JPH0918739A - Dynamic focus circuit - Google Patents

Abstract

PURPOSE: To provide a dynamic focus circuit suitable for a CRT projector. CONSTITUTION: A sawtooth wave HS is generated synchronously with a horizontal parabolic wave HP and a horizontal deflection pulse HD whose level changes in response to the time change for one period of the horizontal deflection pulse HD. A vertical parabolic wave VP is generated, whose level changes in response to the time change for one period of the vertical deflection pulse VD. The vertical parabolic wave VP and the sawtooth wave HS are multiplied. The product wave VP×HS and the sawtooth wave HS are superimposed on the horizontal parabolic wave HP. Dynamic focusing is conducted by using the superimposed signals MIX1, MIX2. Deterioration in surrounding focus caused due to a distance difference from an electron gun up to a fluorescent screen is prevented at the left and right sides in a rester distoted in a trapizoidal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic focus circuit, and more particularly to a dynamic focus circuit for performing dynamic focus control of a CRT projector.

[0002]

2. Description of the Related Art There is known a dynamic focus circuit which dynamically changes a focusing voltage in synchronization with deflection so that a beam is converged also on a peripheral portion of a screen. By using this circuit, a high quality image can be displayed.

By the way, by displaying a raster on the back side of the projection screen, various images are displayed C
RT projectors have R (red), G (green) and B (blue)
Of three CRTs (Ca
a Thode Ray Tube). The CRT used in this CRT projector has a flat fluorescent surface.

When the fluorescent screen is flat, the distance from the electron gun to the fluorescent screen is significantly different between the center and the periphery of the fluorescent screen, and therefore when the center is focused, the peripheral focus is significantly deteriorated. Therefore, the parabola voltage waveform synchronized with the horizontal deflection and the parabola voltage waveform synchronized with the vertical deflection are supplied to and controlled by the focus control device unit of the CRT to thereby improve the focus around the fluorescent screen. Have been commonly used in CRT projectors.

FIG. 6 shows a CR equipped with an electromagnetic focus CRT.
It is a block diagram which shows an example of the conventional dynamic focus circuit in a T projector. This conventional circuit
A waveform generating circuit 1 for generating a voltage waveform of a parabola or the like synchronized with horizontal deflection, a waveform generating circuit 2 for generating a voltage waveform of a parabola or the like synchronized with vertical deflection, and preamplifiers 29 and 4 configured using differential amplifiers. And 30, and an addition circuit 7 using a differential amplifier for adding the parabolic voltage synchronized with the vertical deflection output from the waveform generation circuit 2 and the DC voltage for adjusting the CRT center focus of each of red, green and blue.
It is configured to include 8 and 9.

Further, this conventional circuit uses output circuits 10 and 1 using a differential amplifier which exchanges an input voltage with a current and outputs the current.
1, 12, 13, 14 and 15 and electromagnetic focus CR
Dynamic focus control coil 1 provided in the focus magnet for controlling the focus of T
6, 17, 18 and main magnetic field adjusting coils 19, 20, 2
1 is included.

Next, the operation of the circuit shown in FIG. 6 will be described. The parabolic voltage waveforms output from the waveform generating circuit 1 and synchronized with the horizontal deflection are amplified by the preamplifiers 29, 4 and 30 provided for the red, green and blue CRTs, respectively, and the currents are output from the output circuits 10, 11 and 12, respectively. And is supplied to the dynamic focus control coils 16, 17, and 18. Coil 16 in these focus magnets
Since a parabola-shaped current that is synchronized with the horizontal deflection flows through to 18, the magnetic flux density of the focus magnet also changes to the parabola-shaped in synchronization with the horizontal deflection. Therefore, the focus deterioration due to the difference in the distance from the electron gun to the fluorescent screen in the horizontal direction of the fluorescent screen is corrected.

Next, the parabola voltage waveforms synchronized with the vertical deflection output from the waveform generating circuit 2 are red, green and blue CRTs.
For each CRT by adding circuits 7, 8 and 9 respectively provided for
After being added and increased with a DC voltage for adjusting the center focus of the main magnetic field, and converted into currents by the output circuits 13, 14, 15 respectively, main magnetic field adjusting coils 19, 20, 21
Is supplied to. A parabolic current synchronized with the vertical deflection flows through the main magnetic field adjusting coils 19 to 21 in the focus magnet, so that the magnetic flux density of the focus magnet also changes in the parabola configuration in synchronization with the vertical deflection. Therefore, the peripheral focus deterioration due to the difference in the distance from the electron gun to the phosphor screen in the direction perpendicular to the phosphor screen is corrected.

