PATENT DOCUMENT

Publication Number: US-8903374-B2
Application Number: US-12853408-A
Country: US
Kind Code: B2

Title: System for calibrating wireless communications devices

Abstract:
A wireless electronic device such as a portable electronic device may contain a baseband module. Power amplifier circuitry in the device may amplify radio-frequency signals for transmission. During calibration measurements, a computer directs the baseband module to generate control signals that adjust the gain of the power amplifier circuitry. The computer may also direct the baseband module to generate a series of modulated or unmodulated test tones at one or more communications channel frequencies. A power sensor may be connected to the output of the power amplifier circuitry using a transmission line path. The computer and power sensor may be used in making power measurements on radio-frequency signals at the output of the power amplifier while power amplifier gain and test tone frequency adjustments are being made. Power amplifier calibration data may be produced and stored in the electronic device based on the power measurements.

Claims:
What is claimed is: 
     
       1. A method of calibrating a radio-frequency power amplifier in a handheld electronic device, wherein the handheld electronic device comprises a baseband module having a digital-to-analog converter that produces an analog control voltage that is received at a control input of the radio-frequency power amplifier and that controls how much gain is provided by the radio-frequency power amplifier when amplifying radio-frequency signals, wherein the handheld electronic device has a radio-frequency connector at which amplified versions of the radio-frequency signals are provided by the radio-frequency amplifier, wherein a computer is connected to the handheld electronic device during calibration operations, and wherein a power sensor is coupled to the radio-frequency connector by a transmission line, the method comprising:
 with the power sensor, making power measurements on the amplified versions of the radio-frequency signals over the transmission line; 
 with the computer, producing calibration data for the radio-frequency power amplifier based at least partly on the power measurements; 
 with the computer, directing the digital-to-analog converter to adjust the gain of the radio-frequency power amplifier by changing the analog control voltage while the power sensor gathers the power measurements; 
 storing the calibration data in memory associated with the baseband module, wherein producing the calibration data comprises producing the calibration data in a plurality of radio-frequency communications channels at which the handheld electronic device operates; and 
 with the computer, directing the baseband module to generate test signals at multiple calibration power levels for each of the plurality of radio-frequency communications channels while the power sensor gathers the power measurements, wherein making the power measurements comprises completing the power measurements needed to produce the calibration data by making more power measurements in at least one of the plurality of radio-frequency communications channels than are made in other ones of the plurality of radio-frequency communications channels, wherein at least one power measurement is made in the other ones of the plurality of radio-frequency communications channels. 
 
     
     
       2. The method defined in  claim 1 , wherein the handheld electronic device comprises a cellular telephone. 
     
     
       3. The method defined in  claim 1 , wherein the handheld electronic device comprises a handheld computer. 
     
     
       4. The method defined in  claim 1 , wherein the handheld electronic device comprises a media player. 
     
     
       5. The method defined in  claim 1  wherein directing the baseband module to generate the test signals comprises:
 directing the baseband module to generate an unmodulated test tone for each of the plurality of radio-frequency communications channels. 
 
     
     
       6. The method defined in  claim 1  wherein directing the baseband module to generate the test signals comprises:
 directing the baseband module to generate a modulated test tone from a pseudorandom bit pattern for each of the plurality of radio-frequency communications channels. 
 
     
     
       7. The method defined in  claim 1 , wherein the radio-frequency connector comprises a radio-frequency switch. 
     
     
       8. A method of calibrating wireless circuitry including a radio-frequency power amplifier and a baseband module, the method comprising:
 with a computer, directing the baseband module to generate radio-frequency test signals in a plurality of frequency channels, wherein the radio-frequency test signals are amplified by the radio-frequency power amplifier; 
 with a power sensor, making a first plurality of power measurements on the amplified radio-frequency signals in a first frequency channel of the plurality of frequency channels; and 
 with the power sensor, making a second plurality of power measurements on the amplified radio-frequency signals in a second frequency channel of the plurality of frequency channels, wherein the first plurality of power measurements in the first frequency channel includes more power measurements than the second plurality of power measurements in the second frequency channel. 
 
     
     
       9. The method defined in  claim 8  further comprising:
 with the computer, determining a radio-frequency output power curve based on the first plurality of power measurements in the first frequency channel; and 
 with the computer, generating power amplifier calibration data for the first frequency channel based on the radio-frequency output power curve. 
 
     
     
       10. The method defined in  claim 9  further comprising:
 with the computer, generating offset data from the second plurality of power measurements in the second frequency channel; and 
 with the computer, generating power amplifier calibration data for the second frequency channel by applying the radio-frequency output power curve to the offset data. 
 
     
     
       11. The method defined in  claim 8  wherein directing the baseband module to generate the radio-frequency test signals in the plurality of frequency channels comprises:
 directing the baseband module to generate an unmodulated test tone for each of the plurality of frequency channels. 
 
