Abstract:
A progressive scan display including a matrix of pixels arranged in a plurality of pixel rows and pixel columns. For each pixel row, the display includes a pair of select lines configured to selectively allow video data to be loaded to pixels of that pixel row. For each pixel column, the display includes a data line configured to selectively load video data to pixels of that pixel column. At least one select line for each row of pixels is a shared select line configured to selectively allow video data to be loaded to two different pixel rows.

Description:
CROSS-REFERENCES  
       [0001]     This application claims the benefit of U.S. Provisional Application Nos. 60/512,032, filed Oct. 17, 2003, 60/527,128 filed Dec. 5, 2003, and 60/560,431, filed Apr. 7, 2004, each of which is incorporated by reference. 
     
    
     BACKGROUND  
       [0002]     Many devices now include displays for presenting visual information. In general, a display has several attributes that affect its suitability for a particular purpose. Among these attributes are size, brightness, resolution, clarity, and energy consumption. Display sizes can range from between less than an inch to a few inches diagonal viewing area for handheld devices, such as cellular telephones and portable televisions, to between tens or hundreds of feet for stadium displays. Depending on the desired viewing area for a particular display application, various technologies may be more suitable than others. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0003]      FIG. 1  shows an exemplary differentiating circuit.  
         [0004]      FIG. 2  shows an embodiment of the differentiating circuit of  FIG. 1 .  
         [0005]      FIG. 3  shows a portion of an exemplary duel select diode matrix utilizing dedicated select lines.  
         [0006]      FIG. 4  shows a portion of an exemplary duel select diode matrix utilizing shared select lines.  
         [0007]      FIG. 5  shows exemplary drive waveforms for driving a duel select diode matix that utilizes shared select lines.  
         [0008]      FIG. 6  shows a table corresponding to the drive waveforms of  FIG. 5 .  
         [0009]      FIG. 7  shows a pixel of an exemplary duel select diode matrix that utilizes dedicated select lines with data lines located off of an active matrix array.  
         [0010]      FIG. 8  shows a pixel of an exemplary duel select diode matrix that utilizes shared select lines with the data lines located off of an active matrix array. 
     
    
     DETAILED DESCRIPTION  
       [0011]     Active matrix liquid crystal displays are widely used in a variety of applications, including notebook computers, flat panel monitors, handheld computers, cellular phones, and flat panel televisions. Active matrix liquid crystal displays may be fabricated by depositing and patterning various metals, insulators, and semiconductors on substrates. Such displays commonly employ semiconductor devices, such as amorphous silicon (a-Si) thin film transistors. Each pixel in the active matrix liquid crystal display may be coupled to an address transistor, which controls the voltage on each pixel and therefore its transmittance.  
         [0012]     A growing application for active matrix liquid crystal displays is in large area televisions, which may have a diagonal size of up to 50 inches or more. However, thin film transistor controlled pixel arrays are difficult to manufacture for this application since a relatively large number of process steps are required to construct the thin film transistors. The total mask count may be 5 or 6 or more, which is burdensome. While the yields for small displays can be quite high, it is difficult to obtain an acceptable yield for large area displays. In addition, the design rules for patterning the various insulator, metal, and semiconductor layers are the same for small and large thin film transistor liquid crystal displays, requiring expensive photo-exposure equipment for large area substrates. This all increases the manufacturing expense of such thin film transistor liquid crystal displays.  
         [0013]     Nonlinear resistors can be used in place of transistors in a display circuit. A nonlimiting example of a nonlinear resistor is a thin film diode. Thin film diodes, including those referred to as metal-insulator-metal diodes, can be more economical to fabricate than a-Si thin film transistors. When a single thin film diode is used in series with a liquid crystal pixel, any variation in the thin film diode characteristic across the display area or over time or temperature can lead to a variation in the pixel voltage. This can result in poor gray scale control, poor uniformity, slow response time, and/or image sticking. In addition, it is difficult, if not impossible, to scale up single thin film diode liquid crystal displays to a diagonal size larger than about 10 inches without severe brightness gradients.  
