JPS6190590A - Picture display device - Google Patents

Abstract

PURPOSE:To maintain white balance conditions at the time of 100% modulation when video modulation becomes over-modulated by making constant an input R, G and B video signal level ratio of a pulse width modulation circuit without depending upon the video modulation factor. CONSTITUTION:An R, G and B video signal level from a color demodulation circuit 30 is adjusted by level adjusting volumes 57, 58 and 59 and a PWM pulse width can be obtained for R, G and B video signal levels. A switching diode 60 is clipped to a voltage V1 when a level of an R video signal exceeds 100%, and a switching diode 61 is clipped to a voltage V2 in the same manner when a level of the G video signal exceeds 100%. Consequently, when an R, G and B video signal level respectively exceeds 100% (level equivalent to a white level of the video signal), an output pulse width of the pulse width modulation circuit corresponding to it is saturated and the R, G and B video signal level is maintained respectively to the pulse width at the time of 100%.

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.

Structure of conventional example and its problems Traditionally, cathode ray tubes have been mainly used as display elements for displaying color television images, but conventional cathode ray tubes have a very long depth compared to the screen size. , it was impossible to create a thin television receiver. In addition, although 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 performance such as brightness, contrast, and color display, and have not been put into practical use. However, the aim is to create a flat display device using electron beams. A system was invented in which a television image is displayed as a whole by generating a plurality of lines and deflecting each electron beam in the vertical direction for each section to display a plurality of lines.

First, a basic configuration of the image display element used here will be explained with reference to FIG. This display element consists of, in order from the back to the front, a back electrode (1), a line cathode (2) as a beam source, vertical focusing electrodes (3) (3'), a vertical deflection electrode (4), and a beam flow control Electrode (5), horizontal focusing electrode (
6) It consists of a horizontal deflection electrode (7), a beam acceleration electrode (8), and a screen (9), which are housed inside a flat glass bulb (not shown) that is evacuated. ing. Line cathode as beam source (2)
is stretched horizontally so as to generate an electron beam distributed linearly in the horizontal direction, and a plurality of such linear cathodes (2) are arranged vertically at appropriate intervals ((2a) to (2) in the figure).
2d) only four are shown). In this example, it is assumed that 15 are provided. them (2a
) to (2o), these wire cathodes (2) are constructed by coating the surface of a tungsten wire with a diameter of 10 to 20 μΦ with an acid cathode material for thermionic emission "2t" atbrbs!
・1, and these line cathodes (2a) to (2
0) is heated to generate a thermionic electron beam when a current is passed through it, and as described later, it is controlled to emit an electron beam sequentially for a fixed period of time starting from the line cathode (2a). . 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 directs the generated electron beams only in the forward direction. It has the effect of pushing out. This back electrode (1) may be formed by a coating film of a conductive material attached to the inner surface of the rear wall of the glass bulb. Alternatively, a one-sided electron beam emitting cathode may be used.

The vertical focusing type pi (3) is a conductive plate (11) having a horizontally long slit (10) facing each of the line cathodes (2a) to (2o), and it collects electrons emitted from the line cathode (2). The beam is directed through the slit (10) and focused vertically. 1 horizontal line (
In Figure 0, in which electron beams for 360 picture elements are taken out at the same time, only one section of them in the horizontal direction is shown. The slits (10) may be provided with crosspieces at appropriate intervals in the middle, or may be a row of through holes provided in large number at small intervals in the horizontal direction (intervals that are almost touching). The vertical focusing electrode (3'), which may be configured essentially as a slit, is similar.

A plurality of vertical deflection electrodes (4) are arranged horizontally at intermediate positions between the slits (10),
The upper and lower surfaces of the insulating substrate (12) and the annular groove electric body (
13) (13') is provided. Then, an overlapping deflection voltage is applied between the opposing conductors (13) (13") to deflect the electron beam in the vertical direction. In this example, the pair of conductors (13) (13")
3'') to deflect the electron beam from one line cathode (2) vertically to a position corresponding to 16 lines.