     
     
       12. The method defined in  claim 8  wherein directing the baseband module to generate the radio-frequency test signals in the plurality of frequency channels comprises:
 directing the baseband module to generate a modulated test tone from a pseudorandom bit pattern for each of the plurality of frequency channels. 
 
     
     
       13. The method defined in  claim 8 , wherein the computer comprises a personal computer. 
     
     
       14. The method defined in  claim 8 , wherein the computer comprises a test equipment station having an associated processor. 
     
     
       15. The method defined in  claim 8 , wherein the power sensor comprises a diode and a resistor. 
     
     
       16. The method defined in  claim 8 , wherein the wireless circuitry comprises wireless communications circuitry for a handheld electronic device.

Description:
BACKGROUND 
     This invention relates generally to calibrating electronic devices, and more particularly, to calibrating radio-frequency circuitry in wireless communications devices. 
     Electronic devices such as 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. 
     Electronic devices such as 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 and may use short-range communications to communicate with accessories and local networks. 
     Electronic devices with wireless communications capabilities often undergo calibration operations during manufacturing. A typical device includes a processor and other circuitry that generates data. A typical device also includes radio-frequency transceiver circuitry for transmitting and receiving data over an antenna. Amplifiers may be used to increase the strength of the radio-frequency signals. For example, adjustable-gain radio-frequency power amplifier circuitry may be used to amplify transmitted radio-frequency signals. If the power amplifier circuitry is not properly calibrated, the device may produce radio-frequency signals that are too weak or too strong. Signals that are too weak may cause the device to operate incorrectly. Signals that are too strong may lead to operational and regulatory compliance problems. 
     Conventional calibration systems are built around complex and expensive radio communication test equipment. In a typical scenario, a device to be calibrated is placed in a shielded box and connected to a radio communication tester and a computer via cables. During calibration operations, the radio communication tester establishes a bidirectional communications link with the device and characterizing radio-frequency signal measurements are made. The results of these measurements are then processed to produce power measurement data for device calibration. 
     With conventional calibration schemes of this type, the process of establishing the wireless communications link between the tester and the device limits production line throughput. Moreover, the radio communication test equipment uses expensive spectrum analyzing circuits in making signal measurements, which adds to the complexity and cost associated with calibration. 
     It would therefore be desirable to provide improved techniques for calibrating radio-frequency circuitry in wireless communications devices. 
     SUMMARY 
     Portable electronic devices and other electronic devices with wireless communications capabilities are provided that include radio-frequency power amplifier circuitry. A radio-frequency power amplifier in an electronic device may amplify radio-frequency signals to be transmitted by the device. The gain of the radio-frequency power amplifier may be controlled by a control signal provided at a control input. A baseband module or other circuitry in the electronic device may contain control circuitry. The control circuitry may produce the control signal for the control input of the power amplifier. For example, the control circuitry may contain a digital-to-analog converter or other circuit that produces an analog control voltage or digital signal that serves as a gain-adjusting control signal for the radio-frequency power amplifier. The control circuitry may be used to generate radio-frequency test signals (test tones) at frequencies associated with various communications channels. The test tones may be pure unmodulated carrier tone signals or may be modulated using pseudorandom modulation data (as an example). 
     As initially fabricated, the gain of the power amplifier circuitry in an electronic device may vary somewhat from the nominal gain level that is desired. These manufacturing variations may be overcome by producing radio-frequency power amplifier calibration data. The calibration data may represent a series of corrective gain adjustments that the electronic device is to use when amplifying radio-frequency signals during normal operation. 
     Calibration data may be produced using a computer and a power sensor. The power sensor may be connected to the output of the radio-frequency power amplifier using a test fixture that has an associated transmission line path. During calibration measurements, the computer directs the baseband module in the electronic device to produce a variety of test tones in different communications channels while varying the gain settings of the radio-frequency power amplifier circuitry. The test tones may be provided to the input of the power amplifier circuitry. Corresponding amplified versions of the radio-frequency test tones may be provided at the output of the power amplifier circuitry. The transmission line path may be used to convey these amplified radio-frequency signals to the power sensor. 
     Power measurements may be made of the amplified radio-frequency signals using the power sensor and the computer. The computer can analyze the power measurement data to produce corresponding calibration information. The calibration information may be loaded into memory in the electronic device. During normal operation, control circuitry in the electronic device may calculate appropriate values for the control signals that are to be applied to the power amplifier circuitry based on the calibration data, thereby ensuring that accurate power levels are produced when transmitting radio-frequency signals. 