[0009]

In the CRT projector, as shown in FIG. 7, an image on each phosphor screen of the red, green and blue primary colors CRTs 26 to 28 enlarged by the projection lenses 23 to 25 is projected onto the projection screen. In order to match on 22, the red and blue C are pre-set as shown in FIG.
The RT image (raster) is distorted into a trapezoid. However, in the conventional dynamic focus circuit using the parabola voltage waveform, it is difficult to perform dynamic focus correction to the periphery in a trapezoidally distorted raster in which the distance from the electron gun to the phosphor screen is different on the left and right. . For this reason, there is a drawback that the peripheral focus of the images of the red and blue CRTs is inferior to that of the image of the green CRT which is not distorted into a trapezoid.

Incidentally, Japanese Unexamined Patent Publication No. 1-132282, Japanese Unexamined Patent Publication No. 3-91372 and Japanese Utility Model Laid-Open No. 57-10036.
No. 0 publication discloses a dynamic focus circuit. However, these are all dynamic focus circuits used for general CRTs, and
Even if it is used for a projector, the above problems cannot be solved.

The present invention has been made to solve the above-mentioned drawbacks of the prior art, and an object thereof is to provide a dynamic focus circuit suitable for use in a CRT projector.

[0012]

A dynamic focus circuit according to the present invention has at least two CRs of three CRTs provided corresponding to respective colors forming three primary colors.
A dynamic focus circuit that performs dynamic focusing when a raster is distorted from T in a direction other than the front direction to a substantially flat screen in accordance with an angle with respect to the front direction and is projected on the screen from a horizontal deflection pulse. And a means for generating a sawtooth waveform synchronized with the horizontal deflection pulse, the level of which changes in accordance with the time change during one cycle of the vertical deflection pulse, and the level which changes in accordance with the time change during the one cycle of the vertical deflection pulse. The superimposing means includes means for generating a changing vertical parabolic waveform, multiplying means for multiplying the vertical parabolic waveform and the sawtooth waveform, and superimposing means for superposing the multiplied waveform and the sawtooth waveform on the horizontal parabolic waveform. It is characterized in that dynamic focusing is performed using the generated signal.

[0013]

The horizontal parabolic waveform whose level changes according to the time change of one horizontal deflection pulse and the sawtooth waveform synchronized with the horizontal deflection pulse are generated. A vertical parabolic waveform whose level changes according to the time change of one cycle of the vertical deflection pulse is generated. Multiply the vertical parabolic waveform and the sawtooth waveform. The multiplication waveform and the sawtooth waveform are superimposed on the horizontal parabolic waveform. Dynamic focusing is performed using this superimposed signal.

[0014]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the dynamic focus circuit according to the present invention.
The same parts as are indicated by the same reference numerals. In the figure, a dynamic focus circuit according to an embodiment of the present invention includes a waveform generating circuit 1 for generating a voltage waveform of a parabola and a saw synchronized with horizontal deflection and a waveform for generating a voltage waveform of a parabola etc. synchronized with vertical deflection. Generating circuit 2,
It is configured to include a multiplying circuit 3 for multiplying a sawtooth voltage waveform synchronized with horizontal deflection and a parabola voltage waveform synchronized with vertical deflection.

In addition, the circuit of the present embodiment uses red and blue CRs.
A differential amplifier for adding and subtracting the sawtooth voltage waveform synchronized with the horizontal deflection necessary for the peripheral focus correction of T and the output waveform of the multiplication circuit 3 to the parabola voltage waveform synchronized with the horizontal deflection which is the conventional dynamic correction waveform. Green CR configured using adder / subtractor circuits 5 and 6 and a differential amplifier
In order to control the focus of the T preamplifier 4, the adder / subtractor circuits 5, 6 and the output circuit 10, 11, 12 using a differential amplifier for converting the input voltage from the preamplifier 4 into a current and outputting the current, and the focus of the electromagnetic focus CRT. And a dynamic focus control coil 16, 17, 18 provided in the focus magnet.

