DE4427673B4 - Field emission display - Google Patents

Abstract

A field emission display (10) having a plurality of pixels (12), the field emission display responsive to a signal (45) for controlling the brightness of each pixel (12) during a time that the respective pixel (12) is addressed following features:
a) a sample and hold circuit (65) which forms a sample of the signal (45) at a timing corresponding to the addressing of the respective pixel (12) and holds a charge whose amount depends on the sampled signal value;
b) a discharge circuit (70) connected to the sample and hold circuit (65) and drawing a constant amount of discharge current from the sample and hold circuit (65) via a constant current source (100) to produce a pulse (72 , 51, 151) during a discharge time of the sample and hold circuit (65) whose duration corresponds to the amount of charge in the sample and hold circuit (65); and
c) a field emission pixelator (35, 30, 32, 15, 21) for illuminating each pixel (12), each of which ...

Description

The The invention relates to a field emission display, in particular a system for controlling the gray scale range and the brightness at a Field emission display.

With The advent of portable laptop computers has increased demand for display devices in the form of a lightweight, compact and performance-efficient display. An available technology in this context provides flat screens, especially liquid crystal displays. For laptop computers are currently mainly liquid crystal displays used. However, the liquid crystal displays provide only a weak Contrast and a narrow visual angle range. Furthermore are color liquid crystal displays expensive and energy-consuming to a degree, which the battery operation over longer periods prohibits.

in the With regard to these disadvantages have been different developments in the field of thin-film field emission display technology promoted. conventional Field emission displays use a matrix-addressable field from point to point formed thin-film cold-emitting cathode tips in combination with a fluorescent screen. With such a display, each Tip of a column signal addressed to a single conducting Activate stripes within a grid while on Row or line signal activates a strip of conductors on the the tip is formed. At the intersection of the activated column and the activated line results in a sufficient grid-emitter voltage difference for inducing a field emission, which is an illumination of a associated Fluorescent region of a picture element on the phosphor screen causes. In younger Time, intensive research has led to the production of a cheap, low power full-color high-resolution field emission display and high contrast a reasonable alternative for liquid crystal displays represents.

Around a similar capacity to achieve as with liquid crystal displays, have to Field emission displays a grayscale or greyscale control system exhibit. Conventional methods for controlling the brightness and the gray scale range provide circuits, which overly much Consuming energy, requiring complex manufacturing processes and considerable Surface of a require integrated circuit.

From the US 5 210 472 A For example, a field emission display having a plurality of pixels is known. The field emission indicator is responsive to a signal to control the brightness of each pixel during a time that the pixel is activated. A field emission activating device, also referred to herein as a field emission pixelator, serves to illuminate each individual pixel, which device has an emitter tip which receives a pulse so that the brightness of the pixel is adjusted in response to the duration of the pulse. In other words, pixel brightness control is effected by controlling the sampling time or the turn-on duration of the pixel.

From the DE 41 12 078 A1 For example, a field emission display having a plurality of pixels is known. The field emission indicator is responsive to a signal to control the brightness of each pixel during a time that the respective pixel is being addressed. A sample and hold circuit forms a sample of the signal at a time corresponding to the location of the respective pixel. It holds a charge whose amount depends on the sampled signal value. A discharge circuit draws a discharge current from the sample and hold circuit to generate a pulse during a predetermined portion of the discharge of the sample and hold circuit, the duration of which corresponds to the amount of charge. A field emission pixelator serves to brighten each pixel, it has an emitter tip which receives said pulse.

From the US 5 138 308 A For example, a field emission display is known which has a sample and hold circuit in conjunction with a discharge circuit. The latter deprives the sample and hold circuit of a discharge current to form a pulse during a predetermined portion of the discharge process. The pulse duration corresponds to the charge quantity and specifies the brightness of the pixels. The charging of the sample and hold circuit is carried out in accordance with their own capacity.

In the above-mentioned prior art according to the US 51 20 472 A The pulse duration is set for all emitter tips, so that the brightness (the gray scale) is only possible for the entire display field. In the prior art according to the DE 41 12 078 A1 A pulse is generated by the discharge circuit, the duration of which corresponds to a predetermined portion of the discharging process, and is therefore related to the amount of charge.