         [0014]     However, a differential circuit may mitigate, if not eliminate, the drawbacks of the single thin film diode approach.  FIG. 1  shows an exemplary differential circuit  10 , which includes a light-producing module  12  and a differentiating module  14 . The circuit also includes select line  16  and select line  18 , which are operatively connected to different nodes of differentiating module  14 . The circuit also includes a data line  20  that is operatively connected to the light-producing module. As shown in  FIG. 2 , a differentiating module can include a pair of nonlinear resistors, such as bidirectional diode  22  and bidirectional diode  24 . The light producing module can include a capacitor  26  having a pixel node  28  that is operatively connected to different select lines by way of a differentiating module. The capacitor also may include a data node  30  that is operatively connected to a data line. The light producing module may include an exit polarizer configured to modulate light output responsive to the relative charge of the capacitor. U.S. Pat. Nos. 4,731,610, 6,222,596, 6,225,968, and 6,243,062 describe exemplary arrangements that utilize a differential circuit, and are hereby incorporated herein by reference. Such displays are herein referred to as dual select diode displays.  
         [0015]     The fabrication of a dual select diode matrix array for active matrix liquid crystal displays can be achieved in only two or three mask steps, with relaxed design rules that scale with the display size. When operated in a dual select mode, the pixel circuit can act as an analog switch. The dual select diode circuit is not a two-terminal switching device, but rather a three-terminal switching device similar to a circuit utilizing thin film transistors. A dual select diode circuit can perform comparably to a thin film transistor liquid crystal display as a result of accurate gray scale control, fast response time, and tolerance for variations in thin film diode characteristics over time and across the viewing area. Such a dual select diode liquid crystal display also can be relatively insensitive to RC delays on the select and data lines and can therefore be scaled up to very large area, for example, exceeding 40 inches in diagonal size.  
         [0016]      FIG. 3  shows a portion of pixel row R i  and adjacent pixel row R i+1  of a dual select diode circuit in which each row of pixels is associated with a pair of dedicated select lines. Pixel row R i  is operatively connected to dedicated select lines S i  and S i+1 , which are configured to address only row R i . Similarly, pixel row R i+1  is operatively connected to dedicated select lines S i+2  and S i+3 , which are configured to address only R i+1 . Dedicated select lines in a duel select diode display, and the spacing between the dedicated select lines, can take up a substantial percentage of the total area of a display. This can reduce the percentage of pixel opening, and therefore the brightness of the display when a backlight is used. In other words, a duel select diode display that dedicates two select lines per row may require more energy and/or be less bright than a display that does not dedicate two select lines per row. For portable applications, such as cellular phones and digital cameras, the energy consumption of the display directly affects battery life, and therefore improvements in brightness efficiency can lead to improvements in battery life. By increasing the effective size of a pixel opening, the brightness can be maintained with relatively less energy consumption, thus improving battery life. Furthermore, displays that do not dedicate two select lines per row may be less likely to experience shorts between immediately adjacent select lines. Such shorts may have an impact on the manufacturing yield. Displays that do not dedicate two select lines per row can be operated with fewer row driver outputs and row driver interconnects, further improving manufacturing ease, yield, and expense.  
         [0017]      FIG. 4  shows a portion of pixel row R j  and adjacent pixel row R j+1  of a dual select diode circuit in which each row of pixels is associated with a pair of shared select lines. Pixel row R j  is operatively connected to select lines S j  and S j+1 , and pixel row R j+1  is operatively connected to select lines S i+1  and S i+2 . Select line S i+1  is a shared select line that can be used to progressively address row R j  and adjacent pixel row R j+1 . By sharing select lines, the total number of select lines can be reduced from 2x to x+1, where x equals the number of rows of a display. For example, a display having 720 rows of pixels would have 1440 select lines in a system that uses dedicated select lines and could have only 721 select lines in a system that uses shared select lines. In addition to decreasing the number of select lines and associated drivers and interconnects, the space between adjacent dedicated select lines is eliminated, because adjacent dedicated select lines are consolidated into a shared select line. Therefore, the distance between adjacent pixel openings can be decreased significantly, and the pixel aperture can be increased, compared to a pixel that uses dedicated select lines, without increasing the footprint of the pixel on the display. Pixel aperture can be increased 70% or more. This can increase the display brightness and/or energy efficiency.  
