JP2736308B2 - Field emission display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field emission display. More particularly, the present invention relates to a system for controlling the gray scale range and brightness of a field emission display.

[0002]

BACKGROUND OF THE INVENTION With the advent of portable laptop computers, there has been an increasing demand for display technology for small, lightweight and power saving displays. One of the technologies available has provided flat panel displays, and more particularly liquid crystal displays. Liquid crystal displays are currently used in laptop computers. However, these liquid crystal displays have low contrast and a narrow observation allowable range. In addition, color liquid crystal displays are expensive and consume power at an inappropriate rate to extend battery operation.

[0003] In response to these drawbacks, some developments have recently been made in thin film field emission display technology. Conventional field emission displays use a matrix-addressable array of dot-like, thin-film, cold cathode emission chips in combination with a fluorescent light-emitting plate. In such a display device, each chip is addressed with a row signal to activate a single conductive strip in the grid, while a column signal activates the conductive strip on which the chip is formed. At the intersection of both actuated rows and actuated columns, there is a grid-emitter voltage difference sufficient to induce field emission, thereby exciting the phosphors of the pixels on the phosphor screen. Recent extensive research has shown that low cost, low power consumption and high resolution can replace conventional LCDs.
High-contrast full-color field emission displays can now be manufactured.

[0004]

In order to achieve performance comparable to that of liquid crystal displays, field emission displays require a method of controlling the gray scale range. Prior art techniques for controlling brightness and gray scale range consume excessive power, require complex manufacturing processes, and employ circuits that use too large integrated circuit die surface area.

It is an object of the present invention to provide a field emission display which eliminates the disadvantages of the prior art described above, consumes less power, is simpler to manufacture, and has a smaller integrated circuit die area.

[0006]

That is, the field emission display of the present invention has a gray scale generator cooperating with a field emission pixelator. In operation, an analog signal having a magnitude is input to a display device. The gray scale generation circuit includes a sample and hold circuit and a discharge circuit for converting the analog input signal into a sawtooth signal having a height and a width . In addition, of the sawtooth signal path
The loose width corresponds to the magnitude of the analog signal.

Structurally, the field emission display of the present invention includes a phosphor target and an integrated circuit formed on a substrate. The integrated circuit includes a grayscale generator and a plurality of addressable pixelators. Each pixelator includes a chip that emits electrons toward a target and an addressing transistor. The grayscale generator output is coupled to a respective addressing transistor, thereby controlling the duration and intensity of the emission corresponding to the luminance at each addressed pixel.

In a display according to a first embodiment of the present invention, a gray scale generator includes a sample circuit, a hold circuit, a discharge circuit, and a pixel drive circuit for providing a gray scale generator output. . The discharge circuit of this embodiment includes a discharge start switch and a current supply source.

The second embodiment is a modification of the first embodiment. The main element of the hold circuit is an inherent capacitance.
The pixel drive circuit of the embodiment is omitted. The grayscale generator output is provided by the cooperation of a hold circuit and a discharge circuit.

The third embodiment is another modification of the first embodiment, wherein a main element of the hold circuit is an inherent capacitance,
The pixel drive circuit of the first embodiment is eliminated, and the discharge start switch is eliminated.

The fourth embodiment is a further modification of the first embodiment, and the discharge start switch is omitted.

In another embodiment, contrast control is realized by extending or compressing the gray scale range by changing the slope of the sawtooth portion of the output signal .

In yet another embodiment, the height of the output signal is responsive to an optical sensor to compensate for image plane brightness in accordance with ambient light intensity.

[0014]

The advantages of low power consumption, small size, easy manufacture, and low cost can be realized in different ranges for each embodiment. Other advantages will become apparent to those skilled in the art from a perusal of the following detailed description when read in conjunction with the appended claims and the drawings accompanying this specification.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood on reading the following description of a preferred embodiment, with reference to the accompanying drawings, in which: FIG.

FIG. 1 is a block diagram of a field emission display according to the present invention. The field emission display 10 includes a phosphor target 40 and an integrated circuit formed on the substrate 20. The integrated circuit includes an active matrix array of pixelators , each of which is associated with a field emission chip.
Chip 30 , address transistor 15,
And a resistor 21. The chip 30 is connected to the source 25 of the address transistor 15. The drain 20 of the address transistor 15 is connected to the resistor 21. The resistor 21 is grounded. Further, an address switch 32 is connected in series between the source 25 and the chip 30, and this switch 32 selects one row of pixelators from a plurality of pixelators arranged in a matrix.

