DUT  10 ′ to perform power amplifier calibration operations to generate calibration data  70  for use in performing envelope tracking For example, calibration software  72  may direct baseband processing circuitry  34  on DUT  10 ′ to generate test data to be transmitted by transceiver circuitry  48  (e.g., by providing test and calibration commands over path  73 ) from which performance metric data is gathered for generating corresponding calibration data. In another suitable arrangement, during radio-frequency testing operations, calibration software  72  may provide test data to be transmitted to transceiver circuitry  90  (e.g., via baseband processor  34  or directly to transceiver  48 ). The transmitted radio-frequency test signals may be conveyed to test equipment  24  via antennas  60  and link  30  and/or may be conveyed to feedback receivers  68  via feedback path  64 . Test equipment  24  may process the received radio-frequency test signals to generate radio-frequency performance metric data associated with the wireless performance of DUT  10 ′ based on the test signals. If desired, feedback receiver  68  may process the received radio-frequency test signals to generate radio-frequency performance metric data associated with the wireless performance of DUT  10 ′ based on the transmitted test signals and/or may provide test data corresponding to the received test signals to baseband processor circuitry  34  and/or calibration software  72  for generating corresponding performance metric data. 
     Calibration software  72  may be implemented on baseband processor  34 , on storage and processing circuitry  12 , on dedicated calibration processing circuitry, or on any other desired processing circuitry on DUT  10 ′ and may sometimes be referred to herein as calibration module  72 , calibration circuitry  72 , or calibration engine  72 . Calibration software  72  may process the performance metric data gathered by DUT  10 ′ and/or tester  24  to generate calibration data  70 . For example, calibration software  72  may identify a set of optimal power supply voltages Vcc to provide to amplifier  46  for a variety of different input voltages Vin and for a variety of different operating constraints. Calibration software  72  may provide calibration data  70  to adjustable power supply circuitry  42  via path  73 . Power supply circuitry  42  may use the calibration data  70  for performing envelope tracking operations during normal device operations. Calibration software  72  may be installed onto DUT  10 ′ by test host  22  or by other computing equipment during assembly, manufacture, calibration, and/or testing of DUT  10 ′. 
     If desired, adjustable power supply circuitry  42  may generate control signals based on calibration data  70  and may provide the generated control signals to transceiver circuitry  48  via path  45  and may provide the control signals to DPD circuitry  50  via path  47 . For example, circuitry  42  may generate radio-frequency gain index (RGI) control signals that control radio-frequency gain index provided by transceiver circuitry  48  to the transmitted signals. Circuitry  42  may generate DPD control signals (e.g., DPD coefficient values) based on calibration data  70  and may provide the DPD control signals to DPD circuitry  50  via path  47  to control the predistortion provided to the transmit signals by DPD circuitry  50 . Calibration data  70  may, for example, identify corresponding DPD settings and RGI settings for DPD circuitry  50  and transceiver circuitry  48  for a given transmit signal power level. 
     Ideally, radio-frequency power amplifier  46  exhibits a perfectly linear power response.  FIG. 3  plots output power level versus input power level for an illustrative radio-frequency power amplifier. Response line  200  may represent an ideal power characteristic, whereas line  202  may represent an actual power characteristic of the power amplifier in practice. As shown in  FIG. 3 , line  200  may have a constant slope across all input power levels (i.e., any increase in input power results in a corresponding increase in output power by a predetermined amount). 
     It is, however, challenging to manufacture power amplifiers that exhibit perfectly linear power transfer characteristics. In practice, increases in input power levels may not always increase the output power by the predetermined amount. As shown by line  202  in  FIG. 2 , the slope of line  202  may deviate from the desired slope of line  200  after a certain power level PI*. This undesired deviation may result in a reduction in the gain provided by the power amplifier at input power levels greater than PI* and may therefore sometimes be referred to as gain compression. In general, radio-frequency power amplifier  46  in device  10  may exhibit gain compression and/or may deviate from the ideal transfer characteristic in any other way. 
     As described above in connection with  FIG. 2 , predistortion circuitry  50  may be used to introduce signal distortion that compensates for undesired deviation(s) from the ideal power transfer characteristic (e.g., to counteract any undesirable non-linear behavior associated with power amplifier  32 ).  FIG. 4  plots output power level versus input power level for an exemplary predistortion circuit. Line  204  may exhibit a constant slope of one, whereas line  206  may exhibit the actual power characteristic of the predistortion circuit. For all signals that are received by the predistortion circuitry and that have power levels less than or equal to PI*, these signals may be passed through to the output of the predistortion circuit without any amplification nor attenuation. For all signals that are received with the predistortion circuit and that have power levels greater than PI*, these signals may be provided with an appropriate amount of gain to compensate for the gain compression associated with the power amplifier as described in connection with  FIG. 3 . DPD circuitry  50  may generate response  206  using predistortion coefficient values received from adjustable power supply circuitry  42 , if desired. 
     Line  206  of  FIG. 4  is merely illustrative. In general, predistortion circuitry  50  may exhibit a power transfer curve having an inverse relationship with respect to the input-output transfer characteristic associated with power amplifier  46  (e.g., a positive deviation in line  202  from line  200  at a given first input power level may be accompanied by a negative deviation in line  206  from line  204  at the given first input power level, whereas a negative deviation in line  202  from line  220  at a given second input power level may be accompanied by a positive deviation in line  206  from line  204  at the given second input power level). Adjustable power supply circuitry  42  may provide control signals to DPD circuitry  50  via path  47  so that DPD circuitry  50  exhibits response  206  for a given transmit signal. 
