JP2000098970A - Plasma display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circuit technique which can limit a circuit scale without worsening the power source efficiency and is adaptable to integration. SOLUTION: A plasma display device which lights a display cell of a display panel 4 synchronizing with a frequency of a maintaining discharge waveform is provided with an integrating means 10 to integrate the number of pixel signals given for a predetermined period by each bit signal for gradation display, and a frequency changing means 11 to change the frequency of the maintaining discharge waveform based on the result of the integration by the integrating means 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat panel display device, and more particularly to a PDP which is a self-luminous display cell.
(Plasma Display Panel).

[0002]

2. Description of the Related Art Flat panel display devices frequently used in display devices such as portable personal computers are:
Although the power consumption is much lower than that of a CRT (Cathode Ray Tube) type display device, further power dissipation technology is required in order to achieve long-time battery operation.

FIG. 10 is a conceptual block diagram of a conventional flat panel display device. 1 is an external display control circuit such as a graphic display controller for generating a display signal and various control signals accompanying the display signal, and 2 is a high potential necessary for display (for example, a DC voltage of about 100 V in the case of a PDP). 3) a control circuit for controlling display timing in accordance with horizontal and vertical scanning periods of the screen;
Reference numeral 4 denotes a display panel in which a large number of self-luminous display cells are arranged in a matrix, 5 denotes a driver that generates various drive pulses for driving the display panel, 6 denotes a drive current detection circuit, and 7 denotes an APC signal generation circuit. The drive current detection circuit 6 and the APC signal generation circuit 7 are circuits specially provided for power saving measures.

That is, the drive current detection circuit 6 includes a resistor (not shown) inserted in series on the transmission path of the drive voltage Vs, and an active element (high potential Vs) for detecting the voltage across the resistor. High-voltage transistors that support
And the display panel 4 via the driver 5
(Hereinafter referred to as “driving current Is”) is taken out as a voltage across the resistance element. Also,
The APC signal generation circuit 7 outputs a predetermined control signal Sapc whose duty in the H-level period changes according to the magnitude of the above-mentioned voltage (= driving current Is).

FIG. 11 shows the magnitude of the driving current Is (in FIG.
Is_(L) <Is_(M) <Is _(H) Three stages) and
A predetermined logic level of Sapc (here, H level for convenience)
FIG. 7 is a diagram showing a correspondence relationship between duty changes during a period.
The drive current Is is the display rate of the display panel 4, that is,
It is proportional to the ratio of the light emitting cells in the display cells. Therefore, the display rate
Is higher (in other words, higher brightness is displayed),
The problem is that power consumption increases, as shown in the lower part of FIG.
Next, the driving waveform of the display panel 4 (for example, the
High frequency period of the sustaining discharge waveform) is the H level period of Sapc
The higher the display ratio, the higher the frequency
Can reduce several periods (increase low frequency periods)
Thus, the above-described power consumption problem can be solved.

[0006]

However, in such a conventional flat panel display device, a resistance element is inserted in series on the transmission path of the drive voltage Vs, and the voltage across the resistance element is detected. Because
(1) The power supply impedance of the drive voltage Vs is increased by the resistance element, and the power supply efficiency is deteriorated. (2) It is necessary to build a transistor with a high breakdown voltage, which makes it difficult to cope with an increase in circuit scale and integration. And so on.

[0007] Accordingly, an object of the present invention is to provide a circuit technique which can be suppressed to a circuit scale without deteriorating power supply efficiency and is adapted to integration.

[0008]

According to the present invention, there is provided a plasma display apparatus for lighting a display cell of a display panel in synchronization with the frequency of a sustain discharge waveform. An integrating means for integrating the number of signals, and a frequency changing means for changing the frequency of the sustain discharge waveform based on the integration result of the integrating means.

The integrating means preferably integrates the number of pixel signals applied during a predetermined period in units of bit signals for gradation display.

[0010] Further, a predetermined weight may be added to each of the integration results obtained by integrating the bit signals, and the results may be added.

Further, the integrating means may integrate the number of pixel signals given during a predetermined period after adding a predetermined weight in bit signal units for gradation display.

[0012]

According to the present invention, the frequency of the sustain discharge waveform of the display panel is changed based on the pixel information directly related to the display ratio. Therefore, a resistance element and a high-voltage transistor on the transmission path of the drive voltage Vs are not required, so that deterioration in power supply efficiency and increase in circuit scale are avoided, and integration is facilitated.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 9 are views for explaining an embodiment of a plasma display device according to the present invention.

First, the principle configuration will be described. In FIG. 1, reference numeral 1 denotes an external display control circuit, 2 denotes an external drive power supply, 3 denotes a control circuit, 4 denotes a display panel, and 5 denotes a driver. These circuits 1 to 5 are the same as those in the first conventional example. .

