The present invention relates to an image display device, and more particularly to an image display device of a field emission type.
Recently, attention has been directed to FEDs (Field Emission Displays), as a flat image display device. Many researches have also been conducted as to FED drive circuits. An active matrix system using active elements, for example, disclosed in Japanese patent publication No. 2656843 (patent document 1), is well known FED drive circuit.
An active matrix system, shown in
The TFT array, which is formed of a plurality of thin-film transistors having the same configuration as the thin-film transistor section 1 formed on a substrate, is selected each array driving column in time sharing manner. At the same time, a matrix drive is carried out in sync with the time sharing operation to supply a display signal to each column in the array. Since each thin-film transistor section 1 in the TFT array is connected to each FEC array formed of a plurality of FEC sections having the same configuration as the FEC section, a capacitor voltage of a specific thin-film transistor section is selectively updated. Electrons are emitted due to field electron emission according to the voltage of the capacitor. In the operation, since the other capacitors in the TFT array maintain a present voltage until the voltage of the capacitors are next updated, electrons are continuously emitted from each FEC section during the maintenance of present voltage according to the voltage of each capacitor. In this case, the voltage of the gate electrode 13 is kept at a higher fixed level than that of the cathode section (FEC section).
A fluorescent substance layer 5 is coated over one or plural anode electrodes formed on a display substrate and an anode voltage is applied to the anode electrodes. Electrons emitted from each FEC section impinge on an opposed portion of the fluorescent substance layer to generate luminescence. The opposed portion of the fluorescent substance layer continues to produce luminescence at the same brightness until the capacitor voltage is next updated. A luminous time ratio (duty ratio) is to be approximately 1 so that a high intensity luminescence can be realized.
As described above, the active matrix system known in the art is to adapt such a matrix driving method that each column of the TFT array is selected in time sharing manner and a display signal as a capacitor charging voltage is applied to each row in the array while a constant dc voltage is applied to a gate electrode in the configuration including TFT arrays acting as active elements.
In the active matrix system, the luminous intensity of the fluorescent substance layer depends on the voltage of each capacitor in principle as described above. However, when an overall brightness of an image displayed on a flat image display device or a brightness of a partial area of an image divided into several sections is required to change according to an ambient environment, it has been difficult to establish a condition to change the brightness only without significantly changing hue and contrast, because voltages applied on respective capacitors must be controlled depending on the overall brightness, which makes such control to be very difficult.
The present invention is to provide an image display device for solving the above-mentioned problems. The image display device includes field emission elements, which can easily change an overall or parts of brightness of an image without adversely affecting hue and contrast.
According to the present invention, an image display device, comprises a substrate having an insulating material; emitters connected to each of a plurality of cathode electrodes formed on the substrate; a gate electrode disposed adjacent to the emitters; an anode electrode having a fluorescent substance layer which generate luminescence due to collision of electrons emitted from each of the plurality of emitters; a plurality of cathode current control elements formed on the substrate and having a cathode current control power terminal and a cathode current control terminal, wherein the cathode current control power terminal is connected to each of the plurality of cathode electrodes, the cathode current control terminal controls current passing through the cathode current control power terminal; a plurality of capacitors respectively connected to each of the plurality of cathode current control terminals to hold a voltage corresponding to an amount of electron emission; a plurality of capacitor voltage control power elements having a capacitor voltage control power terminal, a first capacitor voltage control terminal, and a second capacitor voltage control terminal, the capacitor voltage control power terminal being connected to each of the plurality of capacitors, the first capacitor voltage control terminal being mutually connected in a first group to set a voltage held in each of the plurality of capacitors, the second capacitor voltage control terminal being mutually connected in a second group to set some of the plurality of capacitors to keep a voltage corresponding to the amount of electron emission; and a gate electrode control circuit for applying a signal to the gate electrode, wherein the signal has a time rate, or a rate of time a constant voltage is applied repetitively, which is changeable.
