Two dimensional radiation scanner locating position by the time it takes a group of minority carriers to reach a terminal of the device

摘要

1,083,395. Photoconductive scanning devices. INTERNATIONAL BUSINESS MACHINES CORPORATION. Aug. 24, 1965 [Sept. 2, 1964], No. 36218/65. Heading H1K. A device for detecting the position of a beam of radiation consists of a pair of strip-shaped semi-conductor zones forming a PN junction with a third zone overlying and forming a PN junction with the upper of the zones and extending laterally on one or both sides of it. Alternatively the middle zone is replaced by a plurality of separate zones distributed along the length of the first zone. The embodiment shown in Fig. 3, which is of this type, has strip electrode 24 on one edge of the third zone and contacts 70, 72 at the ends of the first zone. Series of square voltage pulses of decreasing amplitude but constant duration are supplied to contacts 24, 26 by generator 28, and ramp voltage pulses interlaced with these pulses are superimposed on a fixed bias voltage applied along the first zone. Each square pulse drives minority carriers generated by light incident at a given point a distance in the Y direction proportional to the pulse amplitude. Consequently after a given pulse minority carrier will lie adjacent one of the P zones 12 if light is incident at a distance therefrom corresponding to the distance travelled in the Y direction by such carriers. The ramp voltage then applied between contacts 70, 72 progressively reverse biases the junctions between zone 14 and zone 12 and the accumulated minority carriers give an output pulse across load 34 at the instant when the junction they lie adjacent becomes back-biased. Thus the instant during the ramp pulse when the output pulse occurs indicates the X co-ordinate of the light beam and the square pulse after which it occurs the Y co-ordinate.