Patent Publication Number: US-10777116-B1

Title: Electronic display emission scanning

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Provisional Application Ser. No. 62/232,935, filed Sep. 25, 2015, entitled “Electronic Display Emission Scanning,” which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     The present disclosure relates generally to techniques for driving a display and, more particularly, to techniques for emission scanning of the electronic display. 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     Emission control for electronic displays may include pulse width modulation to cause various gray levels and luminance values. However, with a relatively high duty cycle (e.g., 75%) emission voltage (IR) drop can effect more strongly. IR drop in the panel can impact the overdrive voltage of the current source inside and cause brightness errors and display artifacts. Severity of the artifacts is display pattern dependent, and the problem is worsened as we only the further the more pixels that serially share a supply. In other words, more pixels sharing a supply may increase the IR drop to cause non-uniformity of the display and/or artifacts which degrade display quality. 
     SUMMARY 
     A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below. 
     Row drivers and column drivers may be used to distribute clock and/or emission controls for the display. In other words, the row and column drivers, in combination, enable the display to accurately pinpoint individual pixels and/or sub-pixels or groups of pixels and/or sub-pixels that are to be driven. These row drivers may have redundant counterparts that increase possible complications/spacing in locating components within a display. To alleviate some complexity of trace and/or spacing. Row driver sets (a primary and slave row driver) may be located at opposing ends of an active area of the display. The task allocations between the sets may include dividing the roles of each row driver by color. For example, a first row driver set may drive red sub-pixels while a second row driver set drives blue and/or green sub-pixels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  is a block diagram of components of an electronic device that may include a micro-light-emitting-diode (μ-LED) display, in accordance with an embodiment; 
         FIG. 2  is a perspective view of the electronic device in the form of a fitness band, in accordance with an embodiment; 
         FIG. 3  is a front view of the electronic device in the form of a slate, in accordance with an embodiment; 
         FIG. 4  is a perspective view of the electronic device in the form of a notebook computer, in accordance with an embodiment; 
         FIG. 5  is a block diagram of a μ-LED display that employs microdrivers (μDs) to drive μ-LED subpixels with controls signals from row drivers (RDs) and data signals from column drivers (CDs), in accordance with an embodiment; 
         FIG. 6  is a block diagram schematically illustrating an operation of one of the micro-drivers (μDs), in accordance with an embodiment; 
         FIG. 7  is a timing diagram illustrating an example operation of the micro-driver (μD) of  FIG. 6 , in accordance with an embodiment; 
         FIG. 8  is a timing diagram with four emission clock phases, in accordance with an embodiment; 
         FIG. 9  is a timing diagram of the four emission clock phases of  FIG. 8  illustrating emission states and related data updates, in accordance with an embodiment; 
         FIG. 10  is a timing diagram with an emission distribution having six emission clock phases, in accordance with an embodiment; 
         FIG. 11  is a timing diagram with an emission distribution having six emission clock phases with a relatively low duty cycle, in accordance with an embodiment; 
         FIG. 12  is an emission patter using six phases and a duty cycle of 75%, in accordance with an embodiment; 
         FIG. 13  is an emission patter using six phases and a duty cycle of 35%, in accordance with an embodiment; 
         FIG. 14  is an emission patter using six phases and a duty cycle that varies by row, in accordance with an embodiment; 
         FIG. 15  illustrates a graph of normalized luminance for the content of  FIG. 14 , in accordance with an embodiment; 
         FIG. 16  illustrates a re-scaled view of the graph of  FIG. 15  emphasizing IR drop, in accordance with an embodiment; 
         FIG. 17  illustrates a graph of normalized luminance with distributed emission periods, in accordance with an embodiment; 
         FIG. 18  illustrates a re-scaled view of the graph of  FIG. 17  emphasizing IR drop, in accordance with an embodiment; 
         FIG. 19  illustrates an emission pattern of content using a relatively high duty cycle, in accordance with an embodiment; 
         FIG. 20  illustrates an emission pattern of the content of  FIG. 19  using a relatively low duty cycle, in accordance with an embodiment; 
         FIG. 21  illustrates a flowchart diagram for reducing IR drop by distributing emission periods throughout the display and distributing the emission periods over time, in accordance with an embodiment; 
         FIG. 22  illustrates a process for operating a display using microdrivers, in accordance with an embodiment; 
         FIG. 23  illustrates a timing diagram for alternatingly driving odd and even rows, in accordance with an embodiment; 
         FIG. 24  illustrates a block diagram of a pixel driving system including a microdriver and driven pixels, in accordance with an embodiment; 
         FIG. 25  illustrates a timing diagram that may be used to drive eight pixels using eight-way time-multiplexing, in accordance with an embodiment; and 
         FIG. 26  illustrates a process for operating a microdriver for driving pixels of a display, in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     As discussed above, IR drop may cause display artifacts. The IR drop may refer to an analog IR drop or a digital IR drop. Analog IR drop is at a low frequency due to the current through the passing through the micro light emitting diodes. Digital IR drop refers to an IR drop caused by digital switching (e.g., emission scanning). One or more of the IR drops may be distributed throughout the display geographically and/or temporally. For example, multiple emission phases may be used to control when and where the display is emitting light. Moreover, using some limitations on duty cycle (e.g., less than 50% and/or less than 12%), a single microdriver capable of driving a single pixel may be used to drive additional pixels with some minor changes (e.g., doubling the buffer). 
