Display device and cathode ray tube

A display device comprising:

• a cathode ray tube which comprises a display screen and a deflection unit for deflecting electron beams, the cathode ray tube including an in-line electron gun for generating three electron beams, said in-line electron gun comprising a main lens portion having means for generating a main lens field and a quadripolar field, and the electron gun has means for generating, in front of the main lens field, a pre-focusing lens field and a further quadripolar field, and the display device includes means for dynamically varying the intensity of the main lens field, the quadripolar field, the pre-focusing lens field and the further quadripolar field such that, in operation, the intensity of said four fields is dynamically varied by means of only one dynamic voltage, and wherein the ratio of the quotient of the change of the beam diameter in the horizontal direction (dBx) as a function of the dynamic voltage (V.sub.dyn) to the quotient of the change of the beam diameter in the vertical direction (dBy) as a function of the dynamic voltage, due to the combined action of the pre-focusing field and the further quadripolar field, complies with:
• -0.6.ltoreq.dBx/V.sub.dyn :
• dBy/V.sub.dyn .ltoreq.-0.2.
• 4.

A cathode ray tube comprising:

• an in-line electron gun which includes three cathodes, a first (G.sub.1), second (G.sub.2), third (G.sub.3) and a fourth electrode (G.sub.4), the third electrode comprising a first, a second and a third sub-electrode (G.sub.3a, G.sub.3b, G.sub.3c), a main lens being formed between the fourth electrode (G.sub.4) and the third sub-electrode (G.sub.3c), a quadripolar lens being formed between the third sub-electrode (G.sub.3c) and the second sub-electrode (G.sub.3b), a further quadripolar lens being formed between the second sub-electrode (G.sub.3b) and the first sub-electrode (G.sub.3a), and a pre-focusing lens being formed by the first sub-electrode (G.sub.3a), the second electrode (G.sub.2) and the first electrode (G.sub.1), and means for applying only one dynamic voltage to the first and third sub-electrodes and a focusing voltage to the second sub-electrode, and wherein the ratio of the quotient of the change of the beam diameter in the horizontal direction (dBx) as a function of the dynamic voltage (V.sub.dyn) to the quotient of the change of the beam diameter in the vertical direction (dBy) as a function of the dynamic voltage, due to the combined action of the pre-focusing field and the further quadripolar field, complies with:
• -0.6.ltoreq.dBx/V.sub.dyn :
• dBy/V.sub.dyn .ltoreq.-0.2.
• 5.

A display device comprising:

• a cathode ray tube including an electron gun for generating three electron beams, a display screen and a color selection electrode,
• a deflection unit mounted on said cathode ray tube, wherein
• said electron gun comprises plural cathode elements, electrode means arranged to form a main lens to derive a main lens field, a quadripole lens to derive a quadripolar field and a dynamic compound lens and which are positioned in the order named between the color selection electrode and said plural cathode elements, said dynamic compound lens producing a prefocussing field and a further quadripolar field and comprising first, second and third apertured electrodes arranged in sequence between the cathodes and the color selection electrode as to form a prefocus lens and a further quadripolar lens for producing said prefocussing field and said further quadripolar field, and said third electrode comprises first and second juxtaposed sub-electrodes with facing apertured surfaces of the first and second sub-electrodes having rectangular apertures with a length-to-width ratio of at least 1.5,
• means for supplying operating voltages to said electrode means for producing said fields, and
• means for applying a single dynamic voltage to a portion of said electrode means so as to dynamically vary the intensity of the main lens field, the quadripolar field, the prefocussing field and the further quadripolar field.

A display device comprising:

• a cathode ray tube including an electron gun for generating three electron beams, a display screen and a color selection electrode,
• a deflection unit mounted on said cathode ray tube, wherein
• said electron gun comprises plural cathode elements, electrode means arranged to form a main lens to derive a main lens field, a quadripole lens to derive a quadripolar field and a dynamic compound lens and which are positioned in the order named between the color selection electrode and said plural cathode elements, said dynamic compound lens producing a prefocussing field and a further quadripolar field,
• means for supplying operating voltages to said electrode means for producing said fields, and
• means for applying a single dynamic voltage to a portion of said electrode means so as to dynamically vary the intensity of the main lens field, the quadripolar field, the prefocussing field and the further quadripolar field, and wherein said means for applying a single dynamic voltage controls the dynamic compound lens so that for the dynamic compound lens the ratio of the quotient of the change of the beam diameter in the horizontal direction (dBx) as a function of the dynamic voltage (V.sub.dyn) to the quotient of the change of the beam diameter in the vertical direction (dBy) as a function of the dynamic voltage complies with:
• -0.6.ltoreq.dBx/V.sub.dyn :dBY/V.sub.dyn .ltoreq.-0.2.
• 15.

A display device comprising:

• a cathode ray tube including an electron gun for generating three electron beams, a display screen and a color selection electrode,
• a deflection unit mounted on said cathode ray tube, wherein
• said electron gun comprises plural cathode elements, electrode means arranged to form a main lens to derive a main lens field, a quadripole lens to derive a quadripolar field and a dynamic compound lens and which are positioned in the order named between the color selection electrode and said plural cathode elements, said dynamic compound lens producing a prefocussing field and a further quadripolar field,
• means for supplying operating voltages to said electrode means for producing said fields,
• means for applying a single dynamic voltage to a portion of said electrode means so as to dynamically vary the intensity of the main lens field, the quadripolar field, the prefocussing field and the further quadripolar field, and wherein;
• said single dynamic voltage varies as a function of the deflection angle of the electron beams, the variation of the electron beam diameter in the horizontal direction as a function of the dynamic voltage is between 20% and 60% of the variation of the beam diameter in the vertical direction, and the dynamic compound lens is a hybrid of a cylindrical lens and a quadripolar lens.