Tokyo Shibaura Elec. Co., Ltd. v. Zenith Radio Corp.

• Decision Date: 07 November 1975
• Docket Number: Civ. A. No. 4672.
• Citation: 404 F. Supp. 547
• Parties: TOKYO SHIBAURA ELECTRIC CO., LTD., et al., Plaintiffs, v. ZENITH RADIO CORPORATION, Defendant.
• Court: U.S. District Court — District of Delaware

404 F. Supp. 547

TOKYO SHIBAURA ELECTRIC CO., LTD., et al., Plaintiffs, v. ZENITH RADIO CORPORATION, Defendant.

Civ. A. No. 4672.

United States District Court, D. Delaware.

November 7, 1975.

COPYRIGHT MATERIAL OMITTED

James M. Tunnell, Jr., of Morris, Nichols, Arsht & Tunnell, Wilmington, Del., Edward F. McKie, Jr., Dale H. Hoscheit, and James A. Sheridan, of Schuyler, Birch, Swindler, McKie & Beckett, Washington, D. C., for plaintiffs.

Thomas S. Lodge, of Connolly, Bove & Lodge, Wilmington, Del., Dugald S. McDougall, of McDougall, Hersh & Scott, Chicago, Ill., for defendant.

OPINION

STAPLETON, District Judge:

I. PARTIES AND JURISDICTION

This is a declaratory judgment action which poses questions regarding the validity, infringement and enforceability of a patent on certain improvements in color television picture tubes. Plaintiffs, Tokyo Shibaura Electric Co., Ltd., Toshiba America, Inc., and Toshiba Hawaii, Inc., (hereinafter collectively referred to as "Toshiba") are respectively, a Japanese corporation and its wholly-owned New York and Hawaiian subsidiaries which sell color television picture tubes in the United States. Defendant, Zenith Radio Corporation ("Zenith") is a Delaware corporation whose principal place of business is neither New York nor Hawaii; venue is properly laid in this district under 28 U.S.C. § 1391(c). Toshiba seeks a judgment declaring the invalidity, non-infringement and unenforceability of Zenith's United States Letters Patent No. 3,146,368 (the "'368 patent"), issued August 25, 1964 to J. P. Fiore and S. H. Kaplan. Zenith, as their assignee, has counterclaimed for infringement of the '368 patent by Toshiba. These issues have been tried,¹ and I find that there exists a substantial and actual controversy between the parties on the issues presented in this action, justifying a declaratory determination of their respective rights.

II. BACKGROUND FACTS

The story of color television picture tube design begins almost half a century ago (see DX 21, p. 1177), but it is sufficient for present purposes to refer only to the period commencing in 1953, when the Federal Communications Commission determined that television pictures transmitted in color had to be "compatible" with — that is, able to be received on — conventional black and white television receivers.² Several different kinds of television picture tubes were proposed for use in the new "compatible" system and competed for favor in industry laboratories for some years. Although only one type ultimately entered commercial production, three types play a role in the present action and a description of the structure and operation of each is necessary.

A. Common Features Of Relevant Tubes

In all three types of tubes, the color picture seen by the viewer is created in the same basic manner. On the inside surface of the viewing screen³ of the picture tube are deposited a very large number of "phosphors" — chemical materials which have the property of emitting visible light when bombarded by electrons (Tr. 47). Different phosphors will emit light of different colors, and by placing phosphors which emit the three "primary" colors of red, blue and green in close conjunction with each other on the viewing screen, any visible color can be reproduced by bombarding a suitable combination of these phosphors (Tr. 61; DX 21, p. 1178). For convenience, these phosphors will hereinafter be called red, blue and green, even though they are in reality whitish except when being bombarded (Tr. 62, 448). The emitted colors can be made brighter or dimmer by varying the intensity of the bombardment (Tr. 46, 50).

This bombardment is accomplished by means of one or more "beams" of electrons generated by one or more "electron guns" which are mounted in the neck of the tube and which project the beams onto the viewing screen (Tr. 46-47). These beams bombard only a small portion of the screen at any one instant, but the different phosphors are so small and so close together, and the beam "scans" the viewing screen at so rapid a pace, that the human eye can perceive only a single color picture (Tr. 46-51).

The electrons striking the glass viewing screen have a tendency to remain there. Their accumulation can cause the screen to repel the similarly charged electrons aimed at it on the beam's next scan (Tr. 52), and for this reason a thin layer of aluminum is ordinarily placed on top of the phosphors on the inside surface of the viewing screen (see Fig. 3, infra). This layer not only conducts the electrons away from the screen after they have bombarded the phosphors but also increases the efficiency of the phosphors by reflecting out to the viewer the light initially emitted by the phosphors towards the inside of the tube (Tr. 52-53, 457).