The 16 vertical deflection electrodes (4) constitute 15 conductor pairs corresponding to 9 of the 15 line cathodes (2), resulting in 240 horizontal lines on the screen (9). Deflect the electron beam as you draw.

Next, the control electrodes (5) are composed of conductive plates (15) each having a long slit (14) in the vertical direction, 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 (15-1)
~(15-n) are provided. (Only 9 lines are shown in the figure). 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, if 180 conductive plates (15-1) to (15-n) for the control electrode (5) are provided, 360 pixels can be displayed per horizontal line. In addition, in order to display images in color, each picture element is R, G,
The display will be performed using phosphors of three colors B, and each control electrode (5
) are sequentially applied with R2O and B video signals for two picture elements. In addition, conductive plates (15
-1) to (15-n) each has 18 lines for one line.
0 sets (2 picture elements per set) of video signals are applied at the same time, and one line of video is displayed at one time.

The horizontal focusing electrode (6) is connected to the slit (14) of the control electrode (5).
) is composed of a conductive plate (17) having a plurality of vertically long slits (16) facing each other, and the electron beam for each pixel divided horizontally is transmitted horizontally. Focus into a narrow beam of electrons.

The horizontal deflection electrode (7) is composed of a plurality of conductive plates (tg) (18') arranged vertically on both sides of the slit (16), and each electrode (1a) 08 ), six levels of horizontal deflection voltages are applied to horizontally deflect the electron beams of each picture element, and two sets of R and G are displayed on the screen (9).

Each phosphor of B is 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 plates (19) installed horizontally in the same position as the vertical deflection electrode (4), and it directs the electron beam to the screen (9) with sufficient energy. Accelerate to cause a collision.

The screen (9) is constructed by applying a phosphor (20) that emits light when irradiated with an electron beam to the back surface of a glass plate (21), and adding a metal back layer (not shown). The phosphor (20) has two phosphors of three colors R2O and B for one slit (14) of the control electrode (5), that is, for each one electron beam divided in the horizontal direction. They are provided in pairs.

It is applied in vertical stripes. In Figure 1, the broken lines drawn on the screen (9) represent multiple wire cathodes (2
), and the two-dot chain line indicates the horizontal division displayed corresponding to each of the plurality of control electrodes (5). As shown in the enlarged view in Figure 2, one section partitioned by
0) and has a width of 16 lines in the vertical direction. For example, the size of one section is 1 in the horizontal direction.
rrtn.

The vertical direction is 9m.

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

In addition, in this example, only one pair of R, G, 'B phosphors (20) for two picture elements is provided for one control electrode (5), that is, one electron beam. Of course, one picture element or three or more picture elements may be provided, and in that case, R, G, and B video signals for one picture element or three or more picture elements are sequentially applied to the control electrode (5). , horizontal deflection is performed in synchronization with this.

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 explained.

The power supply circuit (22) is a circuit for applying a predetermined bias voltage (operating voltage) to each electrode of the display element.

The back electrode (1) has -■1, the vertical focusing electrode (3) (3
') is V,, V,'', and horizontal focusing electrode (6) is V,, V,''.
The acceleration electrode (8) has v9. vg on screen (9)
Apply a DC voltage of

Next, a composite video signal of a television signal is applied to the input terminal (23), and a vertical synchronization signal V and a horizontal synchronization signal H are separated and extracted in a synchronization separation circuit (24).

