JPH0410277B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an apparatus for controlling the passage time of an electron beam by applying a pulse width modulated signal depending on the brightness level of a video signal, thereby displaying 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 was impossible to create a full-sized television receiver. In addition, EL display elements, plasma display devices, and liquid crystal display elements have recently been developed as flat display elements, but all of them are insufficient in terms of performance such as brightness, contrast, and color display, so they cannot be put into practical use. has not yet been reached.

Therefore, in order to achieve a flat display device using electron beams, the present applicant filed a patent application in 1983-
No. 20618 (Japanese Unexamined Patent Publication No. 135590/1983) proposed a new display device.

This method generates an electron beam for each section when the image on the screen is vertically divided into multiple sections, and displays multiple lines by deflecting each electron beam vertically for each section. However, it displays the television image as a whole.

First, a basic configuration example 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, a line cathode 2 as a beam source, vertical focusing electrodes 3, 3', a vertical deflection electrode 4, a beam flow control electrode 5,
A horizontal focusing electrode 6, a horizontal deflection electrode 7, a beam accelerating electrode 8, and a screen plate 9 are arranged, and these are housed in the vacuumed 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 15
This book shall be provided. 2a~2 them
o. These line cathodes 2 are, for example, 10~
It consists of an oxide cathode material for thermionic emission coated on the surface of a 20 μφ tungsten wire.
These line cathodes 2a to 2o are heated so as to generate a thermionic electron beam by passing an electric current through them, and as described later, emit electron beams sequentially for a certain period of time starting from the line cathode 2a. 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. Further, instead of the back electrode 1 and the linear cathode 2, 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 configured as a slit by a row of many through holes arranged horizontally at small intervals (nearly touching intervals). may be done. 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 conductors 13 and 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 embodiment, the electron beam from one line cathode 2 is vertically deflected to positions corresponding to 16 lines 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 embodiment, 180 control electrode conductive plates 15-1 to 15-n are provided (only nine are shown in the figure). Each of the control electrodes 5 extracts the electron beam by dividing it 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 added sequentially. In addition, 180 conductive plates 15-1 to 15 for control electrodes 5
-n, 180 sets of video signals for one line (two picture elements per set) are simultaneously applied, and the video for one line 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 made up of a plurality of conductive plates 18, 18' arranged vertically on both sides of the slit 16, and each electrode 18, 18' has six levels of horizontal deflection. A voltage is applied to horizontally deflect the electron beams of each picture element, so that two sets of R, G,
Each phosphor of B is sequentially irradiated to emit light. In this embodiment, 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 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 embodiment, only one pair of R, G, and B phosphors 20 for two picture elements are provided for one control electrode 5, that is, for one electron beam, but of course, for one picture element or The control electrode 5 may be provided over three picture elements, in which case R, G, and B video signals for one picture element or three or more picture elements are sequentially applied, and horizontal deflection is performed in synchronization with this. Ru.

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 vertical focusing electrodes 3, 3.
DC voltages of V ₃ , V ₃ ', V ₆ to the horizontal focusing electrode 6, V ₈ to the accelerating voltage 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 39 (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. Vertical deflection signal data (here, 10 bits) corresponding to each address is output from the memory 27, and the data is sent to the D-A converter 39 as shown in Fig. 4 (Fig. 3 b, D).
It is converted into vertical deflection signals of υ and υ′ shown in . 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 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 the vertical synchronization signal V and the vertical deflection counter 25.
The line cathode drive pulses b' to o' can be generated using a shift register, and the line cathode drive pulse a' is output from the vertical deflection counter 25. It can be obtained by using the inverted version of (LSB+3) as the clock and transferring it. These drive pulses a' to o' are inverted and set to a low potential only during each pulse period, and converted into line cathode drive pulses a to o, which are set to a high potential of approximately 20 volts during other periods (the third
Figures b, E) are added to each line cathode 2a-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, electrons are emitted from the 15 linear cathodes 2a to 2o only during the 16H period when low potential drive pulses a to o are applied to each of them. During the period when a high potential is applied, the potential applied to the line cathodes 2a to 2o 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 higher potential is positive, no electrons are emitted from the line cathodes 2a to 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, and the emitted electrons are pushed forward by the back electrode 1, and the slits 1 facing each other in the vertical focusing electrode 3
0 and is 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. The vertical deflection signals υ, υ′ are each line cathode pulse a to o.
During the 16H period, it changes in steps of 1H 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 sequentially increases 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 16 lines of raster line by line from the top.

