JPH02109491A - Projection type display device - Google Patents

Abstract

PURPOSE:To compensate deterioration in the focus by forming 2-pole magnetic field for horizontal vertical auxiliary deflection and forming orthogonal 4-pole magnetic fields and controlling the 4-pole magnetic fields in proportion to a waveform including a quadratic function of the scanning position coordinate on the screen. CONSTITUTION:A horizontal deflection sawtooth wave signal X and a vertical deflection sawtooth wave signal Y are inputted to quadratic signal generating circuits 12, 13, from which quadratic function signals k1X<2>+k2XY+k3Y<2>+k4X+ k5Y+k6 (k1-k6 are constants). The quadratic function signal is given to aberration correction coils 18, 19 via negative feedback amplifiers 14, 15 to cause a current in response to the quadratic function signal thereby controlling the orthogonal 4-pole magnetic fields generated from them.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improving the focus of a projection display.

[Prior art] CRT for conventional projection type electromagnetic focus display
Figure 2 shows the arrangement of the main body and its peripheral parts.

In the figure, 1 is a CRT face, 2 is an electron gun, 3 is a deflection coil, 4 is an electromagnetic focus coil, and 5 is an auxiliary deflection coil for convergence correction. McGraw-Hill Publishers [M
cGRAi-HILL BOOK COMPANY, I
"Te1evision" published in 1957 by NC]
Engineer-ing Handbook”by
D, G, Fi, nk, p16-195-p16-19
6 is known.

[Problem M to be solved by the invention] In the prior art, there was a problem in that it was difficult to reduce aberrations caused by dimensional variations in components. A technique has been described in which this aberration is absorbed by mechanically slightly moving the lens, but this adjustment method has the problem of requiring extremely sophisticated techniques. Another problem is that it is difficult to absorb focus deterioration (aberration) caused by variations in the winding distribution of the deflection coil.

An object of the present invention is to provide a means for compensating for focus deterioration in the prior art described above.

[Means for Solving the Problems] The above object is to form at least two conventional magnetic fields for horizontal and vertical auxiliary deflection in an auxiliary deflection yoke for convergence correction.

This is accomplished by providing means for forming quadrupole magnetic fields that are substantially orthogonal to each other, and means for controlling the quadrupole magnetic fields in proportion to a waveform that includes a slightly quadratic function of the scanning position coordinates on the co-screen.

[Effects] As will be clarified by the analysis described below, the main aberration that occurs due to variations in the winding distribution of the deflection coil is astigmatism, and this astigmatism is a quadratic function of the coordinates of the position of one screen. It is expressed as Each quadrupole magnetic field orthogonal to each other corrects two independent astigmatisms.

In addition, since the astigmatism correction amount is controlled by a substantially quadratic function of the screen position coordinates, a desired correction effect can be obtained.

[Example code] FIG. 1 shows the first embodiment of the present invention. An example is shown below.

In the same figure, CRT face 1, main deflection coil 3, electromagnetic)
The cass coil 4 is the same as the prior art shown in FIG. 6 is a well-known horizontal/vertical deflection circuit; 7 is a well-known horizontal/vertical deflection circuit;

The well-known electromagnetic focus circuit 9 is a well-known convergence circuit (or also referred to as a registration circuit).

Sections 8.10 to 19 are the essential parts of the present invention.

8 is an auxiliary deflection and aberration correction yoke including an auxiliary deflection coil and an aberration correction coil. The details are.

As shown in FIGS. 3 and 4.

In FIG. 3, 20 is a six-pole piece. 2
1 (FIG. 3(a)) and 22 (FIG. 3(b)) are horizontal/vertical auxiliary deflection coils, respectively. Each of these generates a magnetic field in the direction of the arrow shown in the space inside the neck of the CRT, thereby auxiliary deflection of the electron beam.

In FIG. 4, 20 is the same 61 pole piece as in FIG. 3. 18 shown in FIG. 4(a) is the first four transverse magnetic field forming windings that form a magnetic field in the direction of the single arrow in the figure, and each part of the spread of the electron beam is minutely deflected in the direction of the double arrow. do. Reference numeral 19 shown in FIG. 4(b) indicates the second four transverse magnetic field forming windings. The first magnetic field and the second magnetic field are approximately orthogonal to each other.