     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 a conventional cellular telephone calibration system based on a radio communication tester. 
         FIG. 2  is a diagram of a calibration system in accordance with an embodiment of the present invention. 
         FIG. 3  is a graph showing how a system of the type shown in  FIG. 2  may be used to take calibrating radio-frequency signal power measurements as a function of different amplifier gain settings in accordance with an embodiment of the present invention. 
         FIG. 4  is a graph illustrating how radio-frequency signal power measurements may be taken at different amplifier gain settings in multiple communications channels in accordance with an embodiment of the present invention. 
         FIG. 5  is a flow chart of illustrative steps involved in calibrating wireless communications devices using a calibration system of the type shown in  FIG. 2  in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention relates to calibrating radio-frequency circuitry in electronic devices with wireless communications capabilities. 
     The electronic devices may be, for example, portable electronic devices such as laptop computers or small portable computers of the type that are sometimes referred to as ultraportables. Portable electronic devices may also be somewhat smaller devices. Examples of smaller portable electronic devices include wrist-watch devices, pendant devices, headphone and earpiece devices, and other wearable and miniature devices. With one suitable arrangement, the electronic devices may be handheld electronic devices. 
     The electronic devices may be, for example, cellular telephones, media players with wireless communications capabilities, handheld computers (also sometimes called personal digital assistants), remote controllers, global positioning system (GPS) devices, and handheld gaming devices. The electronic devices may also be hybrid devices that combine the functionality of multiple conventional devices. Examples of hybrid electronic devices include a cellular telephone that includes media player functionality, a gaming device that includes a wireless communications capability, a cellular telephone that includes game and email functions, and a portable device that receives email, supports mobile telephone calls, has music player functionality and supports web browsing. These are merely illustrative examples. 
     In devices such as these, radio-frequency signals are typically amplified using power amplifier circuitry. For example, a power amplifier may be used to amplify received radio-frequency signals before those signals are processed by receiver circuitry in a device. A power amplifier may also be used to boost radio-frequency signals prior to transmission over an antenna. 
     Radio-frequency amplifiers such as the power amplifiers that are used in amplifying transmitted radio-frequency signals may be adjustable. For example, these amplifiers may include blocks of circuitry that can be selectively enabled and disabled. When a high gain configuration is desired, all of the blocks of amplifier circuitry may be enabled. When a low gain configuration is needed, some of the amplifier circuitry may be disabled to conserve power. Gain blocks may also have analog or digital control inputs for making gain level adjustments. For example, a power amplifier may have an analog voltage control input or digital control input that is used in adjusting the gain of the power amplifier. These control signals may be produced, for example, at the output of a digital-to-analog converter circuit (e.g., when producing an analog control voltage) or at the output of a digital control circuit (e.g., when producing a digital control signal). 
     Due to manufacturing variations, it is generally not possible to produce uncalibrated radio-frequency power amplifier circuitry that exhibits precisely controlled amounts of gain in a wide dynamic range of power levels. Calibration is therefore generally used to ensure that the power amplifier circuitry produces desired amounts of gain across the desired range of power levels. 
     A conventional manufacturing system that may be used to calibrate power amplifier circuitry on a wireless electronic device is shown in  FIG. 1 . As shown in  FIG. 1 , system  10  includes a device under test (DUT) such as device under test  12 . Device under test  12  may be, for example, a cellular telephone. During calibration operations, device under tests  12  communicates with external equipment using a bidirectional link. To avoid interference from adjacent devices in the production environment or other external signals, device  12  is placed within a shielded box such as shielded box  14 . Box  14  may be a metal enclosure that prevents radio-frequency interference from reaching device  12 . 
     Device under test  12  is typically mounted to a test fixture in box  14 . The text fixture is used in coupling transmission line  18  to radio-frequency connector  16 . Radio-frequency connector  16  may be, for example, a radio-frequency connector that normally shorts the output of a power amplifier and other radio-frequency circuitry to an antenna in device  12 . When connected to cable  18 , radio-frequency connector  16  may form an open circuit between the output of the power amplifier and the antenna. At the same time, radio-frequency connector  16  may electrically connect the output of the power amplifier to transmission line  18 . 
     Transmission line  18  may be connected to cable  22  using a connector such as radio-frequency connector  20 . Cable  22  is needed to connect shielded box  14  to radio communication tester  24 . Because radio communication tester  24  is typically fairly large, tester  24  is generally mounted on a stand or other mount that is at a distance from shielded box  14 . As a result, cable  22  may be fairly long and may be subject to wear and failure. 
