High Sensitivity, Wide Range Photo-Amplifier
Original Publication Date: 1979-Jan-01
Included in the Prior Art Database: 2005-Feb-19
When reading optical marks from a moving document, it is necessary to use a photo-amplifier having a wide dynamic range and high sensitivity. Since the document background and mark intensities vary greatly, the amplifier cannot use a fixed threshold level, but must incorporate a variable or compensating reference. This article is directed to a sensing amplifier circuit in which the photodetector output is supplied to the first input of an operational amplifier and a modified photodetector output is supplied to the second input of the operational amplifier.