JP2008139566A - Image display device - Google Patents

Abstract

A highly reliable image display device that suppresses smearing even when the V-I characteristic of an electron source changes with time, has no image quality deterioration, and detects scanning line current. The scanning line current in black display and the scanning line current in halftone or white display are detected by the current detection circuit 40, and the difference calculator 1 calculates the difference between these detection data 21. Based on the difference data 8 from the difference calculator 1, the voltage drop correction circuit 6 calculates the correction amount of the scan electrode voltage and the data electrode voltage, and corrects the scan electrode voltage and the data electrode voltage, thereby correcting the electron source. An image display device that can cope with a change with time, has high reliability, and has high image quality is realized.
[Selection] Figure 1

Description

  The present invention relates to an image display device in which electron-emitting devices are arranged in a matrix.

  In recent years, electron emission elements are provided at the intersections of mutually orthogonal wiring groups, and the amount of electrons emitted from the electron emission elements is controlled by adjusting the voltage or time applied to each electron emission element. A self-luminous matrix display that accelerates the light and irradiates the phosphor is attracting attention.

  This type of display is generally called a field emission display (hereinafter referred to as “FED”), and the electron-emitting devices used are those using a thin film electron source, those using a carbon nanotube, and surface conduction electrons. Some use an emitting element.

  A display panel used for an FED is roughly composed of a plurality of electron-emitting devices arranged in a matrix, a cathode panel provided with wiring for driving these electron-emitting devices, and an anode panel coated with a phosphor. ing. FIG. 8 shows a model diagram of the cathode panel.

  In FIG. 8, the electron-emitting device 201 forms each pixel. Each electron-emitting device 201 is arranged at the intersection of the vertical data wiring 202 and the horizontal scanning wiring 203 and is connected to each wiring. D1 to Dm are data electrodes for applying a data signal to each data wiring, and S1 to Sn are scanning electrodes for applying a scanning selection voltage and a non-selection voltage to each scanning wiring.

  FIG. 9 shows the relationship between the applied voltage V of the electron source and the flowing current I when a thin film electron source is used as the electron-emitting device used in the display panel. In the region where the applied voltage V is low (V <threshold voltage Vth), the current I of the thin film electron source is very small. When the applied voltage exceeds Vth, a current starts to flow through the thin film electron source, and the current I flowing with respect to the applied voltage V increases exponentially.

  FIG. 10 shows a configuration of a drive circuit for driving a display panel using electron-emitting devices. Note that the polarity of the thin film electron source is defined as the polarity through which a current flows when the voltage of the scanning wiring is higher than the voltage of the data wiring.

  In FIG. 10, an image signal 210 and a synchronization signal 204 are input to the timing controller 205. The timing controller 205 generates a control signal 208 and image data 207 for controlling the data electrode driving circuit 7, and generates and outputs a control signal 214 for controlling the scanning electrode selection circuit 30.

  The scan electrode selection circuit 30 performs an operation of selecting one scan wiring among the scan wirings. One of the scan selection switches SH1 to SHn in the scan electrode selection circuit 30 is turned on, and the scan selection voltage VH from the first reference voltage source 211 is applied to one of the selected scan electrodes S1 to Sn. . On the other hand, the non-selection operation is performed using the non-selection switches SL1 to SLn. A plurality of switches corresponding to the scanning wirings to be brought into the non-selected state are turned on, and the non-selected voltage VL is supplied from the second reference voltage source 212 to the scanning electrodes. FIG. 10 shows a state where the scan electrode S2 is selected. Note that the high voltage circuit 220 supplies a high voltage to the anode panel of the display panel 215.

  FIG. 11 shows an operation waveform diagram when the line sequential operation is performed in the drive circuit shown in FIG. In FIG. 11, for example, a signal VSH1 is a control signal for the scan selection switch SH1 shown in FIG. 10, and the scan selection switch SH1 is turned on at a high level.

  In the vertical scanning, the selection operation starts from the scanning wiring connected to the scanning electrode S1 shown in FIG. The scan selection switch SH1 is turned on in the period T1, and the first scan wiring is selected. At this time, the data electrodes Vd11 to Vd1m are supplied to the data electrodes D1 to Dm by the data electrode driving circuit 7, respectively.