     Computer  30  may be coupled to tester  24  via path  28  and may be coupled to device  12  using path  32  and the fixture in box  14 . Path  28  may be used to receive radio-frequency power measurements from tester  24 . Path  32  may be used to covey data signals to device  12 . During calibration measurements, path  32  may be used to direct power amplifier circuitry in device  12  to produce series of different gain settings (e.g., by producing a series of different analog gain control voltages or a series of digital gain control signals). Following measurements with radio communication tester, calibration data may be stored in device  12  over path  32 . The calibration data may be used by device  12  to ensure that the power amplifier circuitry in device  12  operates appropriately (i.e., in accordance with calibrated settings). 
     Radio communication testers such as tester  24  include circuitry for establishing bidirectional radio-frequency communications links with device  12  over paths  18  and  22 . Once this link has been established, device  12  may transmit radio-frequency signals to tester  24  and tester  24  can analyze these signals using circuitry such as spectrum analyzer  26 . In a typical scenario, a vector signal analyzer may be used in tester  24  to extract phase and quadrature (IQ) constellation data from received radio-frequency signals. Power calculations may be performed on the IQ constellation data (e.g., by computing vector lengths in an IQ plot). Average powers can be derived from the IQ constellation data (e.g., by averaging the powers of the symbol vectors in an IQ plot). 
     The need to rely on the use of radio communication testers such as tester  24  to perform calibration operations during manufacturing can be burdensome. The radio communication tester units are expensive because they include circuitry for establishing protocol-compliant bidirectional radio-frequency links with devices being tested. The inclusion of complex spectrum analyzer circuitry and the circuitry used to process IQ constellation data also adds to the cost of radio communication testers. Advanced options are sometimes available to help increase testing speeds, but these advanced options add additional cost and complexity to the test system and add to the burden of training personnel to properly operate the test equipment. Moreover, the use of shielded box  14  and cable  22  are not always desirable. Tester  24 , cable  22 , and box  14  consume valuable real estate on the test floor. Because cable  22  is generally fairly long, cable  22  is be subject to damage and therefore represents an undesirable possible point of failure in typical manufacturing environments. Yet another difficulty related to using conventional test systems of the type shown in  FIG. 1  relates to scalability. If it is desired to manufacture large quantities of wireless electronic devices in a short period of time, it may be impractical to purchase and operate a sufficient quantity of radio communications testers to calibrate all of the devices. In view of these challenges, it would be desirable to be able to provide improved ways in which to calibrate radio-frequency wireless electronic devices during manufacturing. 
     An illustrative calibration system in accordance with an embodiment of the present invention is shown in  FIG. 2 . As shown in  FIG. 2 , system  34  may include computer  70  and power sensor  72  for testing device under test  36 . Computer  70  may include storage  74  such as a hard drive, random-access-memory, solid state drive, non-volatile memory circuit, etc. Computer  70  may be a personal computer, a workstation, a test equipment station with one or more associated processors, a part of a network of computing equipment, or any other suitable computing equipment. Computer  70  may include input-output devices such as keyboards and pointing devices, a monitor, speakers, etc. 
     Radio-frequency power sensor  72  may be a power sensor head of the type that is sometimes attached to the main unit of a power meter. Power sensor  72  may include components such as diodes and/or resistors that are used to measure the amount of radio-frequency power that is being received by power sensor  72  from device under test  36  over path  62 . Power sensor  72  is typically an order of magnitude less expensive than a conventional radio communication tester such as radio communication tester  24  of  FIG. 1 . This is because power sensor  72  is preferably configured to perform only a single operation—namely, measure incoming radio-frequency power. Power sensor  72  need not include spectrum analyzer circuitry, data communications circuitry, or other complex electronics and therefore need not be as physically large or complex as radio communication tester  24 . 
     Because power sensor  72  is more compact than conventional test measurement instruments such as radio communication tester  24 , it is possible to mount power sensor  72  to a test fixture or in the immediate vicinity of a test fixture such as test fixture  80 . Test fixture  80  receives devices to be tested such as device  36 . Test fixture  80  may include pins or other conductors that mate with electrical paths in device  36  (e.g., to help complete path  78  between computer  70  and device  36 , to help complete path  62  between power sensor  72  and device  36 , to apply power to device  36 , etc.). Because power sensor  72  may be mounted close to fixture  80 , communications path  62  may be relatively short, avoiding the need for more extensive failure-prone cables such as cable  22  of  FIG. 1 . 
     Power sensor  72  may be coupled to computer  70  using a path such as path  76 . Path  76  may be, for example, a universal serial bus (USB) path or any other suitable path for conveying signals between power sensor  72  and  70 . If desired, data can flow primarily or entirely from power sensor  72  to computer  70  (i.e., path  76  may be a unidirectional data path). 
     Device under test  36  may be a handheld electronic device, a portable electronic device, or any other suitable device. For example, device under test  36  may be a handheld device that includes both long-range and short-range wireless communications functions that require or benefit from radio-frequency amplifier calibration. As an example, device  36  may be a mobile telephone, a mobile telephone with media player capabilities, a handheld computer, a remote control, a game player, a global positioning system (GPS) device, a laptop computer, a tablet computer, an ultraportable computer, a combination of such devices, or any other suitable electronic device. 
