Patent GB-1333925-A (GB)
Title: Character generator
IPC: H01J29/14
Filed: 1970-10-09
Abstract: 1333925 Facsimile systems RCA CORPORATION 9 Oct 1970 [15 Oct 1969] 48076/70 Heading H4F [Also in Divisions C4 H1 and G2] A system includes a display device with a surface excitable for producing radiant energy (e.g. phosphor layer in a c.r.t.), a mask comprising a photochromic layer 3, means for storing a font of image patterns in respective portions of the photochromic layer and means for reading a selected part of the stored image patterns by exciting selectively the emissive surface adjacent the photochromic layer portion including the selected pattern by scanning of that part, the excitable surface comprising a material to emit radiation in a first frequency band, the photochromic material being normally transparent to this band, except when excited by radiation in a second frequency band, the storing means including means for projecting on to the photochromic layer radiant energy in the second band of interest in the stored image pattern or its negative image, the projection being through a stencil on to the photochromic surface, the reading means further including a device responsive to the first frequency band passed through the p/c layer and a second display device (e.g. c.r.t. 8) scanned in synchronism and modulated by the signal from the responsive device .The phosphor decay time should be #10<SP>-7</SP> sees., e.g. P16 phosphor (CaMgSiO 3  : Ce) emitting at 3800 Š and 800 Š wide, or yttrium aluminium garnet; Ce emitting at 5700 Š and 1200 Š wide. Layer 3 may be CaF 2  : Ce, La, Tb or Gd, absorbing at 5000 to 6000 Š under U.V. radiation (3500-1000 Š), or doped SrTiO 3 , CaTiO 3  or sodalite. Fig. 1 includes dichroic mirror 4, reflecting at 3500 to 4000 Š and transmitting at 5000 to 6000 Š radiant energy source 5, and aperture 6 for insertion of a mask from a plurality of masks with different fonts. Mirror 4 may be evaporated alternate layers of high and low refraction materials such as cryolite and ZnSe. Light detection from the screen 2, 3 may be by photodetector 7 to a display device, e.g. c.r.t. 8. Alternatively, layer 3 may be uniformly coloured by U.V. exposure, and the font bleached on to the layer 3. Mirror 4 may alternatively be a silvered mirror, and moved during transmission from tube 1 to detector 7. The font may be changed by bleaching with  heat or high intensity visible light, 5000 to 6000 Š. Selection of particular stored characteristics for display in another device may be by several methods. A computer may select, and supply two pieces of information, the character and location (two co-ordinates), which may be in ASC 11 code, described in detail with relation to Fig. 2 (not shown). Fig. 3 (not shown) indicates the coding for a particular character and Fig. 4 (not shown) a particular binary word format. Fig. 5 (not shown) illustrates a system for selection and display of a character, and described in detail, as components as illustrated; and including display device 8 as in Fig. 1. The character select gates of Fig. 5 may be as in Fig 6 (not shown), including inverters 25 in series with five input leads to the AND gate. The D/A 22 converter of Fig. 5 may be as in Fig. 7 (not shown). In Fig. 5, decoding logic 11 transmits a signal via line 38 to turn on scan generator 39 (also in Fig. 1) which produces a high frequency sinusoid or tickler voltage coupled to c.r.t.s 1, 8 by lines 40, 41 to Y tickler coils 43, 44. Electrostatic tickling may also be used. A ramp of current, time incident with the sinusoid is connected to the X tickler coils, respective ramps being variable to vary character sizes on the two tubes. Fig. 8 (not shown) illustrates ramp current waveshape (51) and sinusoid (50). Letters, numbers, symbols, lines and map displays are exemplified.