Reference numeral 23 shown in FIG. 4(C) indicates six transverse magnetic field forming windings.

Windings 18 and 19 are shown in FIG. 1, while winding 23 has been omitted in FIG. 1 for simplicity.

Returning to FIG. 1, 10 is a horizontally polarized sawtooth signal;
11 is a vertically polarized sawtooth signal.

This is the well-known sawtooth waveform, each with a horizontal/vertical period. These are respectively expressed as x and y (each a function of time) below.

1-2.13 is a quadratic function that generates a quadratic function signal of the form (7), where 6 is a constant, 1X"+, 2XY+, Y"+, X+, Y+ This is a signal generation circuit. 14 and 15 are negative feedback amplifier circuits. 16 and 17 are resistors for detecting the current flowing through the aberration correction coils 18 and 19. With this configuration, it is possible to flow current in the aberration correction coil according to each quadratic function of -X13', and therefore, the quadrupole magnetic field formed by each coil is controlled according to each quadratic function.

Although not shown in the figure, 23-6 transverse magnetic field winding 2 in Figure 4
3, but 12.14. in FIG. .

A processing amplifier circuit of the same type as No. 16 is used to control the hexapole magnetic field.

The reason why aberration correction is achieved with the above configuration will be explained in detail below.

The present invention was obtained based on detailed analysis described below.

FIG. 5 shows the pattern of the distribution n(α) of the number of turns per unit length of the horizontal deflection winding of the main deflection coil 3. The origin of the orthogonal coordinate system and polar coordinate system is set at the center of the CRT neck cross section.

First, the unevenness of the magnetic field distribution inside the CR, T neck, which causes aberrations, is quantitatively determined as a function of n(α).

n(α) is a periodic function number linear expression with a period of 2π.

It can be decomposed into a Fourier series.

- φ (z) = Real f (z) If the magnetic potential along the inner surface of the deflection coil, that is, the outer circumference of the neck, is φ (Re), then the space outside the deflection coil is made of a core material with sufficiently large relative magnetic permeability. To stay fulfilled.

-P (Re)E f I, n(α)d(Rα
) n n If the magnetic field in the space inside the neck is H(z), then the complex function f
If the real part of (z) is X and the imaginary part is Y, then (X=-φ) f(z)=X+jY f (z) is regular, so from Cauchy's condition aX
aY ay ax holds true. Therefore.

Since there is no magnetic source in the space inside the neck, the magnetic potential φ(z) in the space inside the neck is also given in the same form as formula ■. , Equation (1 represents the magnetic field due to the horizontal deflection coil.

As can be seen from the above equation, the magnetic field of the 2n pole component is proportional to (Z).

Usually, in the formula ■, ao is a real number 1 In the formula ■, −Ja
m means the magnetic field in the imaginary axis direction (X direction), and therefore means the deflection of the electron beam in the horizontal direction (X direction).

0=a2=a, =......If ■ holds true, H(z)Ej Ik a.

That is, a -like magnetic field is obtained.

In order to avoid focus deterioration, the influence of a −-like magnetic field on defocus will be explained step by step.

Effect on geometric distortion In FIG. 6, the activation of the core of the electron beam is shown at 24.

In the figure, the origin corresponds to the starting point of the deflection coil 3, and a real number coordinate ρ is set in the tube axis direction, and a complex number coordinate Z is set in the plane perpendicular to the tube axis. It is approximated that the magnetic field of the deflection coil 3 exists only in the interval Q=[0, Ql]. According to the well-known deflection physics, the electron beam moves in a circular motion at a constant angular velocity within the magnetic field presence zone, and the sine of the resulting deflection angle θ is proportional to a, I, based on the assumption of 20.

sinθ,=ka□1. -■k here
is a proportionality constant, and the amount of deflection Z2 on the faceplate is proportional to tanO. The deflection amount Z at the end point of the deflection section is also approximately tanθ
, is proportional to .

1Z21″r(+Q+z) tanθ8ax+ a,
The influence on the geometric distortion of the image and...■ ・,・2侃Q2(parabolic motion) ρ.

I Z, l ″knee tan θ,
−(!I) 82T a when 2〇 does not hold
The contribution of , will be explained next.