       FIG. 5  is an illustrative plot showing how envelope tracking circuitry  68  in adjustable power supply  42  of DUT  10 ′ may continuously adjust power supply voltage Vcc based on calibration data  70  (e.g., showing how tracking circuitry  68  may perform envelope tracking for amplifier  46 ). In the graph of  FIG. 5 , voltages have been plotted as a function of time. Curve  80  illustrates how the voltage Vin of a given signal transmitted by transceiver circuitry  48  and received at the input of amplifier  46  may vary over time. Curve  80  may, for example, represent a modulation “envelope” of the transmitted signal (e.g., an envelope provided by modulating the transmitted signals using baseband processor  34 ). In order for amplifier  46  to operate properly without generating undesired frequency harmonics of the transmitted signals or other ACLR violations, power supply voltages Vcc provided to amplifier  46  should be greater than the voltage represented by curve  80  during transmission of signals Vin. 
     Dashed line  82  illustrates a bias voltage VccA that may be provided to amplifier  46  without using envelope tracking (e.g., a constant bias voltage that is not adjusted based on the magnitude of Vin). In this scenario, constant bias voltage VccA is provided that is greater than peak magnitude V p  of transmit signal  80  to ensure that bias voltage Vcc is always greater than the voltage Vin of the transmitted signal so that no undesired frequency harmonics or other ACLR performance violations are generated by amplifier  46 . When using a bias voltage VccA as illustrated by line  82 , device  10 ′ may consume excessive power, as signal  80  often has a magnitude that is significantly less than peak voltage Vp and that does not require such a high bias voltage to operate without generating radio-frequency performance violations. Adjustable power supply circuitry  42  may perform envelope tracking to reduce overall power consumption by wireless circuitry  18 . 
     Curve  84  illustrates a bias voltage VccB that may be provided in real time by envelope tracking circuitry  68  to amplifier circuitry  46  by adjusting bias voltage Vcc based on the magnitude of input voltage Vcc without using calibration data  70 . In this example, bias voltage VccB follows the magnitude Vin of signal  80  such that bias voltage VccB always has a magnitude that is a fixed margin ΔV greater than signal  80  regardless of the magnitude of signal  80  (e.g., bias VccB is greater than the relatively high magnitude Vp of signal  80  at time T 2  by margin ΔV, is greater than the relatively low magnitude of signal  80  at time T 1  by margin ΔV, etc.). In this way, overall power consumption in device  10  may be reduced relative to scenarios where a constant bias voltage VccA is used. 
     However, in practice, power amplifier  46  may exhibit insufficient linearity only at excessive input voltage levels Vin. In the example of  FIG. 5 , amplifier  46  may exhibit insufficient linearity only for transmit voltage magnitudes Vin that are greater than voltage level V 4 . In this scenario, providing bias signal Vcc at a voltage level V 2  that is greater than transmit signal  80  by margin ΔV may be sufficient to provide linearity at time T 2  (e.g., when signal  80  has maximum amplitude Vp), but such a high voltage margin ΔV may not be necessary to ensure adequate amplifier linearity at lower input voltage levels Vin such as at time T 1  (e.g., a time when signal  80  has a magnitude that is significantly less than peak magnitude Vp). In other words, providing a bias such as VccB at a magnitude that is always greater than signal Vin by a fixed margin ΔV may consume excessive power for relatively low input voltage levels Vin (e.g., at times when a fixed margin ΔV is not necessary to ensure adequate amplifier linearity for amplifier  46 ). If desired, envelope tracking circuitry  68  may use calibration data  70  to determine suitable bias voltages that exhibit an optimal balance between reducing power consumption in device  10 ′ and allowing for adequate radio-frequency performance of amplifier circuitry  46  in real time. 
     In the example of  FIG. 5 , bias voltages VccD associated with curve  86  may be provided by calibration data  70  and may allow device  10  to reduce power consumption by providing bias signals that are greater than the transmit voltage level by different voltage margins over time (e.g., for different input voltages Vin) without sacrificing the spectral performance of amplifier circuitry  46 . In other words, bias voltage VccD may be provided to amplifier  46  at voltage levels that are greater than input voltage Vin by non-uniform voltage margins over time. For example, calibrated bias voltage VccD may be greater than magnitude Vp at time T 2  by margin ΔV, thereby ensuring adequate spectral performance of amplifier  46  when fed by signals at peak input voltage level Vp. However, calibrated bias voltage VccD may be provided at voltage V 6  that is greater than the magnitude of Vin at time T 1  by a margin ΔV&#39; that is significantly less than margin ΔV, while still ensuring adequate spectral performance of amplifier  46  (e.g., because linearity of amplifier  46  may be more greatly affected by relatively high input voltages such as voltage Vp than at relatively low input voltages such as the voltage of signal  80  at time T 1 ). Because a fixed margin ΔV may not be needed to ensure adequate linearity and spectral performance for low magnitudes Vin, bias VccD may be reduced relative to bias VccB for relatively low voltages Vin and may thereby further reduce power consumption by device  10 ′ relative to scenarios where bias voltage VccB is used (e.g., without sacrificing the radio-frequency performance of device  10 ). The example of  FIG. 5  is merely illustrative. Calibrated bias voltage VccD may have any desired magnitude as a function of time (e.g., depending on the calibration operations which were used to generate calibration data  70 ). In general, calibrated bias voltage VccD may be greater than input voltage Vin by different voltage margins at different times (e.g., for different input voltages Vin), thereby allowing for reduced power consumption relative to scenarios where bias voltage Vcc is always greater than input voltage Vin by a fixed voltage margin. 
