Patent Publication Number: US-2015084998-A1

Title: Method and system for reducing power consumption in a display

Description:
RELATED APPLICATIONS 
     This application is a continuation of pending U.S. patent application Ser. No. 13/584,515, filed Aug. 13, 2012, titled “METHOD AND SYSTEM FOR REDUCING POWER CONSUMPTION IN A DISPLAY,” which is a continuation of U.S. patent application Ser. No. 12/463,877, filed May 11, 2009, titled “METHOD AND SYSTEM FOR REDUCING POWER CONSUMPTION IN A DISPLAY,” which is a divisional application of U.S. patent application Ser. No. 11/097,827, filed Apr. 1, 2005, titled “METHOD AND SYSTEM FOR REDUCING POWER CONSUMPTION IN A DISPLAY,” now issued as U.S. Pat. No. 7,532,195, which claims the benefit of U.S. Provisional Application No. 60/613,404, filed Sep. 27, 2004, titled “METHOD AND DEVICE FOR REDUCING POWER IN INTERFEROMETRIC MODULATION ARRAY.” Each of the foregoing applications is hereby expressly incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Description of the Related Technology 
     Microelectromechanical systems (MEMS) include micro mechanical elements, actuators, and electronics. Micromechanical elements may be created using deposition, etching, and or other micromachining processes that etch away parts of substrates and/or deposited material layers or that add layers to form electrical and electromechanical devices. One type of MEMS device is called an interferometric modulator. An interferometric modulator may comprise a pair of conductive plates, one or both of which may be transparent and/or reflective in whole or part and capable of relative motion upon application of an appropriate electrical signal. One plate may comprise a stationary layer deposited on a substrate, the other plate may comprise a metallic membrane separated from the stationary layer by an air gap. Such devices have a wide range of applications, and it would be beneficial in the art to utilize and/or modify the characteristics of these types of devices so that their features can be exploited in improving existing products and creating new products that have not yet been developed. 
     SUMMARY 
     The system, method, and devices of the invention each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this invention, its more prominent features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description of Preferred Embodiments” one will understand how the features of this invention provide advantages over other display devices. 
     One implementation is an apparatus for displaying image data. The apparatus includes a display device with a plurality of display elements having selectable resolution. The display device is configured to operate at a plurality of selectable operational modes. The apparatus also includes an image data source configured to provide image data to the display device such that in a first operational mode, data at a first resolution is provided at a first data rate, and in a second operational mode, data at a second resolution is provided at a second data rate, where the first and second resolutions are different. 
     Another implementation is a method of displaying image data. The method includes selecting an operational mode for a display device, where the display device includes a plurality of display elements having selectable resolution, and where the display device is configured to operate at a plurality of selectable operational modes. The method also includes providing image data to the display device such that in a first operational mode, data at a first resolution is provided at a first data rate, and in a second operational mode, data at a second resolution is provided at a second data rate, where the first and second resolutions are different. 
     Another implementation is an apparatus for displaying image data. The apparatus includes means for selecting an operational mode for a display device, where the display device includes a plurality of display elements having selectable resolution, and where the display device is configured to operate at a plurality of selectable operational modes. The apparatus also includes means for providing image data to the display device such that in a first operational mode, data at a first resolution is provided at a first data rate, and in a second operational mode, data at a second resolution is provided at a second data rate, where the first and second resolutions are different. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view depicting a portion of one embodiment of an interferometric modulator display in which a movable reflective layer of a first interferometric modulator is in a released position and a movable reflective layer of a second interferometric modulator is in an actuated position. 
         FIG. 2  is a system block diagram illustrating one embodiment of an electronic device incorporating a ×3 interferometric modulator display. 
         FIG. 3  is a diagram of movable mirror position versus applied voltage for one exemplary embodiment of an interferometric modulator of  FIG. 1 . 
         FIG. 4  is an illustration of a set of row and column voltages that may be used to drive an interferometric modulator display. 
         FIGS. 5A and 5B  illustrate one exemplary timing diagram for row and column signals that may be used to write a frame of display data to the 3×3 interferometric modulator display of  FIG. 2 . 
         FIG. 6A  is a cross section of the device of  FIG. 1 . 
         FIG. 6B  is a cross section of an alternative embodiment of an interferometric modulator. 
         FIG. 6C  is a cross section of another alternative embodiment of an interferometric modulator. 
