Patent GB-1248268-A (GB)
Title: Solid state electro-optical image sensor arrays
IPC: H01L27/146
Filed: 1969-07-16
Abstract: 1,248,268. Read-only stores; capacitor data stores. RCA CORPORATION. 16 July, 1969 [23 Oct., 1968], No. 35846/69. Headings G4A and G4C. [Also in Divisions H1 and H4] An electro-optical image translator comprises an array of photodiodes 12, capacitance means 16 serially coupled to each photodiode, each capacitance means having a capacitance value which is independent of voltage thereacross, and means 18 for periodically applying a signal pulse separately to each photodiode of such polarity as to bias each photodiode forwardly across the serial combination of said photodiode and associated capacitance means. The image translator is fabricated in integrated form (see division H1) and Fig. 1 is a schematic representation of the circuit of one embodiment of the invention. As shown, momentary contact of terminal 22 by switch 20 applies a square wave pulse to a storage element 11, thereby charging capacitor 16. If during the interval before another pulse is applied to this same storage element no light falls on the element, capacitor 16 will remain charged. Thus the current pulse through the diode 12 and load resistor 30 will be relatively small. If the element has been illuminated between pulses, however, the charge on the capacitor will have leaked off to a certain extent, depending on the intensity of illumination. Thus a greater amount of current will be needed to charge the capacitor 16, resulting in a relatively large current pulse through the resistor 30. By activating each of the elements in turn with an applied pulse, the voltage output from the systems, taken across the resistor 30, is a train of pulses indicative of the amount of light incident on the separate elements. Fig. 5 shows an embodiment in which the light pattern falling on the array of elements represents digital information. This may be done by exposing the diodes 58 to light that has passed through a punched card or tape, a dark condition representing 0 and a light condition representing 1, with each row of elements corresponding to a "word". To read a "word" a predetermined time after exposure, a switch 62 is used to apply a positive voltage to a selected row conductor 52. Those elements that have been illuminated will produce a large voltage pulse at their respective load resistors 68 whereas unilluminated elements will produce very little voltage output. The sensing elements in this embodiment may also be addressed sequentially to give a television-type image translation, and the embodiment of Fig. 12 is adapted especially for this. As shown, the side of each capacitor 103 remote from the diode 100 has two plates, 105 and 106. Each plate 105 is connected to a row conductor 107, while each plate 106 is connected to a column conductor 108. By sending pulses of predetermined magnitude and spacing along the row and column conductors, a coincidence of a row and a column pulse is made to occur at succeeding elements in a row, row by row. When such a pulse coincidence occurs at an element, the corresponding diode becomes forward biased and transmits a current pulse proportional in magnitude to the light incident since the last pulse coincidence. Thus, the whole array is scanned, and the voltage output at the resistor 114 is a train of pulses indicative of the light patterns on the array.