Apparatus and drive method for display light source

Abstract

A display device comprising a backlight and a light valve array, such as an array of liquid crystal (LC) cells, and a method for operating such display device are provided. The display and the method operate to reduce the intensity of the light source of the backlight during the period when the light valve (LC cell) is in the transition from a dark state to a bright state, and to increase the intensity during the period when the light valve (LC cell) is near or mostly completing its transition. As light transmission is ineffective in the dark or transitional state of the light valve, lighting power efficiency is improved by delivering the light mostly in the final state of the light valve.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority of U.S. Provisional Patent Application No. 61/176,887, filed on May 9, 2009, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image display apparatus and a drive method to operate the display apparatus. The display apparatus comprises a light source and a light modulator that modulates the light from the light source to produce images. The display apparatus further comprises a control means for operating the light source and the light modulator. The control means operates the light source and the light modulator in coordination, and in such a manner that reduces the power of the light source during the transition of the light valves from a dark state to a bright state and increases the light power when the light valves are approaching the final state of the transition, thereby saving the lighting power. Furthermore, the light source comprises light emitting elements with response time substantially faster than the relaxation time of the light modulator, and is operated in such a manner that eliminates the adverse effects from switching the light modulator.

2. Description of the Prior Art

A liquid crystal (LC) cell is a light valve that modulates light directed thereto. A liquid crystal display (LCD) produces images by modulating light with a plurality of spatially distributed liquid crystal cells. As in other light valves such as MEMS, such modulation controls the amount of light delivered to the viewer.

Using the LC display (LCD) as an example, the images are displayed by setting the liquid crystal cells to various gray levels according to the spatial distribution of the brightness and color in the images. Each cell represents a spatial and color point in the image. Accordingly, in displaying motion pictures, the LC cells are set in such a manner that the light directed thereto is modulated to replicate the temporal and spatial image in brightness and color.

A light valve changes states in response to a setting voltage by re-arranging its structure according to the applied voltage. For example, an LC cell changes its molecular alignment according to the applied voltage. Such change of state requires a period of time to settle to the final state. During the transition, the cell does not provide the full optical property as defined by the final state. Accordingly, when an LC cell is reset to a bright state from a dark state, the cell remains dark or partially dark until the later stage of the transition. Consequently, if the light intensity is kept constantly high, the light and the lighting power is not utilized efficiently as the cell is inhibiting the light transmission in a significant portion of time.

In a situation when an LC cell is set to a dark state from a bright state, the optical transmission of the cell remains high at the early stage of the transition from the initial state to the final state. Accordingly, the light continues to be transmitted in a cell where the cell is set dark. Therefore, extra light is light is consumed.

In the conventional display, the illuminating light is not reduced when a light valve (such as an LC cell) is in the transition from a dark state to a bright or in the opposite direction. The present invention provides a display apparatus and method to reduce the consumption of unnecessary lighting power during the period that a light valve, such as an LC cell, is in the transition and only partially performing the optical property of a designated state. Lighting power is provided when the light valve has substantially conformed to the optical property of the designated state.

In this specification, a preferred embodiment of the light valve is a liquid crystal (LC) cell for the purpose of illustration.

SUMMARY OF THE INVENTION

The present invention provides a display apparatus comprising a light source and a plurality of light valves, wherein the response time of the light source is faster than the response of the light valves. A preferred embodiment of such light source is a plurality of light emitting diodes (LED). A preferred embodiment of the light valves is an array of liquid crystal (LC) cells. The light source may comprise multiple lighting elements wherein each lighting element may be switched independently. The light source may also be constructed in a way that the lighting elements are arranged in groups, where all elements in one group is switched on and off together. The display device displays images according to input image signals. The present invention further comprises a control device controlling the output light intensity of the light source and the transmission of the LC cells in synchronism.

In a preferred embodiment of the present invention, the display apparatus is operated in a manner that in refreshing the image data of a light valve, the lighting elements illuminating said light valve are set to provide light output in a fraction of the refreshing cycle and after a delay period. A preferred embodiment of the delay period is a significant fraction of the response time of the light valve. A 5 percent or more of the response time is a significant fraction.

The present invention provides a method for operating the display apparatus in a manner that the light is turned on or increased following a delay period after setting the image data to a light valve illuminated by the light source.

The present invention further provides a display apparatus and a method for operating the apparatus wherein the method of operation comprises setting the illuminating light to dark prior to setting the light valve to represent an image point, a delay period following said setting of the light valve, and setting said illuminating light to a bright level after the delay period.

The present invention further comprises the apparatus and method of operation to operate the apparatus according to the previous paragraph wherein the operation further comprises setting the illuminating light to a dark level, and an operation of setting the light valve to a relaxed state; wherein in a preferred embodiment the relaxed state corresponds to a bright state of the light valve.

In a preferred embodiment, the LC cells are constructed in an orientation that the relaxed state corresponds to the bright state that allows the highest degree of transmission of light to the viewing side.