The result is to find how much the deflection angle θ□ undergoes perturbation displacement due to the contribution of az + a3 along the trajectory of the electron beam in the interval u=[o, Q□ 0 Usually, in a projection display In a CRT for use, θ. The value of is 0.5
rad or less. Therefore, the circular motion of the electron beam can be approximated by a constant parabolic motion in the Q-axis direction.

That is, the problem boils down to finding H I V, which is obtained by averaging H(z) of 20 along the trajectory shown in FIG.

H,,: f H(z) dW (z) −
efi where dW (z) is the weighted component i, ρ1 is the residence time rate.

z1 mi
Variations in geometric distortion occurred on the order of 17% and 3rd order distortion of 0.2S%. However, these were at a level that is normally acceptable for the intended use of the display.

Although the horizontal deflection magnetic field has been described above, the same applies to the vertical deflection magnetic field.

This concludes the explanation of geometric distortion, and next the influence on defocus will be explained.

Influence on Defocus As shown in FIG. 7, the spread diameter of the electron beam in the deflection section is assumed to be 2r. The relative coordinates of each part of the beam with respect to the beam center are set to 20, and in order to obtain the scale of the above formula, standardize it with the mean action magnetic field HM corresponding to the right edge of the horizontal screen and the horizontal deflection magnetic field at that time. .

Hii mijalI.

Expressed as

The average acting magnetic field with respect to the core of the beam is as shown in the above equation 0. Each part of the beam is divided into a set of 0
via a different average working magnetic field. This is expressed as Hl-(z
o). The difference between Hl, (zIll) and H&V is written as Δi(,, (zO). Then, H--(zo)"
fH(z+zo)dW (Z)ΔH,,(za) =
/ (t+(z+z,)-11(z))d W (z
)2〇, substitute 0.

The magnitude of the above equation can be regarded as a relative value of the amount of defocus on the CRT face with respect to the opposite screen width.

At the right end of the screen, it is ``I'', and it is large in the electromagnetic focusing method. Substituting these values.

For narrow displays, it is desirable that the deflection defocus is less than L/1000 converted to formula O.
In order to make the spot size about 1 pixel, the size of Equation 9 is 1. This is because it needs to be less than /1000.

However, in reality, based on the above principle, a defocus of about four times the target was generated. In the above, Iz, l
Because the size of the beam tends to increase along with the increase in the beam current of the electron gun, it has been observed in 2014 that the defocus becomes brighter, especially on bright screens.

Although the horizontal deflection magnetic field has been considered above, non-uniformity of the vertical deflection magnetic field is also a defocusing factor.

The spring distribution of the vertical deflection coil is expressed by the following equation, corresponding to equation (2).

n (α) =: RealΣb, e
=@Here, b is usually a pure imaginary number.

If we rewrite the half-field width aberration amount of Equation 1 including the effects of s, b, ... in Equation 0, we get △Ha-(Za) ax, T, x+ )+21,-
Z.

Here, ■: Horizontal deflection current ■A: Vertical deflection current zo: Spreading coordinate of the electron beam within the deflection magnetic field a, IM: Corresponding to half screen width R: Neck radius 2U: Electron beam at the end of the deflection section The first and second rows on the right side of the central deflection scene equation 0 are astigmatism proportional to the spot spread zal, and the first row is ■.

■The second line is proportional to the linear function of 1. , is proportional to the quadratic function of Ia. Because it is inside zl in the second line, I
This is because it includes a term proportional to a. The third row is an aberration proportional to 1z, 12, 1. , I, is proportional to a linear function of ,I.

Next, the reason why these aberrations can be compensated for by the configuration described in the embodiment of FIG. 1 will be explained below.

I −/IM, I, /IM in equation 0 correspond to sawtooth waves X and Y in FIG.

Furthermore, since Z1/R in equation 0 is located at the right end of the screen and has a real part of the order of approximately 0.5 as described above, the following equation holds true.

Z, X-jY Rewriting equation 0 by replacing these.