The image display device includes a substrate having an insulating material, a plurality of emitters formed on a substrate and connected to a cathode electrode, and a gate electrode disposed adjacent to said emitters. This configuration allows each emitter to emit electrons when a voltage is applied between the gate electrode and the cathode electrode.
A plurality of cathode current control elements, a plurality of capacitors, and a plurality of capacitor voltage control power elements may be formed on the substrate. Each of the plurality of cathode current control elements has a cathode current control power terminal and an emitter voltage control terminal. Each of the plurality of cathode electrodes is connected to each cathode current control power terminal. Each of the plurality of emitter voltage control terminals is connected to each of the plurality of capacitors. Thus, each emitter can emit an amount of electrons corresponding to a voltage kept in each capacitor. Electrons emitted from each emitter flow as an anode current into the anode electrode and then the same amount of the current flows as a cathode current out the cathode electrode.
Moreover, a capacitor voltage control power element may be disposed to set a voltage kept in each of capacitors. Each of the plurality of capacitor voltage control power elements includes a capacitor voltage control power terminal, a first capacitor voltage control terminal, and a second capacitor voltage control terminal. Each of capacitor voltage control power terminals is connected to each of capacitors and each of the first capacitor voltage control terminals is mutually connected in a first group. Thus, a voltage to be kept in a capacitor can be determined. Each of the second capacitor voltage control terminals is mutually connected in second groups to set which of the plurality of capacitors to keep a voltage. Here, a control is conducted by grouping into first group and second group. Thereby, the voltages of capacitors, which correspond to the product of the number of capacitor voltage control terminals belonging to the first group and the number of capacitor voltage control terminals belonging to the second group, can be controlled with control signals, which corresponds to the sum of the number of capacitor voltage control terminals belonging to the first group and the number of capacitor voltage control terminals belonging to the second group.
Moreover, in the signal to be applied to the gate electrode, its time ratio, being a ratio of time during which a constant voltage is applied repetitively, may be changed. The image display device includes a gate electrode control circuit that generates such signals. While the gate electrode control circuit applies a voltage of a constant level to a gate electrode in a period according to a time ratio, the amount of electron emission from the emitter corresponding to the gate electrode can be controlled according to the value of the time ratio. Hence, the brightness of a screen can be adjusted broadly and accurately by just controlling the signal with respect to the gate electrodes.
Another aspect of the present invention, an image display device comprises a substrate having a insulating material; emitters connected to each of plurality of cathode electrodes formed on the substrate; a gate electrode disposed adjacent to the emitters; an anode electrode having a fluorescent substance layer thereon, which produces luminescent due to collision of electrons emitted from each of the plurality of emitters; a plurality of first cathode current control elements formed on the substrate and having a first cathode current control power terminal connected to each of the plurality of cathode electrodes, a second cathode current control power terminal for passing through a current from the first cathode current control power terminal, and a first cathode current control terminal for controlling current passing through between the first cathode current control power terminal and the second cathode current control power terminal, a plurality of first cathode current control elements including each of the second cathode current control power terminals being connected mutually in a first group, each of the first cathode current control terminals being connected mutually in a second group; a second cathode current control element including a second cathode current control terminal for controlling current passing through the second cathode current control power elements connected mutually to the first group; a selection signal generation circuit for applying a selection signal to one of the first cathode current control terminal and the second cathode current control terminal, the selection signal conducting a cathode current control element belonging to a corresponding group; a control signal generation circuit for applying a control signal to the other of the first cathode current control terminal and the second cathode current control terminal, the control signal controlling current flowing a cathode current control element belonging to a corresponding group; and a gate electrode control circuit for applying a signal to the gate electrode, wherein the signal of which a time ratio, or a ratio of time a constant voltage is applied repetitively, changes.
This image display device includes a substrate having an insulating material, plural emitters formed on the substrate and connected to a cathode electrode, and a gate electrode disposed adjacent to said emitters. This configuration allows each emitter to emit electrons when a voltage is applied between the gate electrode and the cathode electrode.
