TV Camera tube

A camera tube circuit for operating a TV camera tube having an envelope containing a glass faceplate and an electron gun including a cathode;

• an n-type transparent electrode layer formed on said glass faceplate;
• a photoconductive target composed at least of a photoconductive layer formed by depositing a thin p.sup.+ -type layer, a p-type layer and n-type layer in succession on said n-type transparent electrode layer, and a block layer formed on said photoconductive layer for blocking an electron beam emitted from said cathode passing through said photoconductive layer;
• a metal mesh disposed in the vicinity of the side of said photoconductive target which is scanned by said electron beam;
• and a collector electrode disposed between said metal mesh and said cathode for collecting secondary electrons emitted from said photoconductive target, whereby said photoconductive target is scanned by said electron beam emitted from said cathode, said camera tube circuit comprising:
• means for connecting said n-type transparent electrode to a preamplifier and the negative terminal of a target voltage source;
• a capacitor connected between said metal mesh and said target, said capacitor maintaining the potential of said metal mesh substantially at a constant level;
• and
• means for connecting said metal mesh to the positive terminal of said target voltage source through a series circuit, said series circuit comprising a resistive means having a resistance which is sufficiently larger than the input impedance of said preamplifier and switching means which is in the off condition only during a blanking period of the scanning effected by said electron beam, whereby a camera output is derived from said preamplifier.

A TV camera tube, comprising

• an envelope having an open end;
• a glass faceplate positioned adjacent the open end of said envelope;
• an electron gun for generating an electron beam located within said envelope, said electron gun including a cathode positioned at the end of said envelope opposite said faceplate;
• an n-type transparent electrode layer formed on the surface of said glass faceplate facing said cathode;
• a photoconductive target including
• a photoconductive layer comprising a p.sup.+ -type layer deposited on said n-type transparent electrode layer, a p-type layer deposited on said p.sup.+ -type layer and an n-type layer deposited on said p-type layer;
• and
• a blocking layer formed on the p-type layer of said photocathode layer, said blocking layer absorbing a portion of the energy in said electron beam inpinging on said photoconductive layer;
• a metal mesh positioned adjacent said blocking layer;
• a collector electrode disposed within said envelope between said metal mesh and cathode for collecting secondary electrons emitted from said photoconductive target;
• a mesh rack positioned on said collector electrode;
• an insulating ring covering said mesh rack, said insulating ring having a skirted portion on which said metal mesh is supported;
• a metallic ring interposed between the open end of said envelope and said glass faceplate;
• a conductive gum sheet interposed between said glass faceplate and said faceplate holder;
• and
• an electrically conductive pin embedded within said glass faceplate connecting said n-type transparent electrode to said conductive gum sheet for measuring the capacitance between said transparent electrode and said metallic ring.