Furthermore, the circuit of this embodiment adds the parabola voltage output from the waveform generating circuit 2 in synchronism with the vertical deflection and the DC voltage for adjusting the CRT center focus of each of red, green and blue. Adder circuits 7, 8, 9 using a differential amplifier, and an output circuit 1 using a differential amplifier for converting the input voltage from the adder circuits 7, 8, 9 into a current and outputting the current.
3, 14, 15 and a main magnetic field adjusting coil 19 provided in the focus magnet for controlling the focus of the CRT by the output currents of the output circuits 13, 14, 15.
20 and 21 are included.

Next, the operation of the circuit of this embodiment will be described. As shown in FIG. 8, in a blue CRT raster distorted in a trapezoidal shape, in order to obtain a uniform focus up to the periphery, as shown in FIG. A sawtooth waveform HS and a multiplication waveform VP × HS of a parabolic waveform synchronized with vertical deflection and a sawtooth waveform synchronized with horizontal deflection are required.

Here, the reason why this multiplication waveform is necessary will be described. Referring to FIG. 2, a blue CR is provided on the phosphor screen 200.
Although a T raster is projected, the raster is a trapezoid whose right end is longer than its left end in the figure. In addition,
It is assumed that the beam scans from left to right and from top to bottom in the figure.

The dynamic focus current required in the horizontal direction of the phosphor screen 200 has a parabolic waveform like the waveform 201. The horizontal focus current required to display the above raster is a waveform 202 obtained by cutting off a part of this waveform 201.

Here, when the waveform 202 is made to correspond to the time axis around the horizontal center of the screen, time t = 0.
From time to time t = H, the level changes, and the waveform 203 having the lowest level at time t = H / 2 is obtained. When this waveform 203 is separated into a parabolic waveform and a sawtooth waveform, a horizontal parabolic waveform (HP) 204 and a horizontal sawtooth waveform (HS) 205 are obtained. The horizontal parabolic waveform 204 and the horizontal sawtooth waveform 205 are current waveforms required for correction in the horizontal direction.

The dynamic focus current required in the vertical direction of the phosphor screen 200 has a parabolic waveform like the waveform 211. The correction currents required to display the above raster are waveforms 212-1 and 212-2. The waveform is divided into two parts in this way because the distance from the vertical center part of the screen to the upper end of the raster gradually changes, and the distance to the lower end also gradually changes. is there.

Here, when the waveforms 212-1 and 212-2 are made to correspond to the time axis centering on the vertical center portion of the screen, the waveform 213-1 and the waveform 213-2 are obtained. Comparing this waveform with the waveforms 212-1 and 212-2, although the slope of the waveform 213-2 does not change with respect to the waveform 212-2, the waveform 213 does not have the slope of the waveform 212-1.
The slope of -1 is changing. The reason why this slope changes is as follows. That is, from left to right in the figure,
Moreover, since the beam scans from the top to the bottom, the upper end of the raster is displayed at a time earlier on the left side than on the right side of the vertical center portion of the screen, so that the time is switched.

By the way, these waveforms 213-1 and 213
−2 can be approximated by the waveform 214. The waveform 214 is a waveform obtained by multiplying the vertical parabolic waveform (VP) by the horizontal sawtooth waveform (HS). Focusing on this waveform 214, the waveform converges toward a time corresponding to the vertical center of the screen, and the waveform diverges again from that time. The reason for such a waveform is that the density of scan lines for displaying the raster gradually decreases from the left end to the right end because the raster has a trapezoidal shape as shown in the drawing, and the central part to the upper end or This is because it gradually decreases as it moves to the lower end.

The waveform 214, that is, the multiplication waveform VP × HS of the vertical parabolic waveform and the horizontal sawtooth waveform is created by the multiplication circuit 3 in FIG. Then, the multiplication waveform VP × HS is added to the addition / subtraction circuit 5, together with the sawtooth voltage waveform synchronized with the horizontal deflection output from the waveform generation circuit 1.
I am typing in 6. The adder / subtractor circuit 6 is suitable for a blue CRT raster which is distorted into a trapezoid by adding and subtracting the parabola voltage waveform HP synchronized with horizontal deflection, which is also used in the conventional circuit for dynamic focus correction. Creating the focus waveform. This waveform is input to the output circuit 12 in FIG.

