PATENT DOCUMENT

Publication Number: US-8437793-B2
Application Number: US-62553409-A
Country: US
Kind Code: B2

Title: Wireless transmitter calibration using absolute power requests

Abstract:
Test systems are provided for performing testing and calibration operations on wireless circuitry in electronic devices. The electronic devices may include cellular telephones and other portable electronic devices. Wireless circuitry in a device may include a radio-frequency transceiver that is controlled based on radio-frequency transceiver control signals. The wireless circuitry may also include power amplifier circuitry. The power amplifier circuitry may receive radio-frequency signals from the transceiver and may produce correspondingly amplified radio-frequency output signals for wireless transmission with an antenna. The power amplifier circuitry may be powered by a bias voltage. The test systems may provide the electronic device with a transmit power request that directs the electronic device to produce a desired output power. The test systems may measure the actual resulting power. After sufficient measurements have been made, the test systems may calibrate the transceiver and power amplifier settings.

Claims:
What is claimed is: 
     
       1. A method for calibrating an electronic device that contains wireless circuitry, comprising:
 with equipment that is electrically connected to the electronic device, providing a transmit power request to the electronic device that directs the electronic device to wirelessly transmit radio-frequency signals at a desired output power; and 
 with the equipment, measuring an actual output power of radio-frequency signals transmitted from the electronic device in response to the transmit power request, wherein the wireless circuitry includes transceiver circuitry that is controlled by a transceiver control signal and includes power amplifier circuitry that receives a bias voltage, and wherein providing the transmit power request comprises requesting that the electronic device identify which value of the transceiver control signal and which value of the bias voltage to use to produce the desired output power. 
 
     
     
       2. The method defined in  claim 1  further comprising:
 comparing the desired output power and the actual output power. 
 
     
     
       3. The method defined in  claim 2  further comprising:
 computing a new value of the transceiver control signal without adjusting the bias voltage. 
 
     
     
       4. The method defined in  claim 3  wherein computing the new value of the transceiver control signal comprises computing the new value of the transceiver control signal based on the desired output power from the transmit power request and based on the measured actual output power. 
     
     
       5. The method defined in  claim 4  further comprising:
 computing the new value of the transceiver control signal only when comparison of the desired output power and the actual output power indicates that the desired output power and the actual output power differ by more than a predetermined threshold. 
 
     
     
       6. The method defined in  claim 1  wherein the electronic device comprises a cellular telephone and wherein providing the transmit power request comprises providing the transmit power request to the cellular telephone over a wired path that contains at least two wires. 
     
     
       7. The method defined in  claim 6  further comprising:
 processing multiple actual output power output measurements, transceiver control signal settings, and power amplifier bias voltage settings to determine calibrated values of an output power table. 
 
     
     
       8. The method defined in  claim 7  further comprising:
 with the equipment, loading the calibrated values of the output power table into the electronic device. 
 
     
     
       9. The method defined in  claim 1 , wherein the equipment and the electronic device are electrically connected by a wired path, wherein the wireless circuitry includes transceiver circuitry that is controlled by a transceiver control signal and includes power amplifier circuitry that receives a bias voltage, and wherein providing the transmit power request comprises sending the transmit power request from the equipment to the electronic device over the wired path without using the equipment to supply the electronic device with a value for the transceiver control signal over the wired path and without using the equipment to supply the electronic device with a value for the bias voltage over the wired path. 
     
     
       10. The method defined in  claim 1  further comprising:
 analyzing at least the desired output power and the actual output power to produce calibration information for the electronic device. 
 
     
     
       11. The method defined in  claim 10  wherein analyzing comprises producing at least one parameter value for an output power characterizing function. 
     
     
       12. The method defined in  claim 10  wherein the calibration information includes a plurality of function parameter values for the output power characterizing function. 
     
     
       13. A method for testing a cellular telephone that has a radio-frequency transceiver that produces radio-frequency signals at a power controlled by radio-frequency transceiver control signals, power amplifier circuitry that receives the radio-frequency signals produced by the transceiver and that provides corresponding amplified radio-frequency output signals, wherein the power amplifier circuitry is powered using an adjustable bias voltage, the method comprising:
 with test equipment, providing a transmit power request to the cellular telephone that directs the electronic device to provide the amplified radio-frequency output signals at a desired output power; 
 measuring power for the amplified radio-frequency output signals provided by the power amplifier circuitry in response to the transmit power request; 
 determining whether the measured power differs from the desired output power by more than a predetermined threshold; and 
 in response to determining that the measured output power differs from the desired output power by more than the predetermined threshold, computing an updated radio-frequency transceiver control signal setting to be used by the electronic device when attempting to produce the desired output power, wherein computing the updated radio-frequency transceiver control setting comprises holding the adjustable bias voltage at a fixed value while updating the radio-frequency transceiver control setting. 
 
     
     
       14. The method defined in  claim 13  further comprising:
 transmitting a plurality of the transmit power requests to the cellular telephone over a wired path between the cellular telephone and the test equipment; and 
 making actual power measurements indicative of how much actual power is associated with the amplified radio-frequency output signals produced in response to each transmit power request. 
 
