Redundant control system for LCD

In an exemplary embodiment, each horizontal and vertical conductor of a TFT array may be in electrical contact with a first and second control system. Initially, the entire display is driven by the first control system. When/if a failure occurs in the first control system, it is powered down and the second control system maintains operation of the entire display. Each control system may contain a set of source/gate drivers, display interface board, and power supply. A reversionary button may allow the user to manually switch between control systems. Alternatively, failure may be detected by the display interface boards or a graphics processor.

TECHNICAL FIELD

Disclosed embodiments relate generally to a redundant interwoven TFT array for a liquid crystal display device.

BACKGROUND OF THE ART

LCDs are becoming popular for not only home entertainment purposes, but are now being used as informational/advertising displays in both indoor and outdoor locations as well as within moving vehicles subject to substantial shock. When used for information/advertising purposes, the displays may remain ‘on’ for extended periods of time and thus would see much more use than a traditional home theatre use. When used for extended periods of time and placed within vehicles subject to shock, durability of the components can become an issue.

Liquid Crystal Displays (LCDs) contain several layers which work in combination to create a viewable image. A backlight is used to generate the rays of light that pass through what is commonly referred to as the LCD stack, which typically contains several layers that perform either basic or enhanced functions. The most fundamental layer within the LCD stack is the liquid crystal material, which may be actively configured in response to an applied voltage/charge in order to pass or block a certain amount of light which is originating from the backlight. The layer of liquid crystal material is divided into many small regions which are typically referred to as pixels. For full-color displays these pixels (color groups) are typically divided into independently-controllable regions of red, green and blue subpixels, where the red subpixel has a red color filter, blue subpixel has a blue color filter, and green subpixel has a green color filter. Each subpixel may be controlled by a grid of intersecting conductors which can apply a specific voltage to each subpixel to create an image.

An LCD will not function satisfactorily without an appropriate and properly-functioning set of source and gate drivers and associated conductor lines. If a conductor were to fail, then the entire column or row of the LCD may cease operations. Further, if either the gate driver, source driver, or the power supply to either of these drivers were to fail, the entire LCD may fail to create an image. While this may be a simple inconvenience when LCDs are used for entertainment purposes, when used for information or data displays this can be very costly. For example, LCDs are now being used in aircraft cockpits as well as the instrument panels or display(s) in ground vehicles and marine equipment. In these applications, when there is a failure within the control system, the LCD may no longer display the important information for the vehicle/aircraft and controls may cease to operate. These situations can be undesirable not only to the passengers of the vehicle/aircraft, but also other soldiers/team members who are counting on this part of the mission.

Some control systems have a limited life span, and eventually their performance may suffer. Some systems may quickly fail simply due to a manufacturing defect or may fail due to shock/forces applied to the aircraft or ground vehicle. Currently when this occurs, the entire LCD device must be manually replaced. This is expensive, and is often time consuming. Alternatively, the LCD device could be removed from the display housing, and the degraded or faulty system elements could be manually replaced. This is typically even more costly, and involves extensive manual labor. In currently known units, this also requires virtual complete disassembly of the LCD to gain access to the electronics. This complete disassembly is not only labor intensive, but must be performed in a clean room environment and involves the handling of expensive, delicate, and fragile components that can be easily damager or destroyed, even with the use of expensive specialized tools, equipment, fixtures, and facilities.

SUMMARY

Exemplary embodiments provide a redundant interwoven TFT array for an LCD device where the odd horizontal conductors are driven by a first gate driver while the even horizontal conductors are driven by a second gate driver. Further, the odd vertical conductors are driven by a first source driver while the even vertical conductors are driven by a second source driver. Separate DIB and power supplies may be used for the first and second set of gate/source drivers. If a failure were to occur, one set of source/gate drivers may be turned off, causing only every other line of pixels to cease operation, while the remaining pixels continue to operate. When the redundant interwoven TFT array is manufactured at a high density, the loss of every other line of pixels may not be noticeable to the observer. Any loss in luminance due to the failure of every other line of pixels can be accounted for by increasing the backlight power/luminance.