     Calibration data  70  may identify optimal (calibrated) bias voltages such as bias voltages VccD of  FIG. 5  to use based on performance metric data obtained during calibration of device  10  (e.g., calibration data  70  may be generated to allow for suitable amplifier linearity while reducing overall power consumption relative to scenarios where a bias voltage is always greater than input voltage Vin by a fixed voltage margin).  FIG. 6  is an illustrative plot showing how calibration software may select optimal amplifier operation points for generating calibration data  70  that identifies optimal bias voltages VccD for use by envelope tracking circuitry  68  during normal device operation to reduce power consumption without sacrificing radio-frequency performance of the device. 
       FIG. 6  plots the input voltage Vin of amplifier circuitry  46  as a function of the output voltage Vout of amplifier circuitry  46 . Curves  300  illustrate the response of amplifier circuitry  46  at different bias voltages Vcc (e.g., a first response  300 - 1  at a maximum bias voltage such as voltage V 2  of  FIG. 5 , a second response  300 - 2  at a bias voltage such as voltage V 4 , a third response  300 - 3  at a bias voltage such as voltage V 5 , and a fourth response  300 - 4  at a bias voltage such as voltage V 6 ). The example of  FIG. 6  is merely illustrative and, in general, there may be any desired number of response curves each corresponding to a particular bias voltage provided to amplifier circuitry  46 . 
     As shown in  FIG. 6 , points  302  may be operation points of amplifier circuitry  46  that are used for determining bias voltages Vcc to provide to amplifier circuitry  46 . Points  302  may be fitted by a line  304 , such that bias voltages Vcc provided according to operation points  302  are always greater than input Vin by a fixed margin (e.g., points  302  may correspond to bias voltages VccB of  FIG. 5  in which bias voltages VccB are provided at a fixed margin ΔV greater than input voltage Vin). Points  306  may be operation points of amplifier circuitry  46  that are used for generating calibration data  70  that identifies calibrated bias voltages Vcc to provide to amplifier circuitry  46 . Points  306  may lie on any desired curve such as curve  308  such that bias voltage Vcc is greater than input voltage Vin by any desired voltage margin for each corresponding input voltage Vin (e.g., points  306  may correspond to bias voltages VccD of  FIG. 5  in which bias voltages VccD are greater than input voltage Vin by different voltage margins as a function of input voltage Vin). By fitting operation points  306  to any desired curve (e.g., as determined by calibration operations), calibrated bias voltages may be provided that optimally reduce power consumption without sacrificing radio-frequency (e.g., spectral) performance of device  10  at any desired transmit signal voltage Vin. 
       FIG. 7  is an illustrative plot showing how insufficient bias voltages Vcc may cause amplifier circuitry  46  to generate undesirable signal contributions at harmonic frequencies of the frequency at which transmit signals TX are transmitted. In the graph of  FIG. 7 , output power level Pout of amplifier circuitry  46  is plotted as a function of frequency of the transmit signals that are amplified by amplifier circuitry  46 . Curve  90  illustrates the output power of amplifier  46  when amplifying transmit signals using a power supply voltage that is sufficiently greater than the voltage of the transmitted signal. For example, curve  90  may illustrate the output power level of amplifier  46  when fed signals associated with curve  80  of  FIG. 5  and when powered using a calibrated supply voltage VccD such as that associated with curve  86  of  FIG. 5 . 
     Signal  90  may be transmitted using a communications protocol having a transmit frequency band around frequency F TX  and a receive frequency band around frequency F RX . Transmitted signal  90  may have a signal peak at transmit frequency F TX . Signal  90  may exhibit a noise floor having a power level P NF  at receive frequency F RX . Noise floor power level P NF  may specify a receive band noise floor value for the transmitted signal. The receive band noise floor value may, if desired, be used to characterize the performance of wireless circuitry  18  during calibration operations. 
     Curve  92  illustrates the output power level of amplifier  46  when powered using an insufficient supply voltage Vcc (e.g., when bias voltage Vcc is provided at a level less than V 2  at time T 2  or at a level less than V 6  at time T 1  in the example of  FIG. 5 ). Signal  92  may have a signal peak at transmit frequency F TX . However, as the bias signal associated with signal  92  is insufficient to ensure adequate performance of amplifier  46 , signal  92  may exhibit a harmonic peak  93  that coincides with receive frequency F RX  (e.g., a frequency F RX  that is equal to 2*F TX ). The harmonic peak of signal  92  may undesirably leak onto the receive path of transceiver circuitry  48  causing interference with radio-frequency receive signals that are received by antenna  60 . By performing envelope tracking operations using calibration data  70  to ensure that an optimal bias voltage Vcc is used for transmit signal  80 , circuitry  18  may reduce power consumption without undesirably impacting radio-frequency performance (e.g., without generating undesirable harmonic power contributions such as peak  93 ). 
