JPS595548A - Flat type cathode ray tube - Google Patents

Abstract

PURPOSE:To eliminate vignette of image due to deflection by performing focus of the vertical component with reference to the focusing voltage of the horizontal component through the effect of asymmetrical two-dimensional electrostatic lens which is formed between a pair of deflecting plates and a high voltage electrode of the final stage of an electron gun. CONSTITUTION:A voltage VH is applied to the phosphor screen 3, namely to a target electrode 6 and a high voltage VRH which is lower than such voltage VH is then applied to an opposing electrode 4. A deflecting plate 11a of the second deflection system is electrically connected to the electrode 4 and a constant voltage VRH is applied to this deflecting plate 11a. Meanwhile, a voltage obtained by superimposing a vertical deflection signal and a dynamic correcting signal voltage for vertical deflection to a constant voltage VRH given to the deflecting plate 11a is applied to the other deflecting plate 11b. A voltage obtained by superimposing the dynamic correcing signal to a DC focus voltage is supplied to the third grid G3. A voltage VG4, which is determined in such a manner that a ratio of such voltage of a voltage Vda (Vda=VRH in the example shown in the figure) to be applied to the deflecting plate 11a is selected in the relation of 0.97<=VG4/Vda<=1, is applied to the fourth grid G4.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flat cathode ray tube in which an electron gun is disposed extending in the direction along the surface of a phosphor screen, so that the tube body is flattened.

This type of flat cathode ray tube is composed of a flat tube body (1), as shown in FIGS. 1 and 2. This tube (1
) is, for example, a glass funnel (1b) that has a glass panel (1a) and a glass funnel (1b) that forms a flat space (2) between them and gradually becomes narrower toward one side, that is, funnel-shaped.
), and a glass neck (IC) provided on one narrow side thereof to communicate with the flat space (2).

Inside the flat tube (1), a phosphor screen (3) is arranged along the flat surface in the flat space (2), and a counter electrode (4) is arranged opposite to the fluorescent screen (3), so that both are connected to the tube (1). are arranged so as to face each other in the thickness direction. Thus, for example, the inner surface K of the funnel (1b) of the tube body (1).

A glass substrate (5) coated with a fluorescent screen (3) is adhered.

A target electrode (6) made of a carbon layer or the like is adhered to this glass substrate (5) K, and a pressure phosphor screen (3 ) is applied. On the other hand, the facing electrode (4) is constituted by, for example, a transparent electrode adhered to the inner surface of the panel (1a).

An electron gun (7) is disposed inside the neck tube (IC), and extends along the surface direction of the fluorescent screen (3) through approximately the center between the fluorescent screen (3) and the counter electrode (4). will be placed in

“This electron gun (7) has a cathode with a first grid Gl and a second grid G2 as shown in FIG.
, a third grid G3, and a fourth grid G4 are arranged in sequence, and the third and fourth grids G3 and G4 form a pi-potential main electron lens.

A high anode voltage is applied to the target electrode (6), that is, the phosphor screen (3), and a lower high voltage is applied to the counter electrode (4), so that the phosphor screen (3) (target electrode (
A first deflection system is formed between 6)) and the counter electrode (4).

Further, a second deflection system is configured between the electron gun (7) and the phosphor screen (3) arrangement section. This second deflection system horizontally and vertically deflects the electron beam emitted from the electron gun (7). Here, horizontal deflection is defined as deflecting an electron beam from an electron gun (7) in a direction that is almost perpendicular to the axial direction of the electron gun (7) and in the direction of the surface of the phosphor screen (3). ) This is a deflection in which the upper button beam is scanned horizontally, and vertical deflection is a deflection in which a similar beam is deflected in a direction perpendicular to the phosphor screen (3), so that the beam is directed onto the phosphor screen (3) in a direction perpendicular to the above-mentioned scanning direction. (8) is a deflection means forming this second deflection system, and this deflection means (8) converts, for example, horizontal deflection, which requires a relatively large deflection angle, into electromagnetic deflection. They are electromagnetic and electrostatic deflection types in which the vertical deflection is performed by electrostatic deflection and the other vertical deflection is performed by electrostatic deflection.

