PATENT DOCUMENT

Publication Number: US-9146304-B2
Application Number: US-201213608973-A
Country: US
Kind Code: B2

Title: Optical proximity sensor with ambient light and temperature compensation

Abstract:
An electronic device may be provided with a proximity sensor. The proximity sensor may include a light source such as a light-emitting diode and a light detector such as a photodiode. The light-emitting diode may be driven with an alternating current drive signal so that alternating current light is produced. The alternating current light may reflect off of an external object and may be received by the photodiode. The photodiode may receive a direct current light signal associated with the presence of ambient light. The efficiency of the photodiode may be affected by the level of ambient light and the efficiency of the light-emitting diode may be affected by the temperature of the light-emitting diode. Ambient light correction circuitry and temperature correction circuitry may be used to ensure that proximity sensor readings are not adversely affected by changes in operating temperature and ambient lighting conditions.

Claims:
What is claimed is: 
     
       1. A light-based proximity sensor, comprising:
 a light source that emits light towards an external object; 
 a photodetector that is configured to measure light from the light source that has reflected off of the external object; 
 an ambient light correction circuit that corrects signals from the photodetector for photodetector efficiency changes due to changes in how much ambient light is received by the photodetector; and 
 an efficiency correction factor generator interposed between the photodetector and the ambient light correction circuit, wherein the ambient light correction circuit comprises a first input that receives an efficiency correction factor signal from the efficiency correction factor generator and a second input that receives an uncorrected photodetector signal from the photodetector. 
 
     
     
       2. The light-based proximity sensor defined in  claim 1  further comprising a temperature correction circuit that corrects signals from the photodetector for light-emitting-diode efficiency changes due to changes in temperature. 
     
     
       3. The light-based proximity sensor defined in  claim 1  wherein the light source comprises a light-emitting diode that emits an alternating current infrared light signal. 
     
     
       4. The light-based proximity sensor defined in  claim 1  further comprising a low pass filter interposed between the photodetector and the ambient light correction circuit. 
     
     
       5. The light-based proximity sensor defined in  claim 1  further comprising a transimpedance amplifier that receives a signal from the photodetector and that outputs a corresponding voltage signal on a node. 
     
     
       6. The light-based proximity sensor defined in  claim 5  further comprising first and second circuit branches coupled to the node, wherein the first circuit branch includes a low pass filter and extracts a direct current signal from the voltage signal on the node and wherein the second circuit branch includes a high pass filter and extracts an alternating current signal from the voltage signal on the node. 
     
     
       7. The light-based proximity sensor defined in  claim 6  wherein the first and second circuit branches include respective first and second analog-to-digital converters. 
     
     
       8. The light-based proximity sensor defined in  claim 6  wherein the ambient light correction circuit receives a signal from the first circuit branch that is proportional to the direct current signal and receives a signal from the second circuit branch that is proportional to the alternating current signal. 
     
     
       9. The light-based proximity sensor defined in  claim 6  wherein the first circuit branch includes a storage circuit that stores a digital efficiency trim value and a scaling circuit configured to scale the extracted direct current signal based on the stored digital efficiency trim value. 
     
     
       10. The light-based proximity sensor defined in  claim 6  wherein the first branch includes a look-up table that receives the extracted direct current signal and that provides a corresponding output signal to the ambient light correction circuit. 
     
     
       11. A light-based proximity sensor, comprising:
 a light-emitting diode that is configured to emit light towards an external object; 
 a photodetector that is configured to measure light from the light-emitting diode that has reflected off of the external object; 
 a low-pass filter that extracts only a direct current component from a photodetector signal from the photodetector; 
 a high-pass filter that extracts only an alternating current component from the photodetector signal; 
 an efficiency correction factor generator that generates an efficiency correction factor based on the direct current component; 
 an ambient light correction circuit that receives the efficiency correction factor and the alternating current component and generates a corresponding corrected photodetector signal; and 
 a temperature correction circuit that corrects the corrected photodetector signal from the ambient light correction circuit for light-emitting diode efficiency changes due to changes in temperature of the light-emitting diode. 
 
     
     
       12. The light-based proximity sensor defined in  claim 11  wherein the temperature correction circuit has a first input that receives the corrected photodetector signal and a second input that receives a temperature efficiency correction factor that is applied to the corrected photodetector signal by the temperature correction circuit. 
     