     
     
       15. The method defined in  claim 14  further comprising:
 computing calibrated settings for an output power control curve based on the actual power measurements. 
 
     
     
       16. The method defined in  claim 15  further comprising:
 storing the calibrated settings in the cellular telephone to calibrate the cellular telephone. 
 
     
     
       17. The method defined in  claim 13  further comprising:
 producing corrective information for the cellular telephone that includes at least one function parameter value for an output power characterizing function; and; 
 storing the corrective information in the cellular telephone to calibrate the cellular telephone.

Description:
BACKGROUND 
     This invention relates generally to wireless communications circuitry, and more particularly, to calibrating 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. 
     Due in part to their mobile nature, portable electronic devices are often provided with wireless communications capabilities. For example, handheld electronic devices may use long-range wireless communications to communicate with wireless base stations. Cellular telephones and other devices with cellular capabilities may communicate using cellular telephone bands. Electronic devices may also use short-range wireless communications links. For example, portable electronic devices may communicate using the Wi-Fi® (IEEE 802.11) bands at 2.4 GHz and 5.0 GHz and the Bluetooth® band at 2.4 GHz. Communications are also possible in data service bands such as the 3G data communications band at 2170 MHz (commonly referred to as UMTS or Universal Mobile Telecommunications System band). 
     Proper operation of the wireless circuitry in an electronic device typically requires calibration. When operated with default settings, electronic devices may, for example, produce radio-frequency output power levels that differ somewhat from expected levels. If these discrepancies are too large in a device, the device may not operate as intended. For example, the device might not transmit signals with sufficient strength during operation, leading to dropped calls or other disruptions in wireless service. 
     With conventional calibration techniques, amplifier bias voltages and other settings in a device are adjusted while measuring resulting output power levels. Measurement results are then processed in an attempt to estimate properly calibrated values for the settings. Traditionally, there is a complex interplay between the different settings used to operate a device, so the process of making measurements and estimating calibration values may not always be sufficiently accurate. 
     It would therefore be desirable to be able to improve calibration techniques for wireless devices such as portable electronic devices. 
     SUMMARY 
     The wireless circuitry in an electronic device may include a transceiver that is controlled by transceiver control signals. The transceiver may produce radio-frequency signals at a power that is adjusted based on the transceiver control signals. A power amplifier may be biased at a bias voltage. The power amplifier may amplify the radio-frequency signals that are produced by the transceiver. The power amplifier gain may be adjusted based on amplifier control signals. Corresponding amplified radio-frequency output signals may be wirelessly transmitted using an antenna. 
     A connector may be interposed in the output path between the power amplifier circuitry and the antenna. During testing, a probe may be connected to the connector to route transmitted radio-frequency signals to a power meter. 
     Test equipment may provide the electronic device with transmit power requests that direct the electronic device to transmit the radio-frequency output signals at a desired output power. The test equipment may use the probe and the power meter to measure the actual output power that is produced by the power amplifier circuitry in response to each transmit power request. 
     The transmit power requests and the actual resulting output powers may be analyzed to produce calibration data for the electronic device. The calibration data may be provided in the form of offsets, function parameters, or other corrective information and may be programmed into the electronic device following testing. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       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 that may be used in an electronic device calibrated in accordance with an embodiment of the present invention. 
         FIG. 3  is a diagram of an illustrative test equipment that may be used in accordance with an embodiment of the present invention. 
         FIG. 4  is a flow chart of steps used in a conventional cellular telephone radio-frequency transmitter calibration process. 
         FIG. 5  is a graph showing how output power may vary as a function of transceiver digital-to-analog converter (DAC) values and power amplifier bias values in accordance with an embodiment of the present invention. 
         FIG. 6  is an output power settings table showing an illustrative set of power amplifier bias voltages and transceiver digital-to-analog converter settings that may be used in producing a desired set of radio-frequency output powers in an electronic device in accordance with an embodiment of the present invention. 
         FIG. 7  is a flow chart of illustrative steps involved in using test equipment to calibrate a wireless device in accordance with an embodiment of the present invention. 
         FIG. 8  is a flow chart of illustrative steps involved in using test equipment to perform calibration measurements based on power requests, analyze the calibration measurements to produce corrective information, and provide the corrective information to a wireless device in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     This relates generally to wireless communications, and more particularly, to calibration of wireless communications circuitry in wireless electronic devices. 
     The wireless electronic devices may be portable electronic devices such as laptop computers or small portable computers of the type that are sometimes referred to as ultraportables. The wireless electronic devices may also be somewhat smaller devices. Examples of smaller wireless electronic devices include wrist-watch devices, pendant devices, headphone and earpiece devices, and other wearable and miniature devices. With one suitable arrangement, the wireless electronic devices may be portable electronic devices such as handheld electronic devices. 
