Optical sensors help save backlight power

Novel light-to-current optical sensors combine a photodiode and a current amplifier on a single chip.

Intersil has introduced two light-to-current optical sensors, both combining a photodiode and a current amplifier on a single chip.

The parts allow devices such as cellphones, laptops or any handheld device to reduce overall system power consumption by dynamically controlling the current sent to the display or backlight.

The EL7900, is an optical sensor that converts light to current.

The device operates in a wide range of lighting conditions from 1 to 10,000 lux.

This information can be used to determine the amount of ambient light present, which allows automatic backlight or brightness control for backlit keyboards and LCD monitors.

Traditional light sensing applications have used photodiodes in combination with complicated signal conditioning circuits.

Easy to use, the EL7900 provides a simple current output that can be converted into a voltage with a single external resistor.

This opens up many new possibilities in motion sensing, intrusion detection and other various medical or industrial sensing applications.

A typical display will consume the same amount of power until a user changes the system settings, which is usually brightness control.

In very bright areas like an outdoor setting, users tend to increase the brightness of the display.

This increases the power consumption of the system.

When the conditions change, like walking into building or operating a laptop on a flight, most users don't change the settings and the system power consumption remains high.

By using the EL7900 ambient light sensor, a system can now detect changing conditions and automatically adjust the settings to keep the display at optimal brightness and reduce overall power usage.

The EL7900 also consumes little power itself, so there is no overhead by integrating it into the system.

There are several key factors for ambient light sensors.

First, the output current must be linear to the light intensity and spectral wavelength sensitivity should be very close to the human eye.

The EL7900 excels in both these areas.

The device's output current is directly proportional to the light intensity on the integrated photodiode and the peak response of 540nm is extremely close to the peak sensitivity of the human eye.

The EL7900 is designed to sense ambient light from 380 to 770nm.

As handheld designers are pushed to extend battery life of their device, innovative methods for saving power are being devised.

Intersil's EL7900 provides better brightness management, as well as an improved solution to discrete photo resistor and/or photodiode use, where linearity is worse, and an additional amplifier is usually needed.

Adding to the family of ambient light sensors, Intersil is also introducing the ISL29000.

This is an extremely low power ambient light sensor suitable for the most demanding portable applications.

Although it consumes less current, the ISL29000 provides the same linear response and wavelength sensitivity of the EL7900.

The EL7900 and ISL29000 perform over a wide operating temperature range from -40 to +85C.

This allows for integration into a number of demanding applications where extreme ranges of temperatures are normal.

The EL7900 is another example of Intersil's approach to providing solutions to real world analogue problems and is an important addition to a growing family of display products.

Intersil's EL7900 is available now in a 5-lead ODFN lead-free finish (RoHS compliant).

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