     
       13. The light-based proximity sensor defined in  claim 12  further comprising a temperature sensor that gathers temperature measurements. 
     
     
       14. The light-based proximity sensor defined in  claim 13  further comprising an analog-to-digital converter that converts the temperature measurements into digital temperature signals, wherein the temperature efficiency correction factor is proportional to the temperature measurements. 
     
     
       15. Proximity sensor circuitry, comprising:
 a photodiode that is configured to receive an alternating current light signal emitted by a light-emitting diode and reflected from an external object and that is configured to receive a direct current ambient light signal; 
 a transimpedance amplifier that produces a photodiode signal having an alternating current component associated with the alternating current light signal and a direct current component associated with the direct current ambient light signal; 
 a first filter that extracts the alternating current component; 
 a second filter that extracts the direct current component; and 
 a correction circuit with a first input that receives the alternating current component and a second input that receives the direct current component, wherein the correction circuit is configured to produce a corresponding corrected photodiode signal that is corrected for efficiency changes due to fluctuations in how much ambient light is received by the photodiode. 
 
     
     
       16. The proximity sensor circuitry defined in  claim 15  wherein the first filter comprises a high pass filter, the proximity sensor circuitry further comprising an analog-to-digital converter and demodulator interposed between the high pass filter and the correction circuit. 
     
     
       17. The proximity sensor circuitry defined in  claim 15  wherein the second filter comprises a low pass filter, the proximity sensor circuitry further comprising an analog-to-digital converter and a look-up table interposed between the low pass filter and the correction circuit. 
     
     
       18. The proximity sensor circuitry defined in  claim 15  wherein the second filter comprises a low pass filter, the proximity sensor circuitry further comprising an analog-to-digital converter and an efficiency correction factor generator interposed between the low pass filter and the correction circuit. 
     
     
       19. The proximity sensor circuitry defined in  claim 15 , wherein the first filter extracts only the alternating current component, and wherein the second filter extracts only the direct current component.