         [0018]     A dual select diode circuit utilizing shared select lines can perform approximately equivalent to a dual select diode circuit utilizing dedicated select lines. As described by nonlimiting example below, for each row of pixels, overlapping select pulses having opposite polarity can be driven through the shared select lines corresponding to that row of pixels. Furthermore, the polarity of a column data line can be controlled over time so as to have the same polarity as the select pulse of the first in time of the corresponding row select lines. As shown below, the data line can be controlled so as to alternate polarity between selection of each successive row of select lines.  
         [0019]     In general, a display can be addressed one row at a time by progressively scanning the rows. Opposite polarity select pulses can be applied to two adjacent select lines which address a particular row of pixels. The duration of the opposite polarity select pulses can be set to about twice the line time, so that the select pulses of subsequent rows overlap by about one line time. In addition, the polarity of the data pulse can be inverted every line time to obtain a row inversion (line inversion) drive scheme. When the polarity of the data pulse is set the same as the polarity of the first in time of the two select pulses applied to a row, the operation of the pixel is similar to a conventional duel select diode circuit that utilizes dedicated select lines. The duel select diode circuit with shared select lines can act as an analog switch, which results in the accurate charging of the pixel to the desired gray level. When the next row of pixels is selected, one of the two select pulses for the previous row can be left active for one more line time. However, due to the row inversion drive scheme, the diodes connected to this select line are not fully switched on and will therefore not discharge the pixels on the previous row. Circuit simulations demonstrate that this leads to accurate gray scale performance.  
         [0020]      FIG. 5  shows two pixels of an exemplary dual select diode circuit in which pixels in adjacent rows R j  and R j+1  share a common select line.  FIG. 5  also shows corresponding drive waveforms for selecting the pixel rows and providing video data to the individual pixels. Such waveforms can be applied by a scan controller and/or data controller.  FIG. 6  is a table corresponding to the exemplary drive waveforms of  FIG. 6 . The drive wave forms shown in  FIGS. 5 and 6  correspond to select lines S j , S j+1 , S j+2 , and data line D j . For the purpose of simplicity, this example is provided with reference to only two pixels of a display which can be virtually any size.  
         [0021]     As illustrated, row R j  is the pixel row between select lines S j  and S j+1 , and row R j+1  is the pixel row between select lines S j+1  and S j+2 . Select line S j+1  is between row R i  and row R j+1  and can be used to address either row. In other words, select line S j+1  is a shared select line that is not dedicated to addressing only one row of pixels. In general, each interior select line will service two adjacent rows of pixels. The times t 0 , t 1 , t 2 , t 3 , t 4  and t 5  denote times when changes are made to the voltages of the select lines.  
         [0022]     During the period before t 2 , row R j  and row R j+1  are deselected. At t 1  a positive voltage is applied to select line S j . At t 2  a negative voltage is applied to select line S j+1 , thus select voltages having opposite polarities are present at the select lines addressing row R j . The opposite polarities of select line S j  and select line S j+1  cause row R j  to be selected. The voltage on the active pixel electrodes of row R j  are reset to the center voltage between the two opposite polarity select voltages. The pixels of row R j  can be accurately charged to the data voltage, which can be applied with the same polarity as the voltage applied to select line S j . Operation during this interval is similar to that of a duel select diode circuit that utilized dedicated select lines.  