In FIGS. 1 and 4, the aberrations to be compensated by the windings 18, 19, and 23 are the real part of A2, the imaginary part of A2, and the
It corresponds to the real part of 3. This is because, as stated before and after 20, the 2n pole magnetic field component is proportional to (d). Since the electron beam is only slightly deflected within the section of the auxiliary deflection and aberration correction yoke 8 in FIG. It can be considered as

It is therefore indicated at 12.13 in FIG. The coefficients of the quadratic function signal generation circuit are klX"+, 2XY+, 3Y2+, 4X10, Y10, etc.

That is, 1 to 6 in the above equations correspond to the real part and imaginary part of A2 of each of the four equations 0.

Therefore, the coefficients of 1 to 6 in the quadratic function generating section shown at 12.13 in FIG. 1 are constructed so that their magnitudes can be variably set. x2. Terms such as xy, y'' can be configured using a well-known multiplication circuit IC (eg, commercially available Motorola Mc1495).Also, of course, these quadratic function generation circuits can be replaced with digital memory.Digital According to memory technology, it is possible to store and generate arbitrary functions of X and Y. However, as can be seen from the physics of defocus described above, the main correction element is required.

It is in the form of a quadratic function.

Next, the magnitude of magnetic field energy required for defocus correction will be considered.

As is well known, the energy of the magnetic field per unit volume is μl, H
”/2. In other words, it is proportional to Hf. If the magnetic field energy required for screen half-width deflection is E2, and the energy for defocus correction is ΔE, then primary EMQ z f ax2
In”ds,,,.

In the above equation, dS is the element of the neck cross-sectional area in the magnetic field section of the auxiliary deflection and aberration correction coil. Further, Q is the length of the magnetic field section of the main deflection coil, and Q2 is the length of the magnetic field section of the auxiliary deflection coil, which is less than or equal to 6, Ql: Q□.Therefore, this term will be omitted from the discussion.

Since the radius measured from the center of the neck is 1 shoulder, 1 area element dS can be expressed as linear.

ds=πd(+-Otsu"12) This is because +Zllll ZO"l ZO3, etc. form an orthogonal function system. Therefore, crosstalk between the windings 18, 19 and 21, 22 in FIG. 1 hardly occurs.

As can be seen from equation O, the values of A, , A, etc. are maximum at the diagonal corners of the screen (X=±1.Y=±1).

When m=T O=82 ” b 2 ” b 3 -
It can be seen that the + energy is a minute amount on the order of about 1/1000 of the horizontal deflection energy. Therefore, defocus can be efficiently compensated with a small amount of electric power.

Moreover, as already mentioned in formula O, z, z in formula O.

This term is particularly the main defocus factor.

The energy required to correct this corresponds to the term 1/7200 in the above. The correspondence relationships are summarized in the table below.

Below is the margin Defocus Co. Required energy Za section, -11500-1/20000zaz1
Term 1 1/300-=1/7200Zo2 ・
11500-1/1200 In the above table, the last 20'
To correct the term.

As already mentioned, the six-pole magnetic field shown in FIG. 423 is required. This Z.

The amount of defocus caused by the term ′ is relatively small. Therefore, depending on the application, this compensation can be omitted.

However, the term corresponding to Za Zl is a major term among the defocus factors, and correction of this term is essential and corresponds to the quadrupole magnetic field of winding 8. )teeth,
It corresponds to a quadrupole magnetic field of 19 windings. The current to be passed through each winding has a parabolic X2 waveform and a so-called butterfly waveform XY waveform.

In recent years, fields other than projection displays to which the present invention relates:
In the field of direct-view displays, it has begun to be possible to correct astigmatism by passing a current in the form of (x"+y"), that is, the sum of parabolic wave signals, through the 18 windings in Figure 4. There is. But the technology...

This is an aberration specific to a display in which three electron guns are arranged in-line, and does not include the XY term.

For projection displays, as described above.

The above analysis clearly clarified that it is essential to correct the XY term in addition to the X2 term.

FIG. 8 shows a butterfly waveform (XY waveform).

As can be seen from the figure, the waveform has a fundamentally different shape from the parabolic waveform.

By the way, in the above equation O, the defocus due to the real part of A can be corrected by the magnetic field of volume g23 in FIG. 4, but the imaginary part of A cannot be corrected.

The real part of A3 is typically caused by a shift in the winding distribution of the main horizontal deflection coil. The imaginary part of A3 is normal.

