Photocell with background cancellation in position sensitive device

摘要

The photocell includes two detectors which each deliver a current depending on a distance of an object, whereby the current delivered by the first element is larger and/or smaller than the one of the second element, if the distance of the object is larger and/or smaller than a predetermined detection range. A processing circuit produces a first voltage signal and a second voltage signal, which correspond to the respective currents, and comprises a main amplifier which compares the voltage signal, to produce a switch signal. A locking comparator is provided, which compares the first voltage signal with a nominal voltage, to produce at its output a signal which holds the switch signal in its inactive condition, as long as the first signal is smaller than the nominal voltage, whereby the nominal voltage corresponds to a distance which is larger than the detection range.