As a result of the above, electron beams are emitted for a period of 16 hours from the top of the 15 line cathodes 2a to 2o, and each electron beam is deflected by one line from top to bottom within 15 vertical divisions. As a result, the electron beam is vertically deflected one line at a time on the screen 9 from the first line at the top end to the 240th line at the bottom end, and a total of 240 raster lines are drawn.

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 is composed of a horizontal deflection counter 28 (11 bits), 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 counts 6 times during 1H and 240H×6/H=1440 times during 1V, 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-
In the A converter 38, h shown in FIG. 7 (FIG. 3 bC),
It is converted into a horizontal deflection signal such as h′. This circuit has a memory address for storing horizontal deflection signals corresponding to each of 6 x 240 lines, and by recording 6 pieces of regular data for each line in memory, 6 step waves are generated in 1H period. horizontal deflection signals can be obtained.

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,
It 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 with H/6 each. Thus, in each line raster, the electron beam is R ₁ ,
Each phosphor 20 of G 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 embodiment generates a reference clock 6f _SC that is six times the color subcarrier f _SC and a reference clock 2f _SC that is twice the color subcarrier f SC. . The reference clock is controlled to always have a constant phase with respect to the horizontal synchronizing signal H.
The reference clock 2f _SC is added to the deflection pulse generation circuit 42, and a signal 6H which is six times the horizontal synchronizing signal H and signal switching pulses r ₁ , g ₁ , b ₁ , r ₂ , g ₂ , b every H/6 are added. ₂ (Figure 3 bB) pulses are obtained. On the other hand, the reference clock 6f _SC is applied to the sampling pulse 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 ~ _Ro1 , _Go1 , _Bo1 , _Ro2 ,
G _o2 and B _o2 (FIG. 3bA) are generated sequentially, and then one transfer pulse width t is generated. These sampling pulses R ₁₁ and B _o2 correspond to each picture element when one line of the video to be displayed is divided into 360 picture elements in the horizontal direction, and their positions are always constant with respect to the horizontal synchronizing signal H. controlled so that

Each of these 1080 sampling pulses R ₁₁ to B _o2 is connected to 180 sets of sample 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.
are transferred all at once by a transfer pulse t, and held here 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 width-modulated and output according to the magnitude of the sampled and held R ₁ , G ₁ , B ₁ , R ₂ , G ₂ , B ₂ video signal. Ru. It is desirable that the repetition period of the reference pulse signal is sufficiently smaller than the pulse width of the signal switching pulses r ₁ , g ₁ , b ₁ , r ₂ , g ₂ , b ₂ , for example, 1:10 to 1:10. A ratio of about 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 display element.
~15-n, respectively. The switching circuits 35-1 to 35-n are simultaneously controlled by switching pulses _r1 , _g1 , _b1 , _r2 , _g2 , _b2 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
Switching signals r ₁ , g ₁ , b ₁ ,
Generate r ₂ , g ₂ , b ₂ .

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) to display an image of 360 picture elements for one line, and then sequentially for 240 minutes 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.

By the way, in the image display device as described above, the brightness displayed on the screen is determined by the control electrode 5.
If the conversion characteristic of the pulse width with respect to the video signal level is linear, then the change in brightness displayed on the screen will also be linear with respect to the video signal level. On the other hand, cathode ray tubes commonly used as video display devices have γ
It has a characteristic (γ=2 to 3), and the transmitting side performs γ correction on this. Therefore, when a broadcast radio signal is displayed using a cathode ray tube having a linear luminance characteristic with respect to an input video signal as described above, there is a problem in that the gradation in bright areas is impaired.

Purpose of the Invention The present invention eliminates such conventional drawbacks and changes the amount of electron beam reaching the phosphor from the line cathode according to the pulse width of the pulse width modulation, thereby changing the brightness characteristic to the gamma characteristic of a general cathode ray tube. An object of the present invention is to provide an image display device having characteristics close to those of the present invention and having good gradation.