         FIG. 7  is a partial system block diagram of an exemplary interferometric modulator display, similar to that illustrated in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     One embodiment is a method of driving a display so as to reduce power consumption of the display that includes a plurality of display elements. In a first mode of operation, the display state of substantially all the display elements is periodically re-set so as to display a first series of image frames. Upon changing to a second mode of operation, a second mode of operations comprises re-setting the display state of only a first portion of the display elements so as to display a second series of image frames at a display element resolution which is less than said display element resolution used to display said first series of image frames. The reduced display element resolution may reduce the color gamut of the display. In one embodiment, the display state of the remaining portion of the display elements is re-set at a rate that is lower than the rate of re-setting the first portion. 
     The following detailed description is directed to certain specific embodiments of the invention. However, the invention can be embodied in a multitude of different ways. In this description, reference is made to the drawings wherein like parts are designated with like numerals throughout. As will be apparent from the following description, the invention may be implemented in any device that is configured to display an image, whether in motion (e.g., video) or stationary (e.g., still image), and whether textual or pictorial. More particularly, it is contemplated that the invention may be implemented in or associated with a variety of electronic devices such as, but not limited to, mobile telephones, wireless devices, personal data assistants (PDAs), hand-held or portable computers, GPS receivers/navigators, cameras, MP 3  players, camcorders, game consoles, wrist watches, clocks, calculators, television monitors, flat panel displays, computer monitors, auto displays (e.g., odometer display, etc.), cockpit controls and/or displays, display of camera views (e.g., display of a rear view camera in a vehicle), electronic photographs, electronic billboards or signs, projectors, architectural structures, packaging, and aesthetic structures (e.g., display of images on a piece of jewelry). MEMS devices of similar structure to those described herein can also be used in non-display applications such as in electronic switching devices. 
     One interferometric modulator display embodiment comprising an interferometric MEMS display element is illustrated in  FIG. 1 . In these devices, the pixels are in either a bright or dark state. In the bright (“on” or “open”) state, the display element reflects a large portion of incident visible light to a user. When in the dark (“off” or “closed”) state, the display element reflects little incident visible light to the user. Depending on the embodiment, the light reflectance properties of the “on” and “off” states may be reversed. MEMS pixels can be configured to reflect predominantly at selected colors, allowing for a color display in addition to black and white. 
       FIG. 1  is an isometric view depicting two adjacent pixels in a series of pixels of a visual display, wherein each pixel comprises a MEMS interferometric modulator. In some embodiments, an interferometric modulator display comprises a row/column array of these interferometric modulators. Each interferometric modulator includes a pair of reflective layers positioned at a variable and controllable distance from each other to form a resonant optical cavity with at least one variable dimension. In one embodiment, one of the reflective layers may be moved between two positions. In the first position, referred to herein as the released state, the movable layer is positioned at a relatively large distance from a fixed partially reflective layer. In the second position, the movable layer is positioned more closely adjacent to the partially reflective layer. Incident light that reflects from the two layers interferes constructively or destructively depending on the position of the movable reflective layer, producing either an overall reflective or non-reflective state for each pixel. 
     The depicted portion of the pixel array in  FIG. 1  includes two adjacent interferometric modulators  12   a  and  12   b.  In the interferometric modulator  12   a  on the left, a movable and highly reflective layer  14   a  is illustrated in a released position at a predetermined distance from a fixed partially reflective layer  16   a.  In the interferometric modulator  12   b  on the right, the movable highly reflective layer  14   b  is illustrated in an actuated position adjacent to the fixed partially reflective layer  16   b.    
     The fixed layers  16   a,    16   b  are electrically conductive, partially transparent and partially reflective, and may be fabricated, for example, by depositing one or more layers each of chromium and indium-tin-oxide onto a transparent substrate  20 . The layers are patterned into parallel strips, and may form row electrodes in a display device as described further below. The movable layers  14   a,    14   b  may be formed as a series of parallel strips of a deposited metal layer or layers (orthogonal to the row electrodes  16   a,    16   b ) deposited on top of posts  18  and an intervening sacrificial material deposited between the posts  18 . When the sacrificial material is etched away, the deformable metal layers are separated from the fixed metal layers by a defined air gap  19 . A highly conductive and reflective material such as aluminum may be used for the deformable layers, and these strips may form column electrodes in a display device. 