     The wireless devices may media players with wireless communications capabilities, handheld computers (also sometimes called personal digital assistants), remote controllers, global positioning system (GPS) devices, handheld gaming devices, or cellular telephones. The wireless electronic devices may also be devices that combine the functionality of multiple conventional devices. An example of a hybrid device is a cellular telephone that includes media player functionality, communications functions, web browsing capabilities, and support for a variety of other business and entertainment applications such as the iPhone® cellular telephone available from Apple Inc. of Cupertino, Calif. These are merely illustrative examples. 
     A schematic diagram of an embodiment of an illustrative wireless electronic device such as a handheld electronic device is shown in  FIG. 1 . 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 . For example, settings that are stored in 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. 
     With one suitable arrangement, 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 Wi-Fi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol, protocols for handling 2G and 3G cellular telephone communications services, etc. 
     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 . 
     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, organic light-emitting diode displays, electronic ink displays, etc.), 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, 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). 
     Storage and processing circuitry  12  may control wireless communications circuitry  18 . For example, storage and processing circuitry  12  may be used to adjust the gain of radio-frequency power amplifier circuitry on device  10  and may be used in adjusting input power levels provided to the input of radio-frequency power amplifier circuitry on device  10  from a transceiver circuit. Storage and processing circuitry  12  may also be used to adjust the power supply voltages (bias voltages) that are used in powering the radio-frequency power amplifier circuitry. These adjustments may be made automatically in real time based on calibration data and operating 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 parameters are adjusted in accordance with calibrated settings (calibrated operating parameters) to produce desired transmit powers (output powers) while meeting other desired performance criteria such as desired adjacent channel leakage ratio values and while minimizing power consumption. 
     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. During test and calibration operations, device  10  may communicate with test and calibration equipment (e.g., a calibration tool) that includes computing equipment. 
     Device  10  can also communicate with wireless network equipment, such as cellular telephone base stations, cellular towers, wireless data networks, computers associated with wireless networks, etc. Such wireless networks may include network management equipment that monitors the wireless signal strength of the wireless handsets such as device  10  that are in communication with the network. To improve the overall performance of the network and to ensure that interference between handsets is minimized, the network management equipment may send power adjustment commands (sometimes referred to as transmit power control commands) to each handset. The transmit power control settings that are provided to the handsets direct handsets with weak signals to increase their transmit powers, so that their signals will be properly received by the network. At the same time, the transmit power control settings may instruct handsets whose signals are being received clearly at high power to reduce their transmit power control settings. This reduces interference between handsets and allows the network to maximize its use of available wireless bandwidth. 
     When devices such as device  10  receive transmit power control settings from the network or at other suitable times, each device  10  may make suitable transmission power adjustments. For example, a device may adjust the power level of signals transmitted from transceiver circuitry to radio-frequency power amplifiers on the device and may adjust the radio-frequency power amplifiers. Adjustments such as these may include gain mode settings adjustments and power supply voltage adjustments. 
     The output signals from the power amplifiers on devices  10  are wirelessly transmitted from device  10  to suitable receivers using antennas in devices  10 . 
     The settings for wireless communications circuitry  18  may include gain mode adjustments that control the gain settings of power amplifiers. For example, a gain mode adjustment may control whether a power amplifier is operating in a high gain mode in which all power amplifier stages that are available are being used or a low gain mode in which one or more of the gain stages on the power amplifier have been shut down to conserve power. Power supply voltage adjustments may be used to help minimize power consumption at a given gain setting. In typical circuit architectures, a transceiver circuit may supply radio-frequency signals to the input of a power amplifier for transmission through an antenna. The power at which the transceiver circuit outputs these radio-frequency signals establishes an input power level (sometimes referred to herein as Pin) for the power amplifier. Input power adjustments (adjustments to Pin) can be made to adjust the power of radio-frequency signals transmitted by 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 devices  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, and the communications band data at 2170 MHz band (commonly referred to as a UMTS or Universal Mobile Telecommunications System band), 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, and the global positioning system (GPS) band at 1550 MHz. 
     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. 
     Illustrative wireless communications circuitry that may be used in circuitry  18  of  FIG. 1  in device  10  is shown in  FIG. 2 . As shown in  FIG. 2 , wireless communications circuitry  44  may include one or more antennas such as antennas  62 . Data signals that are to be transmitted by device  10  may be provided to baseband module (e.g., from storage and processing circuitry  12  of  FIG. 1 ). Baseband module  52  may be implemented using a single integrated circuit (e.g., a baseband processor integrated circuit) or using multiple circuits. 