Reference numeral 10 denotes a pixel number integrating circuit, and 11 denotes an AP.
This is a C signal generation circuit, and these circuits 10 and 11 are unique to this embodiment.

That is, the pixel number accumulating circuit 10 has a function as an accumulating means for accumulating the number of pixel signals of a predetermined level from image signals given in a predetermined period. It has a function as a frequency changing means for changing the panel driving frequency based on the result of integration of 10.

Here, the predetermined period is an arbitrary period synchronized with the screen scanning of the display panel 4, and is preferably a period of one vertical scan or one horizontal scan. The above-mentioned pixel signal of a predetermined level is a pixel signal having a level capable of lighting (self-luminous) a selected display cell of the display panel 4. For example, a digital pixel signal of two gray levels of white / black is used. A predetermined logic level (H level or L level) corresponding to the white level
Level). Also, the above-mentioned panel driving frequency is
This is the frequency of various waveforms required to drive the display panel 4, for example, the frequency of a sustain discharge waveform in the case of a PDP.

The drive current Is is determined by the display rate of the display panel 4,
That is, the display ratio is proportional to the ratio of the light emitting cells in all the display cells, and the display ratio correlates well with the integrated number of pixel signals having a level capable of lighting the selected display cell of the display panel 4 (for example, the integrated number in one vertical period). I do.

Accordingly, since the integrated number (hereinafter referred to as “integrated pixel number”) is a value indirectly representing the magnitude of the driving current Is required for display, as shown in FIG. , The means for directly detecting the drive current Is (such as a resistance element or a high-voltage transistor) can be dispensed with, and the power supply impedance of the drive voltage Vs can be reduced. Thus, a circuit configuration suitable for integration can be realized without causing an increase.

Next, in order to facilitate understanding of the embodiment, some specific examples of the above-described principle configuration will be described. First, a first specific example of the above-described principle configuration will be described.

FIG. 3 shows a specific configuration example of the pixel number integrating circuit and the APC signal generating circuit. Here, for simplicity of description, the total number of display cells of the display panel 4 is set to 256 or less. In FIG. 3, reference numeral 12 denotes an 8-bit output (that is, an integrated value from 0 ₍₁₀₎ to 256 _{(10) )} for counting H-level (a level at which a selected display cell of the display panel 4 can be lit) in the pixel signal DATA. The binary counter 12 is reset every one vertical period in synchronization with the vertical synchronization signal Vsync that has passed through the delay circuit 13 having a minute delay time (the integrated value is reset to 0 ₍₁₀₎₎ . To). From the most significant bit of the binary counter 12 to n bits (n corresponds to the number of frequency variable steps of the panel drive waveform. For example, as shown in FIG. 2, three = n = 2, and practical 16 steps = n
= 4; n = 4 for the sake of convenience in the figure) is n
The n-bit output of the latch 14 (that is, the integrated value of the H level pixel signal during one vertical scan; hereinafter, represented by the symbol Ds for convenience) is latched by the bit latch 14 for one vertical scan. It is provided to one side input (n-bit A input). Comparator 15
The other side input (n-bit B input) has an n-bit output of an n-bit binary counter 16 that counts a clock signal CLKst of an arbitrary frequency (a periodic function that repeats monotonically increasing from 0 to 16 stages, ie, a digital function). A triangular wave; hereinafter, represented by a symbol Dt for convenience), and the comparator 15 outputs (D
When s <Dt), the output Q (becomes Sapc) is set to the H level.

According to such a configuration, as shown in the operation timing chart of FIG. 4, the number of H-level pixel signals DATA input during one cycle of Vsync is integrated, and the integrated value is the timing of Vsync. Latch at 14
After that, 0 is synchronized with the output of the delay circuit 13
Reset to ₍₁₀₎ . Here, the integrated value Ds taken into the latch 14 is the total number of pixel signals of H level (a level at which the selected display cell of the display panel 4 can be turned on) input during one vertical scanning period. , The number of all display cells of the display panel 4 (here, 256).
A locus indicated by a broken line in FIG. 4 is an integrated value locus when all the display cells are turned on, and the power consumption in this case is the largest.

The output (Ds) of the latch 14 in FIG.
Represents three stages: when the number of lit cells is minimum (a), when the number of lit cells is medium (b), and when the number of lit cells is close to the maximum for all cells (c).

In step a, since the value of Ds is small, "Ds
The period of <Dt ”is long, and the output of the comparator 16 (Sa
The H level period of pc) becomes maximum. On the other hand, the period of “Ds <Dt” becomes moderate in Step b because the value of Ds becomes medium, and further, in Step c, the value of “Ds <Dt” becomes large or close to the maximum. The time period is at or near a minimum.

