JPH0316074B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention generates an electron beam for each division when a screen on a screen is vertically divided into a plurality of divisions, and generates an electron beam for each division. The present invention relates to an apparatus for displaying a plurality of lines by vertically deflecting a beam to display a television image as a whole.

Conventional configurations and their problems Traditionally, cathode ray tubes have been mainly used as display elements for displaying color television images, but conventional cathode ray tubes are extremely long and thin compared to the screen size. It would have been impossible to create a television receiver. In addition, EL display elements, plasma display devices, liquid crystal display elements, etc. have recently been developed as flat display elements.
All of them are insufficient in terms of characteristics such as brightness, contrast, and color display, and have not yet been put into practical use.

Therefore, we aimed to achieve a flat display device using electron beams, and when the screen on the screen is vertically divided into multiple sections, an electron beam is generated for each section. A device was invented that displayed a plurality of lines by vertically deflecting each electron beam to display a television image as a whole.

First, a basic configuration of the image display element used here will be explained with reference to FIG. This display element includes, in order from the back to the front, a back electrode 1,
Line cathode 2 as a beam source, vertical focusing electrode 3,
3', vertical deflection electrode 4, beam flow control electrode 5, horizontal focusing electrode 6, horizontal deflection electrode 7, beam acceleration electrode 8
and a screen 9 are placed,
These are housed within the evacuated interior of a flat glass bulb (not shown). A line cathode 2 serving as a beam source is stretched horizontally so as to generate an electron beam distributed linearly in the horizontal direction. Only four (2a to 2d are shown) are provided. In this example, it is assumed that 15 are provided. Let them be 2a to 2o. These wire cathodes 2 are constructed by coating the surface of a tungsten wire with a diameter of 10 to 20 .mu..phi.5 with an oxide cathode material for thermionic emission. These line cathodes 2a to 2o are heated so as to generate a thermionic electron beam when a current is passed through them, and as described later, electron beams are emitted in order from the line cathode 2a for a fixed period of time. controlled as follows.
The back electrode 1 suppresses generation of electron beams from line cathodes other than the line cathode controlled to emit electron beams for a certain period of time, and pushes out the generated electron beams only in the forward direction. act. The back electrode 1 may be formed by a coating of a conductive material applied to the inner surface of the rear wall of the glass bulb. In addition, these back electrode 1 and line cathode 2
Instead, a planar electron beam emitting cathode may be used.

The vertical focusing electrode 3 is a conductive plate 11 having a horizontally long slit 10 facing each of the line cathodes 2a to 2o. Focus. An electron beam for one horizontal line (360 pixels) is extracted at the same time. In the figure, only one section in the horizontal direction is shown. The slit 10 may be provided with crosspieces at appropriate intervals in the middle, or may be substantially formed by a row of through holes arranged horizontally at small intervals (nearly touching). may be configured. The vertical focusing electrode 3' is also similar.

A plurality of vertical deflection electrodes 4 are arranged horizontally in the middle of each of the slits 10, and are each composed of conductive electrodes 13, 13' provided on the upper and lower surfaces of an insulating substrate 12. has been done. And the opposing conductors 13, 13'
A vertical deflection voltage is applied between them to deflect the electron beam in the vertical direction. In this example, the electron beam from one line cathode 2 is vertically deflected to 16 line positions by a pair of conductors 13, 13'. The 16 vertical deflection electrodes 4 constitute 15 pairs of conductors corresponding to each of the 15 line cathodes 2, and in the end, the electron beams are emitted so as to draw 240 horizontal lines on the screen 9. deflect.