       FIG. 8  is a flow chart of illustrative steps that may be performed by device  10 ′ to generate calibration data  70  and to use calibration data  70  to perform optimized envelope tracking operations that reduce power consumption in device  10  without undesirably impacting the performance of wireless circuitry  18 . The steps of  FIG. 8  may, for example, be performed by DUT  10 ′ while coupled to external test equipment  24  and test host  22  or may be performed without the use of external test equipment. In one suitable arrangement, steps  100 - 106  of  FIG. 8  may be performed while coupled to external test equipment, whereas step  108  is performed without external test equipment (e.g., during normal operation of device  10  by an end user). 
     At step  100 , DUT  10 ′ may generate and transmit radio-frequency test signals using a set of different desired power supply voltages Vcc. Calibration software  72  may instruct baseband processor  34  to generate the radio-frequency test signals using multiple different signal power levels (e.g., transmit signal voltages Vin) and may instruct adjustable power supply circuitry  42  to generate different desired bias voltage levels Vcc for transmitting the test signals. For example, baseband processor  34  may generate test signals by instructing baseband processor  34  and/or transceiver  48  to generate test signals by sweeping through a series of different voltage levels Vin while power supply circuitry  42  uses multiple different bias voltages Vcc (e.g., each bias voltage or a subset of the bias voltages Vcc producible by supply circuitry  42 ). The amplified test signals may be transmitted by antenna  60  and/or fed back to feedback receiver  68  via feedback path  64 . 
       FIG. 9  is a plot showing illustrative test signals that may be generated by wireless circuitry  18 . As shown in  FIG. 9 , curve  110  illustrates the voltage level of test signals generated by wireless circuitry  18  (e.g., while processing step  100  of  FIG. 8 ). Test signals  110  may be generated by cycling through N different bias voltages Vcc (e.g., a first bias voltage Vcc 1 , a second bias voltage Vcc 2  , an Nth bias voltage VccN, etc.). While each power supply voltage Vcc is provided to power amplifier circuitry  46 , transceiver circuitry  48  may sweep through a sequence of different voltage levels Vin for test signal  110  so that multiple different voltage levels are provided for each power supply voltage Vcc. Transceiver circuitry  48  may sweep through any desired number of voltage levels Vin (e.g., all possible voltage levels or a subset of the possible voltage levels) between a maximum voltage Vmax and a minimum voltage Vmin. The test signals may be used by DUT  10 ′ and/or tester  24  to measure performance metric data from the test signals for each of the different transmit signal voltage levels Vin and bias voltages Vcc (e.g., to characterize the wireless performance of DUT  10 ′over a wide range of operating conditions). 
     Returning to  FIG. 8 , at step  102 , DUT  10 ′ and/or tester  24  may measure performance metric data from transmitted test signals  110 . For example, tester  24  may measure output power levels of the test signals transmitted by DUT  10 ′, ACLR values, or any other desired performance metric values. If desired, feedback receiver  68  may convert the received test signals to corresponding baseband frequency data and may convey the data to baseband processor  34  and/or calibration software  72 . Baseband processor  34  and/or calibration software  72  may process the data received from feedback receiver  68  to generate corresponding performance metric data. For example, baseband processor  34  and/or software  72  may measure output power level of the signals received by feedback receiver  68 , ACLR values associated with the received signals, receive band noise associated with the transmit signals, or any other desired performance metric data. 
     If desired, feedback receiver  68  may measure one or more performance metrics from the transmitted test signals received on path  64 . For example, feedback receiver  68  may include Fourier transform circuitry (e.g., fast Fourier transform circuitry) that computes Fourier transforms of the received signals. Feedback receiver  68  may compute performance metric data such as receive band noise floor values using the Fourier transforms of the received signals and may provide the receive noise floor values to baseband circuitry  34  and/or calibration software  72 . If desired, feedback receiver  68  may characterize amplifier compression of power amplifier  46  (e.g., may compute one or more amplifier compression values) and may generate power amplifier efficiency values associated with the efficiency of power amplifier  46 . Feedback receiver  68  may provide the efficiency values and compression values to baseband  34  and/or calibration software  72 . In another suitable arrangement, baseband processor  34  may include power amplifier compression measurement circuitry such as measurement circuitry  33  as shown in  FIG. 2 . Compression measurement circuitry  33  may receive test signals from feedback receiver  68  and may process the test signals to determine the compression of amplifier  46 . If desired, DPD circuitry  50  may generate DPD coefficient values based on the signals received over feedback path  64  and may provide the coefficient values to calibration software  72 , baseband processor  34 , and/or adjustable power supply circuitry  42 . 
     At step  104 , calibration software  72  may retrieve and store the measured performance metric data. For example, calibration software  72  may retrieve performance metric data from baseband processor  34  and/or feedback receiver  68  (e.g., over paths  73 ). In scenarios where external test equipment  24  measures performance metric data using the test signals generated by DUT  10 ′, calibration circuitry  72  may retrieve the measured performance metric data from test host  22  via path  26 . Calibration circuitry  72  may store the retrieved performance metric data (e.g., on storage and processing circuitry  12 ) for further processing. 