As shown in the Kx diagram and FIG. A core (9), an electromagnetic wire ring for carrying a horizontal deflection current, and a pair of internal pole pieces arranged in the tube (1) for example Mn-Zn ferrite or Ni for electrostatic deflection.
- It is constituted by deflection plates (lla) and (llb) made of a high permeability magnetic material such as Zn ferrite.

The deflection plates (lla) and (llb) are arranged opposite to each other in the thickness direction of the tube body (1) with the electric beam path in between, that is, juxtaposed with the counter electrode (4) and the fluorescent screen (3), respectively. It is arranged as follows. The magnetic core (9) has an annular shape surrounding the outer periphery of the tube (1), and the deflection plate (lla) of the tube (1)
) and (llb), opposing outer center balls (12a) and (12b) are made to protrude inwardly, and wire rings (10a) and (10b) are attached to the outer peripheries of these outer center balls (t2a) and (12b). or a wire ring (10a) or (10b) is wound around the outer periphery of one of them. In this way, the line ring (Iol ((xoa)
(xob) ) is passed between both outer center balls (12a) and (12b), and further between the inner pole piece/electrostatic deflection plate (lla) and (
llb) to apply a horizontal deflection magnetic field in the thickness direction of the tube (1) across the path of the electron beam. -Kichirei Mukaiita (lla)
A vertical deflection signal voltage is applied between and (llb) to apply a vertical deflection electric field to the path of the electron beam in the thickness direction of the tube body (1).

According to such a configuration, the electron beam b emitted from the electron gun (7) is deflected by the second beam by the horizontal/vertical deflection means (8).
The target electrode (6) (phosphor screen (3)
)) and the counter electrode (4), the electron beam b is deflected toward the phosphor screen (3) by the first deflection system formed between the phosphor screen (3) and the counter electrode (4). (3) made to scan horizontally and vertically; In this way, the luminescence image obtained on the phosphor screen (3) by the scanning of the electron beam b is observed from the panel (1a) side, for example, through the transparent counter electrode (4).

However, in a flat cathode ray tube with a very simple configuration, the scanning position where the horizontal electromagnetic deflection and the vertical electrostatic deflection are maximized, that is, the electrons on the phosphor screen (3), is The largest defocus of the beam spot occurs at scanning positions on the left and right sides of the bottom side of the phosphor screen (3), which correspond to the side closer to the gun (7), for example, and the so-called "blur" caused by this K becomes a problem.

First, with reference to FIG. 4, the occurrence of 6' blurring of the beam spot in relation to vertical deflection will be considered.

Now, as shown in Figure 5, an electron beam b arrives on the axis O-0' between the electrostatic deflection plates (lla) and (llb) facing each other, and ) of this beam spot on the entrance side of the electrostatic deflection system Sp
Let us consider a state in which the electron beam has a circular cross section with a radius ri as shown in the figure, and arrives while being focused by the electron lens of the electron gun (7) described above. In this case, both side plates (l
In an undeflected state where a predetermined positive isopotential V is applied to la) and (11b) with respect to the cathode potential and no deflection voltage is applied between them, beam b is Proceeds on the axis O-0'. At this moment, the fluorescent screen (
Looking at the beam spot 5PIC on the plane fI perpendicular to the axis o-o' at the distance from the deflection plates (lla) and (llb) on the incident side of 3), this spora) 5P
The IC has a nearly circular shape. However, now, for example, fluorescent screens (
A positive potential is applied to the deflection plate (lla) K cathode on the side opposite to the arrangement side of 3), and the deflection plate (llb)
Considering the case where a positive deflection voltage vD is applied to the deflection plate (lla), these deflection plates (lla) and (
The beam b that passes between the deflection plate (lla) and the opposite side corresponds to the potential difference between the two side plates (lla) and (llb), and the beam b passes between the deflection plate (lla) and the opposite side in the direction of the axis O-0' of the electron. The respective speeds va and vb of are different, and in this example, Va < vb
Due to this difference in speed, the deflection plates (lla) and (llb) are closer to and farther from the deflection plate (lla).
) There is a difference in the ease with which vertical electrostatic deflection is received based on the potential difference VD between the two electrodes.