Next, the control electrodes 5 are composed of conductive plates 15 each having a vertically long slit 14, and a plurality of control electrodes 5 are arranged in parallel in the horizontal direction at a predetermined interval. In this example, 180 control electrode conductive plates 1
5-1 to 15-n are provided. (9 in the diagram)
(only books shown). Each of the control electrodes 5 separates and extracts the electron beam into two picture elements in the horizontal direction, and controls the amount of electron beam passing therethrough in accordance with a video signal for displaying each picture element. Therefore, the conductive plates 15-1 to 15-n for the control electrode 5 are
If 180 lines are provided, 360 pixels can be displayed per horizontal line. In addition, in order to display images in color, each picture element is displayed with phosphors of three colors R, G, and B, and each control electrode 5 has each of R, G, and B for two picture elements. Video signals are received sequentially. Also,
180 conductive plates 15-1 to 15-n for control electrodes 5
180 sets of video signals for one line (two picture elements per set) are simultaneously applied to each of the lines, and one line of video is displayed at one time.

The horizontal focusing electrode 6 is composed of a conductive plate 17 having a plurality of vertically long slits 16 (180 slits 16) facing the slits 14 of the control electrode 5, and collects electrons for each picture element divided in the horizontal direction. Each beam is focused horizontally into a narrow electron beam.

The horizontal deflection electrode 7 is composed of a plurality of conductive plates 18, 18' arranged vertically on both sides of the slit 16, and each electrode 18, 18' has a horizontal deflection plate in six stages. A voltage is applied to horizontally deflect the electron beam of each pixel, and on the screen 9 two sets of R,
The G and B phosphors are sequentially irradiated to emit light. In this example, the deflection range is two picture elements wide for each electron beam.

The accelerating electrode 8 is composed of a plurality of conductive electric plates 19 provided horizontally at the same position as the vertical deflection electrode 4, and accelerates the electron beam so that it collides with the screen 9 with sufficient energy.

The screen 9 is constructed by coating the back surface of a glass plate 21 with a phosphor 20 that emits light when irradiated with an electron beam, and adding a metal back layer (not shown). The phosphor 20 has R,
Two pairs of three-color phosphors, G and B, are provided and are applied in stripes in the vertical direction.
In FIG. 1, the broken lines drawn on the screen 9 indicate divisions in the vertical direction that are displayed corresponding to each of the plurality of line cathodes 2, and the two-dot chain lines correspond to each of the plurality of control electrodes 5. Indicates the horizontal division displayed. As shown in the enlarged view of FIG. 2, in one section partitioned by these two, there are R, G, and B phosphors 20 for two picture elements in the horizontal direction.
It has a width of 16 lines in the vertical direction. The size of one section is, for example, 1 mm in the horizontal direction,
The vertical direction is 9 mm.

Note that in FIG. 1, the length in the horizontal direction is greatly enlarged relative to the length in the vertical direction for clarity.

Further, in this example, one control electrode 5, that is, one
For the electron beam of the book, R, G, B phosphor 2
Only one pair of 0's for two picture elements is provided, but of course, one picture element or three or more picture elements may be provided, and in that case, the control electrode 5 has one picture element or three picture elements or more. R, G, and B video signals are sequentially applied to the image signal, and horizontal deflection is performed in synchronization with the R, G, and B video signals.

Next, the basic configuration and waveforms of each part of a drive circuit for displaying television images on this display element will be explained with reference to FIG. First, a driving portion for irradiating the screen 9 with an electron beam to emit raster light will be described.

The power supply circuit 22 is a circuit for applying a predetermined bias voltage (operating voltage) to each electrode of the display element,
-V ₁ to the back electrode 1, and -V 1 to the horizontal focusing electrodes 3 and 3'.
DC voltages of V ₃ , V ₃ ', V ₆ to the horizontal focusing electrode 6, V ₈ to the accelerating electrode 8, and V ₉ to the screen 9 are applied.

Next, a composite video signal of a television signal is applied to the input terminal 23, and a synchronization separation circuit 24 separates and extracts a vertical synchronization signal V and a horizontal synchronization signal H.