Furthermore, the present invention provides a display apparatus with LC cells operated in a manner that a cell of the display is first set to a relaxed state, thereafter set to the state to replicate the image. In an operation of setting a LC cell to the relaxed state, a control signal enabling the writing of data is applied to a group of cells for receiving the input data; such enabling operation may be performed by applying a select signal to the scan electrode connected to the cells thereby turning on a transistor in a pixel circuit that connects to the data electrode. In an alternative embodiment, said group of LC comprises the entire cells of the display.

In coordination with setting the LC cells to the relaxed state, the light source illuminating such cells is operated in synchronous with the dynamic change of state of the cells so that the illumination is reduced (dark) when the cells are in the transition from a dark state to a bright level, or during the operation of setting a group of cells to the relaxed state. The duration of this light-extinguishing period is a fraction of a frame time which is the time for refreshing (updating data for) a full image frame. The operation time for applying the control signals for setting the cells to the relaxed state is approximately the same as that of addressing image data to a single display line. A preferred embodiment is to group the display lines in such a manner that all lines in a group are set to the relaxed state simultaneously. Accordingly, the added operation time for setting to the relaxed state is less than a small fraction of a frame time As the illumination is turned off for the cells being set to the relaxed state or in the transition from a dark to a bright level, the change of state of the LC cells that deviates from the image is not visible and does not produce any disturbing artifact. Accordingly, power efficiency is improved, and a longer time may be allowed for the cell to approach and settle to the relaxed state without introducing adverse effect to image quality.

The present invention further provides an apparatus comprising LC cells and LED elements, and an operation method thereof to set the LC cells to replicate the input image after setting the LC cells to the relaxed state. The LED light source is then turned on to provide distributed illumination as defined by the input image signal.

The present invention provides a display apparatus comprising LC cells and an operation method thereof wherein the illuminating light is reduced during setting the LC cells, and when the LC cell is pre-set to a relaxed state. Accordingly, since the illumination light source is extinguished when the LC cells are in the transition, the leak of light during the transition of cell is eliminated, thereby improving the contrast ratio and eliminating flicker.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1a, 1 b, and 1c are illustrations of a LC cell response in a conventional LC display.

FIGS. 2a, 2b and 2c are schematic diagrams of a preferred embodiment of the present invention.

FIG. 2d is a schematic diagram of a preferred embodiment of the present invention.

FIG. 3 is a schematic diagram of a preferred embodiment of the present invention.

FIG. 4 is a schematic diagram of a preferred embodiment of the present invention.

FIG. 5 is a schematic diagram of a preferred operation of the present invention.

FIG. 6 is schematic diagram of a preferred embodiment of the present invention.

FIG. 7 is a schematic diagram of a preferred embodiment of the present invention.

FIGS. 8a, 8b, 8c are schematic diagrams illustrating a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A light valve is a device that modulates the light directed thereto according to a control signal. Examples of light valve include passive and active liquid crystal cell, and MEMS cell. For the purpose of illustration, the liquid crystal (LC) cell is used as the preferred embodiment for the light valve hereinafter in this description.

A typical LC cell comprises at least two electrodes where a voltage is applied to set the state of the LC cell. The state of the LC cell is determined by the arrangement of LC molecules in combination with other optical components such as the polarizer films integrated as part of the LC cell. The applied voltage sets the optical transmission of the LC cell via changing the alignment of the LC molecules.

Accordingly, in operating a liquid crystal (LC) cell, a voltage is applied to an LC cell on the two electrodes where the liquid crystal is filled between the two electrodes. The LC is switched between the relaxed state and an energized (i.e., charged) state by the applied voltage across the two electrodes, and may be set to any state between the fully relaxed state and the fully charged state according to the applied voltage. In a fully relaxed LC state, the control voltage, as well as the electrical field between the electrodes, is nearly zero and the LC material is relaxed and aligned to the boundary surfaces mostly according to its internal molecular forces, with little or no influence from the externally applied electrical force. In a charged state of an LC cell, an applied voltage and its associated electrical field causes the LC material to have preferential alignment in the direction of the electrical field according to the strength of the electrical field, thereby changing the optical property of the LC cell. Accordingly, different degree of light modulation by an LC cell is effectuated by the applied voltage, thereby modulating the amount of passing light.

A control signal, typically an applied voltage, causes a light valve to change from its current state to a final state. The response time is the measure of time for the light valve to substantially complete such change of state in response to an applied voltage. For example, in a common practice, the time for completing 90 percent of the transition of such change of state is considered as the response time.

In this specification, a significant fraction of a response time (T3) refers to a substantially measurable fraction of T3. In practice, a 5% or more of the response time is a significant fraction in this specification. As described in subsequent paragraphs, a longer delay produces more significant effect in reducing the power consumption.

In this description, a light modulator is a device that modulates the light directed thereto from a light source, according to a control signal. A light modulator may be a single cell or comprises a plurality of cells, wherein each said cell operates to modulate the light directed thereto according to a control signal. A preferred embodiment of a light modulator comprises light valves or optical components that modify the direction, intensity, or both of the light directed thereto. The liquid crystal display (LCD) array is the preferred embodiment hereinafter for the purpose of illustration in this description.