Therefore, the 16 outputs (Sa) of the comparator
Since the H level period of pc) changes in inverse proportion to the number of pixel signals integrated in one vertical scanning period, if the frequency of the driving waveform of the display panel 4 is changed using this Sapc, the driving as in the conventional example will be performed. An appropriate drive current Is corresponding to the display ratio can be obtained without requiring direct detection means (such as a resistive element or a high-voltage transistor) of the current Is. As a result, the power supply impedance of the drive voltage Vs and the circuit It is possible to solve the problem of increase in scale and to provide a circuit configuration suitable for integration.

Next, a second example of the above-described principle configuration will be described. FIG. 5 shows an example constituted by an analog circuit. That is, the resistor 20, the operational amplifier 21, the capacitor 22, and the analog switch 23 constitute a first integrator 24 for integrating the level of the pixel signal DATA, and the integration period of the first integrator 24 is a small delay time. Corresponds to the off period (one vertical scanning period) of the analog switch 23 that is turned on / off in response to Vsync that has passed through the delay circuit 25. Therefore, the integrated value of the pixel signal DATA in one vertical scanning period is output from the first integrator 24, and the integrated value is sampled at a non-delayed Vsync timing.
It is held by the hold circuit 26. The output of the sample-and-hold circuit 26 (that is, the integrated value of the pixel signal DATA in one vertical scanning period; Ds) is supplied to one input of an analog comparator 27 using an operational amplifier, and the other input of the analog comparator 27 is connected to a resistor. 28, operational amplifier 29, capacitor 30, and analog switch 3
Sawtooth voltage Dt from the second integrator 32 comprising
(A voltage that is reset every cycle of the clock signal CLKsw), and the analog comparator 27 outputs a signal (Sapc) that goes high when Ds <Dt.

Therefore, even with such an analog configuration, a signal (Sapc) in which the H level duty changes in inverse proportion to the integrated value of the pixel signal in one vertical scanning period can be generated, and this signal (Sapc) is used. By doing
It is possible to obtain an appropriate drive current Is corresponding to the display ratio without requiring direct detection means (such as a resistance element or a high breakdown voltage transistor) of the drive current Is as in the conventional example. It is possible to solve the problem of increasing the impedance and the circuit scale and to provide a circuit configuration suitable for integration.

Next, a third specific example of the above-described principle configuration will be described. In the first and second specific examples, the APC signal (Sap signal) is applied to a slight change in the luminance of a pixel in the still display screen.
c) responds, that is, for example, in the case of performing a reverse blink for blinking or highlighting a cursor in a still display screen, the integrated value of the pixel signal changes in response to the blink or blink, and the APC signal Due to the change of (Sapc), there is a drawback that the luminance of the entire screen flickers.

In this embodiment, in order to solve such a drawback, in short, the number of pixels at a certain point in time is compared with the number of new pixels subsequently inputted, and the difference exceeds a certain value. In such a case, the driving power of the display panel is controlled based on the new number of pixels. Note that circuit elements common to the first specific example are denoted by the same reference numerals and description thereof is omitted.

In FIG. 6, an n-bit output from an 8-bit binary counter 12 is output from an n-bit subtraction circuit 3.
0 is input to the A input and an n-bit latch 31. Latch 31 latches the n-bit output of counter 12 when the H level appears at the output of AND gate 32, and applies the latched content to B input of subtraction circuit 30. Subtraction circuit 30
Calculates the difference ΔDx between the A input and the B input and calculates the difference ΔD
x is given to the B input of the comparator 33,
3 is the value of the A input (the set value ΔDa of the setting register 34;
A value higher than a value corresponding to a periodic change in the number of pixels such as a blinking cursor or an inverted blink) is compared with a value of the B input (ΔDx). When “ΔDa <ΔDx”, an H level signal from the output Q is output. Take Sc out. The signal Sc is supplied to the AND gate 32
And the other input of the AND gate 32 is supplied with Vsync.

In such a configuration, in the initial state,
The output Q (Sc) of the comparator 33 is at L level,
Since the output of the AND gate 32 is also fixed at the L level, the output (integrated value) of the counter 12 is given only to the subtraction circuit 32, and the subtraction circuit 30 outputs ΔDx having the same value as the integrated value.
Is output. If the value of ΔDx exceeds ΔDa after a certain time, the output Q (Sc) of the comparator 33
Changes to the H level, the output of the AND gate 32 also changes to the H level, and the output of the counter 12 at that time is taken into the latch 31. Then, the subtraction circuit 30 calculates a difference value ΔDx between the content held in the latch 31 (hereinafter, “old integrated value”) and the output of the counter 12 (hereinafter, “new integrated value”), and the comparator 33 calculates the difference value. ΔDx is the set value Δ
The output Q (Sc) is kept fixed at the L level until it exceeds Da.