The vertical deflection drive circuit 40 includes a vertical deflection counter 25, a memory 27 for storing vertical deflection signals, and a digital-to-analog converter 30 (hereinafter referred to as a DA converter). Vertical deflection drive circuit 4
As the zero input pulse, the vertical synchronizing signal V and horizontal synchronizing signal H shown in FIG. 4 are used. The vertical deflection counter 25 (8 bits) is reset by the vertical synchronizing signal V and counts the horizontal synchronizing signal H. This vertical deflection counter 25 counts the effective scanning period (here, a period of 240H) excluding the vertical retrace period of the vertical period, and this count output is supplied to the address of the memory 27. The memory 27 outputs vertical deflection signal data (here, 8 bits) corresponding to each address, and the D-A converter 39 converts the vertical deflection signals υ and υ' shown in FIG. 4 (FIG. 3 bD). is converted to This circuit has memory addresses that store vertical deflection signals corresponding to each line for 240H.
By storing regular data in the memory every 16 hours, a 16-step vertical deflection signal can be obtained.

On the other hand, the line cathode drive circuit 26 uses the vertical synchronization signal V and the output of the vertical deflection counter 25 to create line cathode drive pulses a to o. FIG. 5a shows the relationship between the vertical synchronizing signal V, the horizontal synchronizing signal H, and the lower five bits of the vertical deflection counter 25. FIG. 5b shows a method of creating line cathode drive pulses a' to o' every 16H using these signals. In Figure 5, LSB indicates the lowest bit, and (LSBB+1) is 1 bit lower than LSB.
means more than one bit.

The first line cathode drive pulse a' can be created by an R-S flip-flop using the vertical synchronization signal V and the output (LSB+4) of the vertical deflection counter 25, and the line cathode drive pulses b' to o' are shifted. This can be obtained by using a register to transfer the line cathode drive pulse a' using the inverted version of the output (LSB+3) of the vertical deflection counter 25 as a clock. These drive pulses a' to o' are inverted so that the potential is low only during each pulse period, and the line cathode drive pulse a is set at a high potential of about 20 volts during other periods.
~o (Fig. 3bE), each line cathode 2a~
Added to 2o.

Each of the linear cathodes 2a to 2o is heated by passing a current during the high potential periods of the drive pulses a to o, and the heated state is maintained so that electrons can be emitted during the low potential periods of the drive pulses a to o. Ru. As a result, during the period when low potential drive pulses a to o are applied to each of the 15 line cathodes 2a to 2o, the bias voltage applied to the back electrode 1 and the vertical focusing electrode 3 is applied. Since the high potential applied to the linear cathodes 2a to 2o is more positive than the potential at the determined position of the linear cathode 2, the linear cathode 2a
No electrons are emitted from ~2o. Thus, in the line cathode 2, electrons are sequentially emitted from the upper line cathode 2a toward the lower line cathode 2o for each 16H period during the effective vertical scanning period. The emitted electrons are pushed forward by the back electrode 1, pass through the opposing slits 10 of the vertical focusing electrode 3, and are focused in the vertical direction to form a flat electron beam.

Next, the relationship between the line cathode drive pulses a to o and the vertical deflection signals υ and υ' will be explained using FIG. 6. FIG. 6a is a waveform diagram of a line cathode pulse, b is a waveform diagram of a vertical deflection signal, and FIG. 6c is a waveform diagram of a horizontal deflection signal. The vertical deflection signals υ, υ′ in Fig. 6b are the same as those in Fig. 6a.
1H during the 16H period of line cathode driving pulses a to o.
It changes in minute increments and changes in 16 steps. The vertical deflection signals υ and υ' both have a center voltage of _V4 , and are configured to change in opposite directions so that υ increases sequentially and υ' sequentially decreases. These vertical deflection signals υ and υ' are applied to the electrodes 13 and 13' of the vertical deflection electrode 4, respectively, and as a result, the electron beams generated from the respective line cathodes 2a to 2o are vertically deflected in 16 steps. As mentioned above, on the screen 9, one electron beam is deflected so as to sequentially draw a raster line of 16 lines one line at a time from the top.