In another embodiment, each horizontal and vertical conductor may be in electrical contact with a first and second control system. Initially, the entire display is driven by the first control system. When/if a failure occurs in the first control system, it is powered down and the second control system maintains operation of the entire display.

An exemplary TFT array and LCD thus continues to produce images even after a failure of a gate/source driver, DIB, power supply, or conductor. If the TFT array is applied densely enough, the failure will not be noticeable to an observer.

DETAILED DESCRIPTION

For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the invention.

Much of the detail for constructing a flat panel liquid crystal display (LCD)10, as shown in side sectional view inFIG. 1, is known in the art and is unaffected by the exemplary embodiments, so that detail is not repeated here. For purposes of this application, the relevant details of the exemplary embodiments are typically located between the front and rear plates12,14of the liquid crystal display10. Both front plate12and rear plate14are visually transparent. Both are typically constructed of glass and provide the conventional rigidity. In the applicable art, front plate12is generally referred to as the “color filter” (CF) plate, and rear plate14is generally referred to as the “thin film transistor” (TFT) plate. According to known principles of the relevant art, a layer of liquid crystal material is contained in a thin cavity16maintained between the plates12,14by a sealing adhesive18that extends around a periphery of the plates.

By known principles, electrical interaction of the respective plates12,14with the liquid crystal material causes localized alignment of the liquid crystal material in cavity16. This alignment affects the transmissibility of the backlight27through the plates12,14at that localized point. A display area visible through an external face20of the LCD10is effectively divided into a large plurality of pixels or color groups. In one known arrangement, the pixels or color groups are further divided into red, green and blue sub-pixels. The close proximity of the sub-pixels allows them to co-act to provide a visual perception of a single pixel in one of literally thousands of color variations that can be achieved through combinations of intensity of the aforementioned three colors. Of course, other designs are possible which may use red, green, blue, and yellow sub-pixels and these would be within the scope of the exemplary embodiments. Further, some arrangements may use two of the same color sub-pixels, such as red, green, first blue, and second blue sub-pixels, and this would also be within the scope of the exemplary embodiments. Any number, color, and pairings of sub-pixels would be within the scope of the exemplary embodiments. Further, any type of backlight27may be used with the exemplary embodiments, including but not limited to edge-lit, direct-lit, or a hybrid type of design. Embodiments could also be used with LCD's that are not back-lit and instead rely on reflected ambient light to create an image.

The intensity variations of each sub-pixel are achieved through the selective alignment and non-alignment of the liquid crystal material immediately adjacent to the sub-pixels. Specifically, the TFT array25, when activated, act upon the liquid crystal material to change the polarization plane of the liquid crystal material. The interaction of the liquid crystal material with the front polarizer55and rear polarizer50alters the emission intensity of each sub-pixel to create the overall color of light emitted by the color group or pixel.

FIG. 2illustrates a simplified and enlarged view of traditional TFT array25if viewed from the perspective of an intended observer. A plurality of horizontal conductors37are arranged with a plurality of vertical conductors36to create a plurality of sub-pixels49. As known in the art, a transistor39is preferably placed within each sub-pixel49. A gate driver41is in electrical communication with a display interface board (DIB)47and is used to control the horizontal conductors37. A source driver46is also in electrical communication with the DIB47and is used to control the vertical conductors36. A power supply40may provide power through the DIB47to the gate driver41and source driver46. Each sub-pixel49in the assembly can be controlled when the gate driver41activates the appropriate horizontal conductor37while the source driver46activates the corresponding vertical conductor36.

AsFIG. 2illustrates, the TFT array of25requires the operation of source driver46, gate driver41, DIB47, and power supply40to orient the sub-pixels49and create and image. If any of these devices were to fail, then the entire LCD would fail to create an image. This is sometimes referred to as a ‘single point failure.’ As discussed above, the failure of the entire LCD is undesirable but has traditionally been a significant risk for LCD displays.