The voltage from chip 30 to grid 35 is high enough to emit from chip 30. In one embodiment, this voltage is about 50V. But,
It will be apparent to those skilled in the art that changes in the chip arrangement allow for emission at other voltages.

The tip 30 is placed in a vacuum near the grid 35 and the target 40. The grid 35 and the target 40 are biased such that the grid 35 has a substantially lower voltage than the target 40. In one embodiment, the voltage at grid 35 is 80 volts, while the voltage at target 40 is 1 volt.
500V. However, the voltage of grid 35 is
It will be apparent to those skilled in the art that, as long as the voltage is substantially lower than zero, the arrangement can change these voltages without adversely affecting the function of the field emission display 10. There will be.

Electrons are emitted from the emitter tip 30 due to the voltage difference between the tip 30, the grid 35 and the target 40, and pass through the grid 35 and strike the target 40.
Since the target 40 includes a phosphor screen, the pixels (12) of the target 40 emit light when the emitted electrons collide. The field emission display 10 emits light with higher brightness as many electrons collide with the phosphor screen.

Based on a direct correlation between the number of electrons colliding with the phosphor screen and the brightness of the display, the present invention employs an output amplitude signal method for input to the addressing transistor 15. The analog signal 45 is converted into an output signal 51 by using a gray scale generator 55 in order to realize light emission of high luminance.

Gray scale generator 55 receives analog signal 45 and determines the brightness of addressed pixel 12. Including red, green, and / or blue signals;
Upon receiving the analog signal of the AL signal system or the NTSC system, the grayscale generator 55 samples the analog signal 45 at a predetermined frequency. Sampling is performed using a sample circuit. When the sampling is completed, the sample of the analog signal 45 is held by the hold circuit, and each sample is stored until the next sample is taken out. Both sampling and holding functions are performed by a sample and hold circuit 65.

The discharge circuit 70 includes a sample hold circuit 65
Connected to the output. The discharge circuit 70 is connected to the sample and hold circuit 65 as shown, but instead of a direct connection, a coupling circuit known in the prior art can be used. Since the discharge circuit 70 supplies a predetermined discharge current irrespective of the sampled voltage, the discharge time depends only on the magnitude of the charge stored in the hold circuit 65. Discharge circuit 70 generally provides a means for discharging the output of sample and hold circuit 65. The discharging means is
For example, it can be realized by a current supply source or a current mirror circuit. In the preferred embodiment, discharge circuit 70 includes a variable response current source. In alternative and equivalent embodiments, other current control circuits known in the art replace the variable current source.

In one embodiment of the present invention, a pixel drive circuit or buffer 75 is connected to a discharge circuit 70.
An output signal 72 having a sawtooth shape is input to the drive circuit 75. The pixel drive circuit 75 generates the output signal 51 by comparing the sawtooth output signal 72 with a predetermined threshold. That is, the drive circuit 75 converts the sawtooth output signal 72 to the output signal 51 , so that the pulse width of the signal 72 corresponds to the pulse width of the output signal 51 as shown in FIGS . In addition,
The emitter control circuit of the present invention includes a pixel drive circuit 75 and an emitter control circuit.
Dressing transistor 15, resistor 21, address
And a switch 32.

FIGS. 2 and 3 show the transfer function of the grayscale generator of the present invention. Gray scale generator 55 provides a means for controlling the gray scale range and brightness of field emission display 10. The grayscale range is referred to here as the output signal.
Is defined as the range between the minimum and maximum signal width
You .

The analog signal 45 input to the gray scale generator 55 is sampled at a predetermined frequency. The value of the sampled analog signal 45 is
The output signal whose pulse width directly corresponds to the sampling voltage
No. 51 or 72 is converted. For example, in FIG.
A first voltage V1 which is sampled at time t1 5V der
Ri, which is the pulse width W which is generated by the second voltage V2 sampled at 4V, the time t2 is shown in FIG. 3
This corresponds to a pulse width W1 wider than 2 .

In the first embodiment, the output signal (51) is
It has the shape of a square wave . In the second embodiment, the output signal
(72) has a sawtooth shape . In a second embodiment,
The output signals 72 of FIGS. 2 and 3 have the same slope.
In both the first and second embodiments, signal 51 or 72
Can be terminated to start or ending time different started at the same time in accordance with the necessary signal, or in conjunction with the necessary signals at different times at the same time.