Description:
BACKGROUND 
     This relates generally to electronic devices and, more particularly, to electronic devices with proximity sensors. 
     Electronic devices such as cellular telephones are sometimes provided with proximity sensors. For example, a cellular telephone may be provided with a proximity sensor that is located near an ear speaker on a front face of the cellular telephone. The front face of the cellular telephone may also contain a touch screen display. The proximity sensor may be used to determine when the cellular telephone is near to the head of a user. When not in proximity to the head of the user, the cellular telephone may be placed in a normal mode of operation in which the touch screen display is used to present visual information to the user and in which the touch sensor portion of the touch screen is enabled. In response to determining that the cellular telephone has been brought into the vicinity of the user&#39;s head, the display may be disabled to conserve power and the touch sensor on the display may be temporarily disabled to avoid inadvertent touch input from contact between the user&#39;s head and the touch sensor. 
     A proximity sensor for use in a cellular telephone may be based on an infrared light-emitting diode and a corresponding infrared photodiode. During operation, the light-emitting diode may emit infrared light outwards from the front face of the cellular telephone. The emitted light may be reflected from external objects such as the head of a user. When the cellular telephone is not in the vicinity of a user&#39;s head, the infrared light will not be reflected towards the photodiode and only small amounts of reflected light will be detected by the photodiode. When the cellular telephone is adjacent to the user&#39;s head, the emitted light from the infrared light-emitting diode will be reflected from the user&#39;s head and detected by the photodiode. 
     To reduce the impact of ambient light on the operation of a light-based proximity sensor, an alternating current (AC) signal may be used in driving the light-emitting diode. Corresponding detected signals from the photodiode detector may be filtered to separate direct current (DC) signals that are produced when ambient light illuminates the photodetector from the AC proximity sensor signal associated with the light-emitting diode. 
     Although DC signals can be filtered out of the photodetector signal, the performance of the photodetector in receiving the AC proximity sensor signal may be influenced by the magnitude of the DC signals. Temperature changes can also affect photodetector performance and light-emitting diode performance. Light-emitting diode current-to-optical-power conversion efficiency tends to decrease with increasing temperature and photodetector light-to-electrical current conversion efficiency tends to increase with increasing DC current from ambient light exposure. Environmental factors such as changes in ambient temperature and changes in ambient light exposure may therefore have an adverse impact on the accuracy of proximity sensor measurements. 
     It would therefore be desirable to be able to provide proximity sensors with enhanced immunity to environmental effects. 
     SUMMARY 
     An electronic device may be provided with a proximity sensor. The proximity sensor may include a light source such as an infrared light-emitting diode and a light detector such as a photodiode. The light-emitting diode may be driven with an alternating current drive signal so that an alternating current proximity sensor light signal is produced. The proximity sensor light may reflect off of an external object and may be received by the photodiode. The photodiode may also receive a direct current light signal due to the presence of ambient light. 
     Proximity sensor circuitry may process photodiode signals from the photodiode. The proximity sensor circuitry may include a transimpedance amplifier for converting current signals from the photodiode into a voltage signal. First and second circuit branches may be connected to the output of the amplifier. The first circuit branch may include a low pass filter for extracting a direct current component of the voltage that is representative of the amount of ambient light that is received by the photodiode. The second circuit branch may include a high pass filter for extracting an alternating current proximity sensor component of the voltage that is representative of the alternating current proximity sensor light signal. 
     The second branch may include an analog-to-digital converter and demodulator for converting the extracted alternating current component of the voltage into a digital uncorrected photodiode signal. The first branch may include an efficiency correction factor generator. The efficiency correction factor generator may generate a correction factor based on a digital version of the extracted direct current component of the voltage. 
     An ambient light correction circuit may receive the uncorrected photodiode signal from the first branch and may apply the correction factor to correct the photodiode signal for efficiency changes due to fluctuations in ambient light level. Temperature corrections may be made using a temperature correction circuit that receives input from a temperature sensor. 
     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 perspective view of an illustrative electronic device with a proximity sensor in accordance with embodiments of the present invention. 
         FIG. 2  is a schematic diagram of an illustrative electronic device with a proximity sensor in accordance with an embodiment of the present invention. 
         FIG. 3  is a diagram showing how a light-based proximity sensor may have a light source that emits light and a light detector that detects the emitted light following reflection from an external object in accordance with an embodiment of the present invention. 
         FIG. 4  is a circuit diagram of a proximity sensor processing circuit in accordance with an embodiment of the present invention. 
