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Colour sensor brings new levels of accuracy, light intensity

Posted: 10 Feb 2015 ?? ?Print Version ?Bookmark and Share

Keywords:ams? colour sensor? smartphone? tablet? infrared?

ams AG has announced a colour sensor that the company said is geared for light source detection when operating under a range of light sources. The TCS3490 claims to offer accurate colour and light intensity measurements, and enables designers of portable devices such as smartphones and tablets to implement more complex display management and brightness control.

This integrated five-channel colour sensor boasts extremely accurate measurements of the Correlated Colour Temperature (CCT) of light. In addition to the traditional red, green and blue (RGB) colour sensor channels, included is a dedicated infrared (IR) measurement channel for the reliable detection of the IR signature of ambient light sources. This enables stand-alone cameras and smartphones to adjust the colour temperature of the flash to produce better photographs in both indoor and outdoor environments.

Colour measurements are affected by changes in the IR content of the light, so a passband clear (C) channel photo-diode is included to provide a direct measurement reference for mathematically subtracting unwanted residual IR energy. An integrated IR blocking filter over the RGBC photo-diodes minimises IR spectral component effects, and this also helps to improve colour accuracy measurements.

The fifth IR channel is sensitive to IR light in the spectrum 700nm to 1,100nm. Since every light source has its own spectral fingerprint, with known proportions of UV, RGB and IR light, a system can identify the light source in the user's vicinity by measuring the IR-to-C and Red-to-C channel ratios and applying a detection algorithm to the measurements. In smartphone camera applications and digital still cameras, this ability to reliably detect the light source enables the white-balancing settings in a camera's or smartphone's flash to be optimised, resulting in improved picture quality.

By measuring the CCT and brightness (lux) of ambient light in a system, consumer electronics devices can automatically adjust the colour tones of the display for the best viewing experience under varying lighting conditions and behind attenuating dark inked glass or spectrally distorting materials. By adjusting the display's colour tones and hues, the device can make images appear more vivid, more natural or calmer under any changing lighting conditions.

Four independent ADCs, one for each of the RGB channels and the fourth shared between the Clear and IR channels, enable simultaneous sampling of all four channels, thus eliminating CCT and lux measurement errors in fast-changing lighting conditions. The TCS3490 sensor's photodiodes have a radial structure to create a uniform and optimised response irrespective of the angle of the incident light, especially when placed under a circular aperture. A level-shifter style interrupt pin enables the sensor to alert the applications processor when pre-set light and colour measurement thresholds are crossed, eliminating the need for continuous I2C bus polling, and thus reducing overall system power consumption and extending battery life.

TCS3490 block diagram

The colour sensor TCS3490 is available in a 2mm x 2.4mm dual flat no-lead package and is shipping in production volumes. A demonstration board for the TCS3490 is available online from ams.

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