Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Patent
1989-11-15
1991-03-26
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
340708, 358483, H01J 4014
Patent
active
050031678
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a photosensitive device of the type enabling the reading of a document, that is, a device enabling the formation of an image of an object or of the document, and the conversion of this document into electrical signals with a view, for example, to its reproduction or transmission.
There are known ways, notably in the field of radiology, to convert an image into electrical signals by means of a photosensitive detector, of a surface type, such as a matrix of photosensitive elements. The photosensitive matrix has a system of conductors in rows and a system of conductors in columns. At each intersection between a row conductor and a column conductor, there is a photosensitive assembly hereinafter called a photosensitive dot. The photosensitive dots are thus also organized in rows and columns. Each photosensitive dot is connected between a row conductor and a column conductor.
The number of photosensitive dots in a given surface determines the resolution of the image. It is possible to make matrices of photosensitive elements with great capacity, for example 2000.times.2000 photosensitive dots, to obtain an image with dimensions of the order of 40 cm. by 40 cm. Each photosensitive dot comprises a photosensitive element such as a photodiode, phototransistor, photoconductor etc., sensitive to the visible or near visible light photons.
These light photons are converted into electrical charges, and these electrical charges get collected in an electrical capacitor forming a storage capacity which may be formed, for example, by the capacitor of the photosensitive dot itself. A reading device can be used to interrogate the electrical status of the storage capacity and to convey the electrical charge, constituting the signal, towards a signal amplifier.
An example of a photosensitive matrix, made by the technique of deposition in thin layers, is given in a French patent No. 87 00716, published under No. 2 593 343. This French patent describes, firstly, the detailed working of a photosensitive matrix, each photosensitive dot of which is formed by a photodiode in series with a capacitor. This patent further describes a method for the fabrication of a matrix such as this, and the method for setting up the alternation, on a substrate, of electrically conductive layers, which may or may not be transparent, with semiconducting layers and insulating layers, with a view to obtaining the desired structure of the photosensitive dot.
One of the aims of the present invention is to enable the use of photosensitive matrices such as this in the field of office automation systems, particularly for the reading of documents, notably with a view to their reproduction or transmission.
However, it must be noted that a relatively large number of different structures of photosensitive dots is known but that, whatever may be the type of photosensitive dots used, a large-sized photosensitive matrix is a relatively complicated and, hence, expensive element which means that it is particularly important to be able to use a photosensitive matrix in an economical and profitable manner.
With this fact in view, the invention shows how to use a photosensitive matrix in a device that can fulfil at least two functions which, until now, were fulfilled by different and separate devices. This results not only in a more profitable and economical use of the photosensitive matrix but also in a reduction of the space occupied by equipment as well as in a possibility of extending the field of use, due to the possibility of interaction among different functions combined in one and the same piece of equipment.
According to the invention, a photosensitive device comprising a matrix of photosensitive dots, a source of light, said matrix comprising a system of conductors in rows and a system of conductors in columns, a photosensitive surface consisting of a plurality of elementary surfaces, each comprising a photosensitive dot, each photosensitive dot being connected between a row conductor and a column conductor, the light source producing a l
REFERENCES:
patent: 4451895 (1984-05-01), Slinkowski
patent: 4475239 (1984-10-01), van Raamsdonk
patent: 4707109 (1987-11-01), Kanno et al.
"Thomson-CSF"
Allen Stephone B.
Nelms David C.
Plottel Roland
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