     Device  36  may include processing circuitry, input-output circuitry, and other circuitry  68 . Circuitry  68  may include storage. Storage in circuitry  68  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., battery-backed static or dynamic random-access-memory), etc. 
     Processing circuitry in circuitry  68  may be used to control the operation of device  36 . Processing circuitry in circuitry  68  may be based on a processor such as a microprocessor (also sometimes referred to as a central processor unit or application processor) and other suitable integrated circuits such as power management units, cellular telephone processor chips, audio codecs, etc. With one suitable arrangement, processing circuitry and storage in device  36  may be used to run software on device  36  such as internet browsing applications, voice-over-internet-protocol (VOIP) telephone call applications, email applications, media playback applications, operating system functions, etc. Processing circuitry and storage may be used in implementing suitable communications protocols. Communications protocols that may be implemented using circuitry  68  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 services, etc. 
     Input-output devices in circuitry  68  may be used to allow data to be supplied to device  36  and to allow data to be provided from device  36  to external devices. These input-output devices may include user input-output devices such as buttons, headsets, touch screens, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, cameras, etc. During normal operation, a user can control the operation of the device by supplying commands through user input devices. Display and audio devices may be included in the device such as liquid-crystal display (LCD) screens or other screens, light-emitting diodes (LEDs), and other components that present visual information and status data to a user. The device may also include audio equipment such as speakers and other devices for creating sound. Audio-video interface equipment such as jacks and other connectors for external headphones and monitors may also be included. 
     Device under test  36  includes wireless communications circuitry. The wireless communications circuitry typically includes 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. 
     In the illustrative arrangement of  FIG. 2 , device under test  36  has wireless communications circuitry such as baseband module  38 , power amplifier  52 , radio-frequency (RF) connector  56 , and antenna  66 . 
     Baseband module  38  may be implemented using one or more integrated circuits. Circuits such as module  38  may receive data to be transmitted from processing circuitry  68 . For example, circuits such as module  38  may receive outgoing data corresponding to email and other data messages, voice calls, etc. Circuits such as module  38  may also be used in converting received signals into messages, voice signals, etc. 
     As shown in the example of  FIG. 2 , baseband module  38  may include integrated power amplifier circuitry  50 . Power amplifier  50  may receive radio-frequency signals that are to be transmitted wirelessly over antenna  66  on input  82  and may provide corresponding amplified versions of these signals as an output on path  84 . External power amplifier circuitry such as external power amplifier circuit  52  may also be used in amplifying transmitted radio-frequency signals. Power amplifier  52  may receive radio-frequency signals on path  84  and may provide corresponding amplified signals on path  58 . If desired, radio-frequency signals may be amplified using only an internal power amplifier such as internal power amplifier  50  or only an external power amplifier such as external power amplifier  52 . The example of  FIG. 2  in which both internal and external power amplifiers are provided in device  36  is merely illustrative. The receiver path for device  36  may include a low-noise amplifier such as low-noise amplifier  53 . 
     Baseband modules such as baseband module  38  may include internal circuitry such as digital signal processing circuitry, microprocessor circuitry, analog-to-digital converter circuits, digital-to-analog circuits, and other circuits. These circuits are shown as control circuitry  44  and digital-to-analog converter  46  in  FIG. 2 . Control circuitry  44  may be used in generating radio-frequency signals to provide to path  82  in response to data received from processing circuitry  68 . Control circuitry  44  may also be used in controlling power amplifiers  50  and  52 . If desired, processing circuitry  68  may also be used in controlling power amplifiers  50  and  52 . Arrangements in which control circuitry  44  in baseband module  38  is used in controlling power amplifiers  50  and  52  during calibration operations are sometimes described herein as an example. 
     Control signals may be provided to amplifiers  50  and  52  using paths such as paths  48  and  54 . These control signals may be used to adjust the settings of power amplifiers  50  and  52 . The power amplifier settings may be used, for example, to adjust how many gain blocks are turned on in amplifiers  50  and  52 , may be used to regulate the gain settings of amplifiers  50  and  52 , may be used to provide digital control signals, may be used to regulate the power supply level for power amplifiers  50  and  52  (and thereby control power consumption and/or gain levels), may be used to regulate the biasing for amplifiers  50  and  52 , etc. With one suitable arrangement, which is described herein as an example, digital-to-analog converter  46  or other suitable control circuitry may be used to produce an analog or digital control signal on path  48  that adjusts the magnitude of the gain produced by amplifier  50  and control circuitry  44  may be used in producing a bias voltage or digital control signal on path  54  that controls the gain of power amplifier  52 . This arrangement is merely illustrative. If desired, other circuitry in device  36  may be used in adjusting the gains of power amplifiers  50  and  52 . 