         FIG. 5  is a circuit diagram of a circuit based on a look-up table for correcting photodiode signals to remove efficiency variations due to changes in direct current photodiode current in accordance with an embodiment of the present invention. 
         FIG. 6  is a circuit diagram of a circuit for correcting photodiode signals to remove efficiency variations due to changes in ambient temperature in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     An electronic device may use one or more proximity sensors to detect external objects such as the head of a user. As an example, an electronic device may use an infrared-light-based proximity sensor to gather proximity data. During operation, proximity data from the proximity sensor may be used to determine whether or not the electronic device is near to the user&#39;s head so that the electronic device can take appropriate action. The electronic device may, for example, deactivate touch screen functionality in a display when it is determined that the device is adjacent to the user&#39;s head. 
     A light-based proximity sensor may be used that includes a light source such as an infrared light-emitting diode and a light detector such as a photodiode. To ensure accurate proximity sensor operation, correction circuitry can be included within the processing circuitry that is used to handle signals from the photodiode. The correction circuitry may be used to correct (compensate) the signals from the photodiode for changes in light-emitting diode and photodetector efficiency due to changed operating conditions, thereby minimizing inaccuracies due to environmental effects such as temperature fluctuations and ambient light fluctuations. 
     An illustrative electronic device that may be provided with a proximity sensor that has correction circuitry is shown in  FIG. 1 . Electronic devices such as device  10  of  FIG. 1  may be cellular telephones, media players, other handheld portable devices, somewhat smaller portable devices such as wrist-watch devices, pendant devices, or other wearable or miniature devices, gaming equipment, tablet computers, notebook computers, desktop computers, televisions, computer monitors, computers integrated into computer displays, or other electronic equipment. 
     As shown in the example of  FIG. 1 , device  10  may include a display such as display  14 . Display  14  may be mounted in a housing such as housing  12 . Housing  12  may have upper and lower portions joined by a hinge (e.g., in a laptop computer) or may form a structure without a hinge, as shown in  FIG. 1 . Housing  12 , which may sometimes be referred to as an enclosure or case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials. Housing  12  may be formed using a unibody configuration in which some or all of housing  12  is machined or molded as a single structure or may be formed using multiple structures (e.g., an internal frame structure, one or more structures that form exterior housing surfaces, etc.). 
     Display  14  may be a touch screen display that incorporates a layer of conductive capacitive touch sensor electrodes such as electrodes  20  or other touch sensor components (e.g., resistive touch sensor components, acoustic touch sensor components, force-based touch sensor components, light-based touch sensor components, etc.) or may be a display that is not touch-sensitive. Capacitive touch screen electrodes  20  may be formed from an array of indium tin oxide pads or other transparent conductive structures. 
     Display  14  may include an array of display pixels such as pixels  21  formed from liquid crystal display (LCD) components, an array of electrophoretic display pixels, an array of plasma display pixels, an array of organic light-emitting diode display pixels, an array of electrowetting display pixels, or display pixels based on other display technologies. The brightness of display  14  may be adjustable. For example, display  14  may include a backlight unit formed from a light source such as a lamp or light-emitting diodes that can be used to increase or decrease display backlight levels (e.g., to increase or decrease the brightness of the image produced by display pixels  21 ) and thereby adjust display brightness. Display  14  may also include organic light-emitting diode pixels or other pixels with adjustable intensities. In this type of display, display brightness can be adjusted by adjusting the intensities of drive signals used to control individual display pixels. 
     Display  14  may be protected using a display cover layer such as a layer of transparent glass or clear plastic. Openings may be formed in the display cover layer. For example, an opening may be formed in the display cover layer to accommodate a button such as button  16 . An opening may also be formed in the display cover layer to accommodate ports such as speaker port  18 . 
     In the center of display  14  (e.g., in the portion of display  14  within rectangular region  22  of  FIG. 1 ), display  14  may contain an array of active display pixels such as pixels  21 . Region  22  may therefore sometimes be referred to as the active region of display  14 . The rectangular ring-shaped region that surrounds the periphery of active display region  22  may not contain any active display pixels and may therefore sometimes be referred to as the inactive region of display  14 . The display cover layer or other display layers in display  14  may be provided with an opaque masking layer in the inactive region to hide internal components from view by a user. Openings may be formed in the opaque masking layer to accommodate light-based components. For example, an opening may be provided in the opaque masking layer to accommodate an ambient light sensor such as ambient light sensor  24 . 
     If desired, an opening in the opaque masking layer may be filled with an ink or other material that is transparent to infrared light but opaque to visible light. As an example, light-based proximity sensor  26  may be mounted under this type of opening in the opaque masking layer of the inactive portion of display  14 . 