As a result of the above, electron beams are emitted from the 15 line cathodes 2a to 2o for a period of 16 hours in order from those above them.
In addition, each electron beam is deflected one line at a time from the top to the bottom within the 15 vertical divisions, so that on the screen 9, one line is deflected from the 1st line at the top to the 240th line at the bottom. The electron beam is vertically deflected minute by minute, creating a raster of 240 lines in total.

The electron beam thus vertically deflected is horizontally deflected by 180 degrees by the control electrode 5 and the horizontal focusing electrode 6.
It is divided into sections and taken out. Figure 1 shows one of these categories. The amount of electron beam passing through each section is controlled by a control electrode 5, and horizontally focused by a horizontal focusing electrode 6 into a single narrow electron beam, which is then controlled by horizontal deflection means described below. The light is then deflected in six steps in the horizontal direction, and is sequentially irradiated onto each of the R, G, and B phosphors 20 for two picture elements on the screen 9. FIG. 2 shows the vertical and horizontal divisions. The phosphors corresponding to 15-1 to 15-n of the control electrode 5 are R, G, and B for two picture elements, but for convenience of explanation, one picture element is R ₁ , G ₁ , and B _{1 and the other is R 1 , G 1 , and B 1} . Let R ₂ , G ₂ , and B ₂ .

Next, the horizontal deflection drive circuit 41 includes a horizontal deflection counter 28, an 11-bit counter, a memory 29 storing horizontal deflection signals, and a DA converter 38. The input pulse to the horizontal deflection drive circuit 41 is synchronized with the vertical synchronizing signal V and the horizontal synchronizing signal H, as shown in FIG. 7, and uses a pulse 6H having a repetition frequency six times that of the horizontal synchronizing signal H. The horizontal deflection counter 28 is reset by the vertical synchronizing signal V and counts horizontal six times the pulse 6H. This horizontal deflection counter 28 is activated 6 times during 1H and during 1V.
It counts 240H×6/H=1440 times, and this count output is supplied to the address of the memory 29. The memory 29 outputs horizontal deflection signal data (here, 8 bits) according to the address, and the D-A
A converter 38 converts the signal into horizontal deflection signals such as h and h' shown in FIG. 7 (FIGS. 3B and 3C). This circuit has memory addresses that store horizontal deflection signals corresponding to each of 6 x 240 lines.
By storing six pieces of regular data in the memory for each line, a horizontal deflection signal with six step waves can be obtained in a 1H period.

This horizontal deflection signal is a pair of horizontal deflection signals h and h' that change in 6 steps as shown in FIG. 7, both have a center voltage of V ₇ , and h gradually decreases.
h' increases in sequence and changes in opposite directions. These horizontal deflection signals h, h' are applied to electrodes 18 and 18' of the horizontal deflection electrode 7, respectively.
As a result, each horizontally divided electron beam is transmitted to the R, G, B,
The light is horizontally deflected so that R, G, and B (R ₁ , G ₁ , B ₁ , R ₂ , G ₂ , B ₂ ) phosphors are sequentially irradiated for H/6 periods. Thus, in each line raster, the electron beam is divided into 180 sections in the horizontal direction.
Each phosphor 20 of R ₁ , B ₁ , R ₂ , G ₂ , and B ₂ is sequentially irradiated with light.

Therefore, an electron beam is applied to each horizontal section of each line.
A color television image can be displayed on the screen 9 by modulating the video signals R ₁ , G ₁ , B ₁ , R _{2 ,} G ₂ , and B 2 .

Next, the modulation control portion of the electron beam will be explained. First, the television signal input terminal 23
The composite video signal applied to Combined with Y,
R, G, and B primary color signals (hereinafter referred to as R, G, and B video signals) are output. These R, G, and B video signals are processed by 180 sample and hold circuits 31-
1 to 31-n. Each sample hold circuit 31-1 to 31-n is for _R1 , _G1 ,
It has six sample and hold circuits for _B1 , _R2 , _G2 , and _B2 . These sample and hold outputs are stored in memories 32-1 to 32-n, respectively.
added to.