     Antenna structures in device  36  are represented schematically as antenna  66  in  FIG. 2 . Any suitable antenna structures may be used in device  36 . For example, device  36  may have one antenna or may have multiple antennas. The antennas in device  36  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. As an example, a pentaband cellular telephone antenna may be provided at one end of device  36  and a dual band GPS/Bluetooth®/IEEE-802.11 antenna may be provided at another end of device  36 . Antennas may be formed using stamped metal, slot antenna structures, flex circuits having patterns of conductive traces, hybrid arrangements (e.g., hybrid planar inverted-F and hybrid inverted-F structures), etc. These are merely illustrative arrangements. Any suitable antenna structures may be used in device  36  if desired. The use of a single antenna  66  is sometimes described herein as an example. 
     During normal operation of device  36  by a user, the gain of the power amplifier circuitry  50  and  52  should be set to a level that ensures adequate signal strength for reliable communications, without exceeding maximum desired levels (e.g., maximum levels determined by power consumption and regulatory constraints). If the amount of radio-frequency power that is transmitted by device  36  during normal operation is too high, power may be wasted and regulatory limits on transmitted radiation may be exceeded. If the amount of radio-frequency power that is transmitted by device  36  during normal operation is too low, signal strength may be too weak to maintain an adequate communications link between device  36  and a base station, access point, or other external equipment. 
     Manufacturing variations may make it difficult or impossible to fabricate power amplifiers  50  and  52  with an accuracy that is sufficient to ensure that the desired transmitted radio-frequency power from device  36  will be precisely achieved when operating power amplifiers  50  and  52  at their default settings. As fabricated, power amplifiers  50  and  52  may have either too little gain or too much gain or may not have proper gain linearity across a certain dynamic range. If no calibration adjustments are made, device  36  may not function properly. It is therefore generally desirable to calibrate device  36  as part of the manufacturing process. Calibration operations may involve testing the performance of device  36  at a variety of gain settings for amplifiers  50  and  52  and providing corresponding calibration results. Calibration results may be stored in device  36  (e.g., in battery-backed volatile memory or in nonvolatile memory). As shown in  FIG. 2 , device  36  may have memory such as memory  40  and memory  42  for storing calibration results. Calibration information may be loaded into device  36  via path  78  (as an example). Memory  42  may be internal memory that is build into integrated circuits such as baseband module  38 . Memory  40  may be, for example, an external non-volatile memory (e.g., an erasable programmable read-only memory chip). During normal operation, baseband module  38  and other circuitry in device  36  may use the stored calibration information to ensure that device  36  transmits radio-frequency signals at appropriate powers. 
     During testing, antenna  66  need not be used. Rather, power sensor  72  may be coupled to output  58  of power amplifier  52  using radio-frequency connector  56 . Radio-frequency connector  56  may include a radio-frequency switch that connects path  58  to output  60  and path  64 . During testing, a probe or other structure associated with path  62  may be inserted into radio-frequency connector  56 . The presence of this structure may open the radio-frequency switch and connect path  58  to path  62 . In this configuration, radio-frequency signals from output  58  are routed to power sensor  72  over path  62  rather than antenna  66 . 
     During normal operation of device  36 , the probe or other structure associated with path  62  is not present (i.e., device under test  36  is no longer attached to test fixture  80 ). In this configuration, the radio-frequency switch in radio-frequency connector  56  moves into its normally closed position. The closed position of the radio-frequency switch in radio-frequency connector  56  allows radio-frequency signals to pass from path  58  to output  60  and path  64  for transmission through antenna  66 . 
     Test and calibration software for system  34  may be implemented on computer  70 . During calibration, computer  70  may use this software to direct device  36  to set its power amplifiers to various different gain settings. Gain settings may be adjusted by producing different control signals on power amplifier control path  48  and by producing different control signals on power amplifier control path  54 . With one suitable arrangement, which is described herein as an example, computer  70  directs device  36  to produce a constant bias signal on path  54  (e.g., using control circuitry  44  or other suitable circuitry), so that the gain of external power amplifier  52  is maintained at a constant level. While the gain of power amplifier  52  is being maintained at a constant level, computer  70  may direct baseband module  38  to use digital-to-analog converter  46  or other suitable circuitry to produce a variety of different analog control voltages or digital control signals on path  48 . These control signals, which are sometimes referred to as DAC values, can be received at the gain control input of power amplifier  50  to adjust the gain that is produced by power amplifier  50 . 
     Calibration may involve directing control circuitry  44  in baseband module  38  to supply suitable test signals on path  82  while operating power amplifier  50  at a variety of different gains. At the same time, computer  70  can use power sensor  72  to make measurements of the amount of radio-frequency power that is driven onto path  58 . The signals on path  58  are received by power sensor  72  via radio-frequency connector  56  and path  62 . 
