Circuit for use in determining the position of light incident on a

Abstract

An electronics circuit for use in determining the position light is incident on a position sensing detector. The position sensing detector provides a pair of photoelectric current signals which indicate the position the light is incident on the detector. These photoelectric current signals are converted to negative ramp voltage signals by a dual switched integrator and then provided through a first pair of sample/hold amplifiers to a second pair of sample/hold amplifiers with each of the second pair of sample/hold amplifiers storing for one line of a raster scan the dark current voltage component of one of the photoelectric current signals. Each dark current voltage component, which is a positive voltage, is summed with a negative direct voltage component of the one of the negative ramp voltage signals by a pair of summing/integrating amplifiers which then integrate the summed signals to provide first and second positive ramp voltage signals indicative of the position of the light on the position sensing detector. The first and second ramp voltage signals are next converted to equivalent digital signals by a pair of analog to digital converters.