     Suitable electronic devices that may include a micro-LED (μ-LED) display and corresponding circuitry of this disclosure are discussed below with reference to  FIGS. 1-4 . One example of a suitable electronic device  10  may include, among other things, processor(s) such as a central processing unit (CPU) and/or graphics processing unit (GPU)  12 , storage device(s)  14 , communication interface(s)  16 , a μ-LED display  18 , input structures  20 , and an energy supply  22 . The blocks shown in  FIG. 1  may each represent hardware, software, or a combination of both hardware and software. The electronic device  10  may include more or fewer components. It should be appreciated that  FIG. 1  merely provides one example of a particular implementation of the electronic device  10 . 
     The CPU/GPU  12  of the electronic device  10  may perform various data processing operations, including generating and/or processing image data for display on the display  18 , in combination with the storage device(s)  14 . For example, instructions that can be executed by the CPU/GPU  12  may be stored on the storage device(s)  14 . The storage device(s)  14  thus may represent any suitable tangible, computer-readable media. The storage device(s)  14  may be volatile and/or non-volatile. By way of example, the storage device(s)  14  may include random-access memory, read-only memory, flash memory, a hard drive, and so forth. 
     The electronic device  10  may use the communication interface(s)  16  to communicate with various other electronic devices or components. The communication interface(s)  16  may include input/output (I/O) interfaces and/or network interfaces. Such network interfaces may include those for a personal area network (PAN) such as Bluetooth, a local area network (LAN) or wireless local area network (WLAN) such as Wi-Fi, and/or for a wide area network (WAN) such as a long-term evolution (LTE) cellular network. 
     Using pixels containing an arrangement μ-LEDs, the display  18  may display images generated by the CPU/GPU  12 . The display  18  may include touchscreen functionality to allow users to interact with a user interface appearing on the display  18 . Input structures  20  may also allow a user to interact with the electronic device  10 . For instance, the input structures  20  may represent hardware buttons. The energy supply  22  may include any suitable source of energy for the electronic device. This may include a battery within the electronic device  10  and/or a power conversion device to accept alternating current (AC) power from a power outlet. 
     As may be appreciated, the electronic device  10  may take a number of different forms. As shown in  FIG. 2 , the electronic device  10  may take the form of a fitness band  30 . The fitness band  30  may include an enclosure  32  that houses the electronic device  10  components of the fitness band  30 . A strap  30  may allow the fitness band  30  to be worn on the arm or wrist. The display  18  may display information related to the fitness band operation. Additionally or alternatively, the fitness band  30  may operate as a watch, in which case the display  18  may display the time. Input structures  20  may allow a person wearing the fitness band  30  navigate a graphical user interface (GUI) on the display  18 . 
     The electronic device  10  may also take the form of a slate  40 . Depending on the size of the slate  40 , the slate  40  may serve as a handheld device such as a mobile phone. The slate  40  includes an enclosure  42  through which several input structures  20  may protrude. The enclosure  42  also holds the display  18 . The input structures  20  may allow a user to interact with a GUI of the slate  40 . For example, the input structures  20  may enable a user to make a telephone call. A speaker  44  may output a received audio signal and a microphone  46  may capture the voice of the user. The slate  40  may also include a communication interface  16  to allow the slate  40  to connect via a wired connection to another electronic device. 
     A notebook computer  50  represents another form that the electronic device  10  may take. It should be appreciated that the electronic device  10  may also take the form of any other computer, including a desktop computer. The notebook computer  50  shown in  FIG. 4  includes the display  18  and input structures  20  that include a keyboard and a track pad. Communication interfaces  16  of the notebook computer  50  may include, for example, a universal service bus (USB) connection. 
