US Patent 7935917 Photo detector device having multiple photosensitive transistors

A photo detector device includes a photosensitive transistor capable of detecting an optical signal including an image component and a background component and converting the optical signal into a current including an image current corresponding to the image component and a background current corresponding to the background component, a first amplifier module electrically connected to the photosensitive transistor capable of canceling the background current and amplifying the image current, and a second amplifier module electrically connected to the first amplifier module capable of detecting a direct-current (dc) portion of the image current.