Structure of the Invention The image display device according to the present invention has an output pulse width of the pulse width modulation circuit fixed at the trailing edge or the leading edge,
When the pulse width is extended as the brightness level of the video signal increases from this fixed timing, the amount of electron beam hitting the phosphor changes as the video signal level changes, that is, changes over time from a certain fixed timing. Focusing on the fact that the emission brightness can be given a gamma characteristic, the electrons reaching the phosphor are The beam amount is changed so that the luminance characteristic has a γ characteristic similar to that of a general cathode ray tube.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 8 is a waveform diagram for explaining the operation of the present invention. In FIG. 8, H and 6H are the same as in FIG. 7. The PWM waveform is a voltage waveform applied to the beam current control electrode 5 in FIG. 1, and at the "L" level, the electron beam reaching the phosphor 20 is cut off, and at the "H" level, the electron beam is allowed to pass through. The pulse width controls the passage time of the electron beam, and when the brightness of the image to be displayed is bright, the pulse width becomes wide, and when it is dark, the pulse width becomes narrow as shown by the dotted line. In FIG. 8, it is assumed that the trailing edge of the pulse width is fixed, and the following explanation will also proceed with this trailing edge fixed.

FIG. 9 shows the brightness characteristics when the PWM pulse width is maximum when the electrode voltage V ₃ of the vertical focusing electrode 3 is changed in the cathode ray tube of FIG. 1. When V ₃ exceeds a certain voltage, the brightness becomes saturated, but until then the curve is nearly linear, and as V ₃ increases, the brightness also increases. The reason why the brightness increases with this nearly linear curve is because the potential distribution around the linear cathode 2 is in the space charge limited region, and when the voltage V ₃ of the vertical focusing electrode 3 is increased, the potential gradient around the linear cathode 2 increases. As the emission electron flow increases, the vertical focusing electrode 3
The electron beam passing through the slit 10 increases,
The brightness increases accordingly.

FIG. 10 shows the brightness characteristics depending on the PWM pulse width. When the vertical focusing electrode voltage V ₃ is constant L _L , dotted line A,
When V _M is constant, the brightness characteristic is shown by a dashed-dotted line B, and when V _H is constant, it is shown by a dashed-double line C. From this characteristic,
When the vertical focusing electrode voltage has a voltage waveform such as V ₃ shown in FIG. 8, its brightness characteristic can be made into a curve as shown by the solid line D in FIG. 10. This curve may be appropriately set by selecting the voltages of V _L , _VM , and V _H and switching points PW1 and PW2 of each voltage, so that the gradation of the final display image is optimized.

FIG. 11 shows a specific circuit example of an adjustment circuit for realizing the voltage waveform of V ₃ shown in FIG. 8, and will be described below together with the operating waveform of FIG. 8. In FIG. 11, 43 is an input terminal of a power supply for supplying voltage to the vertical focusing electrode 3, and 44 is an output terminal for supplying voltage to the vertical focusing electrode 3. In FIG.
Shown in V ₃ . 45 is an input terminal of a power supply for applying a base bias to the transistor 46, and the base voltage of the transistor 46 is connected to the resistor 47,
A voltage divided by 48 is supplied. that voltage
Let it be Vr. 49 is the input terminal for the 6H ₂ pulse shown in Figure 8. This pulse triggers the mono multivibrator at the falling edge of the 6H pulse, creating the pulse shown in 6H ₁ , and then another one at the falling edge.
_6H2 pulses can be created by triggering two mono-multivibrators. 50 is the input terminal for the _6H3 pulse shown in Figure 8, and this pulse is
This can be done by setting the flip-flop at the falling edge of the _6H2 pulse and resetting it at the falling edge of the 6H pulse. Reference numerals 51 and 52 indicate current sources whose current values are I ₁ and I ₂ , respectively. Input the above Vr to terminal 4
If you set the input pulses to 9 and 50, that is, the midpoint between the high level and low level of 6H ₂ and 6H ₃ ,
During the period when _6H2 and _6H3 are at low level, that is, when the pulse of _6H1 is at high level according to the operating waveform _in FIG.
6 and does not flow to transistors 53 and 54. Therefore, if the base current of the transistor 55 is ignored at this time, the base-emitter voltage of the transistor 55 (approximately 0.7V) is lower than the voltage at the power input terminal 43.
The voltage at the output terminal 44 is charged to a voltage that is lower than the current value. The voltage is indicated as _VH in Fig. 8. During the high level period of 6H ₂ pulses, the current I ₁ of the current body 51
flows through the transistor 53 and causes a voltage drop across the resistor 56. If the voltage is made to be (V _H -V _M ) with the operating waveform of V ₃ in FIG. 8, the output voltage of the output terminal 44 during this period will be V _M . then 6h ₃
During the period when the _pulse of
A voltage drop occurs across the terminal. The voltage is shown in Figure 8.
If the operating waveform of _V3 is set to ( _VH - _VL ), the output voltage of the output terminal 44 during this period will be _VL .
The current of the current source 52 determines the response time when the output waveform of the output terminal 44 falls, and may be designed as appropriate.

