664 



DISPLAY SYSTEM DESIGN PROBLEMS 



strips. Control of the landing of the electron beam on the proper phosphor 

 strip is accomplished by a grid network placed in front of the phosphor. 

 A grid wire is placed in optical alignment with each red and blue phosphor 

 strip. All the grids associated with the red phosphors are interconnected, 

 as are all the grids associated with the blue phosphors. A high accelerating 

 potential is maintained with the blue phosphors. A high accelerating 

 potential is also maintained between the grid array and the phosphor screen. 

 With the proper deflection conditions and no potential difference between 

 the two grids, the electron beam incident on the grid plane will land on the 

 green phosphor. If a potential difference is placed between the wires, 

 however, the beam will be deflected toward the wire which is most positive, 

 producing a blue or red hue as shown in Fig. 12-41b. 



Electron Beam 



Equal potential on grids. Undeflected 

 electrons strike green phosphor strips. 

 Focusing - field lines are shown between 

 grid wires and phosphor plates. 



Voltage applied to color grid with 

 polarity to deflect electrons to 

 red phosphor strips. 



Fig. 12-41b Color Production by Beam Deflection in Chromatron Tubes. IJ. Gow 

 and R. Dorr, Proc. IRE (Jan. 1954) p. 309] 



Switching between colors can be accomplished by a line or frame se- 

 quence. Line sequence color switching is accomplished by having the beam 

 oscillate over the three color strips, while synchronously providing the 

 correct color video information. Frame sequence color switching is 

 accomplished by applying one-color video information during one frame 

 and then switching to the other colors on succeeding frames. 



In radar systems with long frame times, line sequence color switching is 

 more desirable. Gating circuits for such applications have been developed 

 around sinusoidal switching circuits rather then pulse-type circuits (multi- 

 vibrators) because of the large capacitance associated between the color 

 control grids. Present tubes have as much as 1400 M^f capacitance between 

 the grids. For radar displays where a typical range sweep line might 

 represent 300 microsec (24 n.mi.), a switching frequency of 0.5 to 1 Mc/sec 

 is adequate to present a good color picture. Present mechanizations of 

 gating circuits yield approximately 300 volts rms, utilizing high-Q circuits. 