Of the Invention is based on the object, a field emission display provide individual control of the low energy consumption Brightness of the pixels allows, wherein the brightness control exactly the respective signal sample for the Pixel should correspond.

Is solved this object by the specified in claim 1 and in claim 2 Characteristics.

at the field emission display according to the invention comes a constant current source (claim 1) or a contrast control device (Claim 2) for use. In both cases, during the discharge and holding circuit generates a pulse whose duration depends on the amount of charge in the sample and hold circuit depends. This impulse then becomes received by the field emission pixelator, so that the brightness of the relevant pixel is set depending on the pulse duration.

A Field emission display according to the invention preferably has a gray scale generator connected to a field emission pixelator (Picture element builder) works together. In operation, a one input signal having a certain amplitude is inputted to the display. The gray scale generator contains the sample and hold circuit and the discharge circuit for converting of the analog input signal into a certain height and width exhibiting Sawtooth. About that hangs out the width of the sawtooth signal from the amplitude of the analog signal.

structural seen, contains an emission display according to the invention a phosphor target and an integrated circuit formed on a substrate. The integrated circuit contains a gray scale generator and several addressable pixelators. Each pixelator contains a tip for the emission of electrons towards the target and a Addressing transistor. The output of the gray scale generator is applied to each addressing transistor to determine the duration and strength of the Emission to control which of the brightness for each pixel addressed (Pixels) corresponds.

preferred Embodiments of the invention are specified in the dependent claims.

in the Following are embodiments of Invention with reference to the drawing explained. It demonstrate:

1 a block diagram of a field emission display according to the invention;

2 and 3 Transfer functions of the gray scale generator according to the invention;

4 . 5 . 6 and 7 Block diagrams of gray scale generators according to the invention;

8th a schematic representation of a pixel driver 75 ;

9 the output characteristic of the in 8th shown pixel driver;

10 a block diagram of one in the 4 to 7 illustrated variable current source 100 ;

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

1 is a block diagram of a field emission display according to the invention. The field emission indicator 10 contains a phosphor target 40 and one on a substrate 20 trained integrated circuit. The integrated circuit includes an active array of field emitters, simply referred to hereafter as "pixelators" (pixel imagers, each of which emitters an emitter tip) 30 , an addressing transistor 15 and a resistance 21 contains. The emitter tip 30 is to the source 25 an addressing transistor 15 coupled. The drain 20 of the addressing transistor 15 is with the resistance 21 coupled, which in turn is grounded. In addition, there is a series between the source 25 and the emitter tip 30 an addressing switch 32 which selects a series of pixelators from the plurality of pixelators arranged in a row and column array.

The voltage from the emitter tip 30 to ground is high enough for emission from the emitter tip 30 , In one embodiment, the voltage is about 50 volts. However, it will be apparent to those skilled in the art that modification of the tip geometry allows emission at other voltages.

The emitter tip 30 is located in an approximately vacuum held grid 35 and a target 40 , grid 35 and Target 40 are biased so that the grid 35 a much lower voltage than the target 40 has. In one embodiment, the grid has 35 a voltage of 80 volts while the target 40 has a voltage of 1500 volts. However, it will be apparent to those skilled in the art that by appropriate variation of the geometry, these voltages can be varied without the operation of the field emission display 10 affect as long as the voltage of the grid 35 is much lower than the voltage of the target 40 ,

The voltage difference between the emitter tip 30 and both the grid 35 as well as the target 40 causes from the emitter tip 30 Electrons are emitted, passing through the grid 35 get through and the target 40 bomb. Because the target 40 has a phosphor background, becomes a picture element or pixel 12 of the target 40 , which is bombarded by the electron emission, illuminates. The field emissions show 10 lights up more or less bright depending on the number of electrons bombarding the background of the phosphor.

Assuming a direct relationship between the number of phosphor background bombarding electrons on the one hand and the illumination of the display on the other hand, the present invention uses an output width signal scheme as the input to the addressing transistor 15 , To achieve a brilliant and bright display, an analog signal is generated 45 with the help of a gray scale generator 55 in an output width signal 51 transformed.

The gray scale generator 55 receives an analog signal 45 to the brightness of an addressed pixel 12 set. When receiving an analog signal 45 which contains a red, green and / or blue signal, for example as a PAL signal or as an NTSC signal, the gray scale generator samples 55 the analog signal 45 with a predetermined frequency. The sampling takes place with the aid of a sampling circuit. The sampled sample of the analog signal 45 is held by a holding circuit which stores the sample until the next sample is scanned. The sample and hold functions are provided by a sample and hold circuit 65 perceived.