  Next, the scanning selection switch SH2 is turned on in the period T2 by the signal VSH2, and the scanning selection voltage is supplied to the second scanning electrode S2 to be in the selection state. At this time, the data voltages Vd21 to Vd2m are supplied to the respective data electrodes D1 to Dm. These operations are sequentially performed, and image data for one field is displayed on the display panel.

  In the following Patent Document 1, an anode current detection resistor is provided on the negative electrode side of the high-voltage power source, the current value of the detected anode current is A / D converted, and the current value matches a preset reference value. It describes that the drive waveform of the display panel is controlled.

In Patent Document 2 below, the drive voltage and drive current of the electron-emitting device are detected, the product of the voltage and current is calculated, and the drive waveform is set so that the calculation result is the same as a preset value. It is described to compensate.
Japanese Patent Laid-Open No. 2001-202059 JP-A-11-354209

  Factors that determine the luminance of the display panel include (1) characteristics of current I flowing to the electron source with respect to the voltage V applied to the electron source (hereinafter referred to as “V-I characteristics”), and (2) emission from the electron source. There are three ratios: the proportion of electrons (emission efficiency) and (3) the luminous efficiency of the phosphor. The change with time of elements (2) and (3) appears as a change in luminance of the entire screen. However, the temporal change in the current I of the element (1) causes a luminance step called smear due to the change in voltage drop caused by the scanning wiring resistance and the impedance of the scanning electrode selection circuit in addition to the luminance change of the entire screen. Therefore, it is desirable to deal with this amount of voltage drop.

  Actually, the change in the luminance of the display panel is often caused by the change in the elements (1), (2), and (3) at the same time, and the luminance of a certain gradation can be set to a predetermined luminance only by detecting the emission current. However, the predetermined brightness may not be obtained at other gradations.

  Further, it is necessary to reset the voltage drop amount for a change in the VI characteristics of the electron source. In other words, the VI characteristic change appears on the screen in the form of smear. Smear is a phenomenon that is recognized more remarkably than the luminance change of the entire screen.

  An object of the present invention is to provide a highly reliable image display device that suppresses smearing even when the V-I characteristic of an electron source changes with time, does not deteriorate image quality.

  The present invention emits light by a plurality of scanning wirings parallel to each other, a plurality of data wirings orthogonal thereto, a plurality of electron-emitting devices connected to intersections of these wirings, and electrons from the electron-emitting devices. A display panel made of phosphor; scan electrode voltage correcting means for correcting a scan electrode voltage supplied to the scan wiring; scan electrode selecting means for applying the corrected scan electrode voltage to the scan wiring; and the scan wiring And voltage drop correction means for calculating the influence of the voltage drop caused by the current flowing through the data line and its resistance, data electrode driving means for driving the data line based on the calculation result, and accelerating the emitted electrons from the electron-emitting device And a high voltage means for irradiating the phosphor, the flow to the scanning wiring when a different display pattern is displayed on the display panel A current detection unit configured to detect a first current value and a second current value; and a difference calculation unit configured to perform a difference calculation between the first current value and the second current value. The voltage drop correcting means controls the scanning electrode voltage correcting means and the data electrode driving means.

  As described above, according to the present invention, in an image display device using a display panel that irradiates phosphors with electrons accelerated by applying a high voltage, such as an FED, image quality deterioration due to change over time of the display panel is suppressed. , Enabling optimal image display. Therefore, a highly reliable image display device can be provided. In addition, in a display in which electron-emitting devices are arranged in a matrix, the electron-emitting devices change with time and affect the quality of the displayed image. Therefore, the present invention is suitable for a matrix display. In the present invention, the thin film electron source has been described as an example, but the present invention is also effective for an image display device using other cold cathode elements such as carbon nanotubes and surface conduction electron-emitting elements.

  Embodiments of the present invention will be described below with reference to the drawings.

  An image display apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is a circuit configuration diagram of the present embodiment. FIG. 2 shows an example of the change with time of the thin film electron source characteristics.

  1, the same reference numerals as those in FIG. 10 denote the same components. The scan electrode voltage correction circuit 16 supplies the scan electrode voltage to the scan electrode selection circuit 30. The power source 3 is a power source that supplies power to the scan electrode voltage correction circuit 16. The capacitor 27 is a capacitor that removes a power supply ripple component.