That is, in this case, electrons passing closer to the deflection plate (lla) are more easily deflected than electrons passing closer to the deflection plate (llb) K. This will result in the occurrence of Now, in an undeflected state, the beam beam at the plane fI) of 5PIC,
When the width in the direction orthogonal to the phosphor screen (3) is N, the beam spot 5PI on the plane fi when the above-mentioned deflection voltage of +■D is applied between the deflection plates (lla) and (nb)
Similar to SO1, the width in the vertical direction to the fluorescent screen (3) is N+ΔNV
This is given by the so-called "blur". Here 8 is
The distance between the two side plates (lla)' and (llb), i is the length of the deflection plates (lla) and (llb), and L is the distance between the deflection plates (lla) and (llb).
1a) and (llb) and the plane f). This spora) 5 pss on the phosphor screen (3) due to 8 PIS is such that the incident angle θ (the angle between the direction of incidence of the beam on the phosphor screen (3) and the perpendicular to the phosphor screen (3) K) is θ. Since the angle is 0°, the distortion of spot 5PSS on the trap and fluorescent screen (3) is even greater.
The amount of "brush" in the vertical scanning direction of 5 pss on this phosphor screen (3) is given as follows.

In fact, the beam focusing on the phosphor screen (3) is based on the so-called circle of least confusion, which allows a bright spot to be obtained on the phosphor screen (3) by forming the main spot in the area where the density of paraxial light is high. It is adjusted to slightly overfocus like the one obtained, but in this case, the phosphor screen (
As shown in Figure 4, the beam spot in 3) 5 pss is a spot that is bright in the center and has a wide tail at the periphery, especially in the vertical scanning direction, and this tail increases the noise level of the image. This results in a decrease in resolution.

Next, horizontal deflection pressure will be discussed with reference to FIG.

As mentioned above, this horizontal deflection is performed by using the internal pole pieces/deflection plates (lla) and (llb) as magnetic poles and by the magnetic field between them.
Figure 4 shows the case where an electron beam b having a spot SP is incident on the axis O-0' on the entrance side of an electromagnetic deflection system similar to that shown in Fig. 4. In a state where no magnetic field is formed, that is, no horizontal deflection, beam b has an axis of 0-0.
Suppose that the focus position is point Z' and the distance from the center of deflection of its deflection magnetic field is Z.

When a horizontally deflecting magnetic field (magnetic field in the direction perpendicular to the plane of the paper) is applied between the pole pieces (lla) and (llb), the beam b has a focus position z'' as shown by the solid line in FIG. Its distance from the center of deflection is smaller than the distance Z, and it is located inside an arc f drawn with radius Z around the center of deflection.In FIG. At the center of curvature of the deflection locus for electrons passing through the left and right side lines regarding the direction, λ1 and λ2 indicate the deflection angles, respectively.Yl and Y2 are the front end and the deflection magnetic field due to the pole pieces (11a) and (llb), respectively. Each position of the rear end is shown.As mentioned above, the 7-occus position from the deflection center is different between the non-deflection state and the deflection state.Therefore, the horizontal spot width in the above-mentioned arc f[ is beam deflection in deflection state) 5pa
sQ is larger than the spot width in the non-deflected state, and the difference ΔNH is given by ΔNH=(1180λ−1)Zθ λ2zθ/2 (3). Here, θ is the beam convergence angle, and λ is the beam deflection angle (λ1=λ2=λ). In this way, in the arc fn, the width of the beam spot 5pns in the deflected state is larger than the spot width in the non-deflected state by an amount of 1" blur of ΔNH, but the amount of 'blind' between A plane f that is perpendicular to the center O-0' and where, for example, an undeflected beam forms a circle of least confusion
In ■, it is further expanded, and this amount of 6" is the deflection angle λ
is largest on the left and right sides of the horizontal direction (up and down in FIG. 5).

This kind of "blur" in both the vertical and horizontal directions is
In a flat cathode ray tube in which vertical electrostatic deflection and horizontal electromagnetic deflection are performed at the same position, a mixed defocus occurs due to a 1" blur of both. In other words, as shown in FIG. A circular cross-section spot SP is created by the deflection system between the Seiden deflection plates (lla) and (llb).
Looking at the spot SP' when the electron beam b, which has a
The left and right ends A and B in the horizontal direction and the upper and lower ends C and D in the vertical direction perpendicular to these are the points A' and B', C' and D' of the spot SP' on the phosphor screen (3). Corresponding to this, rotation occurs due to the difference in beam velocities VB and vb explained in FIG. This results in a distorted spot.In this way, the fluorescent screen (
3) Significant distortion occurs in the beam spot, particularly on the left and right sides of the beam incidence side (lower part of the screen), which causes a significant drop in resolution.