The vertical deflection drive circuit (40) includes a vertical deflection counter (2
5), a memory for vertical deflection signal storage (27), and a digital-to-analog converter (30) (hereinafter referred to as a DA converter). As input pulses to the vertical deflection drive circuit (40), a vertical synchronizing signal V and a horizontal synchronizing signal H shown in FIG. 4 are used. Device 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 (in this case, a period of 240H) excluding the vertical retrace period of the mounting period, and this count output is sent to the address of the memory (27). Supplied. The memory (27) outputs vertical deflection signal data (here, 8 bits) corresponding to each address, and the D-A converter (39) outputs the data of the vertical deflection signal corresponding to each address.
Figure (Figure 3(b)D)): Show? ,? ' is converted into a vertical deflection signal. This circuit has memory addresses for storing vertical deflection signals corresponding to each line for 240H, and by storing regular data in the memory every 16H, it is possible to obtain 16 levels of vertical deflection signals. can.

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 a line cathode drive pulse a'=o. FIG. 5(a) shows the vertical synchronizing signal V, the horizontal synchronizing signal H, and the vertical deflection counter (25
) shows the relationship between the lower 5 bits. FIG. 5(b) shows line cathode drive pulses a1 to 0 every 16H using these signals.
We will show you how to make ′. In FIG. 5, LSB indicates the lowest bit, and (LSB+1) means the bit one higher than the LSB.

The first line cathode drive pulse a' is generated using the vertical synchronizing signal V and the output (LSB+4) of the vertical deflection counter (25).
-S flip-flops can be used to generate the line cathode drive pulses b' to 0' using a shift register, and the line cathode drive pulse a' is output from the vertical deflection counter (25) (L S B + 3 ) can be obtained by transferring the inverted version of the clock. These drive pulses a' to O' are inverted and made low in potential only during each pulse period, and converted into line cathode drive pulses a to 0, which are made to have a high potential of approximately 20 volts in other periods (see Fig. 3). (b)E
), are added to each of the wire cathodes (2a) to (2o).

Each line cathode (2a) to (20) is heated by passing a current during the high potential period of the drive pulses a to 0, and is heated so that it can emit electrons during the low potential period of the drive pulse a''o. state is maintained.This allows 15 line cathodes (2
From a) to (20), a low potential drive pulse a is applied to each of a) to (20).
” Electrons are emitted only during the 16H period when o is applied. During the period when high potential is applied.

The voltage applied to the line cathodes (2a) to (20) is higher than the potential at the position of the line cathode (2) determined by the bias voltage applied to the back electrode (1) and the vertical focusing electrode (3). Since the potential is more positive, the line cathode (2
No electrons are emitted from a) to (2o), thus
In the line cathode (2), electrons are sequentially emitted from the upper line cathode (2a) to the lower line cathode (20) for 16H periods 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, line cathode drive pulses a~0 and vertical deflection signals ν, ν′
The relationship between the two will be explained using FIG. Figure 6 (
, ) is a waveform diagram of a line cathode pulse, (b) is a waveform diagram of a vertical deflection signal, and (c) is a waveform diagram of a horizontal deflection signal. The vertical deflection signals Y and ν' in FIG. 6(b) change by IH in 16 steps during the 16H period of each line cathode drive pulse a to 0 in FIG. 6(a).

The vertical deflection signal tube and ν' both have a center voltage of v4, so that the tube increases sequentially and ν' decreases sequentially.
They are designed to change in opposite directions. These vertical deflection signal tubes and 9' are applied to the electrodes (13) and (13') of the vertical deflection electrode (4), respectively, so that the electron beams generated from the respective line cathodes (2a) to (20) are is vertically deflected in 16 steps.

As mentioned above, one electron beam is deflected on the screen (9) so that a raster of 16 lines is drawn 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 (20) sequentially for a period of 16H starting from the top, and each electron beam is sequentially emitted one line from top to bottom within 15 sections in the vertical direction. On the screen (9), from the first line at the top to the 24th line at the bottom.
The electron beam is vertically deflected one line at a time up to the 0th line, and a total of 240 raster lines are drawn.