With the output of the sample and hold circuit 65 is a discharge circuit 70 coupled. The discharge circuit 70 is as shown with the sample and hold circuit 65 connected. However, coupling circuits known in the art may be used instead of the direct connection. The discharge circuit 70 provides a predetermined discharge current independent of the sensed voltage so that the discharge time is only of the amount of that provided by the latch circuit 65 stored charge depends. The discharge circuit 70 basically provides a means for discharging the output of the sample and hold circuit 65 Means for the discharge can be realized, for example, by a current source or a current mirror circuit. In the preferred embodiment, the discharge circuit includes 70 a changeable current source. In alternative and equivalent embodiments, other prior art current control circuits may replace the variable-compliant current source.

In one embodiment of the present invention is a pixel driver or buffer 75 with the discharge circuit 70 coupled. The output width signal 72 , which has the shape of a sawtooth, is in the driver 75 entered. The pixel driver 75 generates an output width signal 51 by giving the sawtooth signal 72 compares with a predetermined threshold. Thus sets the driver 75 the sawtooth width signal 72 into an output width signal 51 , reducing the width of the signal 72 the pulse width of the width signal 51 corresponds, as in 2 and 3 is shown.

2 and 3 show transfer functions of the gray scale generator according to the invention. The gray scale generator 55 forms a means for controlling the gray scale region and the brightness for the field emission display 10 , The grayscale range is defined here as an area between the smallest and largest latitude value of the output latitude signal.

That in the gray scale generator 55 input analog signal 45 is sampled at a predetermined frequency. The value of the sampled analog signal 45 is then converted to the output latitude signal 51 or 72 whose width directly corresponds to the sampled voltage. In 2 For example, at time t _1, first sampled voltage is V ₁ 5 volts, which corresponds to a larger width W ₁ in comparison to the width W ₂ represented by the second sampled voltage V ₂ at time t ₂ is formed with 4 volts as in 3 is shown.

In a first embodiment, the output width signal has a rectangular shape ( 51 ). In a second embodiment, the output latitude signal has a sawtooth shape ( 72 ). In the second embodiment, the output signals 72 in the 2 and 3 the same slope. In both the first and second embodiments, the output width signals 51 or 72 either begin at the same time and end at different times, depending on the required signal width, or they can begin at different times and end at the same time, again depending on the respective signal width.

In 4 is a first gray scale generator 55 represented according to the invention. A sampling circuit 85 receives the analog signal 45 , The sampling circuit 85 contains a field effect transistor with a channel 84 , where the signal 45 is fed into one end of the channel. However, those skilled in the art will appreciate that alternative or equivalent means for sampling are possible, including modified variants in which the sampling circuit 85 is replaced by known circuits. By coupling a control signal 86 to the gate, which is the field effect transistor channel 84 controls, the analog signal can be 45 with one of the periodicity of the control signal 86 to sample the corresponding frequency.

Between the sampling circuit 85 and ground is a holding circuit 90 which each of the samples voltages stored by the sampling circuit 85 to be delivered. The holding circuit 90 includes a capacitor which is charged with a predetermined time constant and discharged at a predetermined time constant from the sampled voltage. In alternative or equivalent embodiments, this holding circuit 90 be replaced by other known charge storage circuits.

In addition, the gray scale generator contains 55 a discharge circuit for discharging each sampled voltage. The discharge circuit includes two elements, namely a discharge start switch 98 and a constant current source 100 ,

The discharge start switch device 98 connected to the sampling circuit 85 at the field effect transistor channel 84 is coupled, allows and disables the coupling of the constant current source 100 with the rest of the circuit. In the preferred embodiment of the invention, the constant current source includes 100 a variable adjustable power source. The design of the device 98 with respect to the power source 100 is not particularly relevant to the circuit branch as a whole. In alternative and equivalent embodiments, other linear discharge circuits may replace the illustrated arrangement.