Then, K that removes such mixed defocus is
The radius ri of the spot SP of the electron beam b entering the deflection system is reduced by (1) to (3) 2 above, and the beam velocity Y3 is
In order to reduce the difference between and vb, it is possible to make the convergence angle θ as small as possible or to make the horizontal deflection angle λ small. However, the reduction of ri and θ is due to the electron gun (
7) It is necessary to make the distance from the main electron lens to the deflection system sufficiently large, which leads to the disadvantage of a large tube length. Furthermore, when the beam current is increased, these ri and θ inevitably become large. turn into. Also, to reduce the deflection angle λ.

In order to obtain a screen of the same size, the tube length must be increased, which hinders the miniaturization and light softening of this flat cathode ray tube.

Furthermore, in the case of the flat cathode ray tube configuration described above, it becomes a post-acceleration type configuration, but in the first deflection system, that is, the deflection system formed between the target electrode (6) and the counter electrode (4). , because a higher voltage is applied to the target pole (6) than to the counter electrode (4), the electron beam arriving here is directed to the side closer to the counter electrode (4) at that spot. and target electrode (6
), there is a difference in the degree of acceleration, and the speed on the side closer to the counter electrode (4)K is smaller than on the side closer to the single pole (6). Therefore, the electrons closer to the counter electrode (4)K are larger than the electrons closer to the target electrode (6) than the electrons closer to the fluorescent screen (3) in the first deflection system.
) is strongly deflected toward the side. Therefore, the electron beam is converged in the thickness direction of the tube by this first deflection system, that is, the spot on the phosphor screen (3) is converged in the vertical direction. This phenomenon becomes more pronounced as the range of the first deflection system is longer, that is, the beam is directed toward, for example, the upper side of the phosphor screen (3), which corresponds to the side farther from the electron gun (7) on the phosphor screen (3). Because the electron beam becomes overfocused, the beam spot on the phosphor screen (3) is
"Bokeh" also becomes noticeable.

In the present invention, the horizontal/vertical electromagnetic deflection means is specially designed to avoid the above-mentioned "brush" in a flat cathode ray tube that has a mixed electromagnetic and electrostatic configuration. The object of the present invention is to provide a flat cathode ray tube that can effectively avoid the occurrence of this 6" blur without or with almost no provision.

That is, the "1 blur" due to electrostatic deflection explained in FIG. 4 is ultimately the result of the convergence effect of the vertical component of the electron beam in the deflection system.It also means a shift from the focal point of the horizontal component.

Therefore, if the focus voltage of the electronic lens system is adjusted to the horizontal component, the vertical component tends to be overfocused. Therefore, to correct this, it is sufficient to diverge only the vertical component. On the other hand, the electromagnetic deflection blur explained in FIG. 5 is a result of the focusing effect of the horizontal component of the electron beam. It also means a vertical component defocus. Therefore, when the two-orcus voltage of the electron lens system is combined with the vertical component, the horizontal component becomes slightly over 7 orcuses.

Therefore, to correct this, it is sufficient to diverge only the horizontal component. The rotation of the beam in the mixed defocus described in FIG. 6 is determined by the horizontal deflection angle and the velocity pressure at the upper and lower ends of the beam. As for the correction method, as described above, it is sufficient to use either the horizontal component or the vertical component focus voltage as a reference and adjust the other.

The present invention focuses on the vertical component based on the focus voltage of the horizontal component on the electron beam entrance side of the pair of deflection plates constituting the deflection system, and on the high-voltage electrode at the final stage of the electron gun. This is done by the effect of an asymmetric two-dimensional electrostatic lens formed between the fourth grid G4 and the fourth grid G4. In this way, the focus voltage of the horizontal component is used as the reference.
The dimensional electrostatic lens is based on the fact that there is almost no lens effect in the direction of the plane in which the electrostatic deflection plate is arranged in this second deflection system, and therefore it is difficult to receive the focusing effect of the horizontal component.

That is, the flat cathode ray tube according to the present invention can have a structure that is almost the same as the cathode ray tube explained in FIGS. The voltage relationship between the fourth grid G4 voltage and the deflection plate constituting the electrostatic deflection system in the second deflection system is specified.