The vertically deflected electron beam is sent to the control electrode (5).
It is divided into 180 sections in the horizontal direction by a horizontal focusing electrode (6) and taken out. In Figure 1, one of them
The electron beam shown in each section is
The amount of electrons passing through is controlled by the control electrode (5), and the electrons are focused in the horizontal direction by the horizontal focusing electrode (6) into a single narrow electron beam.

The light is deflected in six steps in the horizontal direction by the horizontal deflection means described below, and is sequentially irradiated onto the R2O, B capacitive light body (20) for two picture elements on the screen (9). The phosphors corresponding to each of (15-1) to (15-n) of the control electrode (5), whose vertical and horizontal divisions are shown in Figure 2, are R, G, and B for two picture elements. For convenience of explanation, one pixel is R1
, G i 9 B 1 and the other one is R,,G,,B.

Next, the horizontal deflection drive circuit (41) is composed of a horizontal deflection counter (28) (11 bits), a memo (29) for storing horizontal deflection signals, and a D-A converter (38). ing. The input pulses of the horizontal deflection drive circuit (41) are a vertical synchronizing signal V and a horizontal synchronizing signal H, as shown in FIG.
A pulse 6H with a repetition frequency six times that of the horizontal synchronizing signal H is used. The horizontal deflection counter (28) is reset by the vertical synchronizing signal V and receives the horizontal six times the pulse 6.
Count H. This horizontal deflection counter (28) is set 6 times during IH, 240H x 6/H = 144 during 1V.
It counts 0 times and this count output is supplied to the address of the memory (29).

The horizontal deflection signal data (here, 8 bits) corresponding to the address is output from the memory (29), and is processed by the D-A converter (38) as shown in Fig. 7 (Fig. 3 (b) C). ,h
' is converted into a horizontal deflection signal such as '. In this circuit, 6
There is a memory address for storing the horizontal deflection signal corresponding to each of the 240 lines, and by storing 6 pieces of regular data for each line in the memory, a 6-step wave horizontal deflection signal is generated during the IH period. can be obtained. .

As shown in Fig. 7, this horizontal deflection signal is a pair of horizontal deflection signals ri and h' that change in six steps, both of which have a center voltage of vl, where h decreases sequentially and h' increases sequentially. They change in opposite directions as they move forward. These horizontal deflection signals, h' are the electrode (1) of the horizontal deflection electrode (7), respectively.
8) and (18'). As a result, each horizontally segmented electron beam is applied to the R, G of the screen (9) during each horizontal period.

B, R, G, B (R1, al, B,, R,, a,,
The beam is horizontally deflected so that the phosphor of Bt) is sequentially irradiated for H/6 periods. Thus, in each line raster, the electron beam is R1,
The phosphors (20) of G, B, R, G, and B2 are sequentially irradiated.

Therefore, the electron beams are set to R, , G for each horizontal section of each line.
By modulating the video signals of □, B, R2, G, , B, a color television image can be displayed on the screen (9).

Next, the modulation control portion of the electron beam will be explained. First, the composite video signal applied to the television signal input terminal (23) is applied to the color demodulation circuit (30), where the R-Y and B-Y color difference signals are demodulated and the G-Y color difference signal is demodulated. The signals are combined with Madrisk, and further, they are combined with the luminance signal Y to obtain each primary color signal of R2O and B (hereinafter R,
G, B video signals) are output. Those R,G
, B. Each video signal is processed by 180 sample and hold circuits (3
1-1) to (31-n). Each sample hold circuit (31-1) to (31-n) is R1
It has six sample and hold circuits: 1, G1, B1, R2, G2, and B2. Those sample and hold outputs are stored in the holding memories (32-1) to (32-1), respectively.
2-n).

On the other hand, reference clock 9. The vibrator (33) is composed of a PLL (phase-locked loop) circuit, etc., and in this example, a reference clock of 6 fs, which is six times the color subcarrier fsc, is used.
c and twice the standard a to generate 2fsc. The reference axis is controlled so that it always has a constant phase with respect to the horizontal synchronizing signal H.

