662 DISPLAY SYSTEM DESIGN PROBLEMS 



Deflection Coik Shield- 



-Clear Face 

 Fig. 12-39 Physical Arrangement of the Shadow Mask Color CRT. 



Deflection Yoke 



Three Electron Guns 



Axis of 

 Electron Beam 



Fig. 12-40 Operation of Shadow Mask Color CRT. [H. B. Law, Proc. IRE (Oct. 

 1951) p. 1187] 



proper phosphor dots without affecting adjacent color dots. The shadow 

 mask, a thin perforated diaphragm, blocks any one beam (such as the beam 

 designed to excite only green phosphor dots) from striking dots other than 

 the proper one (green in this case). Separation of colors is obtained by the 

 direction of entry of the three beams through the holes of the shadow mask 

 and by the geometry of the shadow mask and phosphor dot screen. To 

 minimize convergence and focus difficulties throughout the front face of the 

 tube, curvature of the shadow mask and phosphor screen are sometimes 

 used. 



In the shadow mask tube different colors are obtained by modulating the 

 three beams to obtain an additive color of any hue, the observer's eyes 

 integrating over the individual dots. All three beams, which are generated 

 by three guns placed symmetrically about the neck of the tube, are deflected 



