Background: Ambient Light Sensor (ALS)

Portable electronic devices such as multi-function smartphones, digital media players, and dedicated digital cameras have display screens that could be used under various lighting environments. Such devices have integrated in them a function that could provide (in real-time) an indication of the current level of visible light in the immediate environment outside the device. This is called an ambient light sensor function (or ALS). The ALS could be used for applications such as automatically managing the brightness of a display screen for better legibility or for conserving battery energy (depending upon the current ambient light level).

Most recently, advanced, consumer grade, ALS integrated circuit (IC) devices have been developed that have a built-in solid state light sensor together with associated analog and digital circuitry that provide, in real-time, a fairly accurate measurement of the ambient visible light that is incident upon the IC device. These IC devices are for the most part manufactured in accordance with a complementary metal oxide semiconductor (CMOS) fabrication process technology.

The Standing Problem

The response of many typical CMOS light sensor structures (e.g., CMOS photodiodes) is dominated by infrared (IR) content, rather than visible content. This creates a problem under some artificial lighting environments. For example, a CMOS-based ALS device would likely indicate that its ambient environment is "brighter" when lit by an incandescent lamp compared to a fluorescent lamp. That is because incandescent lamp lighting has fairly high IR content compared to, for example, fluorescent lamp lighting, and the sensor can't distinguish between lighting conditions where IR dominates and those where visible dominates. To help alleviate this problem, an IR blocking filter (IR cut filter) could be placed in front of the sensor to thereby lessen the sensitivity of the sensor's output to IR content.

In practice of course, the IR cut filter isn't ideal in that there still is an appreciable amount of IR content that will pass through the filter and be detected by the sensor. Although relatively small, such IR leakage may still be too much for an ALS in the following situation. Consider the case where a light transparent cover of a portable electronic device is to have a relatively smooth or uniform front surface, without any physical openings therein. An ALS chip is located below the cover, to sense the ambient light level outside the device. In some cases, it is desired to also make the front surface appear dark from outside (e.g., for aesthetic reasons). To achieve this, a layer of IR transmission ink can be applied to the backside of the cover, which gives the front of the cover a uniform, dark color (e.g., black). The IR ink layer, however, allows very little visible content to pass through and reach the sensor below (e.g., no more than about 5% transmission). This diminishes the ability to distinguish IR from visible in the sensor's output signal (despite the reduction in IR content achieved using the IR cut filter).

Patent Summary

Apple's patent covers a light sensing device that could perform the function of an ambient light sensor (ALS) in a portable electronic device. The elements of the device include a first filter that blocks visible light in a light path, and a set of sensors to detect the light in the light path, after the first filter. These include at least a first color sensor and a clear sensor. The device also has a light intensity calculator that computes a measure of the intensity of visible light in the light path. The calculation is based on a difference between an output signal of the first color sensor, and an output signal of the clear sensor. In other words, the measure of ambient light level is computed based on the differential of at least one color channel and the clear channel. In this manner, the IR content in the light path is advantageously cancelled (when taking the difference between the output signals of the color and clear sensors).

In another embodiment, the calculation of light intensity (representing the ambient light level) uses not just the difference between one color channel and the clear channel, but also a further difference quantity, namely the difference between another color channel and the clear channel. Such a technique may be useful when the first and second color sensors are red and blue sensors, respectively, for example, which are readily available as part of conventional RGB light sensors. Under that scenario, the intensity calculator converts at least two clear-color differentials, which represent cyan and yellow values, respectively, into a green value. The latter may then be used to calculate a lux value, which is a direct measure of the light intensity.

Ambient Light Sensor used in the iPhone

Apple's patent FIG. 3 below shows an example implementation of the ALS portion of the front cover in a portable electronic device like the iPhone.

We see in patent FIG. 3 that the front cover has an ALS portion which together with the light sensor chip 310 and the associated light intensity calculator 112 (see FIG. 1 or FIG. 2) may be deemed to perform an ALS function in an iPhone or iPod touch.

For more information on this patent, see application 20100282953. When this temporary link no longer brings you to the right patent, simply feed the patent number above into this search engine. Apple credits Ching Yu John Tam as the sole inventor of patent application which was originally filed in Q2 2009.

Other Noteworthy Patent Applications Published Today

Another minor but interesting patent covers how an iPod touch or iPhone is able to share preset music lists with an accessory. In particular, Apple's patent FIG. 2 shown below illustrates an iPhone coupled to accessory 210 which could be any accessory that has a radio tuner, e.g., a home stereo system or an in-vehicle media unit.

If you have a modern vehicle with the right radio set up for MP3 players, then this feature could be very convenient to have. Your favorite radio stations on your iPhone could be shared with your vehicle radio station preset buttons. But let's be honest, this isn't for everyone. Then again, the iPhone doesn't have a built-in radio yet: So go figure.

For more information on this patent, see application 20100285763. When this temporary link no longer brings you to the right patent, simply feed the patent number above into this search engine.

If you're interested there are three published Apple patents today covering Flash memory under 20100287329, 20100287353 and 20100287446. If any of these temporary links redirect you to the wrong patent in the future, simply take the numbers noted above and put them into this search engine.  

Finally, if you're interested, there's also an old 2006 continuation patent titled "Mirrored File System" to review under 20100287526. Patently Apple generally doesn't cover continuation patents unless Apple has recently acquired one. And this patent doesn't fit the bill.     

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