A plurality of first cathode current control elements and a plurality of second cathode current control elements are formed on a substrate. Each of the first cathode current control elements includes a first cathode current control power terminal connected to each cathode electrode, a second cathode current control power terminal for passing through current from the first cathode current control power terminal, and a first cathode current control element for controlling current passing through between the first cathode current control power terminal and the second cathode current control power terminal. Respective second cathode current control power terminals are mutually connected in a first group. Respective first cathode current control power terminals are mutually connected in a second group. Moreover, the image display device includes a second cathode current control element having a second cathode current control terminal, which controls current passing through each of the second cathode current control power elements mutually connected in a first group.
Moreover, the image display device may include a selection signal generation circuit that outputs selection signals and a control signal generation circuit that outputs control signals. The selection signal generation circuit inputs a selection signal for conducting a cathode current control element belonging to the first group, to one of the first cathode current control terminal and the second cathode current control terminal. The control signal generation circuit outputs a control signal for controlling current flowing a cathode current control element belonging to the corresponding group, to the other of the first cathode current control terminal and the second cathode current control terminal, that is, to the other of the first cathode current control terminal and the second cathode current control terminal, to which a selection signal is not applied.
The signal applied to the gate electrode corresponds to a signal, of which time ratio, or the ratio of time which a constant voltage is applied repetitively is to be changeable. A gate electrode control circuit is provided that generates such a signal. A voltage of a fixed level is applied to a gate electrode for the time period according to the time ratio. The amount of electron emission from the emitter corresponding to the gate electrode can be controlled according to the value of the time ratio. Therefore, the brightness of a screen can be adjusted widely and accurately by just controlling the voltage applied to the gate electrode.
According to the present invention, an image display device can be provided that includes field emission elements, each of which the brightness of the overall or part of an image can be easily changed, without adversely affecting hue and contrast.
This and other objects, features, and advantages of the present invention will be readily more apparent upon the following detailed description and drawings; wherein:
Now, a best embodiment in accordance with the present invention will be described below with reference to the accompanying drawings.
The electrode configuration and the thin-film transistor section 1nm, shown in
The gate electrode 13 is disposed adjacent to the emitters 16. A single sheet of gate electrode 13 may be disposed for one screen. However, a sheet of gate electrode may be divided into plural sections. For example, a sheet of gate electrode 13 may be divided into four sections, that is, two sections arranged vertically (in column direction) and two sections arranged horizontally (in row direction). Specifically, the gate electrode 13 may be divided into four gate electrodes, that is, a gate electrode 13A (not shown), a gate electrode 13B (not shown), a gate electrode 13C (not shown), and a gate electrode 13D (not shown). When the gate electrode 13 is divided into four sections to display different images (contents) respectively, the brightness can be controlled with respect to each of contents. Holes 13a are formed in the gate electrode 13 so as to oppose to cone-shape emitters 16 respectively. Each emitter 16 emits field-emitted electrons due to the electric field created between a peripheral portion of each of holes 13a and each emitter 16. The emitted electrons pass through the hole and strike the opposed surface of the anode electrode 3 on which a fluorescent substance layer 5 coated to produce luminescence.
The thin-film transistor section 1nm corresponds to a thin-film transistor formed on a substrate, as shown in the background art. Not only an insulating material but also a silicon wafer or a substrate formed of a conductive material coated with an insulating material may be used as the substrate. The thin-film transistor section 1nm includes a transistor Tr1 acting as cathode current control element. The transistor Tr1 has a drain 8 functioning as a cathode current control power terminal connected to each cathode electrode 15 and a gate 11 functioning as a cathode current control terminal controlling current passing through the drain. Each of the transistors Tr1 is connected to each of capacitors 12. Moreover, each of the thin-film transistor sections 1 includes a transistor Tr2 functioning as a capacitor voltage control power element. Each transistor Tr2 has a source 7a functioning as a capacitor voltage control power terminal connected to each capacitor 12, a drain 8a functioning as a first capacitor voltage control terminal for determining a voltage kept in each capacitor 12, and a gate 11a functioning as a second capacitor voltage control terminal for determining which of capacitors 12 to be kept in the voltage.