Although the above description has been focused on the blue CRT raster, a dynamic focus waveform is similarly created for the red CRT raster. In this case, the adder / subtractor circuit 5 produces a waveform that is bilaterally symmetrical to each waveform in FIG. That is, a waveform of each waveform in FIG. 2 viewed from the back side of the paper is output from the addition / subtraction circuit 5 and input to the output circuit 10 in FIG.

Further, description will be made with reference to the waveform chart of FIG.

In FIG. 3, the horizontal deflection pulse HD
(A), horizontal parabolic waveform HP (b), horizontal sawtooth waveform HS (c), vertical deflection pulse VD (d), vertical parabolic waveform VP (e), and multiplication waveform VP × HS of the vertical parabolic waveform and the horizontal sawtooth waveform. (F), output waveform MIX2 (g) of the addition / subtraction circuit 6 and output waveform MIX of the addition / subtraction circuit 5
1 (h) is shown.

A waveform generating circuit 1 in FIG. 1 receives a horizontal deflection pulse HD as an input, and differentiates and integrates this waveform to generate a horizontal parabolic waveform HP (b) and a horizontal sawtooth waveform HS (c). . Further, the waveform generating circuit 2 in FIG. 1 receives the vertical deflection pulse VD (d) and similarly generates a vertical parabolic waveform VP (e). Further, the multiplication circuit 3 in FIG. 1 receives the horizontal sawtooth waveform HS (c) and the vertical parabola waveform VP (e) as input, and generates a multiplied waveform VP × HS (f) of the vertical parabola waveform and the horizontal sawtooth waveform. To do.

Then, the adder / subtractor circuit 6 subtracts the horizontal sawtooth waveform HS (c) and the multiplication waveform VP × HS (f) from the horizontal parabola waveform HP (b), and further inverts the subtraction result to output the output waveform MIX2 (g). ) Is output. On the other hand, in the adder / subtractor circuit 5, a horizontal sawtooth waveform HS (c) and a multiplication waveform VP × HS are added to the horizontal parabolic waveform HP (b).
(F) is added, and the addition result is inverted and output as the output waveform MIX1 (h).

Output waveform MI generated as described above
X1 to the output circuit 10 and output waveform MIX2 to the output circuit 1
The dynamic focus control is carried out by inputting the respective values into 2.

Next, an example of the internal configuration of the adder / subtractor circuits 5 and 6 will be described.

FIG. 4 is a circuit diagram showing a configuration example of the adder / subtractor circuit 5. As shown in the figure, in this circuit 5,
A well-known inverting adder circuit is configured by the differential amplifier 51 and each resistor. The circuit 5 includes a horizontal parabola waveform HP, a horizontal sawtooth waveform HS, and a multiplication waveform VP ×
HS is input, these are added, and the addition result is inverted and output as the output waveform MIX1.

On the other hand, FIG. 5 is a circuit diagram showing a configuration example of the adder / subtractor circuit 6. As shown in the figure, in the present circuit 6, a well-known inverting adder circuit is configured in two stages by the differential amplifiers 61 and 62 and each resistor. Then, the horizontal sawtooth waveform HS and the multiplication waveform VP × HS are input to the inverting addition circuit of the first stage, and these are added. The addition result is inverted and further added to the horizontal parabola waveform HP in the second-stage inverting addition circuit. The addition result is inverted and output as the output waveform MIX2.

As described above, this circuit uses the voltage waveform for correcting the peripheral focus deterioration caused by the difference in the distance from the left and right electron guns to the fluorescent screen in the raster on the red and blue CRT fluorescent screens distorted in a trapezoidal shape. The peripheral focus deterioration of the red and blue CRT images is prevented by superimposing it on the parabola voltage waveform that has been conventionally used for dynamic focus correction.

In this embodiment, the electromagnetic focus CRT is used.
Although the focus circuit in the CRT projector provided with the above is taken as an example, it is obvious that the present invention can be applied to the CRT projector provided with the electrostatic focus CRT. The above is the CR of the rear projection method (rear projection method).
Although the case of the T projector has been described, it is obvious that the present invention can be applied to the case of the front projection method.