     With no applied voltage, the cavity  19  remains between the layers  14   a,    16   a  and the deformable layer is in a mechanically relaxed state as illustrated by the pixel  12   a  in  FIG. 1 . However, when a potential difference is applied to a selected row and column, the capacitor formed at the intersection of the row and column electrodes at the corresponding pixel becomes charged, and electrostatic forces pull the electrodes together. If the voltage is high enough, the movable layer is deformed and is forced against the fixed layer (a dielectric material which is not illustrated in this Figure may be deposited on the fixed layer to prevent shorting and control the separation distance) as illustrated by the pixel  12   b  on the right in  FIG. 1 . The behavior is the same regardless of the polarity of the applied potential difference. In this way, row/column actuation that can control the reflective vs. non-reflective pixel states is analogous in many ways to that used in conventional LCD and other display technologies. 
       FIGS. 2 through 5  illustrate one exemplary process and system for using an array of interferometric modulators in a display application.  FIG. 2  is a system block diagram illustrating one embodiment of an electronic device that may incorporate aspects of the invention. In the exemplary embodiment, the electronic device includes a processor  21  which may be any general purpose single- or multi-chip microprocessor such as an ARM, Pentium®, Pentium II®, Pentium III®, Pentium IV®, Pentium® Pro, an 8051, a MIPS®, a Power PC®, an ALPHA®, or any special purpose microprocessor such as a digital signal processor, microcontroller, or a programmable gate array. As is conventional in the art, the processor  21  may be configured to execute one or more software modules. In addition to executing an operating system, the processor may be configured to execute one or more software applications, including a web browser, a telephone application, an email program, or any other software application. 
     In one embodiment, the processor  21  is also configured to communicate with an array controller  22 . In one embodiment, the array controller  22  includes a row driver circuit  24  and a column driver circuit  26  that provide signals to a pixel array  30 . The cross section of the array illustrated in  FIG. 1  is shown by the lines  1 - 1  in  FIG. 2 . For MEMS interferometric modulators, the row/column actuation protocol may take advantage of a hysteresis property of these devices illustrated in  FIG. 3 . It may require, for example, a 10 volt potential difference to cause a movable layer to deform from the released state to the actuated state. However, when the voltage is reduced from that value, the movable layer maintains its state as the voltage drops back below 10 volts. In the exemplary embodiment of  FIG. 3 , the movable layer does not release completely until the voltage drops below 2 volts. There is thus a range of voltage, about 3 to 7 V in the example illustrated in  FIG. 3 , where there exists a window of applied voltage within which the device is stable in either the released or actuated state. This is referred to herein as the “hysteresis window” or “stability window.” For a display array having the hysteresis characteristics of  FIG. 3 , the row/column actuation protocol can be designed such that during row strobing, pixels in the strobed row that are to be actuated are exposed to a voltage difference of about 10 volts, and pixels that are to be released are exposed to a voltage difference of close to zero volts. After the strobe, the pixels are exposed to a steady state voltage difference of about 5 volts such that they remain in whatever state the row strobe put them in. After being written, each pixel sees a potential difference within the “stability window” of 3-7 volts in this example. This feature makes the pixel design illustrated in  FIG. 1  stable under the same applied voltage conditions in either an actuated or released pre-existing state. Since each pixel of the interferometric modulator, whether in the actuated or released state, is essentially a capacitor formed by the fixed and moving reflective layers, this stable state can be held at a voltage within the hysteresis window with almost no power dissipation. Essentially no current flows into the pixel if the applied potential is fixed. 
     In typical applications, a display frame may be created by asserting the set of column electrodes in accordance with the desired set of actuated pixels in the first row. A row pulse is then applied to the row 1 electrode, actuating the pixels corresponding to the asserted column lines. The asserted set of column electrodes is then changed to correspond to the desired set of actuated pixels in the second row. A pulse is then applied to the row 2 electrode, actuating the appropriate pixels in row 2 in accordance with the asserted column electrodes. The row 1 pixels are unaffected by the row 2 pulse, and remain in the state they were set to during the row 1 pulse. This may be repeated for the entire series of rows in a sequential fashion to produce the frame. Generally, the frames are refreshed and/or updated with new display data by continually repeating this process at some desired number of frames per second. A wide variety of protocols for driving row and column electrodes of pixel arrays to produce display frames are also well known and may be used in conjunction with the present invention. 