FIG. 3illustrates a simplified and enlarged view of an exemplary embodiment of the TFT array if viewed from the perspective of an intended observer. Herein the terms ‘odd’ and ‘even’ will be used to describe alternating conductors where the numerical counting begins in the upper left hand corner of the TFT array. The terms ‘odd’ and ‘even’ are simply used to denote the alternating pattern, and do not require any specific number of conductors or counting scheme. Further, the terms ‘horizontal’ and ‘vertical’ will be used to describe the conductors but these do not require the specific orientation as it is known that LCD's may be rotated 90 degrees. In other words, the gate drivers herein may be used to control vertical conductors and the source drivers may be used to control horizontal conductors or vice versa.

In this embodiment a first gate driver135is used to control the odd horizontal conductors160while a second gate driver137is used to control the even horizontal conductors166. Similarly, a first source driver136is used to control the odd vertical conductors164while a second source driver138is used to control the even vertical conductors162. A first DIB126is in electrical communication with the first gate driver135and first source driver136. A first power supply125provides power through the DIB126and to the first gate and source drivers135and136. A second DIB128is in electrical communication with the second gate driver137and second source driver138. A second power supply127provides power through the DIB128and to the second gate and source drivers137and138.

During normal operations, both sets of conductors160/164and162/166and their associated components would operate simultaneously. In at least one embodiment, both sets of conductors and their associated components would be generating the same image. If the horizontal conductors160, vertical conductors164, first gate driver135, first source driver136, DIB126, or power supply125were to fail, these components (known herein as the first TFT assembly900) would be turned off or powered down. Conversely, if the horizontal conductors166, vertical conductors162, second gate driver137, second source driver138, DIB128, or power supply127were to fail, these components (known herein as the second TFT assembly950) would be turned off or powered down. If the first TFT assembly900were turned off, the second TFT assembly950may continue to create the image on the LCD. Conversely, if the second TFT assembly950were turned off, the first TFT assembly900may continue to create the image on the LCD.

The intersection of conductors160,164,162, and166create a plurality of sub-pixels149, each of which preferably contains a transistor139. Depending on the resolution of the TFT array (i.e. how densely are the conductors laid out) and the specific application for the LCD (i.e. what is being shown graphically) the loss of every other conductor may not be noticeable to the observer. It has been found that modern manufacturing techniques allow the resolution of the TFT array to be constructed sufficiently high so that a loss of every other line is not noticeable to the observer. For example, high resolution TFT arrays (over 300 pixels per inch (ppi)) may lose every other conductor line which would result in about half the resolution (approximately 150 ppi) and despite the application; this may not be noticeable to the user. In medium resolution displays (approximately 150 ppi), this may be slightly noticeable to the observer, depending on the application of the LCD. While it is estimated that the human eye may only be able to perceive resolutions up to 300 ppi, modern manufacturing techniques have shown that TFT arrays can be constructed as high as 325 ppi and very possibly higher. Thus, while the human eye may not perceive the full resolution of an exemplary TFT array in full operation, a failure in any of the source/gate drivers, power supplies, or conductors may not result in any noticeable loss of resolution to the observer.

It has been found that while the change in resolution may not be noticeable to the observer, the display luminance may drop noticeably when either the first900or second950TFT assembly is turned off. To account for this phenomenon, an exemplary system may detect when a failure has occurred and may increase the backlight to account for the change in display luminance. This process is illustrated inFIG. 4.

In some embodiments, the DIB126and DIB128contain built-in-test (BIT) circuitry, which may detect a failure in one of the TFT assembly components and cause the TFT assembly containing the failure to be turned off. In some embodiments, a graphics processor800may be placed in electrical communication with the DIB126and DIB128. The graphics processor800may contain BIT circuitry, either instead of or in addition to the BIT circuitry found in DIB126and DIB128. To determine if there is a failure within a source or gate driver, the BIT circuitry may monitor the ripple carry outputs of the source and gate drivers and report a failure upstream, possibly to the graphics processor800, which may then turn off the TFT assembly containing the failure. In other embodiments, the failure may not be detected by BIT circuitry and may be detected by the observer who can manually select an optional reversionary button870to turn off the failed TFT assembly. The reversionary button870may also accept input from the observer, so as to cycle through several modes including but not limited to: both first and second TFT assemblies900and950(1× backlight), only first TFT assembly900(2× backlight), only second TFT assembly950(2× backlight).