     At step  106 , calibration software  72  may process the retrieved performance metric data to generate calibration data  70 . Calibration software  72  may, for example, determine the optimum (calibrated) power supply voltage Vcc to use during envelope tracking for every possible transmit signal voltage level Vin that can be used to transmit signals. If desired, calibration software  72  may determine optimum supply voltages Vcc for every possible transmit signal voltage level (desired output power level) in order to ensure that an appropriate supply voltage Vcc is available for power supply circuitry  42  for a wide range of different device operating conditions. Calibration software  72  may store the calibration data  70  (e.g., on storage circuitry  12 , on power supply circuitry  42 , or on any other desired storage circuitry) for use during normal device operation. For example, calibration software  72  may generate a list (e.g., table or data structure) of calibrated (optimal) power supply voltages Vcc to use for every possible transmit signal voltage level Vin (or for any desired subset of every possible transmit signal voltage level Vin). 
     If desired, calibration software  72  may be removed (uninstalled) from DUT  10 ′ after generating calibration data  70 . In another suitable arrangement, calibration software  72  may be stored on device  10 ′ for use during normal operation of device  10 ′. For example, calibration software  72  may be called during normal device operation to generate updated (new) calibration data (e.g., to account for any variations or changes in the performance of wireless circuitry  18 ). 
     At step  108 , device  10  (e.g., DUT  10 ′ after calibration operations have been completed) may perform envelope tracking operations for transmitting signals during normal device operations using stored calibration data  70 . For example, when transmitting radio-frequency signals, adjustable power supply circuitry  42  may look up a suitable power supply voltage Vcc to provide to power amplifier circuitry  46  from calibration data  70  based on the signals that are to be amplified using amplifier  46 . Adjustable power supply circuitry  42  may, if desired, provide DPD control signals (e.g., DPD coefficient values) to DPD circuitry  50  and RGI control signals to transceiver circuitry  48  based on calibration data  70 . As an example, adjustable power supply circuitry  42  may provide calibrated bias voltages such as bias voltages VccD to amplifier circuitry  46  when amplifier circuitry  46  receives transmit signals  80  at input voltages Vin as shown in  FIG. 5 . 
       FIG. 10  is a flow chart of illustrative steps that may be performed by DUT  10 ′ to measure performance metric data from the transmitted test signals (e.g., test signals such as test signals  110  of  FIG. 7 ) for generating calibration data  70 . The steps of  FIG. 10  may, for example, be performed by DUT  10 ′ while processing step  102  of  FIG. 8 . 
     At step  120 , DUT  10 ′ and/or test equipment  24  may measure ACLR values and output power level values from transmitted test signals  110 . For example, DUT  10 ′ and/or test equipment  24  may measure a corresponding ACLR value and output power level value for each magnitude Vin of transmitted test signals  110  and for each bias voltage Vcc that is used to produce test signals  110  (e.g., so that an ACLR value and output power level value is generated for each desired or producible combination of Vin and Vcc). Baseband processor circuitry  34  may receive test data from feedback receiver  68  (e.g., generated in response to transmit signals received on feedback path  64 ) and may generate the ACLR value and output power level value in response to the received test data. Baseband  34  may provide the measured ACLR and output power level values to test software  72 . If desired, test equipment  24  may measure output power level values and ACLR power level values from test signals  110  for each desired combination of Vin and Vcc and may provide the measured values to calibration software  72 . Calibration software  72  may store the received ACLR and output power level values in a performance metric data structure for use during subsequent processing and generation of calibration data  70 . 
     At step  122 , feedback receiver  68  may measure receive band noise (e.g., receive band noise floor values) from the transmitted test signals received over feedback path  64 . The receive band noise values may characterize the amount of transmitted signal that leaks into a receive frequency band of wireless circuitry  18 . For example, feedback receiver  68  may perform fast Fourier transform operations to generate a Fourier transform of the transmitted test signals and may generate receive band noise values using the Fourier transform of the transmitted test signals. Feedback receiver  68  may generate a receive band noise value for each transmit signal magnitude value Vin of test signals  110  and for each power amplifier bias value Vcc used to amplify test signals  110 . Feedback receiver circuitry  68  may provide the receive band noise values to baseband processor  34  and calibration software  72 . Calibration software  72  may store the receive band noise values corresponding to each Vin and Vcc of test signals  110  in the performance metric data structure for subsequent processing. 
     At step  124 , feedback receiver circuitry  68  may measure power amplifier compression (e.g., one or more compression values) associated with power amplifier circuitry  46  based on transmitted test signals  110  received over path  64  (e.g., a corresponding compression value for each combination of Vin and Vcc used for transmitting test signals  110 ). Feedback receiver circuitry  68  may pass the compression values to baseband processor circuitry  34  and calibration software  72 . In another suitable arrangement, power amplifier compression measurement circuitry  33  on baseband processor  34  may receive test data corresponding to test signals  110  and may measure compression values associated with amplifier circuitry  46  from the test data. Calibration software  72  may store the compression values corresponding to each Vin and Vcc of test signals  110  in the performance metric data structure. If desired, DPD circuitry  50 , baseband processor  34 , and/or transceiver  48  may generate DPD coefficient values (e.g., based on an inverse of the computed power amplifier compression values) such as the DPD coefficient values associated with curve  206  of  FIG. 4  and may provide the DPD coefficient values to calibration software  72 . The example of  FIG. 10  is merely illustrative and, if desired, steps  120 - 124  may be performed in any desired order (e.g., steps  120 - 124  may be performed concurrently, simultaneously, etc.). DUT  10 ′ and/or tester  24  may be used to gather any desired performance metric data associated with any desired radio-frequency performance metric. 