  The detection resistor 20 detects a current flowing from the power supply 3, that is, a scanning line current flowing through the data wiring through the scanning wiring. The adder / subtractor 5 receives the voltage at both terminals of the detection resistor 20 and outputs a detection signal 12 proportional to the potential difference between both ends of the detection resistor 20. The detection signal 12 is converted into digital detection data 21 by using a digital-analog (A / D) converter 2. These detection resistor 20, adder / subtractor 5 and A / D converter 2 constitute a current detection circuit 40.

  The difference calculator 1 displays the detection data 21 output from the A / D converter 2 and an image pattern having other gradations when a black or low gradation image pattern is displayed on the display panel 215. In this case, the detection data 21 output from the A / D converter 2 is stored, and the difference data 8 obtained by calculating the difference between them is input to the voltage drop correction circuit 6.

  The voltage drop correction circuit 6 generates a correction signal 10 for correcting the scan electrode voltage output from the scan electrode voltage correction circuit 16 based on the difference data 8. Based on this correction signal 10, the scan electrode voltage correction circuit 16 supplies the corrected scan electrode voltage to the scan electrode selection circuit 30.

  Further, the image data 207 is input to the voltage drop correction circuit 6, and the voltage drop amount associated with the scanning wiring resistance and the data wiring resistance is calculated into the image data 207. At this time, the data electrode drive data 11 is generated using the difference data 8 as a calculation parameter, and smear is suppressed.

The current supplied from the power source 3 to the scan electrode voltage correction circuit 16 is obtained by adding the scan line current Iscan and other currents, for example, the bias current Ibias. Here, the resistance value of the detection resistor 20 is Rdet, and the voltage of the detection resistor 20 is Vdet.
Vdet = Rdet (Iscan + Ibias) (1)

Using the expression (1), the detection voltage Vdet1 in black display and the detection voltage Vdet2 in white display are expressed as the following expressions (2) and (3). These differences are given by equation (4).
Vdet1 = Rdet (Iscan1 + Ibias) (2)
Vdet2 = Rdet (Iscan2 + Ibias) (3)
Vdet2-Vdet1 = Rdet (Iscan2-Iscan1) (4)

In equation (4), Iscan1 is a scanning line current in black display, and Iscan1≈0. Therefore, the equation (4) can be considered as the following equation (5).
Vdet2-Vdet1 = Rdet × Iscan2 (5)

  The right side of equation (5) is the product of the scanning line current Iscan2 in white display and the resistance value Rdet of the detection resistor 20, and a detection voltage proportional to the scanning line current is obtained by the difference calculation. That is, the influence of the bias current of the scan electrode voltage correction circuit 16 can be canceled and the accurate scan line current can be detected.

  The characteristic change of the electron source in FIG. 2 represents a change due to two factors. One factor is a change of the threshold voltage Vth at which the electron source current starts to flow to Vth1 (FIG. 2A). For such a change in Vth, the correction signal 10 is used to correct the scan electrode voltage output from the scan electrode voltage correction circuit 16.

  Another factor is a change in slope in which the electron source current does not reach a predetermined value even when a predetermined voltage is applied in a region where the applied voltage is higher than Vth (FIG. 2B). For this change in inclination, the data electrode voltage output from the data electrode drive circuit 7 is corrected by correcting the data electrode drive data 11 output from the voltage drop correction circuit 6 using the difference data 8. . If two factors exist simultaneously, the scan electrode voltage and the data electrode voltage may be corrected simultaneously.

  As a detection method, it is possible to detect the scanning line current value with high accuracy by applying a method for obtaining the difference between the current value in the black display described above and the current value in the image pattern having other gradations. .

  According to this embodiment, since the electron source characteristics can be detected with high accuracy in a display in which electron-emitting devices are arranged in a matrix, smear does not occur even when deterioration with time occurs. Therefore, an image display device with high reliability and high image quality can be provided.

  An image display apparatus according to the present invention will be described with reference to FIG. FIG. 3 is a circuit configuration diagram of the present embodiment, and shows the configuration of two scanning lines and a circuit for driving them for ease of explanation.