The reference clock 2fsc is a deflection pulse generation circuit (42)
signals 6H and H/6, which are six times the horizontal synchronization signal H.
Signal switching pulse per r1+ gt+ ))tt rz
A pulse of eg z p , b 2 (FIG. 3(b)B) is obtained. On the other hand, the reference clock 6fsc is applied to the sampling pulse generation circuit (34), where it is delayed by one clock cycle by a shift register, and is then delayed during the effective horizontal scanning period (approximately 1080 sampling pulses R□, during 50μ5ec).

G-engineer 4. B engineering□, R1□, Gx2. Bi,,R,□,G
21. B.1. R, 2゜G, , B, □~Rn, , Gn
,,Bn□,Rn,,On,tBn,(th.

3(b) A) are generated sequentially, and then one transfer pulse t is generated. This sampling pulse R1
, ~Bn2 is one line of the video to be displayed by 3 in the horizontal direction.
Corresponding to each picture element when divided into 60 picture elements,
Its position is controlled so that it is always constant with respect to the horizontal synchronizing signal H.

Each of these 1080 sampling pulses R11 to Bn2 is connected to 180 sets of sample hold circuits (31-1).
~(31-n) are added six times each, thereby each sample hold circuit (31-1) ~(31-n)
When one line is divided into 180 parts, each 2
Picture elements R1, G, B1. Each of the R, G, B, video signals is individually sampled and held. The 180 sample-held groups R, G, B□,
R2゜G,,B2 video signals are stored in 180 sets of memories (32-1) to (3
2-n), they are transferred all at once by a transfer pulse t, and are held here for the next horizontal period. This retained Ro
.

The signals G□, B, , R, , G, , B are applied to switching circuits (35-1) to (35-n). The switching circuits (35-1) to (35-n) each have R,
,G,,B,.

It is composed of a tri-state or analog gate having individual input terminals for Rz, Gx-Bz 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) circuit (37-1)
(37-n), and here, the reference pulse signal is pulse width modulated according to the magnitude of the sampled and held Rx, Glt Ble Rxe 'Gt-Bz video signal) and is output. The repetition period of the reference pulse signal is the above signal switching pulse rxv glv
It is desirable that the pulse width be sufficiently smaller than the pulse width of bxs rz + g'zt b2, for example, 1:10 to
1: Something about Zoo level 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) to the control electrodes (5) of the display element.
(15-n) respectively. Each switching circuit (35-1) to (35-n) receives a switching pulse r1e gte b, u'r'z* gze applied from a switching pulse generating circuit (36).
Switching is controlled simultaneously by bz. The switching pulse generation circuit (36) is the same as the deflection pulse generation circuit (4) described above.
2) Signal switching from /L'X rat guy b
Each horizontal period is divided into 6 and the switching circuits (35-1) to (35-n) are switched by H/6.
B1. Each video signal of R2, G, B2 is time-divided and outputted sequentially 5, and pulse width modulation circuits (37-1) to (37-n
) to supply the switching signal r1p gLt 'bz*
Generate rz+ gzt bz.

What should be noted here is that the switching circuit (35-1
) to (35=n) R1. G,t 81. R
,.

Switching the supply of video signals G, , B, and electron beam Rit Gll Bit by the horizontal deflection drive circuit (41)
The irradiation switching horizontal deflection of RatGztBt to the phosphor is synchronously controlled so that it completely matches both the timing and the order. As a result, when the electron beam is irradiating the R1 phosphor, the irradiation amount of the electron beam is controlled by the R1 video signal, and the G
G, B, Rt * G 2 g B z are controlled in the same way, and R1, G1 . B□.