On the other hand, the reference clock oscillator 33 is constituted by a PLL (phase locked loop) circuit, etc., and in this example generates a reference clock 6sc of six times the color width carrier wave sc and a reference clock 2sc of twice the color width carrier sc.
The reference clock is controlled to always have a constant phase with respect to the horizontal synchronizing signal H. The reference clock 2sc is added to the deflection pulse generation circuit 42, and the signals 6H and H/6, which are six times the horizontal synchronizing signal H, are
The signal switching pulses r ₁ , g ₁ , b ₁ , r ₂ , g ₂ , b ₂ (Fig. 3b, B) are obtained for each signal switching pulse. On the other hand, the reference clock 6sc is applied to the sampling generation circuit 34, where the clock 1 is inputted by a shift register.
The effective horizontal scanning period (approx.
1080 sampling pulses during 50μsec)
R ₁₁ , G ₁₁ , B ₁₁ , R ₁₂ , G ₁₂ , B ₁₂ , R ₂₁ , G ₂₁ ,
B ₂₁ , R ₂₂ , G ₂₂ , B ₂₂ ~ _{Rn 1} , Gn ₁ , Bn ₁ , Rn ₂ ,
Gn ₂ and Bn ₂ (FIG. 3b, a) are generated in sequence, and then one transfer pulse t is generated. This sampling pulse R ₁₁ ~Bn ₂ is one of the images to be displayed.
It corresponds to each picture element when a line is divided into 360 picture elements in the horizontal direction, and its position is controlled so that it is always constant with respect to the horizontal synchronizing signal H.

These 1080 sampling pulses R ₁₁ to Bn ₂ are each connected to 180 sample and hold circuits 31-1.
~ 31-n, and thereby each sample hold circuit 31-1 ~ 31-n has 1
When the line is divided into 180 lines, the video signals of R ₁ , G ₁ , B ₁ , R ₂ , G ₂ , and B ₂ for each two picture elements are individually sampled and held. The sample-held 180 pairs of R ₁ , G ₁ , B ₁ , R ₂ ,
The video signals of G ₂ and B ₂ are stored in 180 sets of memories 32-1 to 32-n after completing the sample hold for one line.
It is then transferred by a transfer pulse t to one moment, where it is held for the next horizontal period. This held
The signals R ₁ , G ₁ , B ₁ , R ₂ , G ₂ , and B ₂ are applied to switching circuits 35-1 to 35-n. The switching circuits 35-1 to 35-n each have R ₁ ,
It is composed of a tri-state or analog gate having individual input terminals for G ₁ , B ₁ , R ₂ , G ₂ , and B ₂ and a common output terminal for sequentially switching and outputting them.

The output of each switching circuit 35-1 to 35-n is 180 sets of pulse width modulation (PWM) circuits 37-1.
~37-n, where the reference pulse signal is pulse width modulated according to the magnitude of the sampled and held video signals of R ₁ , G ₁ , B ₁ , R ₂ , G ₂ , B ₂ . Output. The repetition period of the reference pulse signal is the above signal switching pulse r ₁ , g ₁ , b ₁ , r ₂ , g ₂ ,
It is desirable that the pulse width be sufficiently smaller than the pulse width of b ₂ , for example, a pulse width of about 1:10 to 1:100 is used.

The outputs of the pulse width modulation circuits 37-1 to 37-n are used as control signals for modulating the electron beam to the 180 conductive plates 15-1 of the control electrode 5 of the front element.
~15-n, respectively. The switching circuits 35-1 to 35-n are simultaneously controlled by switching pulses R ₁ , g ₁ , b ₁ , r ₂ , g ₂ , and b applied from the switching pulse generating circuit 36. Switching pulse generation circuit 36
is controlled by the signal switching pulses r ₁ , g ₁ , b ₁ , r ₂ , g ₂ , b ₂ from the deflection pulse generation circuit 42 described above, and each horizontal period is divided into 6 and divided into H/6. Switch the switching circuits 35-1 to 35-n one by one,
Each video signal of R ₁ , G ₁ , B ₁ , R ₂ , G ₂ , B ₂ is time-divided and outputted sequentially, and the pulse width modulation circuits 37-1 to 3
7-n so that r ₁ , g ₁ , b ₁ , r ₂ , g ₂ , b ₂
occurs.