     Ideally, radio-frequency power amplifier  46  exhibits a perfectly linear power response. It is, however, challenging to manufacture power amplifiers that exhibit perfectly linear power transfer characteristics. In practice, increases in input power levels may not always increase the output power by the predetermined amount. This undesired deviation may result in a reduction in the gain provided by the power amplifier may therefore sometimes be referred to as gain compression. Gain compression of amplifier  46  may be characterized by corresponding gain compression values measured by receiver circuitry  68  and/or measurement circuitry  33 . Receiver circuitry  68  and/or measurement circuitry  33  may measure gain compression values, for example, as the input (or output) power level of amplifier  46  when the gain response of amplifier  46  differs from an idea gain response by a predetermined amount (e.g., 1 dB, 2 dB, etc.). 
       FIG. 11  is an illustrative diagram of a performance metric data structure (e.g., a table, array, or other data structure) that may be generated by calibration engine  72  using performance metric data measured by DUT  10 ′ and/or tester  24 . As shown in  FIG. 11 , performance metric data structure  130  may include multiple cells (entries)  132  in a Vin-Vcc space (e.g., data structure  130  may be arranged in an array of rows corresponding to input voltages from Vmax to Vmin and corresponding columns corresponding to bias voltages from Vcc 1  to VccN). DUT  10 ′ and/or tester  24  may measure ACLR values, output power level values, receive band noise values, power amplifier compression values, and DPD coefficients for each transmit signal magnitude Vin and bias voltage Vcc used for transmitting test signals  110  (e.g., while processing the steps of  FIG. 10 ). Calibration software  72  may populate data structure  130  using the measured data. For example, calibration software  72  may store a first ACLR value, output power level value, receive band noise value, PA compression value, and set of DPD coefficients measured from test signals  110  while test signals  110  have magnitude Vmin and while amplifier  46  receives bias voltage Vcc 1  in a first cell  132 - 1  corresponding to magnitude Vmin and bias voltage Vcc 1 , may store a second ACLR value, output power level value, receive band noise value, PA compression value, and set of DPD coefficients measured from test signals  110  while test signals  110  have magnitude Vmin and while amplifier  46  receives bias voltage Vcc 2  in a second cell  132 - 2  corresponding to magnitude Vmin and bias voltage Vcc 2 , etc. By sweeping through magnitudes Vin and bias voltages Vcc when generating test signals  110 , DUT  10 ′ may fully characterize wireless performance for all possible Vin and Vcc values that may be used for generating radio-frequency transmit signals and may store performance metric data in corresponding cells  132  of data structure  130 . Performance metric data structure  130  may be subsequently processed for generating calibration data  70  (e.g., for determining optimal bias voltages Vcc to use for each transmit signal magnitude Vin and corresponding device operating constraints). 
       FIG. 12  is a flow chart of illustrative steps that may be performed by calibration engine  72  for generating envelope tracking calibration data  70  using performance metric data gathered by DUT  10 ′ and/or tester  24 . For example, calibration software  72  may process performance metric data structure  130  of  FIG. 11  for generating calibration data  70 . The steps of  FIG. 12  may, for example, be performed by calibration software  72  while processing step  106  of  FIG. 8 . 
     At step  150 , calibration software  72  may select a desired test signal output power level from performance metric data structure  130  (e.g., a desired measured output power level as measured at DUT  10 ′ or tester  24  while processing step  120  of  FIG. 8 ). For example, calibration software  72  may select a desired output power level of 30 dB. 
     At step  152 , calibration software  72  may filter out entries in performance metric data structure  130  having output power levels that are different from the selected output power level (e.g., software  72  may generate filtered performance metric data or a filtered data structure from which entries with measured output power levels that are different from the selected output power level are removed). For example, if software  72  selects a desired output power level of 30 dB, software  72  may filter out cells  132  having measured output power levels that are different than 30 dB. In this way, only entries in performance metric data structure  130  having the selected power level may be used for further processing and generation of one or more entries of calibration data  70 . 
     At step  154 , calibration software  72  may select a desired amplifier compression value (e.g., a desired compression value as measured by feedback receiver  68  and/or baseband measurement circuitry  33 ). At step  156 , software  72  may filter out entries from performance metric data  130  having power amplifier compression values that are different from the selected compression value (e.g., software  72  may generate filtered performance metric data or a filtered data structure from which entries with measured compression values that are different from the selected compression values are removed). For example, if software  72  selects a desired compression value of 2 dB, software  72  may filter out cells  132  having compression values that are different than 2 dB. In this way, only entries in performance metric data structure  130  having the selected power level and compression level may be used for further processing and for generation of one or more entries of calibration data  70 . 
     At step  158 , calibration software  72  may compare the performance metric entries (e.g., the cells  132  in filtered data structure  130  remaining after filtering out cells with undesired output power levels and/or undesired compression values) to a selected (e.g., predetermined) adjacent channel leakage ratio threshold. For example, software  72  may identify the corresponding measured ACLR value in each remaining filtered entry of data structure  130  and may compare the identified ACLR values to a desired ACLR threshold value. The ACLR threshold value may be determined by carrier requirements, design requirements, engineering requirements, or any other desired requirements or standards for the radio-frequency performance of device  10 . For example, the desired threshold may be set by a user of device  10  or a designer of device  10  so that device  10  has satisfactory radio-frequency performance after calibration (e.g., a user may specify the desired threshold value prior to processing step  150  or at any other desired time while processing the steps of  FIG. 10 ). By comparing the remaining entries to the ACLR threshold value, software  72  may determine which entries correspond with satisfactory ACLR performance. For example, entries having a measured ACLR value that is less than the ACLR threshold value may indicate satisfactory ACLR performance whereas entries having a measured ACLR value that is greater than or equal to the threshold may indicate insufficient ACLR performance when DUT  10 ′ generated the corresponding test signals. 
