An ambient light sensor (ALS) is a special class of photodiode. Photodiodes are capable of detecting light and converting the light to a voltage or current proportional to the incident light. Photodiodes are PN or PIN (P-type, Insulator, N-type) semiconductor structures. Light enters the top of the photodiode, a thin P-type semiconductor material, into the depletion region where hole-electron pairs are created. The electrical field created in the depletion region causes electrons to be transferred to the N-type material and holes to the P-type material. Thus the incident light is translated into a current proportional to the light intensity. An Ambient Light Sensor is a photodiode that is specially designed to have a light to current response that approximates the way that human psycho-visual model interprets light levels. In other words, an ALS has a spectral sensitivity and response similar to the human eye.

Ambient light sensors output current in response to ambient light. These output currents may be quite low in low light levels and quite high in sunlight. ALS are often used in optically and electrically noisy environments. The electronics around an ambient light sensor often need low input referred noise and high gain. A transimpedence amplifier (TIA) along with application specific filtering is needed to produce clean and useful output voltages from the ambient light sensor. Triad has extensive experience with photodiode, TIA and photo sensor signal chains. If you have an application utilizing ALS or other photodiode sensing and you think your product could benefit from integration, the please select the [ contact ] button in the top navigation menu to speak with a Triad ASIC architect about your application and Triad’s capabilities.