     Light-based proximity sensor  26  may include a light transmitter such as light source  28  and a light sensor such as light detector  30 . Light source  28  may be an infrared light-emitting diode and light detector  30  may be a photodetector based on a transistor or photodiode (as examples). Examples of proximity sensors that are based on photodiodes are sometimes described herein as an example. Other types of proximity sensor may be used if desired. During operation, proximity sensor detector  30  may use the photodiode or other light detector to gather light from source  28  that has reflected from nearby objects. By using correction circuitry in processing photodiode signals from the light detector in the proximity sensor, proximity sensing operations can be provided with enhanced immunity to environmental variables such as temperature and ambient light conditions. 
     Proximity sensor  26  may detect when a user&#39;s head, a user&#39;s fingers, or other external object is in the vicinity of device  10  (e.g., within 5 cm or less of sensor  26 , within 1 cm or less of sensor  26 , or within other suitable distance of sensor  26 ). 
     During operation of device  10 , proximity sensor data from proximity sensor  26  may be used in controlling the operation of device  10 . For example, when proximity sensor measurements from sensor  26  indicate that device  10  is in the vicinity of the user&#39;s head (and that the user&#39;s head is in the vicinity of device  10 ), device  10  can be placed in a close proximity mode. When operating in the close proximity mode, the functionality of device  10  can be altered to ensure proper operation of device  10 . For example, touch screen input can be temporarily disabled so that touch events related to contact between the user&#39;s head and one or more of capacitive touch sensor electrodes  20  can be ignored. Display brightness can also be turned down partly or fully by disabling a backlight in device  10  or by otherwise temporarily disabling display pixels  21 , thereby conserving power. In the event that proximity sensor data indicates that device  10  and the user&#39;s head are not adjacent to each other, (e.g., when it is determined that device  10  is more than 1 cm from the user&#39;s head, is more than 5 cm from the user&#39;s head, etc.), device  10  can be placed in a normal (non-close-proximity) operating mode. Other operations may be controlled in device  10  based on proximity sensor data from proximity sensor  26 . The use of proximity sensor data to control display functions is merely illustrative. 
     A schematic diagram of device  10  showing how device  10  may include sensors and other components is shown in  FIG. 2 . As shown in  FIG. 2 , electronic device  10  may include control circuitry such as storage and processing circuitry  40 . Storage and processing circuitry  40  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. Processing circuitry in storage and processing circuitry  40  may be used in controlling the operation of device  10 . The processing circuitry may be based on a processor such as a microprocessor and other suitable integrated circuits. With one suitable arrangement, storage and processing circuitry  40  may be used to run software on device  10 , such as internet browsing applications, email applications, media playback applications, operating system functions, software for capturing and processing images, software implementing functions associated with gathering and processing sensor data, software that makes adjustments to display brightness and touch sensor functionality, etc. 
     Input-output circuitry  32  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. 
     Input-output circuitry  32  may include wired and wireless communications circuitry  34 . Communications circuitry  34  may include radio-frequency (RF) transceiver circuitry formed from one or more integrated circuits, power amplifier circuitry, low-noise input amplifiers, passive RF components, one or more antennas, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications). 
     Input-output circuitry  32  may include input-output devices  36  such as button  16  of  FIG. 1 , joysticks, click wheels, scrolling wheels, a touch screen such as display  14  of  FIG. 1 , other touch sensors such as track pads or touch-sensor-based buttons, vibrators, audio components such as microphones and speakers, image capture devices such as a camera module having an image sensor and a corresponding lens system, keyboards, status-indicator lights, tone generators, key pads, and other equipment for gathering input from a user or other external source and/or generating output for a user. 
     Sensor circuitry such as sensors  38  of  FIG. 2  may include an ambient light sensor for gathering information on ambient light levels such as ambient light sensor  24 . Ambient light sensor  24  may include one or more semiconductor detectors (e.g., silicon-based detectors) or other light detection circuitry. Sensors  38  may also include proximity sensor components. Sensors  38  may, for example, include a dedicated proximity sensor such as proximity sensor  26  and/or a proximity sensor formed from touch sensors  20  (e.g., a portion of the capacitive touch sensor electrodes in a touch sensor array for display  14  that are otherwise used in gathering touch input for device  10  such as the sensor electrodes in region  22  of  FIG. 1 ). Proximity sensor components in device  10  may, in general, include capacitive proximity sensor components, infrared-light-based proximity sensor components, proximity sensor components based on acoustic signaling schemes, or other proximity sensor equipment. Sensors  38  may also include a pressure sensor, a temperature sensor, an accelerometer, a gyroscope, and other circuitry for making measurements of the environment surrounding device  10 . 