     Baseband processor  52  may receive signals to be transmitted over antenna  62  at input line  89  (e.g., from storage and processing circuitry  12 ). Baseband processor  52  may provide signals that are to be transmitted to transmitter circuitry within RF transceiver circuitry  54 . The transmitter circuitry may be coupled to power amplifier circuitry  56  via path  55 . 
     Control path  88  may receive control signals from storage and processing circuitry  12  ( FIG. 1 ). These control signals may be used to control the power of the radio-frequency signals that the transmitter circuitry within transceiver circuitry  54  supplies to the input of power amplifiers  56  via path  55 . This transmitted radio-frequency signal power level is sometimes referred to herein as Pin, because it represents the input power to power amplifier circuitry  56 . 
     During data transmission, power amplifier circuitry  56  may boost the output power of transmitted signals to a sufficiently high level to ensure adequate signal transmission. Radio-frequency (RF) output stage circuitry  57  may contain radio-frequency switches and passive elements such as duplexers and diplexers. The switches in RF output stage circuitry  57  may, if desired, be used to switch circuitry  44  between a transmitting mode and a receiving mode. Duplexer and diplexer circuits and other passive components in RF output stage  57  may be used to route input and output signals based on their frequency. A connector in stage  57  such as connector  61  may allow an external cable to be connected to device  10 . The external cable may be associated with a test equipment probe and may be used to tap into the outgoing radio-frequency signals and thereby measure Pout during calibration. 
     Matching circuitry  60  may include a network of passive components such as resistors, inductors, and capacitors and ensures that antenna structures  62  are impedance matched to the rest of circuitry  44 . Wireless signals that are received by antenna structures  62  may be passed to receiver circuitry in transceiver circuitry  54  over a path such as path  64 . A low noise amplifier in the receiver circuitry of transceiver circuits  54  may be used to amplify incoming wireless signals from path  64 . 
     Each power amplifier (e.g., each power amplifier in power amplifiers  56 ) may include one or more power amplifier stages such as stages  70 . As an example, each power amplifier may be used to handle a separate communications band and each such power amplifier may have three series-connected power amplifier stages  70 . Stages  70  may have control inputs such as inputs  72  that receive control signals. The control signals may be provided using a control signal path such as path  76 . In a typical scenario, storage and processing circuitry  12  ( FIG. 1 ) may provide control signals to stages  70  using a path such as path  76  and paths such as paths  72 . The control signals from storage and processing circuitry  12  may be used to selectively enable and disable stages  70 . 
     By enabling and disabling stages  70  selectively, the power amplifier may be placed into different gain modes. For example, the power amplifier may be placed into a high gain mode by enabling all three of power amplifier stages  70  or may be placed into a low gain mode by enabling two of the power amplifier stages. Other configurations may be used if desired. For example, a very low gain mode may be supported by turning on only one of three gain stages or arrangements with more than three gain mode settings may be provided by selectively enabling other combinations of gain stages (e.g., in power amplifiers with three or more than three gains stages). 
     Adjustable power supply circuitry such as adjustable power supply circuitry  78  may be powered by voltage source  83 . Voltage source  83  may be, for example, a battery such as battery  14  of  FIG. 1 . Source  83  may supply a positive battery voltage to adjustable power supply circuitry  78  at positive power supply terminal  82  and may supply a ground voltage to adjustable power supply circuitry  78  at ground power supply terminal  84 . Source  83  may be implemented using a lithium ion battery, a lithium polymer battery, or a battery of any other suitable type. 
     Initially, the voltage supplied by battery source  83  may be high. As the battery becomes depleted, the voltage supplied by the battery will tend to drop. By using adjustable power supply circuitry  78 , the amount of voltage that is supplied to power amplifier circuitry  56  over power supply voltage path  86  may be maintained at a desired value. For example, power supply circuitry  78  may, under appropriate conditions, receive a raw battery voltage from source  83  that drops with time and may produce a relatively constant bias voltage Vbias (e.g., voltage Vcc in  FIG. 2 ) on output path  86 . This may help to avoid wasteful situations in which the circuitry of power amplifiers  56  is supplied with excessive voltages while the battery of source  83  is fresh. Such excessive voltages may lead to wasteful power consumption by circuitry  56 . 
     Adjustable power supply circuitry  78  may be controlled by control signals received over a path such as path  80 . The control signals may be provided to adjustable power supply circuitry  78  from storage and processing circuitry  12  ( FIG. 1 ) or any other suitable control circuitry. The control signals on path  80  may be used to adjust the magnitude of the power amplifier bias voltage that is provided to power amplifier circuitry  56  over path  86 . These power supply voltage adjustments may be made at the same time as gain mode adjustments are being made to the power amplifier circuitry  56  and at the same time that adjustments are being made to the power (Pin) on path  55 . By making these adjustments, desired output power levels Pout may be produced as needed. 
     For example, if a transmit power control (TPC) command is received from the cellular network that directs device  10  to produce 23 dBm of output power, power amplifier bias Vbias, the output power Pin, and the gain setting of power amplifiers  56  may be adjusted as needed so as to accurately produce 23 dBm of radio-frequency signal power at the output of power amplifiers  56 . Neglecting the losses in stage  57 , matching circuitry  60 , and antennas  62  (which can be taken into account by device  10 ), these settings will result in 23 dBm of wirelessly transmitted radio-frequency signal power, while satisfying other desired operating criteria (e.g., ACLR, etc.). 