FIG. 4 shows a first gray scale image of the present invention.
A generator 55 is shown. Sample circuit (Sun
The pulling switch 85 receives the analog signal 45. The sample circuit 85 includes a field-effect transistor having a channel 84 and a signal 45 at one end of the channel.
It will be apparent to those skilled in the art that other equivalent means for sampling include changes such as replacing the sample circuit with a known switching circuit. By coupling the control signal 86 to the gate controlling the channel 84 of the field effect transistor, the analog signal 45 can be sampled at a frequency corresponding to the period of the control signal 86.

The hold circuit 90 is connected between the sample circuit 85 and the ground. The hold circuit 90 is a sample circuit 8
5 holds each of the sampling voltages generated. The hold circuit 90 includes a capacitor for charging with a predetermined time constant and discharging from a sampled voltage with a predetermined time constant. In another equivalent embodiment, the hold circuit 90 is replaced by another known charge holding circuit.

The gray scale generator 55 also includes a discharge circuit for discharging each of the sampling voltages.
70 . This discharge circuit includes two elements, a discharge start switching device 98 and a constant current supply source 100.

The discharge start switching device 98 is connected to the sample circuit 85 through the channel 84 of the field effect transistor, and disconnects the connection between the constant current supply source 100 and other circuits. In the preferred embodiment of the present invention, constant current source 100 includes a variable response current source. Current supply source 10
The circuit arrangement of the device 98 for 0 is not particularly relevant for the overall circuit branch. In another equivalent embodiment, other known linear discharge circuits replace the circuit configuration shown.

The discharge start signal 95 input to the switching device 98 has the same period as the control signal 86, but has a longer pulse width than the signal 86. Further, since the discharge start signal 95 is issued after the signal 86, the hold circuit 90 can be charged to the sampling voltage before substantially discharging. In the preferred embodiment, the time between the issuance of signal 86 and the issuance of signal 95 is minimal.

In the preferred embodiment, gray scale generator 55 is connected to the respective gate of addressing transistor 15 for each column of the pixelator. In this design, the operating characteristics of the addressing transistor are adjusted to compensate for the sawtooth input opposite the pulse input, including the threshold voltage VT.

[0033] Another embodiment At a pixel driving circuit 75 is a channel 84 and Trang field effect transistor of the present invention
It is connected between the resistors 15 . The operation of the pixel driving circuit 75 is as described above with reference to FIG. Therefore, the output signal 51 becomes the gray scale generator 5
5 to the display 10 in the form of a square wave.

Referring to FIG. 5, a second grayscale generator 56 of the present invention is illustrated. The gray scale generator 56 is the gray scale generator 5
Similar elements as in 5 have similar reference numerals as previously described.

A parasitic capacitance 87 specific to the display 10 and its structure is connected between the channel 84 of the field effect transistor and the ground. The parasitic capacitance 87 performs the same function as the hold circuit 90 of FIG . The parasitic capacitance 87 stores each of the sampling voltages generated by the sample circuit 85 and discharges each of the stored sampling voltages at an appropriate time. As a result, an output signal 72 is provided from the grayscale generator 56 to the display 10 in the form of a sawtooth wave.

Referring to FIG. 6, a third preferred grayscale generator of the present invention is illustrated. The gray scale generator 57 is similar to the gray scale generators 55 and 56, and similar components already described have similar reference numerals. In this embodiment, the output signal 7
2 is supplied from the gray scale generator 57 to the display 10 in the form of a sawtooth wave.

Referring to FIG. 7, a fourth preferred grayscale generator of the present invention is illustrated. The grayscale generator 58 is similar to the grayscale generators 55, 56, 57, and similar components already described have similar reference numerals.

FIGS. 8 and 9 show a first embodiment of the pixel drive circuit 75. FIG. The driving circuit 75 includes two complementary metal oxide semiconductors (“CMO”) connected in cascade.
S ") includes inverter circuits 92 and 94. Upon receiving the output signal 72 having a sawtooth waveform, the inverter 92 generates an inverted output B having a constant time constant as shown in FIG. Following this, inverter 94 produces another inverted output C with a constant time constant. In the drive circuit 75,
The input voltage threshold level defines the conversion point of each drive circuit, after which point the state of the inverted output changes.