R2l G! = B is the luminescence of each phosphor is R of that picture element, G1゜B it Rm , G 2 , B 2
Each picture element is controlled by the input video signal, and each picture element is displayed by emitting light according to the input video signal. There are 180 sets of such controls for one line (2 pixels each)
This is done at the same time to display an image of 360 pixels per line, and then 240H lines are performed sequentially starting from the upper line, resulting in one image being displayed on 5 screens (9). . , and one or more operations are repeated for each field of the input television signal, and as a result, a moving television image is displayed on the screen (9) in the same way as in a normal television receiver.

Incidentally, in the above image display device, 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. R,G.

The maximum value of the pulse width corresponding to the B video signal is about a period of H/6 (H is one horizontal period). In addition, white balance adjustment in such devices is performed using a color demodulation circuit (3
The color temperature of highlights and lowlights was adjusted by changing the amplitude and DC level of the three primary color output signals of R, G, and B.

Fig. 8 shows an example of the adjustment result. In this example, in order to achieve white balance, R:G:B=80:
The ratio is 90:100. In FIG.

The horizontal axis shows the R, G, and B video signal levels, and their 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 of FIG. 8, in order to make the brightness as high as possible,
When the (blue) video signal level is 100%, 100% is output as the PWM output pulse width. When displaying a received television image in such an adjusted state, the image modulation level on the transmitting side becomes overmodulated and R, G,
B When each video signal level exceeds 100%, in the conversion characteristics shown in Figure 8, the blue PWM output pulse width first saturates, causing the white balance to collapse at the white peak, resulting in a yellowish appearance. As overmodulation progresses, the green PWM output pulse width also becomes saturated and the white peak portion becomes reddish. This has the problem that the whiteness is impaired especially when white characters appear.Purpose of the InventionThe present invention solves the above-mentioned drawbacks of the conventional technology. It is an object of the present invention to provide an image display device with good whiteness and high brightness even during overmodulation, which tends to occur with white characters, by maintaining white balance conditions during % modulation.

Structure 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, and a plurality of screens arranged on the screen in the direction of the throne. an electron beam source that generates an electron beam for each vertical section divided into two; and an electron beam source that separates the electron beam generated by the electron beam source into each horizontal section that divides the screen on the screen into a plurality of horizontal sections. horizontal separation means for irradiating the screen; a deflection electrode for deflecting the electron beam in multiple steps in the direction of the throne and in the horizontal direction before reaching the screen; A beam flow control electrode that controls the amount of light emitted from each pixel on the top, a focusing electrode that controls the size of light emitted by the electron beam on the phosphor surface in each pixel, and a back electrode that controls the amount of light emitted by the electron beam. , sampling means for sampling and holding a video signal for each of the horizontal sections from the received color television signal; a pulse width modulation means which pulse width modulates the electron beam for each horizontal section sequentially for each color using a video signal held by the sampling means and supplies the beam flow control electrode to the beam flow control electrode; and an input signal of the pulse width modulation means; Level adjustment that adjusts the level of the video signal of each color to a certain ratio, and output pulse width of pulse width modulation by the video signal of each color when the brightness level of the video signal of each color exceeds a predetermined rated value. and a holding means for holding the ratio 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 event 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 structural elements 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 RlG and B video signal outputs of the color demodulation circuit (30) are equal. (51)(
52) (53) are input terminals for R, G, and B video signals which are each color demodulated. (54), (55), and (56) are output terminals for R, G, and B video signals, respectively, and the outputs are from the sample hold circuits (31-1) to (31-n) in FIG.
), memory (32-1) to (32-n), and PWM through switching circuits (35-1) to (35-n).
It is input to H paths (37-1) to (37-n). (5
7) (5g) and (59) are level adjustment volumes for R, G, and B video signals, (60) and (61) are switching diodes, and (62 and 63) are voltage sources with a voltage of V 1 g ■@, respectively. R from the six-color demodulation circuit (30),
The G' and B video signal outputs are controlled by the level adjustment volume (57
) (58) and (59) to obtain a PWM pulse width as shown in FIG. 8 for the R2O and B video signal levels. The switching diode (60) clips to the voltage vl when the level of the R video signal exceeds 100% in FIG. 10, and the switching diode (61) does the same.