The alignment of LC molecules and the optical properties of an LC cell are influenced by the electrical field induced by an applied voltage. In the absence of an applied voltage and the associated electrical field, the LC orientation is mostly aligned according to the structures on the surface surrounding the LC cell. In operating an LC cell in a display device, the control signal (typically a voltage for LC cell) and the voltage applied on the LC electrodes change with time according to input image signal. An increasing control voltage causes more charge accumulation on the LC cell and a stronger electrical field, and a decreasing control voltage causes discharging and lowering electrical field. In a preferred embodiment, a stronger electrical field causes the LC to align more preferentially along the direction of the electrical field, and a decreasing electrical field allows the LC to relax more towards its alignment with surface structures. Accordingly, the increase in magnitude of the applied voltage relates to a charging or energizing process, and decrease of voltage relates to the relaxation of the LC.

The response of an LC cell (and other light valves) is substantially slower in relaxation than in energizing. For example, a liquid crystal (LC) cell responds to a zero voltage that sets the cell to a charge neutral state (relaxed state) in about 10 to 30 millisecond; same LC cell responds to a voltage that energizes (or charges) the cell in about 5 milliseconds or less.

During the transition from the initial state to the final state of the LC cell, the optical property of the LC cell changes with the time. For example, for a control signal that sets an initially dark LC cell to a bright state, the LC cell switches from dark to bright in a time frame close to the response time. Accordingly, in the early stage after applying such control signal, this LC cell remains mostly in a state of low optical transmission and the light utilization is ineffective. Consequently, the lighting power is mostly wasted during the transition of an LC cell from a dark state to a bright state.

Preferred embodiments of the present invention are herein described using light emitting diodes (LED) as light source, and liquid crystal display (LCD) cells as illustration. Examples of constructing a display apparatus comprising array of LCD cells and LED light source are found in U.S. patent application Ser. No. 11/754,268 and U.S. Pat. No. 5,408,109, and examples of using organic light emitting diode to form active matrix display devices are found in U.S. Pat. No. 5,684,365, U.S. Pat. No. 6,157,356, and U.S. Provisional Patent Application No. 61/176,887, all of which are hereby incorporated by reference.

A preferred embodiment of the present invention uses an illuminating light source that switches in a fractional time of that of switching the LC cells. An example of such preferred embodiment is using LED as the light source and LCD cells as the light valves. The LED response time (T2) is on the order of 200 micro seconds, and the typical LC response time (T1) is a few milliseconds.

FIGS. 1a-1c illustrate a typical transition of the optical transmission of a preferred embodiment of the LC cell in response to an abrupt increase of the voltage applied to the electrodes of the LC cell. In this preferred embodiment, an applied voltage higher in magnitude (i.e., stronger electrical field) results in a lower optical transmission, and the bright LC state corresponds to V=0. FIG. 1a provides the change of applied control voltage with time. An abrupt voltage change from V0 to V1 occurs at the time t0. FIG. 1b illustrates the change of optical transmission of the LC cell after the voltage change. The initial state of the LC cell has an optical transmission indicated by 110. The optical transmission increases with time after the voltage change at t0, and approaches its final optical transmission 111 with increasing time. The final equilibrium state 111 may take a substantially long time to reach. In practice, a preferred definition of the response time is taken as the time to reach 90 percent of the total transition, i.e. the level 112 at t1. The difference between 111 and 112 is 10 percent of the total change of optical transmission from 110 to 111. A preferred definition of the response time is T3=t1−t0.

In a conventional display system, the light source remains on during the period when the light valve (LC cell) is changing from a dark state to a bright state, i.e., between t0 and t1. As illustrated in FIG. 1c, the light source remains at an intensity level of 102 in the time between t0 and t1. Since the LC cell remains in a state of low optical transmission in this time, the light transmission is inhibited and does not produce any desired lighting effect for the image. The lighting energy indicated by the area 103 is consumed without producing useful effect. Consequently, the utilization of the light is not effective, and the lighting power is wasted.

In a display system where the LC cells are set to a dark state each time when an image is refreshed, the LC cells are driven from a dark state to a brighter state each time the image is refreshed. As described above, significant lighting power in such system is consumed while LC cells are in the dark states, resulting in low brightness and low power efficiency. An example of such system is a display system using the overdrive scheme and with an intermediate black frame.

The present invention provides an apparatus comprising a light source and a light valve such as an LC cell, and a method for operating such display system. According to this method, the lighting power is kept low or off during the period when the LC cell is in the transition from an initial state to a final state. The lighting power is turned on or increased when the LC cell is near the completion or in the late stage of the transition after setting the LC state. FIG. 2 provides an illustration of a preferred embodiment of the present invention. As in FIG. 2a, at t0 a control signal is applied to an LC cell to set the LC cell to a state according to the applied signal V1. An example of the control signal is the data signal of image data refreshing that sets each of the LC cells to a state according to the image data. The response of the LC cell is illustrated in FIG. 2b. A preferred embodiment for setting the light intensity is provided in FIG. 2c, wherein the light intensity is set to low or off between t0 and t1, and the light intensity is set to bright at t1 and maintain to be bright for a period after t1. A delay period T=t1−t0 is provided between setting the LC cell at t0 and setting the light intensity to bright at t1.