         [0023]     At t 3  a positive voltage is applied to select line S j+2 . Because select line S j+1  continues to receive a negative voltage, select voltages having opposite polarities are present at the select lines addressing row R j+1 . Thus, row R j+1  is selected. The pixels on row R j+1  can be accurately charged to an applied data voltage. The data voltage can be applied with the same polarity as the voltage applied to select line S j+1 . Although select line S j+1  is still activated, substantial charge will not leak from the pixels of row R j . Because of the data polarity change from row R j  to row R j+1 , the voltages on the pixel electrodes of row R j  change towards the voltage of select line S j+1 . The voltage difference between the pixels on row R j  and select line S j+1  is not sufficient to cause substantial charge leakage through the pixel diode adjacent select line S j+1  during the line time interval between t 3  and t 4 .  
         [0024]     In the interval between t 4  and t 5 , both rows are deselected. Although a positive voltage is still being applied to select line S j+2 , substantial charge will not leak from the pixels of row R j+1 . Because of the data polarity change from row R j+1  to a row R j+2  (not shown in  FIG. 5 ), the voltages on the pixel electrodes of R j+1  change towards the voltage of select line S j+2 . The voltage difference between the pixels on R j+1  and select line S j+2  is not sufficient to cause substantial charge leakage through the pixel diode adjacent select line S j+2  during the line time interval between t 4  and t 5 .  
         [0025]     As shown in  FIG. 5 , during the next frame, all select pulses and data pulses are applied with the opposite polarity in order to obtain an AC drive for the pixel. A similar reversal of applied polarity can be repeated throughout each frame.  
         [0026]     If the direction of scanning the display is always the same (e.g. from top to bottom), one diode branch at each pixel sees the majority of the current while the other diode is primarily used to balance the pixel voltage. Some of the advantages of the dual select diode circuit, such as insensitivity to diode degradation and non-uniformity, may be lost When the direction of scanning remains the same. To prevent one set of diodes in each row from constantly carrying larger currents than the other set, the direction of scanning can be reversed periodically. The scan direction may be reversed for circuits utilizing dedicated select lines or circuits utilizing shared select lines.  
         [0027]     For example, the initial sequence for selecting the rows in a display with N rows may be: Row 1 , Row 2 , Row 3 , . . . Row N . The sequence may be changed to: Row N , Row N−1 , Row N−2 , . . . Row 1 . Such a change in sequence may be initiated in response to an event, such as reaching a predetermined operating time (5 minutes, 30 minutes, etc.), every time the display is turned on, at the change of a scene in a video image, or upon virtually any other predetermined event. A display system may include a frame buffer to store at least one frame of video data so that the sequence can be reversed at any time without dropping a frame of video. Such buffers can be used on small displays for cell phones, PDAs, and the like, or on relatively large displays for televisions and other monitors.  
         [0028]     In some embodiments, data lines can be located off of the active matrix array. As a nonlimiting example, the data lines can be implemented as indium-tin-oxide stripes on the opposite substrate (the color plate). The absence of data lines on the active matrix array facilitates spacing the color sub-pixels very close to each other when a vertical stripe color filter arrangement is used.  FIG. 7  shows four color sub-pixels arranged in vertical stripe orientation. Displays with four color sub-pixel arrangements can have up to 50% higher brightness than displays with three color sub-pixel arrangements using data lines on the active matrix array. A four color sub-pixel arrangement can be fabricated in three steps. In each step, a different material can be layered in the desired pattern. As a nonlimiting example, a first layer  50  can include indium-tin-oxide, a second layer  52  can include silicon nitride (SiN x ), and a third layer  54  can include a metal or another suitable conductor. As shown in  FIG. 8 , a four color sub-pixel arrangement can be fabricated with a shared select line  60 .  
         [0029]     Although the present disclosure has been provided with reference to the foregoing operational principles and embodiments, it will be apparent to those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope defined in the appended claims. The present disclosure is intended to embrace all such alternatives, modifications and variances. Where the disclosure or claims recite “a,” “a first,” or “another” element, or the equivalent thereof, they should be interpreted to include one or more such elements, neither requiring nor excluding two or more such elements.