In this example, in the curve shown in Fig. 10, 2
However, it is clear from the above description that it is easy to further increase this number. In addition, although the voltage of the vertical focusing electrode 3 is changed to change the brightness, the potential distribution around the line cathode 2 is determined by the voltage relationship between the back electrode 1 and the vertical focusing electrode 3. It is clear that the voltage, or the voltages of the back electrode 1 and the vertical focusing electrode 3, may be varied simultaneously as shown in FIG.

Effects of the Invention As described above, according to the present invention, as shown in the luminance characteristic diagram of FIG.
As a result, it is possible to display images with good gradation even for video signals that have been subjected to gamma correction, such as those used in television broadcasts.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view of an image display element used in an image display device according to an embodiment of the present invention, and FIG.
The figure is an enlarged view of the phosphor screen of the image display element, FIG. 3 is a block diagram of a drive circuit devised prior to the present invention to drive the image display element, and waveform diagrams of various parts. 5, 6, and 7 are waveform diagrams of various parts for explaining the operation of the drive circuit, respectively, and FIG. 8 is a waveform diagram for explaining the operation of the image display device in one embodiment of the present invention. , FIG. 9 is a luminance characteristic diagram of an image display device devised prior to the present invention, FIG. 10 is a luminance characteristic diagram showing the effect of an embodiment of the present invention, and FIG. 11 is a diagram of luminance characteristics in an embodiment of the present invention. FIG. 3 is a circuit diagram of an adjustment circuit. 1... Back electrode, 2,2a-2o... Line cathode, 3...
Vertical focusing electrode, 4... Vertical deflection electrode, 5... Beam flow control electrode, 7... Horizontal deflection electrode, 9... Screen plate, 10... Slit, 20... Phosphor, 22... Power supply circuit, 24... Synchronization separation circuit, 25... Vertical deflection counter, 26... line cathode drive circuit, 27... memory, 2
8...Horizontal deflection counter, 29...Memory, 30...
Color demodulation circuit, 31-1 to 31-n... Sample hold circuit, 32-1 to 32-n... Reader memory, 33... 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... PWM circuit, 38...
D/A converter, 39...D/A converter, 40...Vertical deflection drive circuit, 41...Horizontal deflection drive circuit, 42...
Deflection pulse generation circuit, 43...Power input terminal, 4
4... Vertical focused voltage output terminal, 49, 50... Pulse input terminal, 51, 52... Current source.

Claims (1)

[Claims] 1. A screen coated with a phosphor that emits light when irradiated with an electron beam, and a line cathode as an electron beam source that generates an electron beam in each vertical section of the screen on which the screen is vertically divided. a back electrode for controlling the amount of the electron beam generated; and a separating means for separating the electron beam generated by the electron beam source into a plurality of horizontal sections and irradiating the screen onto the screen; A deflection electrode that deflects the electron beam in multiple steps vertically and horizontally until it reaches the screen, and a trailing edge or a leading edge of the pulse width of the reference pulse signal are fixed, and from this fixed timing, an image is generated. a pulse width modulation circuit that modulates and outputs the reference pulse signal so that the pulse width increases as the brightness level of the signal increases; and a beam current control that controls the passage time of the electron beam using the pulse width modulation output signal. an electrode, a focusing electrode that controls the size of light emitted by the electron beam on the phosphor surface, and an adjustment circuit that changes the voltage applied to the focusing electrode or the back electrode according to the pulse width of the pulse width modulation output signal. Image display device provided.