  In FIG. 3, the same reference numerals as those in FIG. The scan electrode selection circuit 30 monitors the scan electrode voltages of the scan electrodes S1 and S2 using the feedback switches SF1 and SF2. The scan electrode correction circuit 16 is configured using a negative feedback amplifier 13 and an adder 15. By inputting the scan electrode voltages of the scan electrodes S1 and S2 to the negative phase input terminal of the negative feedback amplifier 13, a negative feedback operation is performed and the scan electrode voltage is stabilized. By this negative feedback operation, the scan electrode voltages of the scan electrodes S1 and S2 become the same potential as the positive phase input terminal voltage Vref of the negative feedback amplifier 13. The display panel 215 includes scanning wiring resistors 2031 to 2034 and electron sources 2011 to 2014 for each pixel.

  In this embodiment, an operation for correcting the change with time of the threshold voltage Vth shown in FIG.

  First, in the first horizontal scanning period, when the scanning electrode S1 is selected, the scanning selection switch SH1 and the feedback switch SF1 are turned on, and the non-selection switch SL1 is turned off. At this time, the scan selection switch SH2 for selecting the scan electrode S2 and the feedback switch SF2 are turned off and the non-selection switch SL2 is turned on, and the scan electrode S2 is fixed at the non-selection voltage and is in the non-selection state.

  In the next horizontal scanning period, the scanning selection switch SH2 and the feedback switch SF2 are turned on, the non-selection switch SL2 is turned off, and the scanning electrode S2 is selected. At this time, the scanning selection switch SH1 and the feedback switch SF1 for selecting the scanning electrode S1 are turned off, the non-selecting switch SL1 is turned on, and the scanning electrode S1 is in a non-selected state.

  Here, the scanning line current flows from the power source 3 to the display panel 215 via the power supply terminal 14 of the negative feedback amplifier 13 through the output circuit in the negative feedback amplifier 13 and the scan selection switches SH1 and SH2. A detection resistor 20 is connected between the power supply terminal 14 of the negative feedback amplifier 13 and the power supply 3. A power supply current for the negative feedback amplifier 13 flows through the detection resistor 20. That is, the scanning line current is detected by the detection resistor 20.

  The adder / subtractor 5 receives the potentials of both terminals of the detection resistor 20 and outputs a detection signal 12 proportional to the potential difference between both ends of the detection resistor 20. The detection signal 12 is converted into digital detection data 21 using the A / D converter 2 and input to the difference calculator 1. The difference calculator 1 calculates a difference between detection data at the time of black display and detection data in an image pattern other than black. The difference data 8 is input to the voltage drop correction circuit 6.

  The voltage drop correction circuit 6 generates a correction signal 10 for correcting the output voltage of the scan electrode voltage correction circuit 16 based on the difference data 8. The correction signal 10 and the voltage of the reference voltage source 211 are added by the adder 15 to generate the reference scan electrode voltage Vref.

  The reference scan electrode voltage Vref is input to the positive phase input terminal of the negative feedback amplifier 13, and the negative feedback operation is performed so that the scan electrode voltage becomes equal to Vref. The operation of canceling the bias current of the negative feedback amplifier 13 is the same as the equations (1) to (5) described in the first embodiment, and the description is omitted.

  According to the present embodiment, similarly to the first embodiment, it is possible to provide an image display apparatus with high reliability and high image quality.

  An image display apparatus according to the present invention will be described with reference to FIG. FIG. 4 is a circuit configuration diagram of this embodiment, in which a detection resistor 20 is provided inside the negative feedback amplifier 13. In the figure, the same reference numerals as those in FIG. The negative feedback amplifier 13 includes a pre-differential amplifier 17 and an output circuit 50 (detection resistor 20, transistors 26, 28, 29, current source 24, and voltage source 25).

  The bias current of the output circuit 50 is determined by the bias voltage value of the voltage source 25. The scan line current flows through the detection resistor 20 and the transistor 28 and flows into the scan electrode S1 or S2 via the scan electrode selection circuit 30.

  The current of the detection resistor 20 includes a scanning line current and a bias current of the output circuit 50. In this case, the relationship between the bias current, the scanning line current, and the detection voltage can be expressed in the same way as the equations (1) to (5) described in the first embodiment, and the influence of the bias current of the output circuit 50 can be canceled. it can.