The drain 8 of the transistor Tr1 in the thin-film transistor section 1nm is connected to the cathode electrode 15nm. The gate 11 of the transistor Tr1 is connected to the source 7a of the transistor Tr2. A capacitor 12 is connected to the gate 11 of the transistor Tr1. The thin-film transistor section 1nm, shown in
Of the drains 8a of the transistors Tr2 of M×N, arranged in the thin-film transistor section 1, the drains of M in column row direction (a first group) are mutually connected together. The number in the first group is M. The drains of M mutually connected in the first group functions as a first capacitor voltage control terminal, which determines a voltage kept in each capacitor 12 corresponding to the amount of electron emission. Of the gates 11a of the transistors Tr2 of M×N arranged in the thin-film transistor section 1, gates 11 of N arranged in row direction (a second group) are mutually connected. The number in the second group is N. The gates of N mutually connected in the second group works as a second capacitor voltage control terminal, which determines whether or not a voltage of a specific one of capacitors 12 is updated (or is kept in the voltage). Thus, by dividing transistors into N groups in row direction and M groups in column direction, the anode current values (cathode current values) of respective pixels of M×N can be controlled with control lines (control information) of M×N.
The first group may be selected in row direction (not column direction) while the second group may be selected in column direction (not row direction). Moreover, the first group may be selected in an oblique direction (not in row direction and not in column direction). In such a case, when the second group is selected geometrically perpendicular direction to the oblique direction, the display content can be suitably rotated to a desired angle on the screen, provided that control information input to the control lines does not change. It is not required to orthogonalize the first group to the second group. Not only normal image display but also various trick images can be implemented by any selection of angle. This selection is carried out through previous mutual connection of gates 11a of transistors Tr2 and previous mutual connection of drains 8a and using the signal separation/drive signal generator 25 in the electrode controller 20 (to be described later). The term, “column direction” or “row direction” is not a word intending to indicate a specific direction in this specification. In the explanation of the present embodiment, the term “column direction” represents a direction of the force of gravity and the term “row direction” represents a direction perpendicular to the force of gravity. The technical concepts of the present invention are not influenced by any definition of the direction.
The anode electrode 3 formed on the display substrate is coated with a fluorescent substance 5. An anode voltage is applied to the anode electrode 3. Electrons emitted from each emitter 16 impinge the opposed portion of the fluorescent substance layer 5 to produce luminescence. The opposed portion of the fluorescent substance layer glows at the same brightness until the voltage of the capacitor 12 is updated. The time ratio (duty ratio) Du of luminescence is substantially to be 1 so that a high intensity luminescence can be obtained.
The relationship between the thin-film transistor section 1 and the cathode electrode 15 in the present embodiment is the same as that in the background art shown in
In such an active matrix system, L represents luminous brightness (cd/m×m) and S represents anode area (m×m) and Va represents anode voltage and Ia represents anode current (A) (equal to cathode current) and Du represents time ratio (real number equal to or less than 1) and □ represents luminous efficiency of fluorescent substance (Lm/W), □ represents effective current efficiency (real number equal to or less than 1) and □ r represents light transmission efficiency of fluorescent substance (real number equal to or less than 1). The brightness L is represented by the (formula 1).
L=(Va×Ia×□×Du×□×□ r)/(π×S) (Formula 1)
As apparent from the formula (1), it is required to make the numerator larger and the denominator smaller to produce higher brightness. However, there are restrictions in each parameter. For example, the luminous efficiency of fluorescent substance □, the effective current efficiency □, and the light transmission efficiency of fluorescent substance □ r substantially depend on the type of an image display device. In the active matrix system shown in the background art, the time ratio Du is 1.