When the level of the G video signal exceeds 100%, it clips to the voltage v2. Therefore, if the on-voltage of the switching diodes (60) and (61) is ignored, v
By setting l to a voltage such that the PWM pulse width is 80% and v to a voltage such that the PWM pulse width is 90%, the first
PWM conversion characteristics as shown in Figure 0 are obtained. Other configurations are similar to the conventional example.

In the PWM conversion characteristics shown in FIG. 10, as in FIG. 8, the ratio of the output pulse widths of the pulse width modulation circuit for white balance is set to R:G:B=80:90:100. The difference between Fig. 8 and Fig. 10 is that the R, G, and B video signal levels are each IC0% (white of the video signal).
level), the corresponding P
The WM output pulse width is at the point where it is saturated and the R, G, and B video signal levels are each maintained at the pulse width at 100%. With these characteristics, when displaying a received image of 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 10.
Since the self level of 0% is maintained, whiteness is not impaired. In this embodiment, the saturation points are R and G.

Although it is set to 100% of the B video signal, it goes without saying that it does not have to be exactly 100%. But like this 100
%, you can obtain high brightness as well as white balance.

In the above example, the white balance condition is
R:G:B = 80:90:100, but R2O,
Even when the white balance conditions of B are different, the output circuit R2O of the clip circuit consisting of the level adjustment volume adjustment, switching diode (60), voltage source (62), switching diode (61), and voltage source (63) Selection of connections and output voltage V1. of voltage sources (62) (63). Of course, it is possible to freely design by setting V.

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 the PWM conversion characteristics as shown in FIG.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, when the beam flow to the R, G, and B phosphors is controlled 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 image modulation becomes overmodulated in areas such as white characters during television broadcasting, the white balance will not be distorted.
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 smallest picture element on the screen, Figure 3 is a block diagram of the drive circuit and waveform diagrams of each part, and Figure 4 is the device deflection. Relationship diagram between signals and synchronization signals, Figure 5 is a counter timing chart, Figure 6 is a correlation diagram of drive output pulses, Figure 7 is a relationship diagram between horizontal deflection signals and synchronization signals, and Figure 8 is 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)-(20)・
... 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)...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, (31-2) to (32-n)...memory, (3
3)...Reference clock oscillator, (34)...Sampling pulse generation circuit, (35-1) to (35-n)
... switching circuit, (36) ... switching pulse generation circuit, (37-1) to (37-n) -P
W M circuit, (38) (39)...D/A converter,
(40) Vertical deflection drive circuit, (41) Horizontal deflection drive circuit, (42) Deflection pulse generation circuit, (51) to (53) Input terminal, (54) ~
(56)...Output terminal, (57)-(59)...
Level adjustment volume, (60) to (61)... Switching diode, (62) (63)... Voltage source agent Yoshihiro Morimoto Figure 4L-]: 1U'' Figure 5Ca) ( b) Figure 7 Figure 3 g, white Figure 10 star b)

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. a horizontal separation means for separating the electron beam generated by the electron beam source into each horizontal section of the screen on the screen 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 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, a back electrode that controls the amount of light emitted by the electron beam, and a video signal for each horizontal section from the received color television signal. A sampling means for sampling and holding, and a video signal held by the sampling means in synchronization with the irradiation of the plurality of colors of phosphors by horizontal deflection of the electron beam for each horizontal section, and the electron beam for each horizontal section is A pulse width modulation thickness that is sequentially pulse width modulated for each color and supplied to the beam flow control electrode, and a level adjustment that adjusts the level of the video signal of each color, which is an input signal to the pulse width modulation means, to a constant ratio. and a holding means for maintaining the output pulse width of pulse width modulation by the video signals of the respective colors at the constant ratio when the luminance level of the video signals of the respective colors exceeds a predetermined rated value.