  Further, since the detection resistor 20 is provided between the capacitor 27 and the transistor 28, there is no delay in current response due to the time constant formed by the capacitor 27 and the detection resistor 20 connected to the power supply 3 side, and scanning is performed. The scanning line current for each line can be detected.

  The scanning line current of each scanning line is detected by the current detection circuit 40, the detection data 21 is calculated by the difference calculator 1, and the difference data 8 is stored in the memory 18. The voltage drop correction circuit 6 reads the difference data 8 for each scanning line, and calculates the correction signal 10 and the data electrode drive data 11 based on the difference data 8.

  According to the present embodiment, since the change in the electron source characteristics of each scanning line can be detected as in the first and second embodiments, the correction amount for each scanning line is optimized. Therefore, it is possible to provide an image display device with higher reliability and higher image quality.

  An image display apparatus according to the present invention will be described with reference to FIG. FIG. 5 is a circuit configuration diagram of this embodiment. A short-circuit means (switch element) 19 is connected in parallel with the detection resistor 20, and a power source for supplying a current is a voltage variable power source 60. The same components as those in FIG.

  A scanning line current and a bias current of the negative feedback amplifier 16 flow through the detection resistor 20. Therefore, when performing the detection operation, as described in the above embodiments, Vdet as a product of the resistance value of the detection resistor 20 and the flowing current is generated as a voltage drop. The operation for canceling the bias current of the negative feedback amplifier 13 is the same as the equations (1) to (5) described in the first embodiment.

  The voltage drop Vdet due to the detection resistor 20 reduces the output dynamic range of the negative feedback amplifier 13 and causes the negative feedback amplifier 13 to be saturated. Therefore, during the detection operation, the voltage value of the voltage variable power source 60 is set to the high voltage setting value Vdd1, and the switch element 20 is turned off. During normal operation without detection, the voltage setting value Vdd2 lower than Vdd1 is set, and the switch element 19 is turned on.

  As the set values of Vdd1 and Vdd2, the power supply voltage required for normal operation is Vdd2, and Vdd1 may be determined based on the resistance value of the detection resistor 20 and the maximum current value flowing therethrough. By switching the power supply voltage during the detection operation and the normal operation, useless power loss can be suppressed.

  According to the present embodiment, the same effect as in the first embodiment can be obtained, and the power supply voltage is switched between the detection operation and the normal operation, and the optimum setting of the power supply voltage is performed in each operation mode, so that unnecessary power is consumed. Loss can be suppressed. Therefore, an image display device with low power consumption, high reliability, and high image quality can be provided.

  The image display apparatus according to the present invention will be described with reference to FIGS. FIG. 6 is a circuit configuration diagram of this embodiment, and the detection resistor 20 is provided between the output side of the negative feedback amplifier 13 and the input side of the scan electrode selection circuit 30. The same components as those in FIGS. 1 to 4 are denoted by the same reference numerals. FIG. 7 is an operation waveform diagram of FIG. 6 and shows a horizontal scanning cycle waveform of the scan electrode driving voltage.

  In FIG. 6, the current flowing through the detection resistor 20 is only the scanning line current. The switch element 19 is off during the scanning line current detection operation, and the switch element 19 is on during the normal operation when no detection operation is performed.

  At the time of the detection operation, when it is determined by the resistance value Rdet of the detection resistor 20, the ON resistance Ron of the scan selection switch shown in FIG. 3 in the scan electrode selection circuit 30, and the electron source capacitance connected to one of the scan lines. The scan electrode drive waveform 31 shown in FIG. On the other hand, since the switch element 19 is on during normal operation, the drive waveform 32 rises sharply with a time constant smaller than the time constant during detection operation. Therefore, if the sampling timing of the A / D converter 2 in the detection operation is at Tsp where the scan electrode drive waveform is in a steady state, the scan line current can be detected stably. Therefore, the drive waveform delay during the detection operation does not cause a problem.

  On the other hand, during the normal operation, the rise delay of the scan electrode drive waveform is a cause of lowering the luminance, and the drive waveform rise time is sharpened by turning on the switch element 19.