A schematic drawing of a preferred embodiment of the apparatus for the operation described above is provided in FIG. 4. FIG. 4 is a side view of a display panel, wherein 403 is an illuminating light source such as an LED, 405 is a group of a plurality of LC cells (light valves), and 404 is an LC cell illuminated by the light source 403. In an example where the LC cells are arranged in rows and columns, 404 represents a row of LC cells, and 405 represents a section of the LC rows. In a preferred embodiment, the light source comprises a plurality of lighting element as illustrated by 401 in FIG. 4, and the light valves (LC cells) 402 comprise a plurality of groups of 405. The data electrodes are connected to the plurality of LC cells, such as the column electrodes in a typical LC display array, and the control circuit comprises circuit controlling the LC cells image data setting and circuit for setting the intensity of LED 403.

Accordingly, the present invention provides an apparatus comprising a light source; a plurality of light valves modulating light output from said light source; a data electrode for applying data voltages to said light valves; a control circuit performing recurring operations on said light emitting elements and said light valves; said operations comprising:

3) applying image signal to a light valve according to the image data for displaying image;

4a) a delay period after operation 3);

4b) after said delay period, applying the control signal that sets at least a light emitting element that illuminates said light valve of 3) to a bright state;

wherein the response time of the light valve in response to said operation 3) is T3;

Said delay period is a significant fraction of T3 or at least one-twentieth of T3. Since the light power is not used effectively when the LC is in the transition, a longer delay time, i.e., a larger fraction of the response time when the situation allows, is a preferred embodiment of the present invention.

In a preferred embodiment, the light valves are LC cells.

In a preferred embodiment, applying the image data to set the LC cells and applying signals to set the LED intensity operate in coordination in a group-by-group or section-by-section manner. In a preferred embodiment where the LC cells are in rows and columns, a group of LC cells correspond to a section of rows of LC cells. Such a section of rows of LC cells is represented by 405 in FIG. 4 where the drawing shows a side view of a display panel. In a first period, the image data are applied (i.e., addressed) to the LC cells row by row sequentially in the section. After the completion of the addressing of said section, and after a delay period, a control signal is applied to the LED to turn on the LED light to illuminate the section of the LC cells. Such operation proceeds section by section and scans through the whole display panel. In another embodiment, the section by section operation is controlled in a manner that the addressing the image proceeds line by line continuously, and the LED lighting element are turned on after the full section of LC cells under its illumination has completed the image data setting.

FIG. 2d further provides a preferred embodiment of the operation of the present invention wherein the light intensity is set to a level 206 which is substantially higher than the average intensity 102, and is operated in a short duration T4 substantially shorter than the time for displaying one image frame. An example of the preferred embodiment is to set the light intensity 206 to 3 times or higher than the average intensity 102 in a duration of ⅕ of a frame time. For example, in a display system where the image is refreshed at 120 frames per second, each frame is displayed for a duration of 1/120 second or ˜8.3 milliseconds. The operation of the short duration pulse of high intensity illumination may be performed to set the intensity at 3 times higher than the light level of 102 in 1.7 ms in the later stage of a frame period when the LC transition is near its completion.

FIG. 3 provides a preferred embodiment of the operation sequence of the present invention, wherein 312 is the time period during which an operation is performed to apply image signal to a light valve 404 (in FIG. 4) according to the image data for the image point at the location of 404 for displaying the image, and a delay period 314 after the operation 312 is provided; and wherein, after said delay period 314, in the time period 317, an operation is performed to apply the control signal that sets at least a light emitting element 403 that illuminates said light valve 404 to a bright state.

The efficiency of light power may also be improved by reducing the light intensity in a gradual manner during the period when an LC cell is in the transition. FIG. 5 illustrates a preferred embodiment of the operation wherein the light intensity is reduced at or slightly before applying the control signal at t0 to set the LC cell state. The light intensity is increased at the time t4 in a later stage of the LC transition after setting the LC state at t0. In this operation, the signals controlling the light intensity does not have to be an abrupt change. Either a gradual change or an abrupt change will operate to achieve the improvement of lighting power efficiency.

The present invention further provides a display apparatus according to the previous paragraphs wherein in said operation 4b), said control circuit applies the control signals for setting said light emitting element to a brightness level according to a scaled brightness level. In a preferred embodiment, said scaled brightness level relates to the average or maximum image brightness in the area illuminated by said light emitting element with a scaling relation. In a preferred embodiment, the scaling relation is an increasing function with increasing average or maximum image brightness in said area in at least part of the gray scale range (i.e., part of the range from full dark 0 to full bright 255.) For example, such a scaling relation applies in the range from gray level 100 to gray level 200. In another preferred embodiment, said scaled brightness is in proportion to the average or maximum image brightness in the area illuminated by said light emitting element. The proportionality need not to be linearly proportional.