     A block diagram of the architecture of the μ-LED display  18  appears in  FIG. 5 . In the example of  FIG. 5 , the display  18  uses an RGB display panel  60  with pixels that include red, green, and blue μ-LEDs as subpixels. Support circuitry  62  thus may receive RGB-format video image data  64 . It should be appreciated, however, that the display  18  may alternatively display other formats of image data, in which case the support circuitry  62  may receive image data of such different image format. In the support circuitry  62 , a video timing controller (TCON)  66  may receive and use the image data  64  in a serial signal to determine a data clock signal (DATA_CLK) to control the provision of the image data  64  in the display  18 . The video TCON  66  also passes the image data  64  to serial-to-parallel circuitry  68  that may deserialize the image data  64  signal into several parallel image data signals  70 . That is, the serial-to-parallel circuitry  68  may collect the image data  64  into the particular data signals  70  that are passed on to specific columns among a total of M respective columns in the display panel  60 . As such, the data  70  is labeled DATA[0], DATA[1], DATA[2], DATA[3] DATA[M−3], DATA[M−2], DATA[M−1], and DATA[M]. The data  70  respectively contain image data corresponding to pixels in the first column, second column, third column, fourth column . . . fourth-to-last column, third-to-last column, second-to-last column, and last column, respectively. The data  70  may be collected into more or fewer columns depending on the number of columns that make up the display panel  60 . 
     As noted above, the video TCON  66  may generate the data clock signal (DATA_CLK). An emission timing controller (TCON)  72  may generate an emission clock signal (EM_CLK). Collectively, these may be referred to as Row Scan Control signals, as illustrated in  FIG. 5 . These Row Scan Control signals may be used by circuitry on the display panel  60  to display the image data  70 . 
     In particular, the display panel  60  includes column drivers (CDs)  74 , row drivers (RDs)  76 , and micro-drivers (μDs or uDs)  78 . Each uD  78  drives a number of pixels  80  having μ-LEDs as subpixels  82 . Each pixel  80  includes at least one red μ-LED, at least one green μ-LED, and at least one blue μ-LED to represent the image data  64  in RGB format. Although the uDs  78  of  FIG. 5  is shown to drive six pixels  80  having three subpixels  82  each, each μD  78  may drive more or fewer pixels  80 . For example, each μD  78  may respectively drive 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or more pixels  80 . 
     A power supply  84  may provide a reference voltage (VREF)  86  to drive the μ-LEDs, a digital power signal  88 , and an analog power signal  90 . In some cases, the power supply  84  may provide more than one reference voltage (VREF)  86  signal. Namely, subpixels  82  of different colors may be driven using different reference voltages. As such, the power supply  84  may provide more than one reference voltage (VREF)  86 . Additionally or alternatively, other circuitry on the display panel  60  may step the reference voltage (VREF)  86  up or down to obtain different reference voltages to drive different colors of μ-LED. 
     To allow the μDs  78  to drive the μ-LED subpixels  82  of the pixels  80 , the column drivers (CDs)  74  and the row drivers (RDs)  76  may operate in concert. Each column driver (CD)  74  may drive the respective image data  70  signal for that column in a digital form. Meanwhile, each RD  76  may provide the data clock signal (DATA_CLK) and the emission clock signal (EM_CLK) at an appropriate to activate the row of μDs  78  driven by the RD  76 . A row of uDs  78  may be activated when the RD  76  that controls that row sends the data clock signal (DATA_CLK). This may cause the now-activated uDs  78  of that row to receive and store the digital image data  70  signal that is driven by the column drivers (CDs)  74 . The uDs  78  of that row then may drive the pixels  80  based on the stored digital image data  70  signal based on the emission clock signal (EM_CLK). 
     A block diagram shown in  FIG. 6  illustrates some of the components of one of the μDs  78 . The μD  78  shown in  FIG. 6  includes pixel data buffer(s)  100  and a digital counter  102 . The pixel data buffer(s)  100  may include sufficient storage to hold the image data  70  that is provided. For instance, the μD  78  may include pixel data buffers to store image data  70  for three subpixels  82  at any one time (e.g., for 8-bit image data  70 , this may be 24 bits of storage). It should be appreciated, however, that the μD  78  may include more or fewer buffers, depending on the data rate of the image data  70  and the number of subpixels  82  included in the image data  70 . The pixel data buffer(s)  100  may take any suitable logical structure based on the order that the column driver (CD)  74  provides the image data  70 . For example, the pixel data buffer(s)  100  may include a first-in-first-out (FIFO) logical structure or a last-in-first-out (LIFO) structure. 
