Television camera tube having channeled photosensitive target spaced from signal electrode

摘要

A television camera tube having a discrete structure of photosensitive elements provided on an electrically conductive carrier covered entirely with photoconductive material or another resistance material, so that with a suitable potential applied to the carrier a potential distribution occurs having successive saddle points for the scanning beam. Variation and exposure of the discrete photoconductive elements then results in a variation in beam splitting in the saddle points, as a result of which the tube has a greater or smaller extent of natural amplification. PPThe invention relates to a television camera tube having a target which is to be scanned by an electron beam and which comprises a transparent electrically conductive signal electrode and discrete structure of photosensitive elements provided on an electrically conductive carrier.PPSuch a camera tube is known from the U.S. Pat. No. 3,649,866, It is the object of the camera tube described in said Specification to provide a storage tube which, with a control suitable for that purpose, can store an image up to several days. In order to achieve this, an electrically conductive mesh structure is covered with photoconductive material on the side remote from the electron source. By local differences in exposure of said structure, a larger or smaller part of the scanning electron beam is passed to the signal electrode and hence a beam splitting introduced by the beam acceptance of the target occurs which is also influenced by the extent of exposure of the photoconductive structure. Because the electrically conductive mesh structure is left uncovered on the side facing the electron source, the operation of said tube will not be optimum.P PIt is the object of the invention to provide a television camera tube with which an adjustable natural amplification can be realized while using the beam acceptance of the target. To be considered, for example, is a natural amplification of a decade.P P For that purpose, a television camera tube of the kind mentioned in the preamble is characterized according to the invention in that the structure of photosensitive elements is provided on an electrically conductive carrier, in which, except for the signal electrode, no electrically conductive material which is directly visible for the electron beam is added and with which, in cooperation with the signal electrode, a potential field is adjustable which, proceeding in the direction of movement of the scanning electron beam, shows at least two successive saddle points in which the scanning electron beam experiences a local beam splitting which is a function of potentials to be applied externally and of local exposure of the target.P PSince in a television camera tube according to the invention the inertia is adjustable by applying potentials suitable for that purpose, the tube may be used at will as a normal television camera tube having an inertia and sensitivity which is normal for that purpose or, by the natural amplification to be realized, as an extra sensitive tube having a comparatively large inertia. The latter is favourable for making television scenes in spaces where, for external reasons, a comparatively low light level is desired. The further operation and apparatus of a television camera having a camera tube according to the invention need not experience any drastic alterations in contrast with solutions having a separate image amplification.P PThe structure of photosensitive elements may be provided, for example, on an electrically conductive mesh grid arranged between the mesh electrode of the electron gun and the signal electrode. The photoconductive material is provided on the side of said grid facing the signal electrode. The remaining part of the grid wires is covered with a resistance material. The photosensitive structure may also be provided in a disk of semiconductive material which in the tube occupies a position corresponding to the said grid. The photosensitive structure may also be provided in the form of a line pattern or a mosaic of discrete elements on an electric conductor which is also discrete. Said conductor may be provided directly on the signal electrode, if desired with the addition of a separation layer, and that with such a structure that, when external potentials suitable for that purpose are applied, two saddle points occur in the potential field.