The discharge start signal 95 becomes the switching device 98 with the same periodicity as the control signal 86 supplied, but it has larger pulse widths than the signal 86 , Further, the discharge start signal becomes 95 after the signal 86 generated, so that the holding circuit 90 Charge to the sensed voltage before discharging. In the preferred embodiment, the time is between generation of the signal 86 and the generation of the signal 95 minimal.

In the preferred embodiment, the gray scale generator is 55 to each gate of each addressing transistor 15 connected to a column of pixelators. In this embodiment, the operating characteristics of the addressing transistors 15 including the threshold voltage V _T is set so that a sawtooth input is compensated as opposed to a pulse input.

In another embodiment of the present invention, the pixel driver is 75 between the field effect transistor channel 84 and the ad 10 connected. The operation of the pixel driver 75 became in connection with 1 discussed. As a result, the output width signal becomes 51 from the gray scale generator 55 in the advertising 10 delivered in a rectangular shape.

In 5 is a second gray scale generator 56 represented according to the invention. He is similar to the gray scale generator 55 , wherein similar and like parts are given corresponding reference numerals.

Between the first field effect transistor channel 84 and ground there is a parasitic capacitance 87 that the ad 10 and the associated circuitry is inherent. The parasitic capacity 87 assumes a function equivalent to that of the hold circuit 90 to 4 , The parasitic capacity 87 stores each of the sampling circuitry 85 sampled voltages and discharges at the correct time each stored scanning voltage. As a result, the output latitude signal becomes 72 from the gray scale generator 56 delivered on the display in the form of a sawtooth.

6 shows a third and preferred gray scale generator 57 according to the invention. He is the gray scale generator 55 and 56 similar and provided with corresponding reference numerals. In this embodiment, the output width signal becomes 72 from the gray scale generator 57 in the advertising 10 gelled in the form of a sawtooth.

In 7 is a fourth gray scale generator 58 represented the invention. He is similar to the gray scale generators 55 . 56 and 57 provided with corresponding reference numerals.

8th and 9 show a first embodiment of the pixel driver 75 , The driver 75 contains two cascaded complementary metal oxide (CMOS) negators 92 and 94 , When receiving the wide signal 72 with the sawtooth shape, the negator generates 72 an inverted output signal P having an associated time constant, as in 9 is shown. Subsequently, the negator generates 94 a again inverted output signal C with a corresponding time constant. Regarding the driver 75 For example, an input voltage threshold defines a trip point for each inverter after which the inverted output signal changes state.

10 is a block diagram of a variable replaceable power source 100 , The power source 100 contains a contrast control device 110 , which provides a control signal, and which contains a power source 120 , The device for contrast control 110 is so to the power source 120 coupled, that the control signal, the amplitude of the current through the source 120 flow of electricity. The gray scale range is defined as a range between the minimum value and the maximum value of the width of the output latitude signal. A device for contrast control 110 expands or contracts the gray scale area of the field emission display by setting the tuned electricity from the power source 120 ; this has in one embodiment, a voltage-controlled resistor. In alternative and equivalent embodiments, the voltage controlled resistor is replaced by known switched or linearly controlled current source circuits.

11 Fig. 10 is a block diagram of a control circuit for controlling the pulse height for the ambient light compensation. The control circuit 175 is in series between the discharge circuit 70 and the addressing transistor 15 , In a first embodiment, the control circuit receives 175 the sawtooth signal 72 , In an alternative embodiment, the control circuit receives 175 the output latitude signal 51 , In an alternative embodiment, the control circuit 175 instead of or in series with the pixel driver 75 connected.

The control circuit 175 contains an operational amplifier 78 , a gain adjustment resistor 83 and a photosensitive transistor 82 , The transistor 82 works as ambient light sensor. In conjunction with the variable gain amplifier ( 78 . 83 ) forms the transistor 82 a controller for controlling the amplitude of the output width signal. In operation, the controller provides a control signal 150 to increase the amplitude of the output width signal during high light levels. The amplitude change compensates for ambient light in the vicinity of the field emission display. To facilitate this compensation, the sensor formed on the IC substrate speaks 82 on ambient light by looking at the gain of the amplifier 78 increased or decreased so that the amplitude of the signal 151 depends on the strength of the ambient light.

