Beam forming region having an array of emitting areas

A beam-forming region (BFR) such as used in cathode ray tube (CRT) electron guns includes a cathode, a decelerating first electrode (G1), an accelerating secondelectrode (G2), an accelerating third electrode (G3) and an additional electrode (G2′) that introduces a pre-focusing lens. The decelerating first electrode (G1) and the accelerating second electrode include aperture arrays that introduce multiple emitting areas on the surface of the cathode. Electrons emitted from the cathode surface pass through their respective apertures and are then converged into a single high current beam by the pre-focusing lens. The high current electron beam passes through any one of many possible main-lens structures, which focuses the beam onto a phosphorescent display screen. The beam is swept across the display screen in a rater like manner while being modulated by a video source signal. In an alternate embodiment, a large diameter aperture is included on the display screen side of the first accelerating electrode (G2) in order to form the pre-focusing lens and converge the electrons into a single high current beam.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 19 there is shown a simplified isometric view of a beam-forming region 254 of an electron gun such as used in a CRT in accordance with one embodiment of the present invention. A longitudinal sectional view of the beam-forming region 254 shown in FIG. 19 taken along site line 252 - 252 is shown in FIG. 20 . This BFR 254 is comprised of four components a cathode 256 , a “Wehnelt” or decelerating first electrode (G1) 258 , an accelerating second electrode (G2) 260 , and an accelerating third electrode (G3) 262 . The G1 and G2 electrodes 258 , 260 have aperture arrays 258 a , 260 a that are linearly aligned with an aperture in the G3 electrode 262 a . Electrons emitted from the cathode 256 travel along a path 266 to the display screen and form a beam 268 . In this BFR 254 the G1 and G2 aperture arrays 258 a , 260 a are each comprised of seven smaller apertures 258 b , 258 c , 258 d , 258 e , 258 f , 258 g , 258 h , 260 b , 260 c , 260 d , 260 e , 260 f , 260 g , 260 h. The aperture arrays 258 a , 260 a form multiple emitting areas on the surface of the cathode 254 . In this BFR 112 electrons are emitted from the cathode 256 and are accelerated toward the display screen by the G2 260 and the G3 262 electrodes, which are always of higher potential than the cathode 254 . Along the path 266 toward the display screen electrons pass through the G1 apertures 258 b , 258 c , 258 d , 258 e , 258 f , 258 g , 258 h . Since the G1 electrode 258 is typically of a lower potential than the cathode 256 , the negatively charged G1 electrode 258 repels the electrons causing them to converge and “cross-over.” The electron are now diverging and proceed to pass through their respective G2 apertures 260 b , 260 c , 260 d , 260 e , 260 f , 260 g , 260 h . This BFR 254 is equipped with a dimple or single large diameter screen side of the aperture 260 i . Since the G3 electrode 262 is typically of higher potential than the G2 electrode 260 , the high potential field of the G3 electrode 262 penetrates into the large diameter portion of the G2 aperture 260 i and thus introduces a pre-focusing lens 264 . When electrons pass through the pre-focus lens 264 they are converged more so than in a conventional BFR 112 . By converging the electrons the single high current electron beam 268 is formed and sent through one of many main lens systems. This BFR 254 is beneficial because the strength of the pre-focusing lens 264 can be adjusted by changing the diameter and depth of the large diameter screen side of the G2 aperture 260 i. Referring to FIG. 21 there is shown a simplified isometric view of a beam-forming region of an electron gun such as used in a CRT in accordance with an alternate embodiment of the present invention, where an additional electrode (G2′) 280 is employed to introduce a pre-focusing lens 284 . A longitudinal sectional view of the beam-forming region shown in FIG. 21 taken along site line 270 - 270 is shown in FIG. 22 . The alternate BFR 272 is comprised of five basic components a cathode 274 , a “Wehnelt” or decelerating first electrode (G1) 276 , an accelerating second electrode (G2) 278 , the additional electrode (G2′) 280 and an accelerating third electrode (G3) 282 . The G1 and G2 electrodes 276 , 278 , have aperture arrays 276 a , 278 a that are linearly aligned with apertures in the G2′ and G3 electrodes 280 a , 282 a . Electrons emitted from the cathode 274 travel along a path 286 to the display screen and form a beam 288 . In this BFR 272 the G1 and G2 aperture arrays 276 a , 278 a are each comprised of seven smaller apertures 276 b , 276 c , 276 d , 276 e , 276 f , 276 g , 276 h , 278 b , 278 c , 278 d , 278 e , 278 f , 278 g , 278 h. This alternate BFR 272 uses the additional electrode (G2′) 280 , inserted between the accelerating second electrode (G2) 278 and the accelerating third electrode (G3) 282 , to introduce the pre-focusing lens 284 . The G2′ 280 is always of lower potential than the G2 278 . The high potential electric field of the second accelerating electrode (G3) 282 penetrates into the G2′ aperture 280 a and thus introduces the pre-focusing lens 284 . The predominant functional difference compared to the previous embodiment of the present inventive BRF 254 is that when the electrons pass through the pre-focusing lens 284 they are converged more or less depending