FIG. 7 shows the electrode arrangement of essential parts of a flat cathode ray tube according to the present invention, and parts corresponding to those explained in FIGS. 1 to 3 are designated by the same reference numerals and redundant explanation will be omitted.

In the present invention, the fluorescent screen (3), i.e., targetera)
[A high voltage vH is applied to the pole (6), and a high voltage VRH lower than this high voltage vH is applied to the counter electrode (4). Further, for example, the deflection plate (11a) and the electrode (4) arranged on the same side as the counter electrode (4) of the second deflection system are electrically connected, and a fixed voltage VRH is applied to the deflection plate (lla). give.

In addition, a deflection plate (lla) is attached to the other deflection plate (llb).
A vertical deflection signal voltage is added to the fixed voltage VRH given by K, and further,
A voltage superimposed with a vertical deflection dynamic correction signal voltage synchronized with the horizontal scanning period is applied. Then, a voltage obtained by superimposing a dynamic correction signal voltage synchronized with the vertical scanning period on the DC focus voltage is supplied to the focus electrode, in the illustrated example, the third grid G3. And the electron gun (7
), the fourth grid G4 in the example shown.
The voltage VG4 applied to the polarizing plate (11a) is selected to be a ratio of the voltage Vda (Vda=VRH in the illustrated example) applied to the deflecting plate (11a) on the side juxtaposed with the counter electrode (4).

In order to facilitate understanding of the present invention, FIGS.
Let's look at the focus mode of the electron beam with reference to the figure. Each figure a in FIGS. 8 to 13 is a diagram showing the flight state of the electron beam b, and each figure shows the electron beam b, especially the final stage electrode G4 of the electron gun, the deflection plate (llsi), and the ( llb
) is a diagram showing the lens action of a two-dimensional electron lens formed by
Denote the velocity at the center of the beam b incident on the dimensional electron lens.

va and vb are the deflection plates (tta
) side and the deflection plate (llb) side. In addition, Ea and Eb in each figure are these two
In a dimensional electron lens system, deflection plates (lla) and (ll
b) indicates the electric field experienced by electrons with velocities vB and vb passing through the sides, va' and vb' indicate the respective velocities of electrons with respective velocities va and vb after being deflected by the electric fields Ea and Bb . Then, the voltage VH and VRH of the pole (6) and the counter electrode (4) forming the first deflection system are VH = 8kV, VRH = 6.
This is the case when the voltage is 25kV.

First, with reference to Figures 8 to 10, determine the percentage of the fluorescent screen (3).
Let us consider the case where the electron beam b is landed closer to the electron gun, that is, for example, on the lower side of the phosphor screen (3). In these examples, the applied voltage V to the deflection plate (lla)
da to the same potential VRH as the counter electrode (4), i.e. 6.2
skV, and the deflection plate (llb) has vRH+ Vdef=
This is a case where 6.35 kV is applied and 1.32 kV is applied to the third grid G3, that is, the focus electrode. That is, in FIGS. 8, 9, and 10, although the electron beam b is directed toward the lower side of the phosphor screen (3), the states of the first and second deflection systems are kept constant. This is a case where only the applied voltage VG4 to the fourth grid G4 is changed to change the asymmetric two-dimensional lens formed by the fourth grid G4 and the deflection plates (lla) and (llb). FIG. 8 shows how the voltage VG4 applied to the fourth grid G4 is applied to the deflection plate (ll
a) Applied voltage Vda (in this example, Vda = VRH
) Turn large key 6.35kv ■G4/Vda >
This is the case where it is set to 1. Figure 9 shows the case where VG4 is set to 6.20kV, which is lower than Vda, and VG'/Vda is set to -0.99.Furthermore, Figure 10 shows the case where VG4 is set to 5.Qlcv, which is sufficiently low to raise Vda. = 0.
This is the case where it is set to 96.