The present invention further provides a drive method to operate a display apparatus comprising an illuminating light source and a plurality of light valves modulating light from said light source in a manner that before addressing or refreshing the light valves with new image data, the light valves are set to a charged or over-charged state. The present invention further provides a circuit as the control circuit to perform such operations. Such control circuit operates to deliver a voltage to charge the light valve (LC cell) according to a timing sequence.

The present invention further provides a display apparatus and the operation method according to FIG. 3 and the previous description of paragraph 52, wherein the method further comprises an operation of 5) applying a control signal for setting an LC cell to a charged or over-charged state prior to setting the cell to display image data. FIG. 6 provides a schematic drawing of a preferred embodiment of the operation of the display apparatus, wherein 610 indicates the time period of the operation 5) applying a control signal for setting an LC cell to a charged or over-charged state prior to setting the cell to display image data. The operation 610 precedes operation 312 which corresponds to operation 3) applying image signal to a light valve according to the image data for displaying image. In a preferred embodiment of the LC cell, the charged or over-charged state corresponds to a dark state. For an LC cell, this corresponds to low or no optical transmission for the LC cell.

The present invention further provides a drive method to operate a display apparatus comprising an illuminating light source and a plurality of light valves modulating light from said light source in a manner that before addressing or refreshing the light valves with new image data, the light source is set to a dimming state and the light valves are set to a discharged state. The present invention further provides a circuit as the control circuit to perform such operations.

Accordingly, the present invention further comprises 1) setting a light emitting element to off or a dimming state. An illustration of the operation is provided in FIG. 7 wherein 711 indicates the operation timing for operation 1). A dimming state of a light source corresponds to a light source setting where the light output is near the minimum of the dynamic range of the light output in an operation. For example, a setting to turn an LED off may set the LED to the lowest light level of its operation range where the light output is nearly, but not completely, extinguished. A dimming state in such example represents a setting near the lowest lighting level of the LED.

Furthermore, the present invention further comprises an operation 2) applying a control signal for setting a light valve illuminated by said light emitting element of the previous paragraph to a relaxed state; wherein in an operation cycle, said operation 1) precedes, or overlaps said operation 2). In another preferred embodiment, said operation 2) may lead said operation 1) by a small fraction of the response time. A preferred embodiment of a small fraction of T1 is less than 30% of T1. Since the light valve responds slower than the lighting element in the present invention, the light valve has not changed substantially in the time within a small fraction of the response time. Therefore, the light transmission has not changed substantially in such period. A preferred embodiment of operation 2) is illustrated in FIG. 7 wherein 710 indicates the operation timing of operation 2).

FIG. 8a provides a schematic drawing of the 3-dimensional illustration of a preferred embodiment of a display apparatus of the present invention, wherein the apparatus comprises an array of LC cells 820, and the light source 821 illuminating the LCD array 820. The arrangement of the light source may be a single lighting element, one or more planner light sources, one or more lighting tubes, or an array of lighting elements such as LEDs shown as 822 in FIG. 8b. Preferred embodiment of a planar light source includes a light diffuser or a luminescent layer coupled with a light source. It is construed that the present invention is not limited by the type, shape, or the arrangement of the light source and lighting elements.

FIG. 8c provides a schematic drawing of the circuit diagram of a preferred embodiment of present invention, wherein the scan driver circuits 832 provides multiple scanning signals for the selection of cells in the LCD array 831 to receive data, the data driver 833 delivers image data to LCD array 831, LED driver circuit 836 provides drive current to the LED light source 835, and the control circuit 837 operates to process image data and provide synchronized control signals to the LCD and LED drivers. In one preferred embodiment, the LED driver 836 is constructed to have drivers distributed in the LED array wherein each driver output control an LED or a set of LED in series. Register or memory may also be integrated in the driver to maintain a drive current for a prolonged period of time. In another preferred embodiment, the LED driver 836 is constructed in rows and columns, to address the LED array with drive signals, wherein, each element of LED array is connected to a local driver circuit that responds to the drive signal and sets the LED driver current. In response to the control signals generated by the controller 837, the LED driver 836 increases or decrease drive current to the LED, thereby increasing or decreasing the light output of the LED lighting elements. In response to the controller signals for the LCD array, the LCD driver 832 selects the LCD cells to receive the data input, thereby increasing or decreasing the light transmission of the selected LCD cells according to the data signals.

A preferred scan driver 832 comprises a plurality of outputs. The cells of LCD array 831 are arranged in scan groups wherein all cells in one scan group are connected to the same output terminal of the scan driver 832, and are selected simultaneously to receive the data. A preferred scan group is a row of cells in the array. Without limiting the generality of a scan group, in the following description, a row indicates a scan group that is connected to the full set of data driver outputs. Therefore, different rows of cells must be selected at different time for receiving different image data of their own. For this reason, a scan (or row) driver used in a conventional LCD display operates to select one scan group (or one row) at a time, and operates sequentially.