     During operation of device  10 , device  10  may use proximity sensor  26  to monitor the position of device  10  relative to external objects such as a user&#39;s head and can take suitable actions based on an analysis of the proximity sensor data that has been gathered. As shown in  FIG. 3 , proximity sensor  26  may include light source  28  and light detector  30 . Light source  28  may be an infrared light-emitting diode that emits infrared light  42 . Light detector  30  may be a photodiode or other semiconductor device that detects light  44  (e.g., light  42  that has reflected from the head of a user or other external object  46 ). By measuring the magnitude of reflected proximity sensor light  44  at light detector  30 , device  10  can determine whether external object  46  is in the vicinity of device  10 . 
     Proximity sensor circuitry of the type that may be used in processing proximity sensor signals is shown in  FIG. 4 . As shown in  FIG. 4 , proximity sensor circuitry  50  may be used to process signals gathered by photodiode  30  (or other suitable photodetector). Photodiode  30  may be configured to receive light-emitting diode light  44  and ambient light  45 . Light-emitting diode light  44  may be produced by light-emitting diode  28  ( FIG. 3 ). Ambient light  45  may be produced by sunlight and electrical lighting in the vicinity of device  10 . Ambient light  45  typically has low (DC) frequencies and is sometimes referred to as DC light. Light source  28  may produce AC light  42  that is modulated with an alternating current (AC) waveform (e.g., a 1-1000 kHz sine wave or AC waveforms at other suitable frequencies). As a result, the frequency of AC light  44  is generally significantly larger than DC ambient light  45 . This allows filter circuitry in circuitry  50  to extract the proximity sensor signal that corresponds to reflected light  44  from background light  45 . 
     Photodiode  30  may have a first terminal coupled to power supply  52  (powered by a power supply voltage Vdd) and a second terminal coupled to negative input  84  of amplifier  56 . Positive input  86  of amplifier  56  may be configured to receive a reference voltage Vref. Feedback resistor  54  may be coupled between output node  58  of amplifier  56  and input  84 , thereby forming transimpedance amplifier  88 . Transimpedance amplifier  88  serves as a current-to-voltage signal converter that converts photodiode current Isig into a corresponding voltage Vsig on node  58 . 
     Isig has both AC and DC components. The AC component of Isig (called Isigac) is proportional to AC light  44  from light source  28  that has reflected off of object  46  ( FIG. 3 ) and that has been detected by photodiode  30 . The DC component of Isig (called Isigdc) is proportional to DC light  45 . The magnitude of signal Isigac is representative of the proximity of external object  46  to device  10  and may sometimes be referred to as a proximity sensor signal. The magnitude of signal Isigdc is associated with the amount of ambient light in the vicinity of device  10  and is therefore filtered out of Isig using circuitry  50 . The magnitude of Isigdc can also be used as an input to a correction circuit that corrects Isigac for changes in photodiode efficiency that results from changes in DC ambient light levels. 
     Voltage Vsig on node  58  has a DC component Vsigdc that is proportional to Isigdc and has an AC component Vsigac that is proportional to Isigac. As shown in  FIG. 4 , circuitry  50  may contain parallel first and second branches such as branch  90  and branch  92  that are coupled to node  58  at one end and to correction circuit  76  at an opposing end. Branch  90  may include a high pass filter such as high pass filter  60 . Voltage Vsig is received by the input of high pass filter  60 . High pass filter  60  has a cut-off frequency that is configured to block the DC component of Vsig (i.e., Vsigdc) while passing the AC component of Vsig (i.e., Vsigac). Analog-to-digital converter  62  in branch  92  may be used to covert Vsigac from an analog voltage to a digital representation of the analog voltage. Demodulator  64  may be used to convert the peak voltages in the digital version of AC signal Vsigac to a DC (digital) signal representative of the magnitude of AC light  44  that has been received by photodiode  30 . The signal at the output of modulator  64  is uncorrected for sources of error such as ambient-light-induced changes in photodetector efficiency and temperature-induced changes in photodetector efficiency and may therefore sometimes be referred to as an uncorrected photodiode signal (UNCORRECTED_PD in  FIG. 4 ). 
     Branch  90  of circuitry  50  may be used to extract the DC component of signal Vsig and to use this signal in generating an error correction signal (error correction factor ECF). Low pass filter  66  in branch  90  may have a cutoff frequency that allows DC signals such as Vsigdc to pass while blocking AC signals such as Vsigac, thereby allowing low pass filter  66  to extract Vsigdc from Vsig. Analog-to-digital converter  68  may convert the analog version of Vsig into a corresponding digital version of Vsig called Vsigdc (digital). 
     Efficiency correction factor generator  70  may receive the DC and AC components of the photodiode signal from the output of analog-to-digital converter  68  and demodulator  64  as inputs and may produce a corresponding scaled output (efficiency correction factor) ECF. The efficiency of photodiode  30  tends to increase with increasing DC current (due to increasing ambient light  45 ). If not taken into account, the variability of the efficiency of photodiode  30  will make the AC proximity sensor signal that is extracted from photodiode  30  inaccurate. 