As is clear from comparing these, in the case of FIG. 8, the electron beam b is decelerated on the deflection plate (lla) side, and its velocity v
a becomes small and is further deflected by the electric field Ea generated by the two-dimensional electron lens formed here, but the deflection plate (
Regarding the electrons on the llb) side, their velocity vb is greater than va, and the electric field Eb due to the two-dimensional electron lens here
Since Ea is smaller than Ea, its deflection is small. Therefore, in this case, the electron beam has a strong convergence effect in the vertical deflection direction due to this two-dimensional electron lens system, and the beam b becomes overfocused as shown in Figure f3-a and reaches 6. In contrast, in the case of FIG. 10, the deflection plate (l) of the electron beam b
Since the deflection that the electrons on the la) side receive from the electric field Ea of the two-dimensional electron lens that acts on them is smaller than the effect that they receive from the electric field Eb that acts on the electrons on the deflection plate (llb) side, the beam is deflected by the two-dimensional electron lens. , there is a substantially strong divergence effect in the vertical direction, resulting in the 10th
As shown in Figure 1-a, underfocus occurs, and in this case as well, the beam spot becomes blurred on the fluorescent screen (3). However, in the case of Figure 9, the two-dimensional electron lens system produces a weak divergence effect in the vertical direction, and this is one of the reasons for the occurrence of the 1-boke on the phosphor screen mentioned above. By relaxing the convergence effect, the electron beam b can be brought into just the right focus state on the phosphor screen (3) as shown in FIG. 9-a.

Next K, referring to Figures 11 to 13, fluorescent screen (3)
Let us consider the case where the electron beam b is landed on the side far from the electron gun, that is, for example, on the upper side of the phosphor screen (3). In these examples, the voltage Vda applied to the deflection plate (lla) is set to VRHl, that is, 6.25 kV, f
Li facing plate (llb) K VRH-0,25kV (7
) 6. 1, akV, t, 3skV, to the third grid G3, i.e. the focus electrode
t3okV woin7+oL ta case. 11, 12, and 13, although the electron beam b is directed toward the upper side of the phosphor screen (3), the states of the first and second deflection systems are kept constant, This is a case where the voltage VG4 applied to the fourth grid G4 is changed to change the asymmetric two-dimensional lens formed by the fourth grid G4 and the deflection plates (lla) and (llb). Figure 11 shows the fourth
If the voltage VG4 applied to the grid G4 is 6.35 kV greater than the voltage Vda applied to the deflection plate (LA) (Vda = VRH in this example), then vG4/Vda>1. Figure 12: vG4, vda, low ai 6,2
0kV and vG4/Vda ''-0.99. Fig. 13 shows the case where VO2 is set to Vda by 6.0kV and vG4/Vda is set to 0.96.

In this case, in the case of FIG. 11, the electron beam b is decelerated on the deflection plate (llb) side, its velocity vb becomes small, and the electric field Eb due to the two-dimensional electron lens formed here
However, the electrons on the deflection plate (lla) side have a velocity va greater than vb, and the electric field Ea due to the two-dimensional electron lens here is smaller than Eb K:, so the deflection is small. Therefore, in this case,
This two-dimensional electron lens system causes a strong convergence effect on the electron beam b in the vertical deflection direction, and the beam b
As shown in Figure a, overfocus occurs and "blur" occurs on the phosphor screen (3). In contrast, in the case of FIG. 13, the electrons on the deflection plate (lla) side of the electron beam b are deflected by the electric field Eb of the two-dimensional electron lens acting on them, and the electrons on the deflection plate (lla) side are Since the effect is smaller than that exerted by the acting electric field Ea, the beam undergoes a substantially strong diverging effect in the vertical direction due to this two-dimensional electron lens, resulting in an under-7 orcus as shown in Figure 13-a. Even in this case, the beam spot becomes blurred on the fluorescent screen (3). However, the 12th
In the case shown in the figure, a two-dimensional electron lens system produces a weak divergence effect in the vertical direction.
In order to alleviate the convergence effect in the first deflection system, which is one of the causes of "brushing", the electron beam b can be brought into just the right focus on the phosphor screen (3) as shown in Figure 12-a. This is what you are getting and what you are getting.

In this way, if both the conditions shown in FIGS. 9 and 12 are satisfied, good horizontal and vertical focusing can be achieved over the entire raster area, including the upper and lower regions of the phosphor screen (3). . From the experimental facts, the fourth grid G
4 and the applied voltage VG4 to the image direction plate (lla) and (ll
The voltages Vda and Vdb in b) are as follows: When scanning the bottom of the screen, Vdb >Vda': 2 VO2''・(5) When scanning the top of the screen, vdb <VO2<Vda・''...(6)
It was confirmed that the selection should be made as follows.

