JPH07168546A - Field-emission display - Google Patents

Abstract

PURPOSE: To provide an electric field discharging display having a gray scale generator. CONSTITUTION: An analog signal 45 having an amplitude is inputted to a display, and a gray scale generator 55 is provided with a sample/hold circuit 65, a discharging circuit 70, and a driving circuit 75 for converting the analog signal into a sawtooth wave signal 72. The width of an output amplitude signal 51 is made correspond to the amplitude of the sampling-processed analog signal, and contrast control is operated by the change of the inclination of the sawtooth wave signal 72, or the height of the output amplitude signal 51 is made respond to an optical sensor so that the luminance of the display can be compensated by peripheral optical intensity.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to field emission displays. More particularly, the present invention relates to systems for controlling the grayscale range and brightness of field emission displays.

[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 available technology provides flat panel displays, and more specifically liquid crystal displays. Liquid crystal displays are currently used in laptop computers. However, these liquid crystal displays have low contrast and have a narrow observation range. Moreover, color liquid crystal displays are expensive and consume power at an unsuitable rate for extended battery operation.

In response to these shortcomings, some recent developments have been made in thin film field emission display technology. Conventional field emission displays use a matrix-addressable array of dot-shaped, thin-film, cold-cathode emission chips combined 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. A sufficient grid-emitter voltage difference is created at the intersection of both the activated row and the activated column, which excites the emitter of the pixel on the phosphor screen. In recent years, a wide range of research has replaced the conventional liquid crystal display with low cost, low power consumption and high resolution.
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. Conventional techniques for controlling brightness and grayscale range are excessively power consuming, require complex manufacturing steps, and use circuits that use too large an integrated circuit die surface area.

It is an object of the present invention to provide a field emission display that eliminates the above-mentioned drawbacks of the prior art, has low power consumption, is simple to manufacture, and has a small integrated circuit die area.

[0006]

Thus, the field emission display of the present invention comprises a grayscale generator cooperating with a field emission pixelator. In operation, an analog signal having a magnitude is input to the display device. The gray scale generation circuit includes a sample hold circuit and a discharge circuit for converting the analog input signal into a sawtooth signal having a height and an amplitude. Furthermore, the amplitude of the sawtooth signal 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 pixels. 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, which controls the duration and intensity of the emission corresponding to the brightness at each addressed pixel.

In the display according to the first embodiment of the present invention, the gray scale generator includes a sample circuit, a hold circuit, a discharge circuit, and a pixel driving 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, and the main element of the hold circuit is an inherent capacitance,
The pixel drive circuit of the above embodiment is deleted. The grayscale generator output is provided by the cooperation of the hold and discharge circuits.

The third embodiment is another modification of the first embodiment, in which the main element of the hold circuit is the intrinsic capacitance,
The pixel drive circuit of the first embodiment is deleted, and the discharge start switch is deleted.

The fourth embodiment is a further modification of the first embodiment, in which the discharge start switch is deleted.

In another embodiment, contrast control is realized by changing the slope of the sawtooth portion of the output amplitude signal to expand or compress the gray scale range.

In yet another embodiment, the height of the output amplitude signal is responsive to the photosensor 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 are realized in different ranges for each embodiment. Other advantages will be apparent to those of ordinary skill in the art by reading the following detailed description, with reference to the appended claims and the accompanying drawings.

[0015]

The invention will be better understood by reading the following description of a preferred embodiment with reference to the accompanying drawings.

FIG. 1 is a block diagram of the field emission display of the present invention. The field emission display 10 includes a phosphor target 40 and an integrated circuit formed on a substrate 20. The integrated circuit includes an active matrix array of pixels, each pixel including a chip 30, an addressing transistor 15, and a resistor 21. The chip 30 is connected to the source 25 of the address transistor 15. Drain 2 of address transistor 15
0 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 the switch 32 selects one row of pixilators from a plurality of pixilators arranged in a matrix.

The voltage from tip 30 to ground is high enough for emission from tip 30. In one embodiment, this voltage is about 50V. However, it will be apparent to those skilled in the art that changing the chip layout allows 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 so that the grid 35 has a substantially lower voltage than the target 40. In one embodiment, the voltage on the grid 35 is 80V, while the voltage on the target 40 is 1.
It is 500V. However, the voltage of the grid 35 is the target 4
It will be apparent to those skilled in the art that by changing the arrangement, these voltages can be changed without adversely affecting the functionality of the field emission display 10 as long as they are substantially below the zero voltage. Ah

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

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

The grayscale generator 55 receives the analog signal 45 and determines the brightness of the addressed pixel 12. Contains red, green, and / or blue signals, P
When receiving an analog signal of the AL signal system or the NTSC system, the gray scale generator 55 samples the analog signal 45 at a predetermined frequency. Sampling is performed using a sampling circuit. When the sampling is completed, the hold circuit holds the sample of the analog signal 45 and stores each sample until the next sample is taken out. A sampling and holding circuit 65 performs both sampling and holding functions.