     Transceiver circuitry  54  may contain a digital-to-analog converter that receives digital control values (sometimes referred to as DAC values, DAC signals, transceiver control signals, or transceiver control signal values) on path  88 . These DAC values control the operation of digital-to-analog converter circuitry in transceiver  54  that adjusts the value of Pin. The range of possible DAC values that are used in controlling Pin depends on the type of digital-to-analog converter circuitry used in transceiver circuitry  54 . Valid DAC values may, for example, range from 0 to 1024. As an example, when the control input to transceiver circuitry  54  is low in this type of configuration (e.g., the DAC value on path  88  is near 0), the value of power Pin will be low; when the control input to transceiver  54  is high (e.g., when the DAC value on path  88  is near 1024) the value of power Pin will be high. 
     When device  10  receives a TPC command asking device  10  to produce a particular output power Pout or when device  10  otherwise desires to produce a particular value of Pout, device  10  can consult calibrated settings stored in storage and processing circuitry  12 . These calibrated settings may identify proper values for the control signals used in operating circuitry  44  as a function of desired output power. If, for example, Pout has a desired value of 24 dBm, device  10  may identify a particular set of settings to use (e.g., a particular number of gain stages that are activated in power amplifiers  56 , a particular calibrated DAC value for path  88 , and a particular calibrated bias voltage Vbias for biasing power amplifiers  56 ). By using calibrated operating parameters, device  10  will accurately produce desired amounts of radio-frequency output power. 
     In a typical scenario, calibration of power amplifiers  56  when operating in a high gain mode (i.e., with all gain stages active) can be extrapolated to operations at lower gain settings (e.g., a low gain mode). Accordingly, it is generally sufficient to calibrate device  10  when operating in only its high gain mode. 
     When calibrating device  10 , test and calibration equipment may be used to determine which DAC values (transceiver control signal values) and Vbias values (power amplifier control signal values) are needed to produce various corresponding values of Pout. This calibration data may then be stored in device  10  for future use. When a user is using device  10 , device  10  can consult the stored calibration data to determine appropriate DAC and Vbias values to use in producing desired levels of output power. 
     An illustrative system environment in which a device may be tested and calibrated is shown in  FIG. 3 . Arrangements of the type shown in  FIG. 3  may be used in a factory or other facility in which test and calibration operations are performed. The  FIG. 3  example involves the use of test and calibration equipment  106  to perform both test operations and calibration operations. If desired, separate test equipment and calibration equipment systems may be used (e.g., at one or more different manufacturing and/or test facilities). The use of test and calibration equipment  106  in  FIG. 3  is merely illustrative. 
     As shown in  FIG. 3 , equipment  106  may include a radio-frequency signal probe such as probe  96 . Probe  96  may be connected to connector  61  to tap into the transmitted radio-frequency output signals that are being conveyed over path  92  to antenna  90 . When probe  96  is not present, all radio-frequency signals may pass to antenna  90 . When probe  96  is inserted in connector  61  during testing, the radio-frequency signals may be routed to power meter  98  via probe  96 . 
     Radio-frequency power meter  98  may produce analog or digital output signals indicative of the amount of radio-frequency power that is received from probe  96 . Radio-frequency power meter  98  may be coupled to computing equipment  100  via path  102 . Computing equipment  100  may be based on custom testing and calibration chips, one or more microprocessors, digital signal processors, or other processors, one or more networked general purpose computers, or other suitable computing equipment. Computing equipment  100  may be coupled to device  10  via cable  104 . Cable  104  may contain a pair of signal wires, four signal lines (e.g., a pair of power lines and a pair of data lines in a Universal Serial Bus cable), a parallel set of lines (e.g. in a high-speed parallel data bus), or any other suitable electronic path. If desired, path  104  may include a wireless path (e.g., an IEEE 802.11 wireless link). 
     In a typical scenario, path  104  is used to convey control signals to device  10  during testing. For example, path  104  may be used to send a power request command to device  10  that directs device  10  to transmit radio-frequency signals at a particular output power level (Pout). Power meter  98  may then be used to measure the resulting actual radio-frequency power that is transmitted. After a sufficient number of measurements have been made, device  10  may be calibrated by storing appropriately calibrated operating settings in device  10  (e.g., using path  104 ). If desired, calibrated settings may be stored separately (e.g., by loading device  10  with calibration settings using different equipment than equipment  106 ). 
     As described in connection with  FIG. 2 , the transmitted output power from a device may be affected by DAC values (control signals for the transceiver) and by power amplifier bias voltage Vbias and associated control signals. In a typical device, there is a complex interplay between various transceiver control signal values, power amplifier Vbias, power amplifier control signals and resulting output power levels. In some cases this relationship may not be well defined or actual the control signal values may be unavailable. In other cases, the optimal control values may be dependent on the actual output power of the device. This complexity can lead to inaccuracies when using conventional calibration techniques. Further, the relationships between the control values may lead to a necessity for an iterative based calibration method. 
     Consider, as an example, the conventional testing scheme of  FIG. 4 . 
     At step  108 , test equipment directs a device under test to bias its power amplifier at a fixed known bias voltage Vbias-test. 
