editor's blog
Subscribe Now

More Selective Light Sensing

Smartphones and other similar devices have a number of sensors on them for different purposes. In particular, there are two light-oriented ones that work differently and accomplish different things.

One is an ambient light sensor; it helps decide how bright or dim to make the screen, or perhaps whether your keyboard needs some backlight.

The other is the proximity detector. It works in conjunction with a small IR LED; the sensor measures the reflections of light from that LED to decide whether the sensor is near… something. This is typically used to shut off the touchscreen when the phone is next to your ear so that your face doesn’t inadvertently trigger various strange, unwanted events while you think you’re just on a call (something evidently referred to as “cheeking”). The sensor isn’t always on – apparently in some phones it’s disabled in landscape mode, or perhaps it’s only enabled when a call is in session.

A bit of Googling makes it clear that people very often confuse and conflate these two sensors.

Maxim noted that ambient light sensors can typically be thrown off by large amounts of ambient UV and IR light. So they’ve integrated in an optical filter to reject invisible light. This gives the ambient light sensor (a fusion of two actual photodiodes plus the filter) a range roughly like that of the human eye.

They’ve also integrated a third photodiode on the same chip, tuned to respond to the IR light from the pulsed LED – which is external to the chip. They’ve filtered this as well to reject – of all things – DC IR light. That enables the sensor to respond to the IR pulse from the LED without being thrown off by a constant level of ambient IR light.

So what you end up with is their MAX44000 sensor, just announced. You can find more info in their release

 

Smartphones and other similar devices have a number of sensors on them for different purposes. In particular, there are two light-oriented ones that work differently and accomplish different things.

One is an ambient light sensor; it helps decide how bright or dim to make the screen, or perhaps whether your keyboard needs some backlight.

The other is the proximity detector. It works in conjunction with a small IR LED; the sensor measures the reflections of light from that LED to decide whether the sensor is near… something. This is typically used to shut off the touchscreen when the phone is next to your ear so that your face doesn’t inadvertently trigger various strange, unwanted events while you think you’re just on a call (something evidently referred to as “cheeking”). The sensor isn’t always on – apparently in some phones it’s disabled in landscape mode, or perhaps it’s only enabled when a call is in session.

A bit of Googling makes it clear that people very often confuse and conflate these two sensors.

Maxim noted that ambient light sensors can typically be thrown off by large amounts of ambient UV and IR light. So they’ve integrated in an optical filter to reject invisible light. This gives the ambient light sensor (a fusion of two actual photodiodes plus the filter) a range roughly like that of the human eye.

They’ve also integrated a third photodiode on the same chip, tuned to respond to the IR light from the pulsed LED – which is external to the chip. They’ve filtered this as well to reject – of all things – DC IR light. That enables the sensor to respond to the IR pulse from the LED without being thrown off by a constant level of ambient IR light.

So what you end up with is their MAX44000 sensor, just announced. You can find more info in their release

Leave a Reply

featured blogs
Dec 12, 2018
For years chip designers have dealt with ECO'€™s when their source code was written in RTL. But the move to high-level synthesis (HLS) means that their source code is now one step further removed from... [[ Click on the title to access the full blog on the Cadence Communit...
Dec 12, 2018
A joint demonstration between Samtec and eSilicon — an eSilicon 7 nm 56 Gbps DSP SerDes over a Samtec 5 meter ExaMAX® backplane cable assembly — caught a lot of attention at SC18. The demo showed a true long-reach capability with a high-performance, flexible, eas...
Dec 10, 2018
With Apple'€™s '€œWearable'€ category of sales setting a new record this September with growth over 50%, and FitBit seeing growth in both trackers......
Nov 14, 2018
  People of a certain age, who mindfully lived through the early microcomputer revolution during the first half of the 1970s, know about Bill Godbout. He was that guy who sent out crudely photocopied parts catalogs for all kinds of electronic components, sold from a Quon...