In the present embodiment, the system for controlling the time ratio Du of the voltage applied to the gate electrode 13 is employed as a new control method. That is, the time ratio Du is to be changeable by using the gate electrode control circuit 23 (to be described later). The voltage Va, or anode electrode voltage, has a limited level because it cannot exceed the maximum voltage (withstanding voltage) between the anode electrode 3 and the cathode electrode 15. Moreover, the current Ia, or current flowing the anode electrode 3 (equal to the current flowing the cathode electrode), is specified in principle by the potential difference between the voltage VY applied to N drains mutually connected in a first group and the voltage VG of the gate electrode 13. When the voltage VG of the gate electrode 13 is fixed, the current Ia flowing the anode electrode 3 (equal to the current flowing the cathode electrode) is controlled with the voltage VY.
When the brightness of the image display device is changed under the above-mentioned conditions, the voltage VY, or the drain voltage of the transistor Tr2 in the first group, and the voltage VX, or the drain voltage of the transistor Tr2 in the second group are controlled, so that the voltage VC kept in each capacitor 12 is changed. The control of the time ratio Du will be described later.
For example, when the voltage VX1 becomes a high level (an upper potential in
Next, as electrode control section 20 shown in
The signal separation/drive signal generator 25 receives a composite picture signal Sv and generates a horizontal synchronous signal, a vertical synchronous signal, and a picture signal. The signal separation/drive signal generator 25 outputs voltages from VY1 to VYM, which are picture signals arranged in row direction flowing in column direction, to the drain drive circuit 21 based on the horizontal synchronous signal. The drain drive circuit 21, which is a power amplifier circuit, generates a power for driving the drain 8a of each of transistors Tr2. The signal separation/drive signal generator 25 outputs the voltages from VX1 to VXN for determining as to which of the rows arranged in column direction respectively to the gate drive circuit 22, based on the vertical synchronous signal. Each of the voltages from VX1 to VXN is a voltage for turning on or off a channel between a drain and source of the transistors Tr2. When the voltage is to be at a high level, the channel between the drain and source of the transistor Tr2 is turned ON, whereas when the voltage is to be at a low level, the channel is turned OFF. The gate drive circuit 22, which is a power amplifier circuit, generates the power for driving the gate electrode 11a of each transistor Tr2. The signal separation/drive signal generator 25 produces a first gate control signal to the gate electrode control circuit 23. The optical sensor 24 produces a second gate control signal to the gate electrode control circuit 23. The first gate control signal and the second gate control signal will be explained later.
As to the image display device having the above-mentioned configuration, a representative example of a novel system for driving the gate electrode 13 incorporated in the present embodiment, will be explained below.
The waveform of a voltage applied to the gate electrode 13 in the first embodiment is a repetitive waveform, similar to that in other embodiments to be described later. That is, a voltage applied to the gate electrode 13 is set to a constant value enabling field emission for a period during one cycle. A voltage disenabling field emission is applied to the gate electrode 13 for the remaining period during the cycle. With one cycle defined as a ratio of 1, the time ratio Du ranges from 0 to 1. That is, during a time corresponding to the time ratio Du, or during a time represented by the product of one cycle time multiplied by the time ratio Du, the voltage applied to the gate electrode 13 allows the emitters 16 to generate the field emission. During the remaining period in one cycle, the voltage applied to the gate electrode 13 is set to suppress the field emission from the emitter 16. In the first embodiment, when the time ration is 1, voltages from VY1 to VYM, which make a luminous brightness of a screen in a white color level, are output to the drain drive circuit 21. By doing so, the brightness of the whole of an image can be easily changed by varying the time ratio Du over 1 to 0 without adversely affecting hue and contrast.