     If no entries in filtered data structure  130  remain that have a corresponding measured ACLR value that is less than the ACLR threshold value, processing may loop back to step  154  as shown by path  160  to select a different desired amplifier compression value (e.g., to adjust the filtering of data  130  to include a different set of cells  132  upon filtering by amplifier compression value). 
     If at least one entry in filtered performance metric data structure  130  includes a corresponding measured ACLR value that is less than the ACLR threshold value, processing may proceed to step  164  as shown by path  164 . At step  164 , calibration software  72  may filter out the remaining entries from filtered performance metric data  130  having ACLR values that are greater than or equal to the ACLR threshold value (e.g., software  72  may generate filtered performance metric data entries from which entries having excessive measured ACLR values have been removed). In this way, only entries in performance metric data structure  130  having satisfactory measured ACLR values may be used for generating a corresponding calibration data entry. 
     At step  166 , calibration software  72  may compare the remaining performance metric data entries (e.g., the cells  132  in filtered data structure  130  remaining after filtering out cells with excessive ACLR values) to a selected (e.g., predetermined) receive band noise threshold. For example, software  72  may identify the corresponding receive band noise value in each remaining filtered entry  132  of data structure  130  and may compare the identified receive band noise values to a desired receive band noise threshold value. The receive band noise threshold value may be determined by carrier requirements, design requirements, engineering requirements, or any other desired requirements or standards for the radio-frequency performance of device  10 . For example, the desired threshold may be set by a user of device  10  or a designer of device  10  so that device  10  has satisfactory radio-frequency performance after calibration (e.g., a user may specify the desired threshold value prior to processing step  150  or at any other desired time while processing the steps of  FIG. 10 ). By comparing the remaining entries to the receive band noise threshold value, software  72  may determine which entries correspond with satisfactory receive band noise performance of wireless circuitry  18  (e.g., values for which amplifier  46  does not generate power at harmonic frequencies of the transmit frequency that overlap with a receive frequency of transceiver  48 ). For example, entries having a measured receive band noise value that is less than the receive band noise threshold value may indicate satisfactory receive band noise performance whereas entries having a measured receive band noise value that is greater than or equal to the threshold may indicate insufficient receive band noise performance when DUT  10 ′ generated the corresponding test signals. 
     If no entries in filtered data structure  130  remain that have a corresponding measured receive band noise value that is less than the receive band noise threshold value, processing may loop back to step  154  as shown by path  168  to select a different desired amplifier compression value (e.g., to adjust the filtering of data  130  to include a different set of cells  130  upon filtering by compression value). If at least one entry in filtered performance metric data structure  130  includes a corresponding measured receive band noise value that is less than the receive band noise threshold value, processing may proceed to step  172  as shown by path  170 . 
     At step  172 , calibration software  72  may filter out entries from the filtered performance metric data  130  having receive band noise values that are greater than or equal to the receive band noise threshold value (e.g., software  72  may generate filtered performance metric data entries from which entries having excessive measured receive band noise values have been removed). In this way, only entries in performance metric data structure  130  having satisfactory measured receive band noise values may be used for further processing and for generation of corresponding entries of calibration data  70 . 
     At step  174 , calibration software  72  may use the remaining entry of filtered performance metric data structure  130  for generating calibration data  70 . For example, software  72  may store the remaining entry  132  as an entry in calibration data  70  (e.g., as shown in  FIG. 7 ) so that the corresponding bias voltage Vcc of that remaining entry is used for the associated transmit signal magnitude Vin when performing signal transmission during normal device operation. In the example of  FIG. 11 , if entry  132 - 1  is the sole entry of performance metric data structure  130  remaining, the ACLR value, output power value, receive band noise value, power amplifier compression value, and DPD coefficients of entry  132 - 1  may be stored as an entry in calibration data  70 . If more than one entry  132  remains in filtered data structure  130 , software  72  may select the filtered entry having the least bias voltage Vcc. For example, if two entries in filtered data structure  130  remain after filtering by receive band noise, software  72  may select the entry having the smallest (least) bias voltage value Vcc for use as calibration data  70 . In this way, software  72  may minimize power consumption in device  10  while ensuring that each desired performance metric requirement is satisfied (e.g., while ensuring satisfactory wireless performance of device  10 ). The threshold values of  FIG. 12  (e.g., the ACLR threshold value, the RX band noise values, etc.) may define a set of operating constraints on device  10 . The operating constraints may be specified by a user, designer, tester, calibrator, or manufacturer of device  10  so that device  10  has desired radio-frequency characteristics (e.g., characteristics that allow for satisfactory radio-frequency performance). 
     The entry of data structure  130  stored as calibration data  70  may correspond to a particular output power level, transmit voltage magnitude Vin, and power amplifier compression value (e.g., set of DPD coefficient values). The steps of  FIG. 12  may be repeated for each desired output power level (e.g., each transmit voltage magnitude Vin) until calibration data  70  is populated with a complete set of bias voltages Vcc for any desired combination of operating constraints and transmit signal magnitudes (e.g., so that an optimal bias voltage value Vcc may be used for any desired transmit signals and operating conditions while performing envelope tracking operations on the transmit signals). If desired, calibration may be performed only on a subset of operating conditions and transmit signal magnitudes (e.g., to reduce the time required for generating calibration data  70 , etc.). 