       FIGS. 4 and 5  illustrate one possible actuation protocol for creating a display frame on the 3×3 array of  FIG. 2 .  FIG. 4  illustrates a possible set of column and row voltage levels that may be used for pixels exhibiting the hysteresis curves of  FIG. 3 . In the  FIG. 4  embodiment, actuating a pixel can involve setting the appropriate column to −V bias , and the appropriate row to +ΔV, which may correspond to −5 volts and +5 volts respectively. Releasing the pixel can be accomplished by setting the appropriate column to +V bias , and the appropriate row to the same +ΔV, producing a zero volt potential difference across the pixel. In those rows where the row voltage is held at zero volts, the pixels are stable in whatever state they were originally in, regardless of whether the column is at +V bias , or −V bias . As is also illustrated in  FIG. 4 , it will be appreciated that voltages of opposite polarity than those described above can be used, e.g., actuating a pixel can involve setting the appropriate column to +V bias , and the appropriate row to −ΔV. In this embodiment, releasing the pixel is accomplished by setting the appropriate column to −V bias , and the appropriate row to the same −ΔV, producing a zero volt potential difference across the pixel. 
       FIG. 5B  is a timing diagram showing a series of row and column signals applied to the 3×3 array of  FIG. 2  which will result in the display arrangement illustrated in  FIG. 5A , where actuated pixels are non-reflective. Prior to writing the frame illustrated in  FIG. 5A , the pixels can be in any state, and in this example, all the rows are at 0 volts, and all the columns are at +5 volts. With these applied voltages, all pixels are stable in their existing actuated or released states. 
     In the  FIG. 5A  frame, pixels (1, 1), (1, 2), (2, 2), (3, 2) and (3, 3) are actuated. To accomplish this, during a “line time” for row 1, columns 1 and 2 are set to −5 volts, and column 3 is set to +5 volts. This does not change the state of any pixels, because all the pixels remain in the 3−7 volt stability window. Row 1 is then strobed with a pulse that goes from 0, up to 5 volts, and back to zero. This actuates the (1, 1) and (1, 2) pixels and releases the (1, 3) pixel. No other pixels in the array are affected. To configure row 2 as desired, column 2 is set to −5 volts, and columns 1 and 3 are set to +5 volts. The same strobe applied to row 2 will then actuate pixel (2, 2) and release pixels (2, 1) and (2, 3). Again, no other pixels of the array are affected. Row 3 is similarly configured by setting columns 2 and 3 to −5 volts, and column 1 to +5 volts. The row 3 strobe sets the row 3 pixels as shown in  FIG. 5A . After writing the frame, the row potentials are zero, and the column potentials can remain at either +5 or −5 volts, and the display is then stable in the arrangement of  FIG. 5A . It will be appreciated that the same procedure can be employed for arrays of dozens or hundreds of rows and columns. It will also be appreciated that the timing, sequence, and levels of voltages used to perform row and column actuation can be varied widely within the general principles outlined above, and the above example is exemplary only, and any actuation voltage method can be used with the present invention. 
     The details of the structure of interferometric modulators that operate in accordance with the principles set forth above may vary widely. For example,  FIGS. 6A-6C  illustrate three different embodiments of the moving minor structure.  FIG. 6A  is a cross section of the embodiment of  FIG. 1 , where a strip of metal material  14  is deposited on orthogonally extending supports  18 . In  FIG. 6B , the moveable reflective material  14  is attached to supports at the corners only, on tethers  32 . In  FIG. 6C , the moveable reflective material  14  is suspended from a deformable layer  34 . This embodiment has benefits because the structural design and materials used for the reflective material  14  can be optimized with respect to the optical properties, and the structural design and materials used for the deformable layer  34  can be optimized with respect to desired mechanical properties. The production of various types of interferometric devices is described in a variety of published documents, including, for example, U.S. Published Application 2004/0051929. A wide variety of well known techniques may be used to produce the above described structures involving a series of material deposition, patterning, and etching steps. 
     Data describing a monochrome display image may include one bit of data per pixel. One embodiment of a monochrome display includes one interferometric modulator per pixel, the on or off state of the modulator being set based on the value of the one bit of data per pixel. A greyscale image may include several bits of data per pixel. For example, a “3 bit” grayscale display includes 3 bits of data per pixel that correspond to one of eight shades of gray that may be assigned to each pixel. One embodiment of a display for displaying an exemplary 3 bit grayscale image includes three interferometric modulators for each pixel. To obtain the eight shades, the three modulators reflect light according to a ratio of 1:2:4. In one such embodiment, each of the interferometric modulators includes minors having a reflective surface area that varies according to the ratio of 1:2:4. A particular shade in a pixel is obtained in such an embodiment by setting each modulator to an on or off state based on the binary value of a corresponding bit of the 3 bits of data. One embodiment of a color display works similarly except that the color display includes a group of red, green, and blue interferometric modulators. For example, in a 12-bit color display, 4 of the 12 bits correspond to each of 16 intensities of red, green, and blue which are produced by red, green, or blue interferometric modulators. Such greyscale or color displays thus have more display elements to address than does a monochrome display. 