In a preferred embodiment of the present invention, the driver circuit 832 further incorporates a function that operates to select a plurality of rows of the LCD cell array simultaneously by a control signal. The driver circuit 832 in another embodiment of the present invention further incorporates a function that operates to select all rows of the LCD cell array simultaneously. In yet another preferred embodiment of the present invention, the scan driver incorporates a function to set all the selected rows of cells simultaneously to a state that corresponds to a relaxed state of the LC cell. The driver circuit 832 may be a single integrate circuit (IC) that has sufficient output terminals to connect to and control the LCD rows as described, or an assembly of multiple driver ICs each one having the full function as described above and operating on the LCD lines connected to its output terminals independently according to its control signal.

In the present invention, the control circuit 837 provides a synchronized timing control to drive the LED 835 and LCD 831. FIG. 3 provides a timing diagram of a preferred embodiment of the synchronized drive of LED and LCD. The time axis indicates the direction of the time.

A preferred embodiment of the control means is a control circuit comprising a programmed integrated circuit (IC) or a plurality of integrated circuit elements. The program comprises executable instructions to perform the operations provided in this invention. Such control circuit is typically assembled on a printed circuit board.

A preferred embodiment of the LCD display is structured so that the relaxed state of the LCD cells corresponds to a bright state. In a relaxed state, the electrical field between the two electrodes is nearly zero, and the LC is aligned to the surfaces according to the molecular forces and the surface structures. A preferred embodiment is structured so that the directions of LC alignment at the light entering surface (i.e., the back side of the LC cell) and at the light exiting surface (the front side of the LC cell) are different by an angle; the orientations of the polarizer at the entering surface and the orientation of the polarizer at the existing surface are different by a similar angle. Accordingly, highest amount of light passes from the back side to the viewing side when LC is in the relaxed state. Furthermore, the transition of the LC material from a relaxed state to a charged (i.e., energized) state is substantially faster than the transition in the opposite direction. In such typical embodiment, a relaxed state of LC cell corresponds to the bright state. The description herein illustrates the present invention using such embodiment. Furthermore, in a preferred embodiment of the LC cell, the charged state corresponds to a dark state.

Since the lighting element is turned off or dimmed during the delay period, the duration of light output is shortened. Accordingly, the light intensity is increased during the lighting period. A preferred embodiment here is to set a substantially higher light intensity during the lighting period than in the situation of the constant light source. An example of the preferred embodiment is to set the light intensity in reverse proportion to the duration during which the light source is turned on.

As described herein above, the operation of the display device may continue in a subsequent cycle for another input image data, which may be different from the previous input image data or repeating the same data, with all the operations and variations described above included or partially included in such subsequent operation cycle.

In a preferred embodiment, the operations or parts of the operations are programmed into an integrated circuit (IC). Such IC comprises the circuit for performing such operations and may also include circuits for peripheral operations such as input and output, and image processing. The control circuit comprises said integrated circuit and is typically fabricated on a printed circuit board with other circuitry, or completely integrated in one IC. In further detail, such control circuit comprises at least a timing management or generating circuitry and control signal circuitry to provide clock and control signals to operate the light emitting element and the LC cells according to the sequences described herein above. Such circuit may be constructed by programming a logic array, or by designing or converting to an application specific IC.

Furthermore, the present invention comprises a control circuit comprising scan driver circuit to enable the selection of all LCD lines in a group, as illustrated by area 405 of FIG. 4. A scan driver is so constructed and assembled with the display apparatus to operate to select all lines corresponding to the cells in area 405. Furthermore, a data driver is constructed and assembled in the display to deliver a data signal synchronously with the scan driver to set all data lines to a voltage state corresponding to the charged state, or the relaxed state of the LC cells, according to the operations.

A typical liquid crystal display comprises scan electrodes for selection and data electrodes for delivering image data to the LC cells. Each LC cell comprises a thin-film transistor (TFT) having a gate terminal and a data terminal (drain terminal of the TFT). A plurality of LC cells, typically a row of LC cells, are connected via the gate terminals to a scan electrode. Applying a SELECT signal on a scan electrode selects all cells connected thereto to receive image data from the data electrode.

The present invention further provides a control circuit comprising the scan driver described above, and a data driver circuit for delivering image data to its data output terminals according to the input image signal; wherein during said discharging operation, output terminals of said data driver are set to a discharge voltage according to a control signal.

A control circuit is provided in the present invention that operates a recurring function comprising:

3) applying image signal to a light valve according to the image data for displaying image;

4a) a delay period after operation 3);

4b) after said delay period, applying the control signal that sets at least a light emitting element that illuminates said light valve of 3) to a bright state.

A preferred embodiment of the control circuit of the previous paragraph comprises a scan driver circuit, a data driver circuit, and a lighting control circuit, wherein the circuits operate to

a) setting image data at the output terminals of the data driver circuit according to the input image data;

b) enabling a scan driver terminal that select a group of LC cells connected to said scan driver terminal to receive the image data;

c) allowing a delay period;

d) applying a signal via the lighting control circuit to set the light intensity to a light level according to the image.