on the potential of the G2′ electrode 280 . This inventive BFR 272 is beneficial because the strength of the pre-focus lens 284 can be adjusted. This method allows individual guns to be adjusted without the re-tooling of parts. Referring to FIG. 23 there is shown a simplified isometric view particularly in phantom of an electron gun 292 such as used in a conventional monochrome CRT with a BFR 294 that is in accordance with one embodiment of the present invention and with a low uni-potential (standard einzel) electrode configuration. A longitudinal sectional view of the electron gun 292 shown in FIG. 23 taken along site line 290 - 290 is shown in FIG. 24 . The standard-einzel main lens 296 is comprised of three electrodes. A first electrode (G3) 298 and a third electrode (G5) 302 are electrically connected and held at a high potential, which is equal to the display screen anode potential. A second electrode (G4) 300 is held near ground potential. The presence of the lower potential G4 electrode 300 between the two high potential G3 and G5 electrodes 298 , 302 forms a converging main lens 296 that focuses an electron beam 304 onto the display screen. By adjusting the potential of the G4 electrode 300 the beam's focus can be fine adjusted to match the beam's location on the display screen. Referring to FIG. 25 there is shown a simplified isometric view shown particularly in phantom of an electron gun 308 such as used in a conventional monochrome CRT with a BFR 310 that is in accordance with one embodiment of the present invention and with a high uni-potential (high-einsel) electrode configuration. A longitudinal sectional view of the electron gun 308 shown in FIG. 25 taken along site line 306 - 306 is shown in FIG. 26 . The high-einzel main lens 312 is similar in construction to the standard-einzel main lens 296 . The high-einzel main lens 312 is comprised of three electrodes. A first electrode (G3) 314 and a third electrode (G5) 318 are electrically connected and held at anode potential. A second electrode (G4) 316 is held at a potential that is typically 20-40% of the anode potential. The potential of the G4 electrode 316 is used as the focusing adjustment for an electron beam 320 . The only functional difference between the standard-einzel 296 and high-einzel 312 main lenses is that the high-einzel G4 316 is held at a high potential. Referring to FIG. 27 there is shown a simplified isometric view shown particularly in phantom of an electron gun 324 such as used in a conventional monochrome CRT with a BFR 326 that is in accordance with one embodiment of the present invention and with a bi-potential electrode configuration. A longitudinal sectional view of the electron gun 324 shown in FIG. 27 taken along site line 322 - 322 is shown in FIG. 28 . The bi-potential main lens 328 is comprised of two electrodes. A first electrode (G3) 330 is held at a high potential, which is typically 20-40% of the anode potential. A second electrode (G4) 232 is held at a high potential equal to the display screen anode potential. In this lens system the potential of the G3 electrode 330 is used as the focusing adjustment for an electron beam 334 . Referring to FIG. 29 there is shown a simplified isometric view shown particularly in phantom of an electron gun 338 such as used in a conventional monochrome CRT with a BFR 340 that is in accordance with one embodiment of the present invention with a quad-potential electrode configuration. A longitudinal sectional view of the electron gun 338 shown in FIG. 29 taken along site line 336 - 336 is shown in FIG. 30 . The quad-potential main lens 342 is comprised of four electrodes. A first electrode (G3) 344 and a third electrode (G5) 348 are electrically connected and held at a high potential, typically 20-40% of the anode potential. A second (G4) 346 is held at low potential. A forth electrode (G6) 350 is held at anode potential. In this lens system the potential of the first (G3) 344 and third (G5) 348 electrodes are collectively used as the focusing adjustment for an electron beam 352 . Referring to FIG. 31 there is shown a simplified isometric view shown particularly in phantom of an electron gun 356 such as used in a conventional inline-color CRT with BFRs 358 a , 358 b , 358 c that are in accordance with one embodiment of the present invention. A longitudinal sectional view of the electron gun 356 shown in FIG. 31 taken along site line 354 - 354 is shown in FIG. 32 . In the inline color electron gun 356 three horizontally aligned beams 362 a , 362 b , 362 c are sent through the distinctly isolated main-lenses 360 a , 360 b , 360 c . The inline color electron gun 356 is essentially three separate electron guns assembled from common parts. Referring to FIG. 33 there is shown a simplified isometric view shown particularly in phantom of an electron gun 366 such as is used in a conventional Trinitron-color CRT with BFRs 368 a , 368 b , 368 c that are in accordance with one embodiment of the present invention. A longitudinal sectional view of the electron gun 366 shown in FIG. 33 taken along site line 364 - 364 is shown in FIG. 34 . In the Trinitron electron gun 366 three horizontally aligned beams 372 a , 372 b , 372 c are sent at through the center of the common shared main-lens 370 . The beams 372 a , 372 b , 372 c are then redirected toward the display screen by a group of deflection plates 374 a , 374 b , 374 c , 374 d. While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects. Therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.