Device for receiver for optical signals

Claim 1

In a receiver for optical signals of the type comprising a photosensitive element arranged to pick up comparatively weak optical signals and to convert such optical signals into useful electrical signals, said receiver including an amplifier and associated signal processing members connected to the output of the photosensitive element for processing said useful electrical signals, the improvement wherein said receiver includes additional means for rendering said receiver relatively insensitive to incident radiation of significantly higher levels than the levels of said comparatively weak optical signals thereby to separate said useful electrical signals from undersirable signals produced when said photosensitive element is subjected to direct incident sunlight or other comparatively strong sources of interfering radiation, said improvement comprising a separate signal-responsive device the operation of which is dependent only on the magnitude of the slowly varying high-level signal at the output of said photosensitive element, said signal-responsive device including a switching device operative to switch said amplifier and its associated signal processing members from a higher fixed sensitivity to a lower fixed sensitivity when the magnitude of the electrical signal produced at the output of the photosensitive element exceeds a predetermined value in response to exposure of said photosensitive element to interfering radiation from the sun or other strong source of disturbance.