What should be noted here is that the switching circuit 3
R ₁ , G ₁ , B ₁ , R ₂ in 5-1 to 35-n,
G ₂ , B ₂ video signal supply switching and electron beams R ₁ , G ₁ , B ₁ , R ₂ ,
The horizontal deflection for switching the irradiation of G ₂ and B ₂ to the phosphor is
They are synchronously controlled to completely match both timing and order. As a result, when the electron beam is irradiating the R ₁ phosphor, the irradiation amount of the electron beam is controlled by the R ₁ video signal, and the same applies to G ₁ , B ₁ , R ₂ , G ₂ , and B ₂ R ₁ , G ₁ , B ₁ , of each picture element are controlled by
R ₂ , G ₂ , B ₂ The emission of each phosphor is R ₁ ,
Each picture element is controlled by the video signals of G ₁ , B ₁ , R ₂ , G ₂ , and B ₂ , and each picture element is displayed by emitting light according to the input video signal. Such control is performed simultaneously for 180 sets of one line (2 picture elements each), so that an image of 360 picture elements per line is displayed, and then sequentially for 240 H of lines starting from the upper line. One image will be displayed.

The above operations are repeated for each field of the input television signal, and as a result,
The screen 9 is similar to a normal television receiver.
The television footage of the video is shown above.

Incidentally, in the image display device as described above, the brightness displayed on the screen is controlled by the pulse width applied to the beam flow control electrode 5, but in the configuration shown in FIG.
The maximum value of the pulse width corresponding to the G and B video signals is about a period of H/6 (H is one horizontal period). Also,
In such a device, the white balance is adjusted by changing the amplitude and DC level of the R, G, and B primary color output signals of the color demodulation circuit 30, in the same way as the conventional CRT white balance adjustment method. and was adjusting the color temperature of the low lights. FIG. 8 shows an example of the adjustment results. In this example, R:G:B=80:90:100 is used to maintain white balance. In FIG. 8, the horizontal axis indicates R, G, and B video signal levels, of which 100% is a level corresponding to the white level of the video signal. The vertical axis indicates the PWM output pulse width, and 100% thereof is the maximum value (approximately H/6) of the PWM output pulse width. In the example shown in FIG. 8, in order to make the brightness as high as possible, 100% is output as the PWM output pulse width when the B (blue) video signal level is 100%. When the received television image is displayed under such adjustment conditions, the image modulation level on the transmitting side becomes overmodulated and the R, G, and B image signal levels exceed 100%, as shown in Figure 8. With conversion characteristics like this, the blue PWM output pulse width first saturates, causing the white balance to collapse at the white peak and becoming yellowish, and as overmodulation progresses, the green PWM output pulse width also saturates. The white piece part becomes reddish. This had the problem that the whiteness was impaired, especially when white characters appeared.

Purpose of the Invention The present invention solves the above-mentioned drawbacks of the conventional art, and by maintaining the white balance condition at 100% modulation when the video modulation becomes overmodulated, it is possible to avoid overmodulation, which tends to occur with white characters, etc. It is an object of the present invention to provide an image display device with good whiteness and high brightness even during overmodulation.