The discharge circuit 70 is a sample hold circuit 65.
Connected to the output of. 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 art can be used. Since the discharge circuit 70 supplies a predetermined discharge current regardless of the sampled voltage, the discharge time depends only on the magnitude of the charges 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 alternate and equivalent embodiments, other current control circuits known in the art replace the variable corresponding current source.

In one embodiment of the present invention, the pixel drive circuit or buffer 75 is connected to the discharge circuit 70.
The output amplitude signal 72 having a sawtooth shape is input to the drive circuit 75. The pixel drive circuit 75 compares the sawtooth wave output signal 72 with a predetermined threshold value to generate the output amplitude signal 51. That is, the drive circuit 75 converts the sawtooth output amplitude signal 72 into the output amplitude signal 51, so that the amplitude of the signal 72 corresponds to the pulse amplitude of the output amplitude signal 51, as shown in FIGS.

2 and 3 illustrate the transfer function of the grayscale generator of the present invention. Grayscale generator 55 provides a means for controlling the grayscale range and brightness of field emission display 10. The grayscale range is defined herein as the amplitude from the minimum value to the maximum value of the amplitude of the output amplitude signal.

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 amplitude signal 51 whose amplitude directly corresponds to the sampling voltage.
Or converted to 72. For example, in FIG. 2, time t
The first voltage V1 sampled at 1 is 5V, which is a signal amplitude W1 of 4V shown in FIG. 3 which is wider than the amplitude generated by the second voltage V2 sampled at time t2.
It corresponds to.

In the first embodiment, the output amplitude signal has a square wave shape (51). In the second embodiment, the output amplitude signal has a sawtooth shape (72). In the second embodiment, the output signals 72 of FIGS. 2 and 3 have the same slope. In both the first and second embodiments, the signal 51 or 72 may start at the same time and end at a different time depending on the desired amplitude signal, or may be different times depending on the desired amplitude signal. It can start at the same time and end at the same time.

FIG. 4 shows the first gray scale of the present invention.
A generator 55 is shown. The sample circuit 85 receives the analog signal 45. The sample circuit 85 includes a field effect transistor having a channel 84, and the signal 45 is input to one end of the channel. However, the sample circuit is known as another equivalent sampling means. It will be apparent to those skilled in the art that changes such as replacement with switching circuits are included. By coupling the control signal 86 to the gate that controls 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 the sample circuit 8
Each of the sampling voltages generated in 5 is held. The hold circuit 90 includes a capacitor for charging with a predetermined time constant and discharging a sampled voltage with a predetermined time constant. In another equivalent embodiment, the hold circuit 90 is replaced by another known charge hold circuit.

Grayscale generator 55 also includes a discharge circuit for discharging each of the sampling voltages. This discharge circuit includes a discharge start switching device 9
8 and a constant current 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 constant current supply source 100 from other circuits. In the preferred embodiment of the present invention, the constant current source 100 includes a variable response current source. Current source 10
The circuit layout of the device 98 for 0 is not particularly concerned with the overall circuit branch. In another equivalent embodiment, other known linear discharge circuits replace the illustrated circuitry.

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 being substantially discharged. In the preferred embodiment, the time between the issuance of signal 86 and the issuance of signal 95 is minimal.

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

In another embodiment of the invention, a pixel drive circuit 75 is connected between the field effect transistor channel 84 and the display 110. The operation of the pixel drive circuit 75 is as already described with reference to FIG. Therefore, the output amplitude signal 51 is supplied from the grayscale generator 55 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 shown. Grayscale generator 56 is grayscale generator 5
5 and like parts already described have like reference numerals.

A parasitic capacitance 87 peculiar to the display 10 and its structure is coupled 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 sampling voltages stored at an appropriate time. As a result, the output amplitude signal 72 is provided from the grayscale generator 56 to the display 10 in the form of a sawtooth wave.

In FIG. 6, a third preferred grayscale generator of the present invention is shown. Grayscale generator 57 is similar to grayscale generators 55, 56, and similar elements already described have like reference numerals. In this embodiment, the output amplitude signal 72 is provided from the grayscale 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 shown. The grayscale generator 58 is similar to the grayscale generators 55, 56, 57, and similar elements already described have like reference numbers.

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

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 source 120 so that the current signal controls the magnitude of the current passing through the current source 120. The gray scale range is defined as the range from the minimum amplitude to the maximum amplitude value of the output amplitude 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 supply source. In one embodiment, current source 120 includes a voltage controlled resistor. In another equivalent embodiment, the voltage controlled resistor is replaced by a known switching current supply circuit or a linear control current supply circuit.

FIG. 11 is a block diagram of a control circuit for controlling the pulse height as a 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, the control circuit 175 receives the sawtooth signal 72. In another embodiment, the control circuit 175 receives the output amplitude signal 51.
For example, in another embodiment, the control circuit 175 is connected instead of the pixel driving circuit 75 or in combination with the pixel driving circuit 75.