     As discussed briefly above, power consumption in an interferometric modulator display is a function of changing the state of the interferometric modulator display elements in the display. Thus, power consumption of such a display can be varied by changing the frequency of updates of the display elements. In addition, color or greyscale interferometric modulator displays that have pixels, or rows of pixels subdivided into sets of interferometric modulators, tend to have increased power consumption as compared to monochrome displays because of the increased number of interferometric modulators in such displays. 
     One way of reducing power consumption in an interferometric display is to reduce the frequency of updates of the display elements in the display. In particular, it has been found that in a greyscale or color display, the display elements corresponding to the least significant bits of greyscale or color shade data can be updated at a lower rate than the remaining display elements to reduce power consumption of the display. 
       FIG. 7  is a partial schematic diagram of an exemplary interferometric modulator display, similar to that shown in  FIG. 2 . In the embodiment of  FIG. 7 , each of the rows of the pixel array  30  is subdivided into three subrows, A, B, and C. Each of the subrows defines one interferometric modulator display element  100  at each column. The subrows are each connected to the row driver  24 . As compared to  FIG. 2 , the row driver  24  thus includes additional connections to the subrows to drive the color or greyscale pixel array  30 . In  FIG. 7 , the display elements  100  are each illustrated in exemplary reflecting (white) or absorbing (hashed) states. 
     In the embodiment of  FIG. 7 , the processor  21  is in communication with a network interface  102  that communicates over a network  104  with a content server  106 . The network interface  102  may support communication over any suitable data communications network. In one embodiment, the network interface  102  is a cellular radio transceiver that supports a code division multiple access (CDMA), or other wireless voice and/or data communications protocol such as time division multiple access (TDMA), frequency division multiple access (FDMA), or Global System for Mobile Communications (GSM). In other embodiments, the network interface  102  may support one or more additional, or alternative, radio interface protocols such as Bluetooth, IEEE 802.11, or other wireless protocols. In one embodiment, the network interface  102  supports a wired data interface, such as Ethernet, a serial port, a universal serial bus (USB) port, Firewire, IEEE 1394, a synchronization cradle coupled to a network or other computing device, or an interface to a GPS receiver. 
     The network  104  may include an Internet Protocol (IP) network, wireless networks, or any other suitable data communications network. The content server  106  may include any suitable computer system configured to transmit image data, including motion picture data in any format suitable for transmission over the network  106 . 
     In one embodiment, the array controller  22  controls the rate of update of the display elements  100 . The processor  21  may configure the refresh rate of the array controller  22 . In one embodiment, the array controller is configured to operate in two or more modes of update. In one mode, each of the rows of the pixel array  30  is updated using a method such as described above with reference to  FIG. 5B . In a second mode, at least one of the subrows is updated at a lower frequency. For example, in one embodiment, in the second mode, subrows A and B are updated 30 times a second and the remaining rows, e.g., subrow C is updated only once a second. Thus, power consumption is reduced with the tradeoff of lower color resolution and, thus, color gamut in the second mode. In another embodiment, the lower frequency of updating the remaining rows, e.g., row C, is very low, e.g., only when the display is initialized, or when the mode changes. 
     In one embodiment, the array controller  22  is configured to update the rows and subrows of display elements  100  by applying a series of row voltage strobes to each subrow to configure the state of the subrow. In one embodiment, in the second mode, the array controller  22  is configured to skip row voltage strobes for some of the subrows. For example, in one embodiment, in the first mode, the array controller  22  applies a series of row voltage strobes to each of the subrows A, B, and C of each row. When switched to the second mode, the array control  22  applies the row voltage strobes to subrows A and B of each row but skips subrow C. In one embodiment, as available battery power becomes lower, the array controller  22  skips more subrows, for example, by applying row voltage strobes to subrows A but skipping subrows B and C of each of the rows. In one embodiment, the array controller  22  applies a series of row voltage strobes to configure the states the non-updated subrows to a selected state, e.g., non-reflecting, upon entering the second mode. In one embodiment, the array controller  22  maintains the non-updated subrows in the selected state by applying a bias voltage across the display elements  100  of such subrows. In another embodiment, the array controller  22  periodically applies row voltage strobes to the otherwise non-updated subrows in the second mode to configure the state of the display elements  100  in such subrows to a new selected state. For example, the array controller  22  periodically fails to skip the subrows C and updates the display elements  100  in the subrows C to a new selected state. This periodic application of row voltage strobes to the otherwise non-updated subrows may be at a frequency much lower than the frequency of application of row voltage strobes to the other subrows. In one embodiment, the lower frequency period is non-constant. In one embodiment, the lower frequency period is based on image data and varies based on the image data. 