     A graph of illustrative power measurements that may be made as a function of the DAC value on path  48  is shown in  FIG. 3 . In the graph of  FIG. 3 , DAC values (i.e., voltage settings for the output of digital-to-analog converter circuitry  46 ) are plotted on the horizontal axis and measured radio-frequency power values are plotted on the vertical axis. For each DAC value (or other suitable gain setting level), there is both a desired radio-frequency output level and an actual uncalibrated radio-frequency output level. The desired radio-frequency output level corresponds to the nominal value of radio-frequency signal power that should be produced when operating device  36  at a particular power amplifier gain setting. In some situations, the actual measured value for the radio-frequency signal power that are produced at that power amplifier gain setting are accurate, even before calibrating device  36 . More generally, however, the power amplifier circuitry of device  36  will exhibit deviations from perfect behavior due to manufacturing variations. In this situation, the measured output power from device  36  prior to calibration will differ somewhat from the desired output power. 
     In the example of  FIG. 3 , desired output values  88  of radio-frequency output power on path  58  are plotted as a function of DAC value (gain setting). As indicated by the bar-shaped icons  88  in the graph of  FIG. 3 , each desired output power may be characterized by a range of permissible DAC values centered about the most probable point. During calibration measurements, power sensor  72  may be used to make measurements  86 . If desired, the gain of power amplifiers  50  and  52  may be adjusted after one or more initial measurements, to ensure that the dynamic range of power sensor  72  is being used effectively. If these initial measurements indicate that the measured power  86  is significantly different than the desired power  88 , the gain of the power amplifier circuitry can be adjusted prior to making subsequent measurements. This may increase the accuracy of the subsequent measurements. 
     In the example of  FIG. 3 , connecting the icons  88  produces the desired operating characteristic curve for the radio-frequency amplifier circuitry in device under test  36  and shows how the actual uncalibrated output powers  86  for device under test  36  may follow the curve shape of the desired operating characteristic, but may be offset to a different power level or may have an incorrect slope along the curve. In this illustrative situation, manufacturing variations have resulted in power amplifier circuitry  50  and  52  that is producing a radio-frequency output power on path  58  that is larger than expected. The gain of power amplifiers  50  and  52  (i.e., the gain produced by amplifier  50  for a given DAC setting) is therefore too high and should be reduced. The amount by which the gain setting should be reduced (i.e., the calibrating offset that should be used in operating amplifier  50 ) may be computed by computer  70  following measurement of data  86  of  FIG. 3  and comparison to desired values  88 . This calibration information may then be provided to device  36  over path  78  and stored in memory  40  or memory  42  for use in calibrating the operation of device  36  in normal operation. 
     Wireless electronic devices may operate at more than one frequency. For example, a device may operate in a variety of communications bands such as an 1800 MHz cellular telephone band and a 1900 MHz cellular telephone band. Even within a given band, a device may operate at more than one frequency. These different frequencies are typically referred to as channels. 
     As shown in  FIG. 4 , calibration measurements with system  34  may involve multiple operating frequencies (e.g., multiple channels). During these measurements, computer  70  may direct baseband module  38  to produce test signals (sometimes called test tones) for various different channels and various different power amplifier gain settings. The test tones may be pure (unmodulated) tones or may be formed by modulating radio-frequency tones (e.g., using pseudorandom bit sequences). If unmodulated test tones are used, the spectrum of the test signals will not generally exhibit side bands and will therefore be somewhat narrower in frequency than when modulated test tones are used. The power measurements  86  that are made based on unmodulated test tones may therefore be shifted somewhat from the results that would be obtained using tones that have been modulated with real-life data or pseudorandom data. A correction factor can be applied by computer  70  to account for this mismatch when pure test tones are used instead of modulated test tones. 
     Baseband module  38  may use its control circuitry  44  (e.g., digital signal processing circuitry, microprocessor circuitry, etc.) in generating modulated and unmodulated test tones. Baseband module  38  may also use its control circuitry (including DAC  46 ) to generate the control signals for power amplifier  50  (and, if desired, for power amplifier  52 ). Baseband module  38  may take these actions in response to control signals from computer  70 . These control signals may be supplied to baseband module  38  over a data path or other suitable link  78 . Control signals for baseband module  38  may be provided in real time (e.g., to direct baseband module  38  to produce tones in a particular order) or may be provided in advance (e.g., in the form of a set of batch instructions for baseband module  38 ). If instructions are provided in advance, computer  70  may be used to invoke the test during calibration. 
     Calibrating measurements that involve more than one communications channel may be performed by measuring one channel (or other subset of channels) more extensively than others. This allows the shape of the gain setting versus radio-frequency output power curve to be gathered accurately in the more extensively measured channel. This shape may then be applied to the other channels, whose measurements are primarily used to generate appropriate calibrating offset data. In the  FIG. 4  example, more characterizing power measurements  86  have been made for channel C than for channels S. In a typical scenario, the channel or channels that are measured with relatively more measurements  86  may be characterized by five or more separate measurements, whereas the channel or channels that are measured with relatively fewer measurements  86  may be characterized using two, three, or four individual gain settings and corresponding power measurements (as an example). If desired, all channels may be measured the same number of times or each channel may be measured a potentially different number of times. These are merely illustrative examples. Any suitable pattern for making power measurements that cover a variety of gain settings, signal frequencies, and resulting radio-frequency powers may be used if desired. 