In some techniques, the backlight is controlled using a power feedback loop, where the power to the backlight is controlled based on measurements of current and/or power and these measurements are monitored by a feedback loop. For these techniques, the desired power is roughly doubled when the system or observer detects a failure and one of the TFT assemblies is turned off. This embodiment is illustrated inFIG. 4, which provides a logical flowchart that can be executed by many types of software drivers or microprocessors. In some embodiments, the logic illustrated inFIG. 4may be operated by the graphics processor800.

In other techniques, the backlight may be controlled using a luminance feedback loop, where the luminance within the backlight cavity is controlled based on luminance measurements from a light sensor placed within the cavity and monitored through an electrical feedback loop. For these techniques, the desired luminance may be roughly doubled when the system detects a failure and turns off the TFT assembly containing the failure.

Unlike traditional digital binary logic buffers which can be tri-stated to selectively allow a single output from multiple tri-state buffered output signals to interface to a single electrical wire or trace, LCD source drivers are analog based which are traditionally not capable of being tri-stated. Furthermore, even in a powered down state, back-driving a source/gate driver could result in permanent damage to the powered-down source/gate driver or improper operation of the LCD. The preferred embodiment is to incorporate a logic switch or circuit on the TFT matrix which effectively electrically isolates the two source/gate drivers. A second embodiment is to incorporate this logic switch or circuit in the source/gate drive IC.

FIG. 5illustrates a simplified and enlarged view of another embodiment of the interwoven redundant TFT array if viewed from the perspective of an intended observer. In this embodiment, control block1is controlling every even horizontal row of subpixels through horizontal conductors315. As used herein, every even horizontal row of subpixels is considered to be the 2ndline, 4thline, etc. Control block2is controlling every odd horizontal row of subpixels through horizontal conductors320. As used herein, every odd horizontal row of subpixels is considered to be the 1stline, 3rdline, 5thline, etc.

Control block1also has a plurality of vertical conductors310which control every odd horizontal row of subpixels. Control block2also has a plurality of vertical conductors305which control every even horizontal row of subpixels. Also it should be noted that each of the horizontal conductors315and320are positioned immediately below the odd rows of subpixels. Also, there are no horizontal conductors placed below the even rows of subpixels. Here, it can be observed that during full operation, both control blocks1and2are operating so that every subpixel is active. If control block2were to fail, then only the odd rows of subpixels would be active. If control block1were to fail, then only the even rows of subpixels would be active. Because of the intersection300, more than one source layer may be required.

FIG. 6illustrates a simplified and enlarged view of another embodiment of the interwoven redundant TFT array if viewed from the perspective of an intended observer. In this embodiment, control block1is controlling every odd horizontal row of subpixels through horizontal conductors415. Control block2is controlling every even horizontal row of subpixels through horizontal conductors420. As used herein, every odd horizontal row of subpixels is considered to be the 1stline, 3rdline, 5thline, etc.

Control block1also has a plurality of vertical conductors410which control every odd horizontal row of subpixels. Control block2also has a plurality of vertical conductors405which control every even horizontal row of subpixels. Also it should be noted that each of the horizontal conductors415and420are positioned immediately below the odd rows of subpixels. Also, there are no horizontal conductors placed below the even rows of subpixels. Here, it can be observed that during full operation, both control blocks1and2are operating so that every subpixel is active. If control block2were to fail, then control block1would power only half of the remaining subpixels. If control block1were to fail, then control block2would power only half of the remaining subpixels. Because of the intersection400, more than one source layer may be required.