     In this way, a designer or user of DUT  10 ′ may specify desired requirements for wireless performance of circuitry  18  and engine  72  may autonomously select an optimal (e.g., minimum) bias voltage for those requirements and for each possible transmit signal magnitude Vin (e.g., so that an optimal bias voltage Vcc is used for any desired transmit signal that minimizes power consumption while ensuring satisfactory wireless performance). 
     The example of  FIG. 12  is merely illustrative. If desired, steps  150 - 172  may be performed in any desired order. Any desired performance metrics may be measured and stored in performance metric data structure  130  and any desired performance metric thresholds or requirements may be applied to filter data structure  130  for generating calibration data  70 . 
       FIG. 13  is a diagram showing exemplary calibration data such as calibration data  70  that may be generated by calibration engine  72  and stored on device  10  for use in performing envelope tracking operations on transmitted signals. As shown in  FIG. 13 , calibration data  70  may be arranged in a table or data structure having multiple entries (rows) that each corresponding to a calibrated bias voltage Vcc to provide to amplifier circuitry  46 . Table  70  may, for example, be generated by calibration software  72  while processing step  106  of  FIG. 8 . 
     Envelope tracking circuitry  68  in adjustable power supply  42  may process table  70  to determine an optimal bias voltage Vcc to provide to amplifier circuitry  46  in real time as radio-frequency signals are transmitted by transceiver circuitry  48  (e.g., while processing step  108  of  FIG. 8 ). For example, tracking circuitry  68  may receive a transmit signal from baseband processor  34  and may identify a corresponding output power level Pout associated with the transmit signal. Tracking circuitry  68  may identify entries in calibration data  70  corresponding to the identified output power level Pout may provide the corresponding calibrated bias voltage Vcc (e.g., as specified in table  70 ) to amplifier circuitry  46 . If desired, tracking circuitry  68  may provide corresponding RGI control signals and DPD coefficients to transceiver circuitry  48  and DPD circuitry  50 , respectively, based on the identified entry in calibration data  70 . 
     In the example of  FIG. 13 , at a given point in time, tracking circuitry  68  may determine that signals are to be transmitted at desired output power level P 1 . Power level P 1  may, for example, correspond to peak input voltage level Vp of the transmit signal  80  as shown in  FIG. 5 . Tracking circuitry  68  may determine that the first entry (row) of calibration data  70  corresponds to power level P 1  and may select the corresponding RGI value RGI 1 , bias voltage (e.g., 3.8 V), and DPD coefficients DPD A  from that entry in table  70  to provide to transceiver circuitry  48 , power amplifier circuitry  46 , and DPD circuitry  50 , respectively. At a subsequent point in time, tracking circuitry  68  may determine that the signals are to be transmitted at desired output power level P 2 . Power level P 2  may, for example, correspond to input voltage level V 5  of transmit signal  80  as shown in  FIG. 5 . Tracking circuitry  68  may determine that the second entry in calibration data  70  corresponds to power level P 2  and may select the corresponding RGI value RGI 2 , bias voltage (e.g., 2.0 V), and DPD coefficients DPD B  from that entry in table  70  to provide to transceiver circuitry  48 , power amplifier circuitry  46 , and DPD circuitry  50  respectively. By operating on that transmit signal using the settings identified by calibration data  70 , device  10  may ensure that a minimum amount of bias voltage is provided to amplifier  46  to ensure satisfactory radio-frequency performance (e.g., thereby reducing overall power consumption in the device). 
     The example of  FIG. 13  is merely illustrative. If desired, calibration data  70  may include any desired device operating constraints and settings for the transmission of signals using device  10 . Any desired calibrated bias voltages may be identified by calibration data  70  (e.g., as determined by the calibration steps of  FIG. 12 ). If a transmit signal that is to be transmitted has a signal power level at a given point in time that is between two signal power levels identified by calibration data  70  (e.g., a power level less than power level P 1  and greater than power level P 2 ), envelope tracking circuitry  68  may select the greater power level (e.g., power level P 1  in a scenario where the power level to transmit is less than power level P 1  and greater than power level P 2 ) for identifying an entry in calibration data  70  (e.g., to ensure that satisfactory radio-frequency performance is maintained at the expense of using slightly more power in device  10 ). 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20141027
Publication Date: 20170103
Grant Date: 20170103
Priority Date: 20140908
Inventors: EL-HASSAN WASSIM
SUBRAHMANIYAN RADHAKRISHNAN GURUSUBRAHMANIYAN
Assignee: APPLE INC
CPC Classifications: [{"code": "H03F1/0266", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F2200/451", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F3/19", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F3/245", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/13", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F1/0227", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F2200/102", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F1/3247", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B1/0475", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B17/0085", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B1/0475", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B1/0475", "inventive": true, "first": true, "tree": "[]"}, {"code": "H03F1/0227", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F1/0266", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F1/3247", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F3/19", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F3/245", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F2200/451", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B17/0085", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/13", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F3/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F2200/102", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F2200/102", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B2001/0408", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F1/0227", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F1/0266", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F1/3247", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F3/19", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F3/245", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F2200/451", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B17/0085", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/13", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F3/24", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 55438504