datasheets.com EBN.com EDN.com EETimes.com Embedded.com PlanetAnalog.com TechOnline.com   UBM Tech
UBM Tech

Technology enables TV to consume under 60-watts

-January 09, 2013

Sensors enable TV to exceed Energy Star 6.0 proposals while delivering highest quality viewing experience, including 3D

Energy Star has finally come up with a meaningful revision to the standard. The present standard (version 5.3) only tests at two ambient light levels-- 0 lux and 300 lux (office equivalent lighting). Most people do not watch TV in total darkness. This prompts manufacturers to design their maximum backlighting level at the 300 lux ambient lighting---not very efficient at normal lower levels that we watch TV normally, and this spec makes it easy for most manufacturers to pass with almost no benefit to the environment.

The new Energy Star standard (version 6.0), which goes into effect in March 2014, tests at four ambient light levels---10, 100, 150 and 300 lux. This will force manufacturers to maximize their efficiencies at each of these levels. This bodes well for ams since they sell a system solution, not just a sensor like many other low-end suppliers provide. The electronics will now truly have to be smart, digital and match component capabilities to the application requirements.

ams has always considered a number of factors in their Digital Ambient Light Systems (ALS) devices:

Interrupt architecture: The digital design has an interrupt feature that signals the controller when light levels drop below predetermined levels. There is an upper and lower limit where the light level either increases above the upper limit or decreases below the lower limit, thus reducing the processing power required. In this way the processing power can be available for other applications or can go into a low power mode.

Persistence: The intelligence in the digital ALS device is used to avoid rapid changing of display light levels. The programming only triggers an interrupt after ambient light level have been below or above a pre-determined threshold level for a defined amount of time. With sampling intervals of 100 ns to 500 ms, false signals caused by someone walking in front of the sensor are eliminated.

IR blocking: Since silicon photodiodes are sensitive to light energy across a broad range of the spectrum, an ALS system would have to filter out this unwanted light, so if IR energy is not taken into account, the silicon-based reading would show the ambient light at a much higher level than the viewer would actually perceive. This would cause improper display adjustment. A patented dual-diode solution allows a second diode to be responsive only to IR light and that can be subtracted from that of the primary diode (which is responsive to both visible and IR light)

TMD27711 and  TMD27713 are examples of Digital ALS, Proximity sensor and IR LED in an optical module

Sensitivity requirements: It’s not enough to read room lighting conditions accurately, however. Flat panel television designers typically want to create a bezel that is as uniform and aesthetically pleasing to the end customer as possible; drilling a hole in the bezel for a light sensor is not an acceptable solution in most cases.

However, it is possible to hide the sensor behind a translucent plastic or glass bezel, even if it appears to be solid black. This is because some light will be transmitted through the bezel, and even though it’s a small fraction of the ambient light in the room, its levels remain proportional with the room light levels.

One complication is that the certain bezel materials can be transparent to IR wavelengths while visible light can be attenuated by 100 times or more, so the ability to compensate for the IR component is essential.

As a result, this requires a digital ALS that is far more sensitive at very low-light levels than might be needed for other applications.

The ams digital ALS product family supports analog gain setting options up to 120X that are ideal for challenging low-light level applications such as when the light sensor is operating behind darkened glass. Additionally, ams digital ALS devices can be further fine-tuned to match the specific transmissivity of the bezel glass or plastic in order to achieve the optimum system performance. Programmable gain, when combined with programmable integration times, supports up to a 1,000,000:1 dynamic range which enables them to operate effectively in very low-light conditions (tenths of lux) as well as in high light conditions.

TSL45311, TSL45313 and TSL45315 are Digital ALS with Direct lux


Loading comments...

Write a Comment

To comment please Log In

DesignCon App
FEATURED RESOURCES