     In one embodiment, the display elements  100  of the subrows that are updated at the lower frequency, e.g., row C in the exemplary embodiment, are all set to the same state. In one such embodiment, the display elements of the less frequently updated subrows are set to a non-reflecting state. In another embodiment, the less frequently updated subrows are set to display an overall average visual shade of grey or color that may, for example, be based on an average brightness or color for some or all display elements  100  calculated over one or more image frame or frame portions. 
     In another embodiment, the display state of the less frequently updated subrows of display elements is based on particular portions of the image data stream. For example, motion video data, e.g., MPEG data, comprises reference frames describing all pixels that are sent relatively infrequently and intervening data frames that update only a portion of the pixels in the video image. In one embodiment, the less frequently updated subrows may be updated only when reference frames are displayed, and may be held at a particular state until the next reference frame is received. The particular state may be a calculated state, as described above, or the actual state for the less frequently updated display elements  100  in the reference state. 
     In one embodiment, additional modes may include updating a different number of subrows at different frequencies. For example, in one embodiment, in a first mode each of subrows A, B, and C is updated at a first rate; in a second mode, subrow A and B are updated at a first rate and subrow C at a lower rate, or at varying rate, such as described above based on receiving video reference data frames; and in a third mode, subrow A is updated at a first rate, subrow B at a second rate, and subrow C at a third rate. It is to be recognized that in embodiments with more subrows, additional modes of operation may be defined to have varying power consumption properties. 
     In one embodiment, the array controller  22  changes the display mode when available power level conditions, such as from a battery (not shown) providing power to the array  30 , fall below a threshold level, or satisfy other predetermined conditions. In one embodiment, the processor  21  determines when to change display mode and signals the array controller  22  to change operational mode. In another embodiment, a user of an electronic device that contains the pixel array  30  may trigger the change to a different mode manually, or may configure the device to switch between modes under predetermined conditions. 
     In is to be recognized that while certain embodiments are discussed herein with respect to reducing display resolution by skipping row strobes, in other embodiments, updates of particular columns may be skipped to reduce power consumption. For example, in one such embodiment, rather than transitioning column voltages as image data for a given column changes from row to row, the voltage applied to some columns may be held at a potential that maintains the display elements of the skipped columns in an actuated or released state. In the embodiment of  FIG. 5 , for example, the columns in which column transitions are skipped can be held at a constant 0 V −5 V to remain released during frame updates, or at a constant 10 V-15 V to remain activated during frame updates. 
     In one embodiment, the image data being displayed by the display array  30  includes data being received over the network  104  from the content server  106 . In one embodiment, the processor  21  communicates data describing the current display mode being used by the array controller to the content server  106 . The content server  106  may thus filter the image data so that the image data for non-updated display elements is not sent. Thus, the total bandwidth consumed by the communicated data signal is reduced in proportion to the number of display elements that are not being updated at the fastest display rate. This reduction in data rate may further reduce power consumption associated with the display as the network interface  102  and the processor  21  have less data to process. In one embodiment, the content server  106  may determine the state, shade, or color for the less frequently updated subrows to display between updates and communicate that state to the processor  21 . 
     In addition to varying the data rate based on the operational mode of the display, the content server  106  may also control or select the operational mode of the array  30 . For example, based on information available to the content server  106  such as operational or power data associated with the display array  30  or controller  22 , the content server  106  may send control data to the processor  21  for selecting the operational mode of the array  30 . The content server  106  may also select the operational mode based on other data such as stored user preferences, rules associated with the content, or the desired rate of transfer of data on the network  104 . 
     While the above detailed description has shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art without departing from the spirit of the invention. As will be recognized, the present invention may be embodied within a form that does not provide all of the features and benefits set forth herein, as some features may be used or practiced separately from others. The scope of the invention is indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.