FIG. 7illustrates a simplified and enlarged view of another embodiment of the interwoven redundant TFT array if viewed from the perspective of an intended observer. In this embodiment, gate235and source236are able to control every subpixel through horizontal conductors200and vertical conductors210. Further, gate237and source238are also able to control every subpixel through horizontal conductors200and vertical conductors210. In this embodiment, if gate235or source236were to fail, all of the subpixels could still be controlled by gate237and source238. Alternatively, if gate237and source238were to fail, all of the subpixels could still be controlled by gate235or source236.

In this embodiment, a first DIB126is in electrical communication with the first gate driver235and first source driver236. A first power supply125provides power through the DIB126and to the first gate and source drivers235and236. A second DIB128is in electrical communication with the second gate driver237and second source driver238. A second power supply127provides power through the DIB128and to the second gate and source drivers237and238.

FIG. 8provides a logical flow chart for an exemplary method for controlling the redundant TFT array system shown inFIG. 7. If the first gate driver235, first source driver236, DIB126, or power supply125were to fail, these components (known herein as the first control assembly298) would be turned off or powered down. Conversely, if the second gate driver237, second source driver238, DIB128, or power supply127were to fail, these components (known herein as the second control assembly299) would be turned off or powered down. If the first control assembly298were turned off, the second control assembly299may continue to create the image on the LCD. Conversely, if the second control assembly299were turned off, the first control assembly198may continue to create the image on the LCD.

In some embodiments, the DIB126and DIB128contain built-in-test (BIT) circuitry, which may detect a failure in one of the TFT assembly components and cause the TFT assembly containing the failure to be turned off. In some embodiments, a graphics processor800may be placed in electrical communication with the DIB126and DIB128. The graphics processor800may contain BIT circuitry, either instead of or in addition to the BIT circuitry found in DIB126and DIB128. To determine if there is a failure within a source or gate driver, the BIT circuitry may monitor the ripple carry outputs of the source and gate drivers and report a failure upstream, possibly to the graphics processor800, which may then turn off the TFT assembly containing the failure. In other embodiments, the failure may not be detected by BIT circuitry and may be detected by the observer who can manually select an optional reversionary button870to turn off the failed TFT assembly.

FIG. 9illustrates a simplified and enlarged view of another embodiment of the interwoven redundant TFT array if viewed from the perspective of an intended observer. In this embodiment, control block1is split into top-left source drivers500and top-right source drivers400. Further, control block2is split into bottom-left source drivers525and bottom-right source drivers526. The subpixels on the left hand side of the display can be controlled by the left-gate drivers545through the horizontal conductors555. The subpixels on the left hand side of the display can also be controlled by either the top-left source drivers500or the bottom-left source drivers525through the vertical conductors580. Similarly, the subpixels on the right hand side of the display can be controlled by the right-gate drivers540through the horizontal conductors550. The subpixels on the right hand side of the display can also be controlled by either the top-right source drivers400or the bottom-right source drivers526through the vertical conductors585.

Here, if the top-left source drivers500were to fail, the subpixels on the left side of the display could still be controlled by the bottom-left source drivers525, and vice versa. Further, if the top-right source drivers400were to fail, the subpixels on the right hand side of the display could still be controlled by the bottom-right source drivers526, and vice versa.

FIG. 10illustrates a simplified and enlarged view of another embodiment of the interwoven redundant TFT array if viewed from the perspective of an intended observer. Here, every odd horizontal row of subpixels is controlled by control block1through horizontal conductors700. Further, every odd column of subpixels is controlled by control block1through vertical conductors710. Similarly, every even horizontal row of subpixels is controlled by control block2through horizontal conductors735. Finally, every even column of subpixels is controlled by control block2through vertical conductors725.

In this embodiment, if control block1were to fail, control block2could continue to drive 25% of the available subpixels. If control block2were to fail, control block1could continue to drive 25% of the available subpixels.

Having shown and described preferred embodiments of the invention, those skilled in the art will realize that many variations and modifications may be made to affect the described embodiments and still be within the scope of the claimed invention. Additionally, many of the elements indicated above may be altered or replaced by different elements which will provide the same result and fall within the spirit of the exemplary embodiments.