     At step  110 , the test equipment uses individual commands or a batch process to load a series of DAC values into the device while directing the device to produce an output power Pout for each loaded DAC value. At the same time, the test equipment measures the resulting actual output powers Pactual corresponding to each loaded DAC value. This operation allows the test equipment to capture a Pactual versus DAC curve for a particular Vbias value (Vbias-fixed). 
     A similar process is then used to characterize output power as a function of power amplifier bias voltage at a given DAC setting. The fixed DAC setting is established at step  112 . 
     At step  114 , using a step-by-step approach or using a batch process, the test equipment instructs the device under test to produce a series of output powers Pout corresponding to each of a series of different bias voltages Vbias. While instructing the device under test to produce output powers in this way, the test equipment measures the resulting actual output powers. The operations of steps  112  and  114  therefore allow the test equipment to capture a Pactual versus Vbias curve at the fixed DAC setting. 
     Once these characterizing curves have been captured, modeling operations may be performed at step  116  in an attempt to estimate optimum Vbias and DAC settings to use at each of multiple Pout values. This computed information may be stored in an output power table and is therefore sometimes referred to as calibrated output power table data or an output power curve. The output power curve is loaded into the device under test at step  118 . 
     Although it is generally better to calibrate a device using the conventional calibration technique of  FIG. 4  than to forgo calibration completely, conventional calibration processes of this type may not always be sufficiently accurate. Because of the complex interplay between DAC settings and Vbias settings, procedures that manually adjust one of these operating parameters while holding the other constant are unable to reflect changes to the output power that arise only when both parameters are changed simultaneously (e.g., nonlinearities). Further, there may be more large set of possible control signal settings, making it undesirable to step through all possible combinations. 
     The graph of  FIG. 5  illustrates how changes in both DAC and Vbias settings may influence the amount of transmitted power from device  10  (i.e., Pout). In the  FIG. 5  graph, Pout has been plotted as a function of DAC value and Vbias value for a range of Vbias values between VB 1  (a non-zero minimum bias voltage) and VB 2  (an illustrative maximum bias voltage) and for a range of DAC values between a minimum of 0 and a maximum of 1024. 
     At low values of the DAC setting (e.g., when DAC is zero), the output power Pout is low (e.g., 0), regardless of the amount of Vbias. This is because the output power of transceiver circuitry  54  is low (e.g., 0). At a given non-zero DAC value, power Pout rises with increases in Vbias. The curve shapes for all possible combinations of DAC value and Vbias value give rise to a complex output power “surface” (i.e., warped non-planar two-dimensional surface  123 ). The non-planar nature of surface  123  is due to the nonlinear interactions between DAC value and Vbias value when producing powers Pout. 
     During operation of device  10 , device  10  produces various desired output power levels (e.g., in response to received TPC commands). For each given value of desired output power, the output power curve in device  10  can be used to produce a corresponding pair of optimal values for DAC and Vbias. The relationship between output power Pout and the optimal values of DAC and Vbias is represented graphically as output power curve  120  in  FIG. 5  and are represented as entries in an output power table in  FIG. 6 . At each point  122  on curve  120  of  FIG. 5 , the values of DAC and Vbias on curve  120  correspond to calibrated optimal settings to use to produce the corresponding value of Pout at that point  122 . 
     In a properly calibrated device, the values of output power curve  120  are stored in memory in the device (e.g., in the form of the table of  FIG. 6 ) and can be used to determine the appropriate DAC and Vbias settings to use under each required Pout condition. 
     Conventional calibration techniques of the type described in connection with  FIG. 4  attempt to approximate the complex warped shape of surface  123  with a plane. During conventional operations such as steps  110  and  112  of  FIG. 4 , the test equipment captures curve  126  of  FIG. 5 . Conventional operations such as steps  114  and  116  of  FIG. 5  are used to capture curve  124 . Based on curves  126  and  124 , and based on the modeling assumptions of step  116  (e.g., assuming surface  123  is planar), the test equipment then attempts to compute the shape of curve  120 . Because this type of independent measurement of curves  124  and  136  is unable to take into account complex non-linear interactions between Vbias and DAC value and other control signals, conventional calibration techniques are not generally able to compute curve  120  accurately. This leads to potential calibration errors when a conventionally calibrated version of curve  120  is programmed into a device. 
     Illustrative steps involved in testing and calibrating device  10  using test and calibration equipment of the type shown in  FIG. 3  are shown in  FIG. 7 . 
     At step  128 , the power out table for device  10  (e.g., the power out table of  FIG. 6 ) may be initialized (e.g., set to default values). The default values may be chosen based on an initial set of measurements on a typical device, may be improved over time (e.g., by training based on a number of data samples), etc. 
     At step  130 , an initial value may be chosen for the desired output power for device  10  (i.e., desired output power Pout-desired may be set to an initial value of Pinit). 
     At step  132 , the power output table may be programmed into device  10  (e.g., using path  104 ). The initial programming operations of step  132  will involve programming a default table into device  10 . Subsequent programming operations will involve the programming of successively more calibrated tables into device  10 . 
     At step  134 , test equipment  100  may be used to send an output power request (radio-frequency wireless transit power request) to device  10  (e.g., over path  104 ). The output power request includes a command directing device  10  to transmit a radio-frequency signal of output power Pout equal to the current value of Pout-desired (i.e., the value that, at least initially, was initialized to the initial value Pinit at step  130 ). 