Configuration of the Invention In order to achieve the above object, an image display device of the present invention includes a screen coated with phosphors of multiple colors that emit light when irradiated with an electron beam;
An electron beam source that generates an electron beam for each vertical division in which the screen on the screen is divided into a plurality of vertical sections; and an electron beam source that generates an electron beam in each vertical division, and horizontal separation means for separating and irradiating the screen into each horizontal section; a deflection electrode for deflecting the electron beam in a plurality of steps in the vertical and horizontal directions before reaching the screen; A beam flow control electrode that controls the amount of electron beam irradiated to control the amount of light emitted from each pixel on the screen, a focusing electrode that controls the size of light emitted by the electron beam on the phosphor surface in each pixel, and an electron beam. a back electrode for controlling the amount of light emitted by the camera; a sampling means for sampling and holding a video signal for each of the horizontal sections from the received color television signal; pulse width modulation means that pulse width modulates the electron beam for each horizontal section sequentially for each color using a video signal held by the sampling means in synchronization with the irradiation of the phosphor, and supplies the electron beam to the beam flow control electrode; Level adjustment to adjust the level of the video signal of each color, which is the input signal of the pulse width modulation means, to a fixed ratio, and the video signal of each color when the luminance level of the video signal of each color exceeds a predetermined rated value. and a holding means for holding the output pulse width of the pulse width modulation at the above-mentioned constant ratio.

That is, the present invention has a configuration in which a PWM circuit with a finite maximum pulse width is used in the video output section as shown in FIG. , G, and B video signal level ratios are kept constant regardless of the video modulation degree, so that the white balance condition does not collapse even in the case of overmodulation, and maximum brightness can be obtained under the white balance condition. It will be done.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 9 is a circuit diagram of a main part of an image display device according to an embodiment of the present invention, and the same components as those shown in FIG. 3 are given the same reference numerals and their explanations will be omitted. In FIG. 9, it is assumed that the black levels of the R, G, and B video signal outputs of the color demodulation circuit 30 are equal. Reference numerals 51, 52, and 53 are input terminals for color-demodulated R, G, and B video signals, respectively. Reference numerals 54, 55, and 56 are output terminals for R, G, and B video signals, respectively, and the outputs are sent to the sample and hold circuits 31-1 to 31-n and the memory 32-n in FIG.
1 to 32-n, and switching circuits 35-1 to
PWM circuits 37-1 to 37-n through 35-n
is input. 57, 58, 59 are R, G, respectively.
B video signal level adjustment volume, 60, 61
is a switching diode, 62 and 63 are each
It is a voltage source with voltages V ₁ and V ₂ . Color demodulation circuit 3
The R, G, B video signal output from 0 is adjusted with level adjustment volume 57, 58, 59,
PWM pulse widths as shown in FIG. 8 are obtained for the G and B video signal levels. The switching diode 60 detects the level of the R video signal as shown in FIG.
When the level of the G video signal exceeds 100%, the voltage is clipped to _V1 , and similarly, when the level of the G video signal exceeds 100%, the switching diode 61 clips the voltage _{to V2.}
It clips to a voltage of Therefore, if the on-voltage of the switching diodes 60 and 61 is ignored, the PWM pulse width of V ₁ will be 80%, and the PWM pulse width of V ₂ will be 80%.
By setting the voltage such that the PWM pulse width is 90%, the PWM conversion characteristics shown in FIG. 10 can be obtained. Other configurations are similar to the conventional example.

The PWM conversion characteristics in Figure 10 are similar to Figure 8, with the ratio of the output pulse widths of the pulse width modulation circuit for white balance being R:G:B=80:90:
It is set at 100. The difference between Figure 8 and Figure 10 is R,
When the G and B video signal levels each exceed 100 or higher (relative to the white level of the video signal), the corresponding PWM output pulse width is saturated and the R,
The point is that the G and B video signal levels are each maintained at 100% pulse width. With these characteristics, when displaying a received image from television broadcasting, even if there is overmodulation in areas such as white characters, the R, G, B pulse width ratio for white balance will be 100%.
Since the white level is maintained, the whiteness is not impaired. In this example, the saturation point was set to 100% of the R, G, and B video signals, but
Of course, it does not have to be 100%. However, by setting it to 100% like this, you can obtain high brightness as well as white balance.

In the above embodiment, the white balance condition was set to R:G:B=80:90:100, but R,
Even when the white balance conditions for G and B are different, the adjustment of the level adjustment volume, the switching diode 60, the voltage source 62, and the R,
G, B output circuit connection selection and voltage sources 62, 6
Of course, it is possible to design freely by setting the output voltages V ₁ and V ₂ of No. 3.

