Intersil has announced a new RGB sensor, and they’ve laid out some of the things that it’s good for. But let’s back up a sec before diving in.
RGB sensors sound pretty straightforward, and their utility seems pretty obvious. But they’re not the only light sensors in town, so first let’s position them with respect to other light sensors on that system that everyone wants a piece of: the smartphone.
There’s already an RGB sensor on your phone: it’s in the camera. It’s on the back of the phone, typically. On the front side, there are two other light sensors. There’s the ambient light sensor (ALS), which simply detects light intensity so that it can decide how much to dim the screen (and other things like lighting a keyboard). The main difference between an ALS and an RGB sensor is that the RGB sensor provides three channels of data for the three colors; the ALS just gives one number. And the ALS typically costs less, although Intersil sees cost parity on the horizon.
The other light sensor on the phone is the proximity sensor; it combines an IR LED with an IR detector to figure out whether you’re holding the phone to your cheek so that it can disable screen functionality. While Intersil’s new sensor actually can detect down into the near infrared range, it can’t function as the detector in the proximity sensor, so we won’t travel down that path any further.
If you subscribe to cost parity between ALS and RGB sensors, then having and RGB sensor handle the ALS function can help with the various kinds of glass now being used on phones. Colored glass in particular can complicate detection, so a tunable RGB setup can help deal with that. Sensitivity is important here, since the glass on most phones can block up to 90% of the light.
Light intensity is measured in “lux” units; full daylight is 100K luxes; moonlight is 1 lux. But if you only get 10% of the light, then full daylight will look like 10K lux behind the glass. So they focused on sensitivity up to that range, going down to 0.005 lux at the bottom end for dark environment performance.
So that’s phones, but there are other ideas afloat as well. Color calibration of screens to printers is one. More interesting, since it’s a dynamic application, is compensation for display aging. In particular, with OLEDs, the blue color component is newer and less “perfected,” so it ages more quickly than the others. That means that the color mix changes over time.
Using an RGB sensor, that change can be detected and compensated by boosting blue power to keep consistent color over the life of the screen. They can sync with multiple sensors for the case where the display is divided into regions, each with its own sensor. The same can be done for projectors (minus the regional thing).
Meanwhile, LEDs are bringing some fundamental changes to room lighting. In the past, there were a couple discrete choices for light “temperature” (a measure of the “whiteness” color): incandescent and fluorescent. But LEDs can be tuned to some extent, and individual LEDs also vary, so identical arrays of LEDs might have different temperatures.
For all of these cases, an RGB sensor can help detect the temperature and maintain consistency both unit-to-unit and over time. You could even change the lighting color to suit your mood.
In a camera, a sensor can detect the ambient light temperature and compensate the exposure accordingly. In fact, by having a separate sensor do that, the exposure can be pre-computed, significantly reducing some of the lag time between button-push and picture-take.
From a spec standpoint, Intersil says they’re differentiated by three characteristics: size, accuracy, and – of course – power.
They claim the smallest device, with a 1.65×1.65-mm2 package. Their accuracy (“total error” on the data sheet) is 10%, as compared to 15% and higher with other parts.
Power is specified at less than 1.45 µA quiescent, 85 µA active. Those are the max numbers; other numbers floating around reflect typical numbers (and they have measured against their competition to establish who has lowest typical power as well – they say they have the data to prove that they do).
You can find more in their announcement.