     At step  136 , device  10  uses the stored output power table (also sometimes referred to as the power out table or output power curve) to determine which values of DAC and Vbias are to be used in producing Pout-desired. After determining which DAC and Vbias values to use by looking up these values in the output power table (i.e., by applying the current version of the output power curve), device  10  will produce an output power of magnitude Pactual. 
     At step  138 , test and calibration equipment  106  may use probe  96 , power meter  98 , and computing equipment  100  to measure and store the magnitude of Pactual. Computing equipment  100  may then compare the measured and stored output powers. For example, computing equipment  100  may compute the absolute magnitude of Pactual minus Pout-desired. The resulting value (Pdiff) can be compared to a threshold power value Pth. The magnitude of Pth represents the maximum acceptable divergence between the actual output power and the intended output power for device  10  (i.e., the maximum allowable error). 
     If Pdiff is more than Pth, computing equipment  100  can conclude that additional calibration operations at Pout-desired are needed. A new and more appropriate value of DAC value corresponding to output power Pout-desired can then be computed at step  144 . For example, if it was determined that the actual output power Pactual was 10% larger than the desired output power Pout-desired, the operations of step  144  may be used to reduce the DAC value corresponding to Pout-desired by approximately 10%. 
     During the computations of step  144 , the magnitude of Vbias is preferably not changed, so as to avoid introducing bias changes that could adversely affect performance. As an example, Vbias reductions might increase ACLR, which might violate design constraints. By holding Vbias constant during the operations of step  144 , the possibility that ACLR specifications might be undesirably violated by changes in Vbias is eliminated. If desired, however, both Vbias and DAC may be changed (e.g., in a weighted fashion). Once the new trial DAC value for Pout-desired has been computed, processing may loop back to step  132 , as indicated by line  146 . 
     Once the Pactual and Pout-desired values are sufficiently close (i.e., Pdiff&lt;Pth), the DAC value that has been identified can be stored in the output power table and a new value of Pout-desired can be selected for calibration (step  140 ). Processing may then loop back to step  134 , as indicated by line  142 . 
     Once a sufficient number of values of Pout-desired have been calibrated, the output power table will contain a number of properly calibrated Vbias and Pout settings. The output power table may also contain settings that have not been calibrated. For example, the output power table may contain hundreds of rows, each corresponding to a power value that is offset from its nearest neighbor by 0.1 dBm. During calibration measurements, the table entries at integer output power levels may be calibrated (as an example). For example, the settings in the table may be updated for powers Pout-desired=24 dBm, Pout-desired=23 dBm, Pout-desired=22 dBm, etc. If finer-grained entries are contained in the output power table, interpolation operations may be performed during step  148  based on the known calibrated entries. The original default output power settings in the output power table may then all be replaced with the interpolated (calibrated) data. Once the table has been fully calibrated, the calibrated output power table may be programmed into device  10  (e.g., using equipment  100  to load the data into device  10  over path  104 ). If desired, the device may be programmed with the calibrated data using different equipment (e.g., at a different portion of the manufacturing line). 
     Calibrated devices may be operated by a user (step  150 ). During operation of a calibrated device, the device may receive transmit power commands from an external source such as a cellular network or may otherwise be instructed to produce a particular output power level. When processing a request to produce a particular output power Pout, the calibrated device will use its calibrated output power table entries (i.e., the calibrated output power curve) to produce appropriate values of Vbias, DAC value, and other appropriate settings for wireless communications circuitry  18 . Because the performance of the device in responding to these same types of output power requests has already been substantially tested during the calibration operations of  FIG. 7 , accurate operation is ensured. 
       FIG. 8  is a generalized flow chart of illustrative steps involved in calibrating a wireless device using transmit power requests. 
     At step  152 , the wireless device may be initialized. For example, default settings may be loaded into device  10  using equipment  106 . Default settings may also be loaded into device  10  using other equipment (e.g., default settings may be incorporated into nonvolatile memory in device  10  during a preceding manufacturing operation). Default (initial) device settings may include control parameters such as an output power table and other settings that control the operation of wireless circuitry  18 . These settings may include, for example, settings for controlling Vbias, DAC values, gain stage state settings, settings that control how device  10  responds to various transmit power histories, settings that device  10  uses in determining how to adjust circuitry  18  in response to measured variables such as temperature, internally measured tapped power values (feedback), etc. 
     Changes in some of these parameters may affect others, so the process for controlling radio-frequency output power in device  10  may or may not be straightforward to model in equipment  106 . For example, in some situations, control parameters in device  10  may be inaccessible to equipment  106 , making effective modeling difficult or impossible. In other situations, equipment  106  may be able to accurately model how device  10  will respond to at least some of these control parameters. Calibration operations by equipment  106  may therefore be tailored depending on the type of device that is being calibrated. 