Further, the present invention is not limited to the specific circuit configuration described above, and any other configuration may be used as long as the circuit can obtain PWM conversion characteristics as shown in FIG.

Effects of the Invention As explained above, according to the present invention, when controlling the beam flow to R, G, and B phosphors using a PWM circuit with a finite maximum pulse width, the video input level to the PWM circuit will not exceed. The white balance condition is maintained even when the pulse width is saturated at the maximum pulse width.
Therefore, even when the video modulation becomes overmodulated in white text areas in television broadcasting, the white balance is not disrupted and an image with good whiteness is displayed. Furthermore, the brightness can be high under the above white balance conditions.

[Brief explanation of the drawing]

Figure 1 is an electrode configuration diagram of a conventional image display device, Figure 2 is a diagram showing the minimum picture element on the screen, and Figure 3 is a diagram showing the minimum picture element on the screen.
The figure shows a block diagram of the drive circuit and waveform diagrams of each part,
Figure 4 is a relationship diagram between vertical deflection signals and synchronization signals, Figure 5 is a counter timing chart, Figure 6 is a relationship diagram of drive output pulses, Figure 7 is a relationship diagram between horizontal deflection signals and synchronization signals, FIG. 8 is an explanatory diagram of PWM conversion characteristics, FIG. 9 is a circuit diagram of a main part of an image display device according to an embodiment of the present invention, and FIG. 10 is an explanatory diagram of PWM conversion characteristics of the image display device. 1... Back electrode, 2, 2a to 2o... Line cathode, 3,
3'...Vertical focusing electrode, 4...Vertical deflection electrode, 5...Beam flow control electrode, 7...Horizontal deflection electrode, 9...Screen, 10...Slit, 20...phosphor, 24...Synchronization separation circuit, 25...For vertical deflection Counter, 26...
Line cathode drive circuit, 27...Memory, 28...Horizontal deflection counter, 29...Memory, 30...Color demodulation circuit,
31-1 to 31-n...sample hold circuit, 3
1-2 to 32-n...Memory, 33...Reference clock oscillator, 34...Sampling pulse generation circuit, 3
5-1 to 35-n... Switching circuit, 36... Switching pulse generation circuit, 37-1 to 37-n
...PWM circuit, 38, 39...D/A converter, 40
...Vertical deflection drive circuit, 41...Horizontal deflection drive circuit,
42... Deflection pulse generation circuit, 51-53... Input terminal, 54-56... Output terminal, 57-59... Level adjustment volume, 60-61... Switching diode, 62, 63... Voltage source.

Claims (1)

[Claims] 1. A screen coated with phosphors of multiple colors that emit light when irradiated with an electron beam, and an electron beam source that generates an electron beam for each vertical division of the screen on the screen. , horizontal separation means for separating the electron beam generated by the electron beam source into each horizontal section of the screen, which is divided into a plurality of horizontal sections, and irradiating the electron beam onto the screen; a beam flow control electrode that controls the amount of electron beam irradiated onto the screen to control the amount of light emitted by each pixel on the screen;
a collecting electrode for controlling the size of light emitted by the electron beam on the phosphor surface in each pixel; a sampling means for sampling and holding a video signal for each horizontal section from the received color television signal; In synchronization with the irradiation of the plurality of colors of phosphors by the horizontal polarization of the electron beam, the electron beam for each horizontal section is sequentially pulse-width modulated for each color using the video signal held by the sampling means to control the beam flow. A pulse width modulation means for supplying the control electrode, a level adjustment means for adjusting the level of the video signal of each color, which is an input signal of the pulse width modulation means, to a certain ratio, and a luminance level of the video signal of each color that is rated, respectively. and holding means for maintaining the output pulse width of pulse width modulation by the video signal of each color at the constant ratio when the ratio exceeds a predetermined value.