Photosensor and ambient light sensor with constant bias voltage

Abstract

A method of operating a photosensor comprising: applying a bias voltage to a photosensor (12) comprising n (n>1) photo-sensitive elements (8) connected in series, and determining the photocurrent in the photosensor (12) at a time when the applied bias voltage across the photosensor maintains the photosensor at or close to the point at which it has the greatest signal-to-noise ratio. This may conveniently be done by determining the current in the photosensor at a time when the applied bias voltage across the photosensor is equal or approximately equal to n×Vbi, where Vbi is the bias voltage about which the current in a single one of the photo-sensitive elements (8), in the dark, changes sign. In an embodiment in which the photo-sensitive elements (8) are photodiodes, the bias voltage Vbi is the “built-in” voltage of the photodiodes. The photocurrent generated when n series-connected photodiodes are illuminated is approximately equal to the photocurrent generated when one photodiode is illuminated. However, the leakage current (i.e., the dark current) for the n series-connected photodiodes is significantly lower than the leakage current for one photodiode. The signal-to-noise-ratio is therefore significantly increased.

Dependencies are inferred from the claim text.