The present invention further provides the control circuit of the previous paragraph further comprising an operation of 5) setting a group of LC cells to charged or over-charged state. A preferred embodiment of such operation in the control circuit is a circuit function of setting the data driver output terminals to a charging voltage corresponding to said charged state, and enabling a scan output terminal or a section of scan driver output terminals to select a subset of LC cells that corresponds to a row or a section of rows to receive the charging voltage.

The present invention further provides a control circuit according to the previous paragraph further operating a function of setting an LC cells to the relaxed state, and setting the light emitting elements that illuminates said LC cell to off or a dimming state. A preferred embodiment of such circuit function is to provide in the circuit the operation of

1) setting all data output terminals to a discharging or neutral voltage;

2) enabling a scan output terminals or a section of scan driver terminals to select a row or a section of rows connected to the scan driver terminals to receive said discharging or neutral voltage.

In a preferred embodiment, a scan driver terminal is connected to a row of LC cells, and a section of scan driver terminals connects to a section of rows.

A preferred embodiment of the scan driver circuit in the present invention comprises a plurality of output terminals for operating a liquid crystal display, wherein each output terminal operates to deliver a SELECT signal cyclically according to a control timing to enable the liquid crystal cells connected thereto to receive image data, and to inhibit data transfer to said cells when said SELECT signal is not present; wherein said scan driver further comprises a cyclic discharge operation according to a control signal; said discharge operation operating on a section of or all scan output terminals at the same time.

A preferred discharge operation comprises applying a discharge signal at said section of or all scan output terminals simultaneous. A preferred discharge signal is a signal the select all cells connected thereto to receive a discharge data voltage from the data electrodes. Such a signal is preferably the same as the SELECT signal. The scan driver described here may be constructed in an integrated circuit on silicon.

It is construed that the scope of present invention is not limited by the above structural illustration. Furthermore, a single control circuit IC may comprise multiple control programs to control both rows and columns, or comprises both LED control programs and the image processing of data for LCD control. Furthermore, it is construed that the present invention is not limited by the type, shape, or the arrangement of the light source, lighting elements, and the LC cells. The applicability of the principle of the present invention is not limited by such variations. Examples of variations include: the arrangement of LCD cell elements being arranged in a non-orthogonal arrangement; the LED elements being arranged with multiple colors or comprising multiple LEDs in one unit; the LED elements being arranged on one side of the display and illuminates on the LCD cells via a light guide.

Various structures may be used to achieve the function of the circuit operation and timing scheme of the display disclosed in the present invention. Specific preferred embodiments of its construction were provided in this description to illustrate the driving scheme, operation principles, and functional definition of the driver, of this invention. The application of the principles of the present invention, however, is not limited by such examples. It is conceivable that various types of circuit implementation and cell assembly may be used to construct such display operate under the principles of the present invention. All such variations are embraced by the present invention.

Although various embodiments utilizing the principles of the present invention have been shown and described in detail, it is perceivable those skilled in the art can readily devise many other variances, modifications, and extensions that still incorporate the principles disclosed in the present invention. The scope of the present invention embraces all such variances, and shall not be construed as limited by the number of elements, specific arrangement of groups as to rows and column, and specific circuit embodiment to achieve the architecture and functional definition of the present invention.

Claims

1. A display device comprising: said delay period is at least one-twentieth of T3.

a plurality of light emitting elements; wherein the response time of said light emitting elements is T2;

a light modulator comprising a plurality of light valves modulating light directed thereto; wherein the relaxation time from the fully charged state to the fully relaxed state of said light valve is T1, and wherein T1 is substantially greater than T2;

a control circuit performing recurring operations on said light emitting elements and said light valves; said operations comprising setting the light valves according to an image information to display image; said operations comprising:

3) applying image signal to a light valve according to the image data for displaying image;

4a) a delay period after operation 3);

4b) after said delay period, applying the control signal that sets at least a light emitting element that illuminates said light valve in 3) to a bright state; wherein the response time of the light valve in response to said operation 3) is T3;

2. The device according to claim 1 wherein said control signals for setting said light emitting element to a bright state set the light emitting element to an intensity substantially higher than the average light output of the light emitting element averaged over a period of one or more operation cycles.

3. The device according to claim 1 wherein the duration of operation 4a) is longer than operation 4b).

4. The device according to claim 1 wherein said operations further comprise: wherein said operation 1) precedes operation 3).

1) applying the control signals for setting a light emitting element to off or a dimming state;

5. The device according to claim 4 wherein said operations further comprises 2) applying a control signal that sets a light valve illuminated by said light emitting element to a relaxed state.

6. The device according to claim 5 wherein in an operation cycle, said operation 2) precedes said operation 1) by a small fraction of T1; or

said operation 1) precedes said operation 2); or

said operation 1) leads and overlaps operation 2);

wherein a small fraction of T1 is less than 30% of T1.