In the control method in the first embodiment, it may be sometimes difficult, due to variations in radiation characteristic of each FEC section, to control the brightness under only the control of the voltage from VY1 to VYM. For example, even if all the voltages from VY1 to VYM are set at the same value in the low brightness region, a certain FEC section often emits electrons sufficiently so that the light emission is recognized visually, but another certain FEC section does not. This disadvantage occurs because of characteristic errors of each transistor, variations in magnitude of leakage current caused in each capacitor, and the like. When variations in brightness occur in each of portions (pixels) on the display screen, the variations must be often corrected in each case. The second embodiment was implemented in consideration of the above-mentioned problems.
Nv1=Var(Ia1ij)
Nv2=Var(Ia2ij) (Formula 2)
Therefore, when the whole of the screen is illuminated at a low brightness, images with more improved quality can be obtained by the control where the time ratio Du is decreased on application of the voltage VG of the gate electrode 13 and the voltage VY is increased, compared with the control where a dc (constant) voltage VG is applied to the gate electrode 13 (the time ratio Du of 1) and the voltage VY is reduced. For that reason, when the voltage VG is continuously applied (the time ration is 1), the voltage VG is set to a voltage at which the brightness of the fluorescent substance layer exceeds the white color level. The time ratio Du is set to a value at which the brightness of the fluorescent substance layer 5 does not exceed the white color level. By doing so, a good image quality can be obtained. For example, in the case of a dc voltage (the time ratio is 1), the voltage VG that can flow twice the current Iw corresponding to the white level is previously applied and the time ratio Du is set to 0.5. Thus, structural variations of the transistors Tr1 and Tr2, capacitors 2, and the emitters 16 disposed on the cathode electrode are suppressed. Thus, better images can be obtained.
In such a case, when the voltage VG is fixed at a large value and the time ratio Du is adjusted over 0 to 0.5, good control can be obtained through control of the time ratio Du. That is, when the luminous efficiency is low, the time ratio Du is set to a small value, so that the effect of small variations can be maintained. Moreover, since the absolute value of variation becomes small proportional to a decrease of the time ratio Du, such control allows a good screen quality to be obtained.
In a specific example of performing the above-mentioned brightness adjustment, the optical sensor 24 detects an ambient brightness. When the ambient area is dark, the time ratio Du of the voltage VG of the gate electrode 13 is decreased. When the ambient area is bright, the time ratio Du of the voltage VG is increased. In such an operation, the brightness of the whole of an image can be easily adjusted without adversely affecting hue and contrast. In
The gate electrode 13 may be divided into plural portions and respective divided portions may display different images, respectively. For example, the screen in the range covered by the gate electrodes 13A may receive a broadcast of baseball or the screen in the range covered by the gate electrodes 13B may receive a broadcast of news. In such a configuration, by differently setting the time ratio Du of the voltage VG of the gate electrode 13A and the time ratio Du of the voltage VG of the gate electrode 13B, one screen can be easily adjusted in a relatively dark state.
In the adjustment of the time ratio Du, an operator of the image display device may manually control the time ratio Du to obtain desired image brightness. However, the time ratio Du may be controlled in various other methods. For example, the time ratio Du of the voltage VG is controlled with the first gate control signal from the signal separation/drive signal generator 25. The optical sensor 24 detects the ambient brightness. The voltage VG may be controlled using the second gate control signal based on information from the optical sensor 24. Alternatively, the voltage VG may be controlled with the first gate control signal and the time ratio Du may be controlled with the second gate control signal. Thus, the control of voltage Vg may be performed together with the control of time ratio DU.
The signal separation/drive signal generator 25 includes a RAM (Random Access Memory) (not shown). The signal separation/drive signal generator 25 can absorb variations in the current Ia, flowing through the anode electrode 3, with respect to the voltage VY, for each cathode electrode 15. As shown in
Referring to
[Iaij]=[kij]×[VYj]−[Vkij] (Formula 3)
The formula (3) represents each current Iaij with respect to a predetermined voltage VY. If the voltage VY is corrected, each current Iaij can be set to a constant value with no variations. That is, it is considered to conduct the process based on the formulas (3) and (4). [Lij] is a matrix previously obtained to equalize each current Iaij when the same voltage is applied the drains 8a of the transistors Tr2 belonging to each column.
