Ambient light sensor produces digital output

The first ambient light sensor that converts light intensity to a digital signal output capable of direct SMBus interface is now available from Pacer Components.

The first ambient light sensor that converts light intensity to a digital signal output capable of direct SMBus interface is now available from Pacer Components.

The TSL2550, manufactured by Texas Advanced Optoelectronic Solutions (TAOS) is designed to help reduce overall system power by measuring the ambient or available light as a means of controlling display screen backlighting in portable equipment such as laptop computers, mobile phones, PDAs, camcorders and GPS systems.

In addition to portable communications equipment the TSL2550 can also be used to monitor lighting conditions for commercial and residential lighting.

Display screen backlighting which can account for 30-40% of total power can now be adjusted automatically with the help of this new single-chip light sensor.

This device will help portable equipment users achieve significant power savings by adjusting display brightness to ambient conditions.

Research has shown that portable equipment power consumption is directly proportional to display luminance.

Dimming can reduce display power by as much as 70%.

The TSL2550 uses an all-silicon technique that combines two photodetectors to measure ambient light brightness as perceived by the human eye.

One of the photodetectors is sensitive to both visible light and infra-red light.

The second photodetector is sensitive to only infra-red light.

The output of both detectors is converted to a digital format and stored in separate registers accessed through the SMBus.

The combined information compensates for the effect of the infra-red content of ambient light, thereby approximating the response of the human eye.

This information can be used to calculate light intensity in commonly used units of lux.

This technique eliminates the need to use an expensive photopic filter.

Additionally the ratio of infra-red light to visible light can be used to determine the type of ambient light source (incandescent, fluorescent or sunlight) thereby allowing more intelligent control of display contrast and/or colour.

The TSL2550 uses a companding analogue to digital convertor to provide light measurements over an effective 12bit dynamic range.

The integrating conversion technique used by the TSL2550 effectively eliminates the effect of flicker from AC powered lamps, thereby increasing the stability of the measurement.

A single supply operation (2.7 to 5.5V) makes this device well suited for use in 3V systems.

Moreover a power-down mode, which shuts off the device on command when not in use, ensures that the TSL2550 consumes as little power as possible.

Back to top