7. The device according to claim 5 wherein in an image refreshing operation cycle, operation 2) precedes operation 3).

8. The device according to claim 1 wherein said plurality of light valves and said light emitting elements are arranged separately in plurality of groups; wherein the groups of light valves are operated in coordination with the groups of light emitting elements in a manner that said operation 3) operates on a group of light valves, setting the light valves according to image data, and said operation 4b) operates on a group of light emitting elements illuminating said group of light valves to a bright level after the delay period of 4a).

9. The device according to claim 5 wherein said operation step 1) sets all said light emitting elements to off or a dimming state, and wherein said operation 2) sets all Light valves to a relaxed state; wherein in an operation cycle, said operation 1) precedes or overlaps said operation 2), and said operation 2) precedes said operation 3).

10. The device according to claim 5 wherein a group of said light valves are arranged to connect to a first common electrode, and wherein said operation 2), setting a light valve to a relaxed state, is effectuated on said group of Light valves by applying a control voltage to said first common electrode.

11. The device according to claim 10 wherein said common electrode connects to all light valves of the display, wherein said operation 2) operates on all light valves by applying a voltage to said common electrode, setting all light valves to the relaxed state.

12. The device according to claim 1 wherein a group of said light emitting elements is arranged to connected to a second common electrode, wherein said operation 1) is effectuated on the group of light emitting elements by applying a control voltage to the second common electrode.

13. The device according to claim 5 wherein the relaxed state of a light valve corresponds to a state where the voltage applied on the light valve is zero or near neutral.

14. The device according to claim 5 wherein said plurality of light valves form array of cells; said control circuit comprising at least a data driver circuit for delivering image data to said light valves, and at least a scan driver circuit for selecting light valve cells to receive the image data according to a control timing; wherein said scan driver comprising a plurality of output terminals each connecting to a plurality of light valve cells via a scan electrode; wherein said scan driver further comprises a recurring discharge operation; said discharge operation enabling a selected group of said scan driver terminals at a time so that all light valves connected to said group of scan driver output terminals are enabled at the same time to receive data from said data driver during such discharge operation.

15. The device according to claim 14 wherein said data driver operates to set a discharging voltage to its data output terminals for the period when said scan driver performs said discharging selection; said discharging voltage setting the light vales to a relaxed state.

16. The device according to claim 1 wherein said operations further comprises 5) applying a control signal for setting a light valve to a charged or over-charged state.

17. The display device according to claim 16 wherein said charged or over-charged state of the light valve corresponds to a voltage near or higher than the voltage for operating said light valve for displaying a full range of gray scale.

18. The device according to claim 16 wherein said charged or over-charged state of the light valve corresponds to a dark state of said light valve.

19. The device according to claim 16 wherein said operation 5) precedes said operation 3).

20. The device according to claim 19 further comprising an operation 7) applying a control signal that sets a light emitting element to off or a dark state.

21. The device according to claim 20 wherein said operation 7) precedes operation 4b).

22. The device according to claim 1 wherein in said operation 4b), said control circuit applies the control signals for setting said light emitting element to a bright state according to a scaling relation with the average or maximum image brightness in the area illuminated by said light emitting element, wherein said scaling relation provides a brightness setting that increases with increasing average or maximum image brightness in said area for at least part of the brightness range.

23. The device according to claim 1 wherein a said light valve is a liquid crystal (LC) cell or a MEMS cell.

24. The device according to claim 5 wherein said relaxed state of said light valve corresponds to a bright state at which the LC cell allows the light to pass to the viewing side.

25. A method of operating a display device; said device comprising: a plurality of light emitting elements; a plurality of light valves modulating light output from said light emitting elements; said method comprising recurring operations of: said delay period is at least a significant fraction of T3.

3) applying image signal to a light valve for displaying an image;

4a) a delay period after operation 3);

4b) after said delay period, applying a control signal that sets at least a light emitting element that illuminates said light valve of 3) to a bright state; wherein the response time of the light valve in response to said operation 3) is T3;

26. The method according to claim 25 wherein said operations further comprise: wherein said operation 1) precedes operation 3).

1) applying the control signals that sets a light emitting element to off or a dimming state;

27. The method according to claim 25 wherein said control circuit performs recurring operations on said light emitting elements and said light valves; said operations further comprising 2) applying a control signal that sets a light valve in the area illuminated by said light emitting element to a relaxed state.

28. A circuit for operating a light valve and a light emitting element in coordination, said circuit performing recurring operations of: wherein said delay time is substantially greater than zero.

applying a SELECT signal for enabling said light valve to receive an image data;

providing a delay time;

after said delay time, applying a lighting control signal for enabling power for driving said light emitting element;

29. The circuit according to claim 28 wherein said delay time is at least a significant fraction of the response time of said light valve in response to receiving said image data.

30. The circuit according to claim 28 wherein said operations further comprise a step of applying a control signal for setting said light valve to a charged or over-charged state.

31. The circuit according to claim 30 wherein said charged or over-charged state of the light valve corresponds to a voltage setting near or higher than the voltage that sets said light valve to the lowest gray scale.

32. The circuit according to claim 30 wherein said charged or over-charged state of the light valve corresponds to a dark state of said light valve.