[VYnj]=([Lij])([Ia]+[Vkij])=[knij]([Ia]+[Vkij]) (Formula 4)
Provided that the value of matrix [knij] and the value of matrix [Vkij], having (M×N) factors, are previously obtained, the characteristic changes can be easily absorbed using the conversion formula (2). In this case, The RAM stores coefficients of 2×M×N.
If the factor of variations in brightness of the fluorescent substance layer 5 is put into the formula (4), variations in electron impingement effect and variations in a fluorescent substance luminous efficiency □, and variations in a fluorescent substance light transmission efficiency □ r can be absorbed. As a result, variations in brightness can be further reduced. The signal separation/drive signal generator 25 computes the conversion formula (4) and controls the gate electrode control circuit 2 with the second gate control signal.
As described above, while the voltage conversion operation is being conducted, the control of the gate electrode 13 is conducted, as shown in the second embodiment. That is, the brightness in the low brightness region is adjusted by controlling the time ratio Du of the voltage VG. For example, when the time ratio Du of the voltage VG applied to the gate electrode 13 is halved, the brightness L is halved without controlling the voltage VY1 to VYM, as apparent from the formula (1). By varying the time ratio Du of the voltage VG, the brightness can be controlled completely proportionally and very preferably. In other words, When the whole of the screen glows in low brightness, the time ratio Du is set to a small value and the voltage VY between the gate electrode 13 and the cathode electrode 15 is increased. This operation can compress variations due to differences in electric field strength distribution based on the structure of the transistors Tr1 and Tr2, the capacitor 12, and the emitter 16 disposed on each cathode electrode. This simple circuit configuration allows images with good quality.
Moreover, in an example like the second embodiment, the optical sensor 24 detects an ambient brightness. In the case of the dark state, the time ratio Du of the voltage VG of the gate electrode 13 is set to a small value. In the case of the bright state, the time ratio Du of the voltage VG is set to a large value. Thus, the brightness of the whole of an image can be easily changed without adversely affecting hue and contrast.
An image display device in a fourth embodiment will be explained by referring to
Moreover, the electrode controller 30 includes a signal separation/drive signal generator 35 (equivalent to the signal separation/drive signal generator 25), a control signal generation circuit 31 (having the same function as the drain drive circuit 21), a selection signal generation circuit 32 (equivalent to the gate drive circuit 22), and an optical sensor 34 (equivalent to the optical sensor 24). The voltages VX′1 to VX′N, each being a selection signal for conducting the source 57 of each transistor Tr3 belonging to the corresponding column, are respectively applied to the gates 51 of transistors Tr3 belonging to each row in the row direction. The selection signal generation circuit 32 generates the selection signal. The voltage VY′1 to VY′M, each being a control signal for controlling current flowing each transistor Tr3 belonging to the corresponding row, are respectively applied to the gates 41 of the transistors Tr4. The control signal generation circuit 31 generates the control signal.
Moreover, the present embodiment includes a gate electrode control circuit 33, having the same function as the gate electrode control circuit 23, for changing the time ratio Du being the ratio of time for which a fixed voltage is applied to the gate electrode 13. A fixed voltage VG′ is applied to the gate electrode 13 for the time corresponding to the time ratio Du. In such a state, the amount of electron emission from the emitters confronting with the gate electrode 13 can be controlled according to the time ratio Du. The brightness of a large area of the screen can be adjusted accurately under control only to the gate electrode 13.
The foregoing description was primarily directed to a preferred embodiment of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.
Number | Date | Country | Kind |
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2005-326019 | Nov 2005 | JP | national |