In short, the dynamic focus circuit of the present invention is arranged such that at least two CRTs among the three CRTs provided corresponding to the three primary colors are provided on the back side of the substantially flat screen and from directions other than the front direction thereof. It is premised on a dynamic focus circuit that distorts rasters according to the angle with respect to the front direction and performs dynamic focus when projecting on the screen. Then, a horizontal parabolic waveform whose level changes according to the time change during one period of the horizontal deflection pulse and a sawtooth waveform synchronized with the horizontal deflection pulse are generated, and the vertical deflection pulse 1
A vertical parabolic waveform whose level changes according to the time change during the cycle is generated, the generated vertical parabolic waveform is multiplied by the sawtooth waveform, and the multiplication waveform and the sawtooth waveform are superimposed on the horizontal parabolic waveform. is there. By performing dynamic focusing using this superimposed signal, peripheral focus deterioration caused by the difference in distance from the electron gun to the fluorescent screen is corrected.

In addition, when the superimposition is performed, the multiplication waveform and the sawtooth waveform are added and subtracted from the horizontal parabolic waveform.

Further, in the above three CRTs, each projection output surface is a substantially flat surface.

[0040]

As described above, according to the present invention, in the trapezoidally distorted raster, the voltage waveform for correcting the peripheral focus deterioration caused by the distance difference between the electron gun and the phosphor screen on the left and right is used as the parabolic waveform for the dynamic focus. By superimposing on the image, it is possible to prevent the peripheral focus deterioration of the image.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a dynamic focus circuit according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing a dynamic focus waveform necessary for a trapezoidally distorted raster.

3A and 3B are waveform diagrams of respective parts of the dynamic focus circuit of FIG. 1, in which FIG. 3A is a horizontal deflection pulse HD, FIG. 3B is a horizontal parabolic waveform HP, and FIG. 3C is a horizontal sawtooth waveform HS.
(D) is the vertical deflection pulse VD, (e) is the vertical parabolic waveform VP, (f) is the multiplication waveform VP × HS of the vertical parabolic waveform and the horizontal sawtooth waveform, (g) is the output waveform MIX2 of the adder / subtractor circuit 6, ( h) is the output waveform MIX of the adder / subtractor circuit 5.
It is one.

FIG. 4 is a circuit diagram showing an internal configuration example of an adder / subtractor circuit 5 in FIG.

5 is a circuit diagram showing an example of an internal configuration of an adder / subtractor circuit 6 in FIG.

FIG. 6 is a block diagram showing a configuration of a conventional dynamic focus circuit.

FIG. 7 is an optical diagram showing image formation of a CRT projector.

FIG. 8 is a diagram showing the shape of a raster in a CRT projector.

[Explanation of symbols]

 1, 2 Waveform generation circuit 3 Multiplication circuit 4 Preamplifier 5, 6 Addition / subtraction circuit 7-9 Addition circuit 10-15 Output circuit 16-21 Coil

Claims (3)

[Claims] 1. From at least two CRTs of three CRTs provided corresponding to the respective colors forming the three primary colors to a substantially flat screen from a direction other than the front direction thereof according to an angle with respect to the front direction. A dynamic focus circuit that performs dynamic focusing when distorting each raster and projecting on the screen, and a horizontal parabolic waveform and a level of the horizontal deflection pulse whose level changes according to the time change during one period of the horizontal deflection pulse. Means for generating a sawtooth waveform that is synchronized with, a means for generating a vertical parabolic waveform whose level changes according to the time change during one period of the vertical deflection pulse, and the vertical parabolic waveform and the sawtooth waveform are multiplied. And a multiplication means for superposing the multiplication waveform and the sawtooth waveform on the horizontal parabolic waveform. A dynamic focus circuit characterized by performing a dynamic focus by using a signal on which is superimposed. 2. The dynamic focus circuit according to claim 1, wherein the superimposing means adds and subtracts the multiplication waveform and the sawtooth waveform to and from the horizontal parabolic waveform. 3. The dynamic focus circuit according to claim 1, wherein each of the three CRTs has a substantially flat projection output surface.