The solid and broken line curves in FIGS. 14 to 19 indicate the difference between the third grid voltage VG3 and the fourth grid voltage VG4, which can obtain good focus conditions in the horizontal and vertical directions in each scanning state for each part of one screen. The measurement results are shown. In either case, VH = 8.0kV, Vd
a = VRH = 6.25kV, vctb -
In the case of 6,35 kV, Figs. 14, 15, and 16 are scans for the right, left, and center portions of the lower part of the screen (the side near the electron gun), and Figs. 17 and 18 19 and 19 respectively show the scanning conditions for the left, right, and center portions of the upper part of the screen (position far from the electron gun). The applied voltage Vda to 11a) is around 6.25 kV,
and below, good focus is obtained in both the horizontal and vertical directions, and from this, the K that obtains good focus in both the horizontal and vertical directions is based on the conditions of equations (5) and (6) above, so VO2<, Vda. It's fine if you're satisfied. And the ratio of both is VG4. /'N'da is 0.9
7 <VG4/Vda<1 (7)
It has been confirmed that it is good if it is selected, and in the present invention,
It is selected so as to satisfy this equation (7).

In the specific configuration, as shown in FIG. 20, the potential vH of the phosphor screen (3) is selected to be 8.0 kV, and the
□ Plate (lla) and fourth grid q4 are pressed against the same t-pressure vRH of the counter electrode (4) ■RH = 6.2
The potential is fixed at 0 to 6.25 kV, the electric field between the fluorescent screen (3) (target electrode (6)) and the counter electrode (4), that is, the electric field E of the first deflection system is tokV/clear, and the other deflection Plate (llb) 6,0 with K vertical deflection signal voltage applied
~a+kV, and the potential of the third grid G3 is 1.25~
Apply dynamic focus correction voltage at 1.38 kV.

Next, looking at the allowable range of 1" blur due to electromagnetic deflection, from equation (3) above, this deflection blur is proportional to the square of the deflection angle λ, and the radius Z from the center of deflection to the focus point Z'
is proportional to the first power of the convergence angle θ, but in the above equation (3), λ2ZmiW is used, and the allowable range of this W was determined based on experimental results. Table 1 shows the results. Note that Table I shows a comparative example in which the fourth grid G4 is connected to a deflection plate (llb) as shown in FIG. It can be seen that the

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a front view of a flat cathode ray tube used for explaining the present invention, FIG. 2 is a partially sectional side view, and FIG. 3 is a configuration diagram of the electrode arrangement. 4 through 6 are explanatory diagrams of the deflection brush, FIG. 7 is an electrode configuration diagram of an example of a cathode ray tube according to the present invention, and FIGS. 8 through 13 are respectively illustrations of optical paths of electron beams used to explain the present invention. 14 to 19 are explanatory diagrams of focus conditions, and FIGS. 20 and 21 are concrete configuration diagrams of an example of a cathode ray tube according to the present invention and a comparative example, respectively. (1) is a flat tube, (3) is a fluorescent screen, (4) is a counter electrode, (6) is a target electrode, (7) is an electron gun, (8) is a deflection means, (lla) and (llb) is an internal pole piece and electrostatic deflection plate. Figure 4 Figure 5 P. Figure 6 Figure 9-a Figure 9-b

Claims (1)

[Claims] A phosphor screen and a counter electrode that face each other in the thickness direction are provided in the flat tube, and a first deflection system is formed between the two, and a phosphor screen that faces the first deflection system in the plane direction of the phosphor screen is provided. An electron gun is disposed extending along the phosphor screen, and between the electron gun and the first deflection system, a second deflection system is formed by electromagnetic deflection and electrostatic deflection for horizontal and vertical scanning deflection of the electron beam with respect to the phosphor screen.
A deflection system is formed, and the second deflection system is juxtaposed with the fluorescent screen and the counter electrode across the path of the electron beam emitted from the electron gun and directed toward the first deflection system. The electron gun is provided with a pair of internal pole pieces and electrostatic deflection plates arranged to face each other so that a deflection electric field and a deflection magnetic field are formed between the pair of internal pole pieces and electrostatic deflection plates. The ratio between the voltage VG4 of the high-voltage electrode at the final stage and the voltage Vda of the internal pole piece and static deflection plate on the side juxtaposed with the counter electrode is vG4/Vda 0.97 <V
A flat cathode ray tube selected for G4/Vda<''.