     A flow chart of illustrative steps involved in using a system of the type shown in  FIG. 2  in making calibrating radio-frequency signal power measurements is shown in  FIG. 5 . These measurements may be made using computing equipment such as computer  70  while device under test  36  is mounted to a suitable test fixture such as test fixture  80  or while the test equipment of system  34  is otherwise connected to device under test  36  to make calibrating measurements. 
     At step  90 , a desired channel is selected for which to perform testing. Any suitable order may be used for selecting channels to test. For example, system  34  may be used to test channels in order, from lowest frequency to highest frequency. System  34  may also be used to test channels in a pseudorandom order, in an ordered or pseudorandom fashion within each of multiple communications bands, etc. 
     At step  92 , computer  70  may be used to direct device under test  36  to generate a radio-frequency test tone on path  82  that corresponds to the frequency of the selected channel. Instructions for device under test  36  may be supplied to device under test  36  via path  78 . Baseband module  38  may use control circuitry  44  to respond to the test tone generation instructions from computer  70 . The test tone may be a pure carrier tone or may be a modulated tone (e.g., a tone that is modulated by baseband module  38  using a pseudorandom bit pattern). Because it is not necessary to set up a full protocol-compliant bidirectional radio-frequency link with external test equipment during step  92 , the time required to generate the test tone may be modest, facilitating rapid testing. 
     At step  94 , computer  70  may be used to direct device under test  36  to adjust power amplifiers such as power amplifiers  50  and  52  to produce desired amounts of gain for the radio-frequency test tone. If desired, control circuitry  44  may, for example, produce a constant bias or may direct external integrated circuits to produce a constant bias on path  54  for power amplifier  52  while simultaneously using digital-to-analog converter  46  or other suitable circuitry to produce a desired analog control voltage or digital control signal on path  48  that adjusts power amplifier  50  so that power amplifier  50  exhibits a desired amount of gain in amplifying the radio-frequency test tone signal on path  82 . 
     After a desired radio-frequency test tone is being produced and after amplifier circuitry  50  and  52  has been adjusted to produce a desired amount of gain for the radio-frequency test tone, computer  70  may use power sensor  72  to gather a power measurement of the radio-frequency signal that is being produced on path  58  (step  96 ). During this test measurement, the radio-frequency signal on path  58  may be routed to power sensor  72  via radio-frequency connector  56  and transmission line path  62  (e.g., a radio-frequency cable). 
     Test measurement results may be stored at step  98 . Computer  70  may store measurement results in storage  74  in any desired format (e.g., tables, etc.). 
     As indicated by line  104 , if additional test measurements are desired, processing may loop back to steps  90 ,  92 ,  94 ,  96 , and  98 . During these calibration measurements, calibration system  34  may step through various different test tone frequencies (wireless channels) and various different gain settings for amplifier circuitry  50  and  52  (e.g., DAC settings for power amplifier  50 ) using any suitable pattern. For example, channels may be calibrated one at a time while gain of the power amplifier circuitry (i.e., the gain of amplifier  50 ) may be adjusted by stepping through the possible gains settings from a desired minimum to a desired maximum value. Alternatively, all of the calibration measurements for a particular gain setting may be made by adjusting the frequency of the test tone while holding the gain setting constant. If desired, combinations of these approaches may be used (e.g., to produce measurement patterns in which both channel settings and gain settings are adjusted in each pass through loop  104 ). 
     After power measurements have been completed, computer  70  may process the test data to produce calibration data for the device under test. For example, if it is determined that each measured power is about 10% higher than expected, calibration data may be produced that will inform device under test  36  to reduce the gain setting of its power amplifier circuitry (e.g., power amplifier  50 ) by 10% to compensate. The calibration data that is produced at step  100  may be provided to device  36  over path  78 . Baseband module  38  may store the calibration data in memory such as internal memory  42  or external memory  40 . During operation by a user, a calibrated device  36  will use the calibration data to make necessary corrections to the control signals used in controlling power amplifier circuitry  50  and  52  (e.g., by adjusting DAC settings on path  48 ), thereby ensuring that device  36  produces desired output power levels. 
     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: 20080528
Publication Date: 20141202
Grant Date: 20141202
Priority Date: 20080528
Inventors: TAKEYA TOMOKI
GREGG JUSTIN
CABALLERO RUBEN
Assignee: APPLE INC
CPC Classifications: [{"code": "H04B1/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B17/0007", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/003", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B1/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B17/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B1/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/101", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/101", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 41380436