The control circuit 175 includes an operational amplifier (operational amplifier) 78, a gain compensation resistor 83, and a phototransistor 82. Transistor 82 operates as an ambient light sensor. In cooperation with the variable gain amplifiers (78, 83), the transistor 82 provides the control means for controlling the magnitude of the output amplitude signal. In operation, the control means provides a control signal 150 for increasing the magnitude of the output amplitude signal during high light levels. The varying size compensates for ambient light surrounding the field emission display. To simplify this compensation, the sensor 82 formed on the integrated circuit substrate 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 the illustrated embodiments, this description should not be taken as limiting the invention. While the present invention has been described in a preferred embodiment, various modifications of the illustrated embodiment, as well as further embodiments of the present invention, are described in the appended claims. It should be understood that it can be realized by those skilled in the art with reference to the present specification, without departing from the scope of the invention. Accordingly, the appended claims are to be regarded as embracing all of these variations or embodiments within the scope of the invention.

[0043]

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

[Brief description of 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 grayscale generator of the present invention.

FIG. 3 is a diagram showing a transfer function of the grayscale 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 source 100 illustrated in FIGS. 4 to 7.

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

[Explanation of symbols]

 10 Field Emission Display 12 Pixel 15 Address Transistor 21 Resistance 30 Chip 32 Address Switch 35 Grid 45 Analog Signal 51 Output Amplitude Signal 65 Sample Hold Circuit 70 Discharge Circuit 72 Sawtooth Output Signal 75 Pixel Drive Circuit 82 Phototransistor 115 Control Signal 150 Control signal 151 Signal 175 Control circuit

 ─────────────────────────────────────────────────── --Continued Front Page (72) Inventor Thomas W. Bochelle, E. Woodvine City, Boyes, Iowa, 83706, USA 1227

Claims (10)

[Claims] 1. A signal (4) comprising a plurality of pixels, each pixel having an address and a luminance, for determining the luminance of each pixel (12).
A field emission display (10) responsive to 5), comprising: a. A sample and hold circuit (6) for taking a sample of the signal (45) at a time corresponding to the address of each pixel (12) and holding a charge of a magnitude corresponding to the sample.
5), and b. A pulse (72, 51, 151) connected to the sample-and-hold circuit (65), passing a discharge current characterized by a constant magnitude during the passage, thereby having a period responsive to the magnitude of the charge. A discharge circuit (70) for generating c. A field emission pixelator (35) comprising a chip (30) in series with a transistor (15) each responding to the pulse (72, 51, 151) and causing each pixel (12) to emit light in response to the period. , 30, 32,
15, 21). 2. A signal (4) comprising a plurality of pixels, each pixel having an address and a luminance, for determining the luminance of each pixel (12).
A field emission display (10) responsive to 5), comprising: a. A sample and hold circuit (6) for taking a sample of the signal (45) at a time corresponding to the address of each pixel (12) and holding a charge of a magnitude corresponding to the sample.
5), and b. A contrast control means (110) for outputting a control signal (115); c. A pulse (72, 72) connected to the sample-and-hold circuit (65) passes a discharge current characterized by a magnitude according to the control signal while passing, thereby having a period responsive to the magnitude of charge. Discharge circuit (70) for generating 51, 151), and d. A field emission pixelator (35) comprising a chip (30) in series with a transistor (15) each responding to the pulse (72, 51, 151) and causing each pixel (12) to emit light in response to the period. , 30, 32,
15, 21). 3. Pixelators (35, 30, 32, 1)
5, 21) are switches (3) in series with the transistor (15) for selectively enabling emission by the pixelator.
The display according to claim 1 or 2, further comprising 2). 4. A. The discharge circuit (70) produces a sawtooth wave (72) having an amplitude corresponding to the magnitude of the charge, b. The display is connected in series between the discharge circuit (70) and the transistor (15) and has pulses (51, 15) whose duration corresponds to the amplitude.
Display according to claim 3, further comprising a drive circuit (75, 175) for providing 1). 5. A. Said pulse (51, 151) comprises 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).
The display 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 (150). 6. A. The sample hold circuit (65)
And the discharge circuit and the field emission pixelator (3
5, 30, 32, 15, 21) are both formed on a single substrate, and b. 6. The display of claim 5, wherein the sample and hold circuit includes an intrinsic capacitance to hold substantially all of the charge. 7. The pulse (72, 51, 151) comprises pulse height, b. Said transistor is responsive to said pulse height to determine the brightness of said 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 display 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 (150). 8. The discharge circuit (70) produces a sawtooth wave (72) having an amplitude corresponding to the magnitude of the charge, b. The display is connected in series between the discharge circuit (70) and the transistor (15) and has pulses (51, 15) whose duration corresponds to the amplitude.
Display according to claim 1 or 2, further comprising a drive circuit (75, 175) for providing 1). 9. The pulse (72, 51, 151) comprises 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).
9. The display 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). 10. The pulse (72, 51, 151) comprises 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).
A display according to claim 1 or 2, further comprising a control circuit connected in series during 5) for controlling the pulse height in response to the second control signal (150).