FIG. 10 is a block diagram of the variable response current supply source 100. The source 100 includes a contrast control means 110 for providing a control signal, and a current source 120.
The contrast control means 110 is connected to the current supply 120 so that the current signal controls the magnitude of the current passing through the current supply 120. The gray scale range is defined as the range from the minimum width to the maximum width value of the output signal . The contrast control means 110 expands or contracts the gray scale range of the field emission display by adjusting a predetermined current of the current source. In one embodiment, current source 120 includes a voltage controlled resistor. In another equivalent embodiment, the voltage controlled resistor has been replaced by a known switching current supply circuit or a linearity control current supply circuit.

FIG. 11 is a block diagram of a control circuit for controlling the pulse height as compensation for the ambient light intensity. The control circuit 175 is connected in series between the discharge circuit 70 and the address transistor 15. In the first embodiment, control circuit 175 receives sawtooth signal 72. In another embodiment, control circuit 175 receives output signal 51 . For example, in another embodiment, the control circuit 175 is connected in place of the pixel driving circuit 75 or in combination with the pixel driving circuit 75 in series.

The control circuit 175 includes an operational amplifier (operational amplifier) 78, a gain compensation resistor 83, and a phototransistor.
(Light receiving device) 82. Transistor 82 operates as an ambient light sensor. Variable gain amplifier (78, 8
In conjunction with 3), transistor 82 provides control means for controlling the magnitude of the output signal . In operation, the control means provides a control signal 150 for increasing the magnitude of the output signal during high light levels. Changing the magnitude compensates for ambient light surrounding the field emission display. To simplify this compensation, a sensor 82 formed on the integrated circuit board 20 increases or decreases the gain of the amplifier 78 in response to ambient light so that the magnitude of the signal 151 corresponds to the amount of ambient light.

Although the present invention has been described with reference to illustrative embodiments, this description is not meant to be construed as limiting the invention. Although the present invention has been described in a preferred embodiment, various changes in the illustrated embodiment, as well as further embodiments of the present invention, are set forth in the appended claims, as set forth in the claims. It should be understood that, without departing from the scope of the invention, it will be apparent to one skilled in the art from reference to the specification. It is therefore intended that the following appended claims be interpreted as including all such alterations or embodiments as fall within the scope of the invention.

[0043]

As is apparent from the above description, according to the present invention, since the field emission pixelator corresponding to the pulse width corresponding to the magnitude of the electric charge held in the sample and hold circuit is provided, the power consumption is reduced. The advantage is that a field emission display that is low, has a simple manufacturing process and a small integrated circuit die area can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of a field emission display of the present invention.

FIG. 2 is a diagram showing a transfer function of the gray scale generator of the present invention.

FIG. 3 is a diagram showing a transfer function of the gray scale generator of the present invention.

FIG. 4 is a block diagram of the grayscale generator of the present invention.

FIG. 5 is a block diagram of the grayscale generator of the present invention.

FIG. 6 is a block diagram of the grayscale generator of the present invention.

FIG. 7 is a block diagram of the grayscale generator of the present invention.

FIG. 8 is a schematic diagram of a pixel drive circuit 75.

9 is an output characteristic diagram of the pixel drive circuit shown in FIG.

FIG. 10 is a block diagram of the variable response current supply 100 shown in FIGS. 4 to 7;

FIG. 11 is a block diagram of a control circuit for controlling a pulse height for ambient light compensation.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Field emission display 12 Pixel 15 Address transistor 21 Resistor 30 Chip 32 Address switch 35 Grid 45 Analog signal 51 Output signal 65 Sample hold circuit 70 Discharge circuit 72 Saw wave output signal 75 Pixel drive circuit 82 Phototransistor (light receiving device) 115 Control signal 150 Control signal 151 Signal 175 Control circuit

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Thomas W. Bochel, United States, 83706 Idaho, Boise, E Woodbine City, 1227 (56) References JP-A-5-100629 (JP, A) JP-A-3-295138 (JP, A) JP-A-55-156994 (JP, A) JP-A-49-79120 (JP, A) JP-A-6-130909 (JP, A) JP-A-2-2033387 (JP, A) JP, A) JP-A-4-58286 (JP, A)

Claims (10)