  According to the present embodiment, as in the second embodiment, in the display in which the electron-emitting devices are arranged in a matrix, no smear occurs even if the electron source characteristics deteriorate due to the change of the display panel over time. Further, it is possible to prevent a decrease in luminance by suppressing a drive waveform delay. Therefore, an image display apparatus with high reliability and high image quality can be provided.

The circuit block diagram of Example 1 of this invention. FIG. 3 is an electron source characteristic diagram for explaining the first embodiment. The circuit block diagram of Example 2 of this invention. The circuit block diagram of Example 3 of this invention. The circuit block diagram of Example 4 of this invention. FIG. 6 is a circuit configuration diagram of Embodiment 5 of the present invention. FIG. 10 is an operation waveform diagram for explaining the fifth embodiment. FIG. 3 is a structural diagram of a display panel in which electron-emitting devices are arranged in a matrix. The voltage-current characteristic view of a thin film electron source. FIG. 9 is a configuration diagram of a drive circuit for driving the display panel of FIG. 8. FIG. 11 is an operation waveform diagram for explaining the operation of the drive circuit of FIG. 10.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Difference calculator, 2 ... Analog-digital converter, 3 ... Power supply, 5 ... Adder / subtractor, 6 ... Voltage drop correction circuit, 7 ... Data electrode drive circuit, 8 ... Difference data, 10 ... Correction signal, 11 ... Data Electrode drive data, 12 ... detection signal, 13 ... differential amplifier, 14 ... power supply terminal, adder, 15 ... adder, 16 ... scanning electrode voltage correction circuit, 17 ... pre-differential amplifier, 18 ... memory, 19 ... Switch element (short-circuit means), 20 ... detection resistor, 21 ... detection data, 24 ... current source, 25 ... voltage source, 26, 28, 29 ... transistor, 27 ... capacitor, 30 ... scan electrode selection circuit, 40 ... current Detection circuit, 50... Output circuit, 60.
DESCRIPTION OF SYMBOLS 201 ... Electron emission element, 202 ... Data wiring, 203 ... Scanning wiring, 204 ... Synchronization signal, 205 ... Timing controller, 207 ... Image data, 208 ... Control signal, 210 ... Image signal, 211 ... First reference voltage source, 212 ... second reference voltage source, 214 ... control signal, 215 ... display panel, 220 ... high voltage circuit,
2011-2014 ... Electron source, 2031-2034 ... Scanning line resistance corresponding to one pixel.

Claims (5)

A plurality of scanning wirings parallel to each other, a plurality of data wirings orthogonal to the scanning wirings, a plurality of electron-emitting devices connected to the intersections of these wirings, and a phosphor that emits light by electrons from the electron-emitting devices A display electrode, a scan electrode voltage correcting unit that corrects a scan electrode voltage supplied to the scan line, a scan electrode selecting unit that applies the corrected scan electrode voltage to the scan line, and the scan line and the data line. Voltage drop correction means for calculating the effect of the voltage drop caused by the flowing current and its resistance, data electrode driving means for driving the data wiring based on the calculation result, and phosphors that accelerate the emitted electrons from the electron-emitting device In an image display device comprising high-pressure means for irradiating
A first current value that flows through the scanning line when a black or low gradation image pattern is displayed on the display panel and a second current value that flows through the scanning line when an image pattern having other gradations is displayed. And a difference calculation means for calculating a difference between the first current value and the second current value, and based on the difference calculation result, the voltage drop correction means detects the scan electrode voltage. An image display device which controls a correction means or a data electrode driving means.   The image display apparatus according to claim 1, wherein the current detection unit detects a power supply current of the scan electrode voltage correction unit.   The image display apparatus according to claim 1, wherein the current detection unit is connected in series with an output unit in the scan electrode voltage correction unit and detects a current flowing through the output unit.   The image display apparatus according to claim 1, wherein the current detection unit is provided between the scan electrode voltage correction unit and the scan electrode selection unit to detect an output current of the scan electrode voltage correction unit. In parallel with the current detection means, a short-circuit means for short-circuiting the current detection means is provided, and the short-circuit means is in an open state when current detection is performed, and is short-circuited when current detection is not performed. The image display apparatus according to claim 1, wherein the image display apparatus is a display apparatus.

Images