It is caused by a deviation in the winding distribution of the main vertical deflection coil. A
The size of the imaginary part of 3 can be considered to be about half or less of the size of the real part of A3. This is because, in the actual structure of the main deflection coil 3, the horizontal coil is wound inside along the CRT neck, so the value of R in equation 0 is small, and the vertical coil is wound outside, so the R value is approximately This is because it is larger than f1 times.

As can be seen from equation O, the influence of Δ on defocus is 1/
It is proportional to R2. Therefore, the influence of the imaginary part of A is half that of the real part, and can be almost ignored.

Finally, the pole pieces of the auxiliary deflection and aberration correction yoke of the present invention do not necessarily have to have a six-pole shape as shown in FIG. be able to. In the same figure, 24 is a toroidal core, and 18.19 is a winding for a numerical difference correction coil. Although the windings are shown in a toroidal shape in the figure, they may alternatively be constructed in a saddle shape.

Further, the quadratic function generating circuits 12 and 13 in FIG. 1 may be of the same type as the so-called well-known digital convergence, in which a desired waveform is stored and stored in a digital memory.

Finally, specific numerical examples of each winding shown in FIGS. 31 and 4 are shown based on the following usage.

Application Horizontal frequency: 64 Vertical frequency 260 7 Number of pixels: 1280 dots 4: 25T 22 volumes! (L cape 32μH) 22-1: 14T 22-2: 28T 22-3: 14T 22-4: 14"L' 22-5 7 28T 22-6: 14T These windings have a power supply of ±24V B It is driven by a class push-pull amplifier (corresponding to the output of the auxiliary deflection circuit 9 in FIG. 1).

Fig. 4 Winding of 18 (L valve 4μH) 18-1:12T 18-2:12T 58-3:12T 18-4:12T Winding of 19 (L valve 4μH) 19-1: 7T 19-2 : 14T 19-3: 7T 19-48 7T 19-5: 14T 19-6: 7T 23 winding (L valve 3μH) 23-1: 7T 23-27 7T 23-3: 7T 23-48 7T 23- 5: 7T 23-6: '7T These windings are driven by a class B push-pull amplifier (output of the negative feedback amplifier 1.5.16 in FIG. 1) whose power supply is ±5V.

[Effects of the Invention] According to the present invention, it is possible to correct focusing aberrations caused by unevenness of the magnetic field of the deflection coil with extremely small electric power. A high-definition projection display can be constructed. Furthermore, since the same core can be used commonly as the auxiliary deflection coil and the aberration correction coil, it can be realized at low cost, and therefore has high industrial value.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the prior art, and FIGS. 3 and 4 are main parts 8 of the present invention.
Figure 5 shows the winding distribution and coordinate system of the deflection coil. Figure 6 shows the trajectory of the electron beam.
7 is a diagram showing the spread of an electron beam, FIG. 8 is a diagram showing a butterfly waveform, and FIG. 9 is a diagram showing an alternative example of the main part 8 of the present invention. Explanation of symbols 1: CRT Face, 2: Electron gun, 3: Deflection carp Bi,
4: Electromagnetic T) lr h S Th il, 6: (
r+! direction circuit. 7: Focuser circuit, 8 auxiliary deflection Jr aberration i11'i
+', 1. :,, Yoke, 9: Auxiliary deflection signal generation circuit, 10.118 Sawtooth wave (Nos. 1 to 12, 13: Quadratic function generator/JE circuit, 14.358 Negative feedback amplifier circuit. Figure 5 (a) Legs 1st figure 4th figure

Claims (1)

[Claims] 1. A projection display using a CRT, comprising an aberration correction magnetic field generating means for correcting astigmatism caused by non-uniformity of the magnetic field formed by the main deflection coil. , the correction magnetic field is formed as at least two types of quadrupolar magnetic fields that are substantially perpendicular to each other, and the strength of the correction magnetic field is equal to the two on the screen.
A projection display that is controlled according to a pattern of a quadratic function of dimensional coordinates (X, Y), and the quadratic function contains a small amount of both XY components. 2. A projection type display according to claim 1, wherein the aberration correction magnetic field generating means comprises a group of windings provided on a six-pole pole piece, and the six-pole pole piece functions as an auxiliary deflection and aberration correction yoke. .