Claims (7)

Field emission display ( 10 ) with a plurality of pixels ( 12 ), whereby the field emission indication is based on a signal ( 45 ) to adjust the brightness of each pixel ( 12 ) during a time in which the respective pixel ( 12 ), comprising the following features: a) a sample and hold circuit ( 65 ), which is a sample of the signal ( 45 ) at a time which corresponds to the addressing of the respective pixel ( 12 ), and holds a charge whose amount depends on the sampled signal value; b) a discharge circuit ( 70 ) connected to the sample and hold circuit ( 65 ) and connected via a constant current source ( 100 ) has a constant amount discharge current from the sample and hold circuit ( 65 ) pulls to a pulse ( 72 . 51 . 151 ) during a discharge time of the sample and hold circuit ( 65 ) whose duration of the charge quantity in the sample and hold circuit ( 65 ) corresponds; and c) a field emission pixelator ( 35 . 30 . 32 . 15 . 21 ) to brighten each pixel ( 12 ), each field emission pixelator ( 35 . 30 . 32 . 15 . 21 ) an emitter tip ( 30 ) having the pulse ( 72 . 51 . 151 ), so that the brightness of the pixel ( 12 ) is adjusted in response to the duration of the pulse. Field emission display ( 10 ) with a plurality of pixels ( 12 ), whereby the field emission indication is based on a signal ( 45 ) to adjust the brightness of each pixel ( 12 ) during a time in which the respective pixel ( 12 ), comprising the following features: a) a sample and hold circuit ( 65 ), which is a sample of the signal ( 45 ) at a time which corresponds to the addressing of the respective pixel ( 12 ), and holds a charge whose amount depends on the sampled signal value; b) a contrast control device ( 110 ), which is a control signal ( 115 ) supplies; c) a discharge circuit ( 70 ) connected to the sample and hold circuit ( 65 ), wherein the discharge circuit ( 70 ) a discharge current from the sample and hold circuit ( 65 ) whose strength depends on the control signal ( 115 ), so that the discharge circuit ( 70 ) a pulse ( 70 . 51 . 151 ) during a discharge time of the sample and hold circuit ( 65 ) is generated such that the duration of the pulse of the amount of charge in the sample and hold circuit ( 65 ) depends; and d) a field emission pixelator ( 35 . 30 . 32 . 15 . 21 ) to brighten each pixel ( 12 ), each field emission pixelator ( 35 . 30 . 32 . 15 . 21 ) an emitter tip ( 30 ) having the pulse ( 72 . 51 . 151 ), so that the brightness of the pixel ( 12 ) is adjusted in response to the duration of the pulse. Field emission display according to claim 1 or 2, characterized in that each field emission pixelator ( 35 . 30 . 32 . 15 . 21 ) for address or column addressing an addressing transistor ( 15 ) connected in series with the emitter tip ( 30 ) and via which the emitter tip receives the pulse, and one in series with the addressing transistor ( 15 ) addressing switch ( 32 ) for selectively releasing the emission by the field emission pixelator. Field emission display according to claim 1, 2 or 3, characterized in that the field emission display comprises a gray scale generator ( 55 . 56 . 57 . 58 ) detected by the sample and hold circuit ( 65 ) and the discharge circuit ( 70 ) is formed. Field emission display according to claim 1, 2, 3 or 4, characterized in that a) the discharge circuit ( 70 ) a sawtooth ( 72 ), whose width depends on the strength of the charge, and b) the gray scale generator ( 55 . 58 ) a driver ( 75 . 175 ) connected in series between the discharge circuit ( 70 ) and the transistor ( 15 ), the driver providing the pulse such that the duration depends on the width of the sawtooth. Field emission display according to one of the preceding claims, characterized in that a) the pulse ( 51 . 151 ) has a pulse height, b) the transistor ( 15 ) is responsive to the pulse height to increase the brightness of the pixel ( 12 ); and c) the field emission display (1) comprises a photosensitive component ( 82 ) to form a second control signal ( 150 ) for ambient light compensation; and (2) one in series between the discharge circuit ( 70 ) and the transistor ( 15 ) connected control circuit for controlling the pulse height in response to the second control signal ( 150 ) having. Field emission display according to claim 6, characterized in that a) the sample and hold circuit ( 65 ), the discharge circuit ( 70 ) and the field emission pixelator ( 35 . 30 . 32 . 15 . 21 ) are formed together on a substrate; and b) the sample and hold circuit has a self-capacitance ( 87 ) to hold virtually the entire load.