     At step  154 , one or more transmit power requests may be conveyed from equipment  106  to device  10 . In some situations, it is only desirable to send a single request at a time. In this type of arrangement, it may be desirable to repeatedly calibrate device  10  until a desired level of calibration has been achieved. In other situations, throughput may be enhanced by queuing and processing multiple transmit power requests. With this type of approach, multiple power requests may be formulated and transmitted to device  10  during the operations of step  154 . 
     By using transmit power requests rather than commands that direct device  10  to use particular control parameters to produce a corresponding output power, equipment  106  is able to directly characterize how device  10  operates along line  120  of  FIG. 5  (e.g., at points  122 ). This eliminates the need for equipment  106  to implement complex models of the relationships between control parameters and output power in device  10 . Particularly in situations in which proper control parameter selection depends on actual rather than intended output powers, use of power requests rather than direct iteration through control parameters may help to reduce or eliminate sources of test error. 
     Each output power request that is received and processed by device  10  results in a corresponding actual transmitted radio-frequency power. At step  156 , equipment  106  may measure the actual output power corresponding to each requested output power. 
     At step  158 , equipment  106  may analyze the measurement results to determine what actions should be taken to calibrate device  10 . Equipment  106  may, for example, produce corrective information (calibration information) to provide to device  10  during step  160 . The operations of steps  154 ,  156 , and  158  may be repeated if desired to ensure a satisfactory level of calibration has been obtained. Once device  10  has been sufficiently calibrated, device  10  may be operated by a user (step  162 ). 
     Because equipment  106  has requested particular output powers during step  154 , equipment  106  can determine whether device  10  is operating accurately at step  158  without implementing a full functional model of the operation of device  10 . Device  10  may, for example, implement an operating algorithm that is not completely accessible to equipment  106  (e.g., because some of the parameters, equations, or hardware mechanisms that are used in device  10  to produce a given output power are not modeled, are embedded within an inaccessible portion of device  10 , or are otherwise not available to equipment  106 ). Even in this situation, equipment  106  can effectively analyze the test measurements made during the operations of step  156  to produce corrective information for device  10 . 
     The corrective information that equipment  106  produces to calibrate device  10  may take any desired form. Examples of suitable corrective information include fully-calibrated output power tables, offset values for control parameters (e.g., corrective offsets for device  10  to use for Vbias, DAC value), output power offsets for device  10 , etc. After device  10  has been provided with this corrective information, device  10  will operate in a calibrated fashion. For example, if device  10  is producing an output power Pout by looking up appropriate Vbias and DAC settings in a table, following the implementation of suitable corrective offsets in Vbias and/or DAC or following the loading of an entirely new table, device  10  will produce accurate output powers. 
     In some situations, it may be desirable for the corrective information that is provided by equipment  106  to device  10  to include only corrective information for a subset of the control parameter information that is used by device  10 . For example, device  10  may produce output power Pout based on control parameters a, b, c, and d. The corrective information that is provided by equipment  106  to device  10  during step  160  may only correct parameters a and b (as an example). The corrective information (in this example) may only include a calibrating offset in parameter a and a calibrating offset in parameter b that are to be used to device  10  to produce accurate output powers. 
     It may also be desirable to provide corrective information from equipment  106  to device  10  using calibration parameters that are inputs to potentially complex functions of multiple control parameters. Consider, as an example, a situation in which curve  120  of  FIG. 4  is a hyperbolic output power characterizing function f(Vbias, DAC, Q, and R), where Vbias and DAC represent the power amplifier bias voltage and transceiver DAC value used by device  10  and Q and R represent constants that define the shape of the hyperbolic function). During the calibration operations of step  158 , equipment  106  may process the measurement results of step  156  to determine optimal calibrated values of Q and R. The values of Q and R may then be used as some or all of the corrective information that is provided to device  10  during step  160 . 
     In operation of device  10 , Q and R are affected by numerous factors, which may be difficult or impossible to independently ascertain. Nevertheless, because equipment  106  has requested that device  10  produce particular output powers, rather than attempting to directly adjust the underlying control parameters that produce those output powers, the analysis operations of step  158  can determine a best fit for Q and R without need to understand all underlying influences on the value of the output power that is produced. The values of Q and R (in this example) may therefore be sufficient to calibrate device  10 . 
     Corrective information (e.g., the function parameter values Q and R in this present example) may represent curve slopes, curve shapes, curve offsets (e.g., intercepts), constants in hyperbolic functions or other functions, etc. In the present examples, particular types of corrective information have been described to illustrate how device  10  may be calibrated based on analyzing the results of the output power requests. These examples are, however, merely illustrative. Any suitable corrective information may be provided to device  10  to calibrate device  10  if desired. 
     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.

Metadata:
Filing Date: 20091124
Publication Date: 20130507
Grant Date: 20130507
Priority Date: 20091124
Inventors: DONOVAN DAVID A.
GREGG JUSTIN
Assignee: APPLE INC
CPC Classifications: [{"code": "H04B17/13", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B17/13", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 44062473