On May 15, 2014, the US Patent & Trademark Office published a patent application from Apple that reveals their work on a next generation ambient light sensor system that will improve display clarity on iDevices when in bright environments.

Apple's Patent Background

Cellular telephones and other portable devices with displays such a tablet computers sometimes contain ambient light sensors. An ambient light sensor can detect when a portable device is in a bright light environment. For example, an ambient light sensor can detect when a portable device is exposed to direct sunlight. When bright light is detected, the portable device can automatically increase the brightness level of the display to ensure that images on the display remain visible and are not obscured by the presence of the bright light. In dark surroundings, the display brightness level can be reduced to save power and provide a comfortable reading environment.

With conventional devices, ambient light sensors are implemented using first and second silicon photosensors to receive ambient light. The first photosensor is used to detect an amount of infrared light in the ambient light, whereas the second photosensor is used to detect an amount of visible light and infrared light in the ambient light. Readings from the first and second photosensors are subtracted to obtain a corresponding visible light level. This visible light level is then used to increase or decrease the display brightness level accordingly.

Computing visible light levels in this way, however, requires the infrared sensing capabilities of the first and second photosensors to be accurate and consistent relative to one another. Any mismatch in infrared sensitivity can cause the visible light reading to be erroneous. Designing and manufacturing two silicon photosensors that are well-matched in performance may be challenging.

It would therefore be desirable to be able to provide improved ambient light sensor systems for electronic devices.

Apple Invents Ambient Light Sensors with Infrared Compensation

Apple's invention relates to sensors and, more particularly, to improved ambient light sensors for electronic devices.

An electronic device may have a display with a brightness that is adjusted based on ambient light data from one or more ambient light sensors. The electronic device may be operated in an environment in which the electronic device is exposed to ambient light from at least a given one of a plurality of light sources each producing a different respective ratio of infrared light to visible light.

For example, the ambient light may be one of light-emitting-diode (LED) light, fluorescent light, solar light, incandescent light, tungsten light, a mix of some of these lights, and/or other types of light.

The ambient light sensor may be used to characterize the ambient light to determine which of the plurality of light sources produced the ambient light. The electronic device may also include control circuitry for adjusting the display brightness based at least partly on which of the plurality of light sources produced the ambient light. In particular, the electronic device may include at least one silicon-based photosensor that can be used to measure a total ambient light level and to generate a corresponding raw sensor output.

The control circuitry may be used to identify the lighting type of the ambient light (i.e., may determine which of the plurality of light sources produced the ambient light) by computing a ratio of signals generated by at least two silicon-based photosensors on the electronic device, identifying a color temperature of the ambient light, identifying a modulation frequency of the ambient light, using a combination of these techniques, or by obtaining other parameters associated with the ambient light.

The control circuitry may then select a suitable compensation factor based on the identified light type by referring to a lookup table stored on the control circuitry. The control circuitry may then output a visible light reading indicative of how much visible light is contained in the ambient light (e.g., by taking the product of the raw sensor reading and the selected compensation factor).





About Apple's Patent Figures

Apple's patent FIG. 1 noted above is a perspective view of an illustrative electronic device with ambient light sensor structures in accordance with an embodiment of the present invention; FIG. 5 is a plot showing a mismatch between the human eye photopic response and silicon sensor photosensitivity; FIG. 6 is a plot showing how a silicon photosensor may respond to various light sources; and FIG. 13 is a flow chart of illustrative steps involved in operating an ambient light sensor to output a compensated sensor output in accordance with an embodiment of the present invention.

Patent Credits

Apple credits Dong Zheng as the sole inventor of patent application 20140132578 which was originally filed in Q4 2012. Considering that this is a patent application, the timing of such a product to market is unknown at this time.

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