The invention relates to a circuit provided with an exposure measuring portion for sensor-controlled range finding where two linear semi-conductor image sensors are provided, each having individual sensor elements. Line segments corresponding to the two images and separately obtained from the object are projected onto the image sensors. Switching circuits are connected to the sensor elements which are switchable between two different states and an evaluator is provided for evaluating these two state sensor signals in dependence upon different position displacements with respect to a maximum correlation. A comparing sensor element is also provided and receives optically generated charge quantities corresponding to sensor elements in the image sensors.
Circuits of this type are described in German patent application P No. 28 38 647.2, incorporated herein by reference. If the linear image sensor, arranged next to the comparison-sensor element, is exposed as a projected line section which has a very great brightness over a small portion of its length, whereas the other, predominant portion of its length is dark, difficulties then occur during the determination of an integration time necessary for a precise telemetry. By the term integration time, the time span is understood in which an optical charge generation takes place in the individual sensor elements as a consequence of the exposure. In the case of a strongly non-uniform brightness distribution of this type, a portion of the optically generated charge can overflow from the sensor elements, aligned (or orientated) to the bright portions of the line section, into the adjacent elements, before the integration time determined by the comparison-sensor element has been terminated. However, this leads to signal falsifications in the sensor elements which impede a precise telemetry.
If one were to provide, next to the linear image sensor and next to the comparison-sensor element, an anti-blooming channel, known per se, consisting of a re-doped semiconductor strip, and if one were to arrange laterally adjacent to the latter, an anti-blooming gate, insulated in relation to the semiconductor member, and subjected to a fixed voltage, then this anti-blooming gate will control the overflow of the excess charge quantities into the channel. Then, in the case of the previously noted strongly non-uniform exposure of the comparison-sensor element, there would result therein a mean charge value uniformly distributed over the entire surface of the same. This value would lie only slightly above the dark value resulting for a dark line section. The analyzer connected with the comparison-sensor element would bring about a termination of the integration time only when the charge mean value reaches the magnitude of the reference charge. However, up to this time-point, also the sensor elements, aligned with respect to the dark locations of the line section, would have taken up optically generated charges which would lie only slightly below their reference charges. The digital switching states resulting in the associated analyzers are very strongly dependent upon parameter fluctuations of the sensor elements and analyzer circuits, so that a brightness progression, actually not present along the slightly exposed portion of the sensor line, is simulated.