     As shown in  FIG. 4 , a digital efficiency trim value for efficiency correction factor generator circuit  70  may be stored in storage  72 . This trim value may be used as an input to circuit  74  (e.g., a digital multiplier or other scaling circuitry) to adjust the ratio between input Vsigdc (digital) and output ECF. The ratio between Vsigdc (digital) and ECF is preferably selected so that ECF can be used to remove the impact on photodiode efficiency that is experienced by photodiode  30  as a function of ambient light exposure  45 . Signal ECF may also be made proportional to signal UNCORRECTED_PD so that more correction is applied to larger UNCORRECTED_PD signals. Signal ECF may be provided to the negative input of correction circuit  76  (e.g., an adder or other combiner). Signal UNCORRECTED_PD may be supplied to the positive input of correction circuit  70 . Correction circuit  70  may correct signal UNCORRECTED_PD by applying efficiency correction factor ECF. In this way, the DC-photodiode-current dependence of photodiode efficiency can be removed from signal UNCORRECTED_PD to produce corrected signal CORRECTED_PD on line  82 . Signal CORRECTED_PD can serve as accurate ambient-light-corrected proximity sensor data for use in operating electronic device  10 . 
     As shown in  FIG. 5 , signal Vsigdc (digital) may, if desired, be processed using an efficiency correction factor generator  70  that is based on digital circuitry such as look-up table  98 . Look-up table  98  may contain entries that map a set of expected Vsigdc (digital) values to a corresponding set of correction factor signals ECF. In effect, the functions of digital efficiency trim value  72  of  FIG. 4  and the associated scaling function of circuit  74  of  FIG. 4  may be embodied into the entries of table  98 . During operation, correction circuit  76  may apply efficiency correction factor ECF to signal UNCORRECTED_PD on line  78  to produce accurate ambient-light-corrected proximity sensor data (signal CORRECTED_PD) on line  82 . 
     As shown in  FIG. 6 , circuitry  50  may, if desired, include temperature correction circuitry  100 . Temperature correction circuitry  100  may be used to correct for temperature-induced changes in light-emitting diode efficiency for light-emitting diode  28 . 
     Temperature correction circuitry  100  may include a temperature sensor such as temperature sensor  102  for use in monitoring the ambient temperature of device  10 . Temperature sensor  102  may produce an analog output that is received by analog-to-digital converter  104 . Analog-to-digital converter  104  may provide a digital version of the temperature signal measured by temperature sensor  102  to an optional filter circuit such as noise filter  106  (e.g., an averaging circuit). 
     The output of noise filter  106  represents a correction factor based on the temperature measured by temperature sensor  102  and is applied to input  112  of correction circuit  108 . If desired, scaling circuitry and/or a look-up table such as look-up table of  FIG. 5  may be used to ensure that the magnitude of temperature efficiency correction factor TECF that is produced on line  112  is appropriate for correcting CORRECTED_PD for light-emitting diode efficiency changes induced by temperature changes. The look-up table or other scaling circuit may, for example, be interposed between noise filter  106  and correction circuit  108  or may be incorporated into circuitry  106 . 
     During operation, correction circuit  108  may receive ambient-light-corrected proximity sensor signal CORRECTED_PD on line  82  and may provide a corresponding temperature-corrected output signal OUT on line  110  based on light-emitting diode temperature efficiency correction factor TECF on path  112 . 
     In the example of  FIG. 6 , both temperature-based light-emitting-diode-efficiency-change corrections and ambient-light-based photodiode efficiency change corrections have been made using circuitry  50 . This is merely illustrative. Proximity sensor signal processing circuitry such as circuitry  50  may be provided with only ambient-light-based photodiode efficiency compensation circuitry or may be provided with only temperature-based light-emitting-diode efficiency compensation circuitry. Additional types of correction circuitry (e.g., circuitry for correcting for other changes in photodiode efficiency due to fluctuations in operating conditions) may be included in circuitry  50 , 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. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20120910
Publication Date: 20150929
Grant Date: 20150929
Priority Date: 20120910
Inventors: LAND BRIAN R.
ZHENG DONG
Assignee: APPLE INC
CPC Classifications: [{"code": "H04W52/0254", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/497", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S17/88", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/0254", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04M2250/22", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01S17/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04M2250/22", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04M2250/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01S7/493", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04M2250/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01S17/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S17/88", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/497", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/493", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04M2250/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W52/0254", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S17/88", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/497", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S17/026", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04M2250/22", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04M1/72522", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/493", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04M1/72403", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04M1/72403", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y02D30/70", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y02D30/70", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 50232273