(57) [Claims] 1. A field emission chip (30) for a pixel (12).
With respect to the analog input voltage corresponding to the pixel.
A field emission display (10) providing an average current;
What is a. An image including at least one field emission tip (30)
Element (12); b. An analog signal receiving an analog input voltage for the pixel
Log entry (45); c. Capacity (87, 90); d. The analog input (45) and the capacitors (87, 9
0) and its input switch is on
Connect the analog input to the capacitance when in state
And compare the capacitance to a sample of the analog input voltage.
In order to charge to the example voltage,
Sampling switch (85) that can be switched periodically
And e. Connected in parallel with the capacitors (87, 90),
The sampling switch (85) is turned off from the on state
After switching to the state, said capacity at a controlled rate
Conduct current from the capacity to discharge
Pulse width and peak proportional to the sample of the analog input voltage
A sawtooth-shaped gradually decreasing sawtooth with c-pulse amplitude
Discharge for generating a voltage pulse (72) through the capacitor
A circuit (70, 98, 100); f. In order to receive the sawtooth voltage pulse, the capacitance (87,
90) a control input (72) connected to the chip;
(30) having an output connected in series, and
The period during which the sawtooth voltage pulse exceeds the threshold (W ₁ , W
₂ ) During this time, the air is configured to pass a current through the chip.
Mitter control circuit (75, 15, 21, 32)
A field emission display characterized by the above-mentioned . 2. The discharge circuit (70, 98, 100).
But to adjust the contrast of the display,
A circuit (11) for adjusting the current derived from the storage capacity
0, 120).
Field emission display . 3. An emitter control circuit (75, 15, 2)
1, 32) are: a. When the sawtooth voltage pulse exceeds the threshold
A transistor for passing a current to the chip (30)
(15), b. Connected in series with the transistor and the chip
To selectively enable the flow of current to the chip
And, as a result, a switch for selectively causing the pixels to emit light.
The electric field emission device according to claim 1 or 2, further comprising (32).
Out display . 4. a. The discharge circuit (70) includes the capacitor
Has a pulse width corresponding to the magnitude of the
Generating a sawtooth voltage pulse (72), The emitter control circuit (75, 15, 21, 32)
The discharge circuit (70) and the transistor (15)
And a drive circuit (75, 175) connected in series between the first and second pulses for providing a pulse (51, 151) having a duration corresponding to the pulse width.
A field emission display according to claim 1 . 5. A method according to claim 1, wherein: a. Said pulses (51, 151) include a pulse height; b. The transistor (15) determines the brightness of the pixel (12) in response to the pulse height; c. The display comprises: (1) a light receiving device (82) for providing a second control signal (150); (2) the discharge circuit (70) and the transistor (1).
5. The field emission diode of claim 4, further comprising: a control circuit connected in series during 5) for controlling the pulse height in response to the second control signal.
Spray . 6. The sampling switch (85) and
Sample and hold circuit including the capacitors (87, 90)
(65), the discharge circuit (70), and the field emission pin.
With xerators (35, 30, 32, 15, 21)
The electric field emission device according to claim 5, wherein the electric field emission device is formed on a single substrate.
Out display . 7. A method according to claim 1, wherein: a. The pulses (72, 51, 151)
Contains the pulse height, b. The transistor is responsive to the pulse height to determine the brightness of the pixel (12); c. The display comprises: (1) a light receiving device (82) for providing a second control signal (150); (2) the discharge circuit (70) and the transistor (1).
5. The field emission diode of claim 3, further comprising: a control circuit connected in series during 5) for controlling the pulse height in response to the second control signal.
Spray . 8. An a. The discharge circuit (70) includes the capacitor
Has a pulse width corresponding to the magnitude of the
Generating a sawtooth voltage pulse (72), The emitter control circuit (75, 15, 21, 32)
The discharge circuit (70) and the transistor (15)
Further comprising a drive circuit (75, 175) connected in series between and for providing a pulse (51, 151) having a duration corresponding to said pulse width.
Or a field emission display according to 2 . 9. A. The pulses (72, 51, 151)
Includes the pulse height; b. The transistor (15) determines the brightness of the pixel (12) in response to the pulse height; c. The display comprises: (1) a light receiving device (82) for providing a second control signal (150); (2) the discharge circuit (70) and the transistor (1).
9. The field emission diode of claim 8, further comprising: a control circuit connected in series during 5) for controlling the pulse height in response to the second control signal (150).
Spray . 10. A. The pulses (72, 51, 15)
1) includes the pulse height, b. The transistor (15) determines the brightness of the pixel (12) in response to the pulse height; c. The display comprises: (1) a light receiving device (82) for providing a second control signal (150); (2) the discharge circuit (70) and the transistor (1).
3. The electric field of claim 1, further comprising: a control circuit connected in series during 5) for controlling the pulse height in response to the second control signal (150). 4.
Emission display .