B. The Shadow Mask Tube⁴

It is essential for any color picture tube to have means for assuring that the electron beam bombards the proper phosphor at the proper time and with the proper intensity — otherwise the resulting picture will not be the picture intended. The shadow mask tube, which is the type of tube used in every commercially available color television set today (DX 20, p. 2), accomplishes this essential function of color selection by utilizing three electron guns and a "shadow mask" from which it takes its name.

A shadow mask is a thin metal membrane which is placed inside the tube, immediately behind and parallel to the screen, as shown in this cross-sectional view:⁵

The mask is perforated with a very large number (a third of a million would be a typical number — DX 20, p. 42) of small apertures,⁶ each aperture positioned directly behind the center of a set or "triad" of three adjacent phosphor dots or stripes, one of each primary color.

In the shadow mask tube, the electron beams that bombard the phosphors come from a cluster of three electron guns, with each gun emitting the electrons intended to strike only the phosphors of a given color (DX 20, pp. 42-43). The geometrical relationship of the guns, the mask and the screen is designed such that the beams from the three guns converge at the mask, with each beam at a different angle. The result is that only so much of each beam as will strike the correct phosphor is able to pass through the mask:

(see Tr. 63-69; DX 20, pp. 12-14; PX 116 generally). It is in this manner that the color selection is achieved in a shadow mask tube.

Figure 2 is especially exaggerated in showing the shadow mask midway between the electron guns and the viewing screen. In reality, the mask is mounted immediately behind the screen (see PX 172), so that for practical purposes the size of the aperture in the shadow mask and the size of the electron beam landing area will be the same (Tr. 200, 598).

C. The Post-Deflection Focusing Tube

One disadvantage of the simple shadow mask tube, as can be seen in Figure 2, is that the mask intercepts the bulk of the electrons generated by the electron guns, thus considerably reducing the brightness of the picture which can be generated by a gun of a given efficiency (see Tr. 72-74). The post-deflection focusing, or "PDF", tube is a shadow-mask tube with a particular additional feature intended to mitigate this problem. The apertures in the mask are enlarged, permitting more electrons to pass through. Without more, this would defeat the color selection function of the mask. However, by operating the viewing screen at a higher voltage or potential than the shadow mask, the electron beams passing through the apertures can be focused down to acceptable size (see Tr. 197-199; 454-55; DX 20, pp. 14, 135). This type of tube, while offering an easily-achieved improvement in brightness, has a number of practical disadvantages not encountered in simple shadow mask tubes and has never entered commercial production (Tr. 116-17, 161, 196-97; DX 20, pp. 14, 154).

D. The Index Tube

In index tubes, the phosphors are deposited on the viewing screen in stripes. Only one electron gun is used; its single beam sweeps across the screen, bombarding the phosphors of each color in turn. There is no shadow mask; the electron beam has direct, unimpeded access to the screen. Color selection must thus be accomplished by precise synchronization of the position and modulation of this beam, so that, for example, it bombards only the red phosphors during those moments when it is transmitting red picture information (Tr. 1013-19; DX 20, pp. 15-16, 155-172). The practical problem involved in achieving this sort of control with the required precision has never been overcome with sufficient success to make commercial use practicable (Tr. 488).

III. PROBLEMS IN EARLY COLOR TELEVISION TUBES

Shadow mask color picture tubes of the sort described above were built in the laboratory as early as 1950, and were in commercial production by 1954 (DX 39, pp. 4-6). However, these early or "conventional" tubes did not project as good a picture as contemporaneous black and white television tubes. The reason lay in the interrelated problems of achieving "color purity", "white uniformity", "brightness" and "contrast".

Color purity and white uniformity are two sides of the same coin, the coin being proper registration of the electron beams with the proper phosphor areas on the screen. Ideally, the landing area of, for example, the red beam would be exactly coincidental with the red phosphor. If, however, the red beam is not in such perfect registration and impinges on a portion of a neighboring blue phosphor, the viewer will see blue where he was meant to see red (or, if the primary colors are being combined to produce an intermediate tint, the proper tint will not be seen). This is known as a loss of color purity and the misregistration causing it is called "clipping" because the electron beam "clips" a portion of the wrong phosphor.⁷ A loss of white uniformity, on the other hand, occurs when less than all of the electron beam reaching the screen falls within the confines of the...