Therefore, while the output Q (Sc) is at the L level,
That is, as shown in FIG. 7, until the difference value ΔDx between the old integrated value and the new integrated value exceeds the set value ΔDa, the latch 3
The same integrated value (old integrated value) is continuously output from 1 and Sa
Since the H level duty of pc does not change, flickering of the luminance of the entire screen can be suppressed, and the display quality can be improved.

Next, a first embodiment of the plasma display device according to the present invention will be described. This embodiment is an example of application to multi-tone display. FIG. 8 is a diagram showing the configuration. The first counter 40 counts the first bit DATA ₀ of the pixel signal, and the second counter 41 counts the second bit DATA ₁ of the pixel signal. Two counters 40, 4
The n-bit outputs of 1 are added by an adder circuit 42,
The added value (that is, the integrated value of the four gradation display pixel signals) is taken into the latch 43 at the timing of Vsync, and the output Ds of the latch 43 is compared by the comparator 15 as in the first specific example.

In the present embodiment, the integration of the number of pixels is performed in accordance with the weighting of the gradations of a plurality of image data signals. FIG. 8 shows that the image data signal is DATA
_This is the case of 2 bits of ₀ and DATA ₁ , that is, 4 gradations, and DATA ₀ and DATA ₁ are counters 4 respectively.
After integration at 0 and 41, the integration result is added to an addition circuit 42.
However, since the integrated value of the counter 41 is a value corresponding to the second bit of the gradation, it is necessary to add double weighting. In this embodiment, the integrated value of the counter 40 corresponding to the first bit of the gradation is shifted by one bit (1/2).
The value corresponding to the second bit of the gray scale is relatively weighted twice by inputting it to the addition circuit 42.

Although FIG. 8 shows an example of four-gradation display, when the present invention is applied to multi-gradation display of three or more gradations, the number of counters is increased in accordance with the bit configuration of the pixel signal. At the same time, a plurality of adder circuits may be hierarchically connected so as to add weights.

Next, a description will be given of a second embodiment of the plasma display device according to the present invention. FIG. 9 shows an example in which the configuration of the first embodiment is realized by an analog circuit.
This is a modification of the specific example.

That is, the difference from the first specific example is that the input resistance of the first integrator 50 is changed to the bit DATA of the pixel signal.
_0, resistance DATA _every respect (DATA ₀ 5
1 and a resistance 52 for DATA _{1 and} the value of each resistance is made to correspond to the bit weight (resistance 52).
Is at a point (１ ／) of the resistance 51, and the remainder is common to the first specific example.

[0038]

According to the present invention, the number of pixel signals applied during a predetermined period is integrated, and the frequency of the sustain discharge waveform is changed based on the integrated result, thereby deteriorating the power supply efficiency. The circuit technology can be reduced to the circuit scale without any problem, and a circuit technology suitable for integration can be provided.

[Brief description of the drawings]

FIG. 1 is a principle configuration diagram of an embodiment.

FIG. 2 is a principle waveform diagram of an embodiment.

FIG. 3 is a specific configuration diagram (first specific example) of the principle configuration.

FIG. 4 is an operation waveform diagram of FIG.

FIG. 5 is a specific configuration diagram (second specific example) of the principle configuration.

FIG. 6 is a specific configuration diagram (third specific example) of the principle configuration.

FIG. 7 is an operation waveform diagram of FIG. 6;

FIG. 8 is a specific configuration diagram (first embodiment) of the embodiment.

FIG. 9 is a specific configuration diagram (second embodiment) of the embodiment.

FIG. 10 is a principle configuration diagram of a conventional example.

FIG. 11 is a principle waveform diagram of a conventional example.

[Explanation of symbols]

 4: Display panel 10: Pixel number integrating circuit (integrating means) 11: APC signal generating circuit (frequency changing means)

Claims (3)

[Claims] 1. A plasma display apparatus for lighting a display cell of a display panel in synchronization with a frequency of a sustain discharge waveform, wherein the number of pixel signals applied during a predetermined period is integrated for each bit signal for gradation display. A plasma display apparatus comprising: an integrating means; and a frequency changing means for changing a frequency of the sustain discharge waveform based on an integration result of the integrating means. 2. The plasma display device according to claim 1, wherein said integrating means adds a predetermined weight to each of the integrated results obtained in units of said bit signals. 3. A plasma display apparatus for lighting a display cell of a display panel in synchronization with a frequency of a sustain discharge waveform, wherein the number of pixel signals applied during a predetermined period is determined by a predetermined bit signal unit for gradation display. A plasma display apparatus, comprising: integrating means for adding after adding weights; and frequency changing means for changing the frequency of the sustain discharge waveform based on the integration result of the integrating means.