     When the pixel data buffer(s)  100  has received and stored the image data  70 , the RD  76  may provide the emission clock signal (EM_CLK). A counter  102  may receive the emission clock signal (EM_CLK) as an input. The pixel data buffer(s)  100  may output enough of the stored image data  70  to output a digital data signal  104  represent a desired gray level for a particular subpixel  82  that is to be driven by the μD  78 . The counter  102  may also output a digital counter signal  106  indicative of the number of edges (only rising, only falling, or both rising and falling edges) of the emission clock signal (EM_CLK)  98 . The signals  104  and  106  may enter a comparator  108  that outputs an emission control signal  110  in an “on” state when the signal  106  does not exceed the signal  104 , and an “off” state otherwise. The emission control signal  110  may be routed to driving circuitry (not shown) for the subpixel  82  being driven, which may cause light emission  112  from the selected subpixel  82  to be on or off. The longer the selected subpixel  82  is driven “on” by the emission control signal  110 , the greater the amount of light that will be perceived by the human eye as originating from the subpixel  82 . 
     A timing diagram  120 , shown in  FIG. 7 , provides one brief example of the operation of the μD  78 . The timing diagram  120  shows the digital data signal  104 , the digital counter signal  106 , the emission control signal  110 , and the emission clock signal (EM_CLK) represented by numeral  122 . In the example of  FIG. 7 , the gray level for driving the selected subpixel  82  is gray level  4 , and this is reflected in the digital data signal  104 . The emission control signal  110  drives the subpixel  82  “on” for a period of time defined as gray level  4  based on the emission clock signal (EM_CLK). Namely, as the emission clock signal (EM_CLK) rises and falls, the digital counter signal  106  gradually increases. The comparator  108  outputs the emission control signal  110  to an “on” state as long as the digital counter signal  106  remains less than the data signal  104 . When the digital counter signal  106  reaches the data signal  104 , the comparator  108  outputs the emission control signal  110  to an “off” state, thereby causing the selected subpixel  82  no longer to emit light. 
     It should be noted that the steps between gray levels are reflected by the steps between emission clock signal (EM_CLK) edges. That is, based on the way humans perceive light, to notice the difference between lower gray levels, the difference between the amount of light emitted between two lower gray levels may be relatively small. To notice the difference between higher gray levels, however, the difference between the amount of light emitted between two higher gray levels may be comparatively much greater. The emission clock signal (EM_CLK) therefore may use relatively short time intervals between clock edges at first. To account for the increase in the difference between light emitted as gray levels increase, the differences between edges (e.g., periods) of the emission clock signal (EM_CLK) may gradually lengthen. The particular pattern of the emission clock signal (EM_CLK), as generated by the emission TCON  72 , may have increasingly longer differences between edges (e.g., periods) so as to provide a gamma encoding of the gray level of the subpixel  82  being driven. 
     In some embodiments, voltage (IR) drop may distributed in time and/or space to reduce or remove the appearance of display artifacts resulting from IR drop. The IR drop may refer to an analog IR drop or a digital IR drop. Analog IR drop is at a low frequency due to the current through the passing through the micro light emitting diodes. Digital IR drop refers to an IR drop caused by digital switching (e.g., emission scanning). One or more of the IR drops may be distributed throughout the display geographically and/or temporally. For example, multiple emission phases may be used to control when and where the display is emitting light. 
       FIG. 8  illustrates a timing diagram  1000  that includes a phase 0 emission clock  1002 , a phase 1 emission clock  1004 , a phase 2 emission clock  1006 , and a phase 3 emission clock  1008 . Although the timing diagram  1000  includes four phases, the electronic display may use more or less phases. For example, the electronic display may include 2, 3, 4, 5, 6, or more phases for the emission clock. These phases or “base clocks” are generated in the emission TCON  72  or the video TCON  66 . Each row driver in the display elects one of the phases. The timing diagram  1000  illustrates that a first row  1010  uses the phase 0 emission clock  1002 , a second row  1012  uses the phase 1 emission clock  1004 , a third row  1014  uses the phase 2 emission clock  1006 , a fourth row  1016  uses the phase 3 emission clock, a fifth row  1018  that uses the phase 0 emission clock  1002 , a sixth row  1020  that uses the phase 1 emission clock  1002 , and a seventh row the uses the phase 2 emission clock  1002 . As illustrated, the emission clock may be in an initialization state where, each row adopts its phase in sequence, but the phase of the row may be derived based on the number of base clock phases used and the number of the row. Essentially, each row uses a phase selected using the following formula: 
                     Phase     EM   ⁢   _   ⁢   CLK       =       Row     N     EM   ⁢   _   ⁢   CLK         -   1             (     Equation   ⁢           ⁢   1     )               
where PhaseEM_CLK is the phase for of emission clock for a row (e.g., Phase 0); Row is the row for which the phase is being determined, and NEM_CLK is the number of phases available (e.g., 4). Thus, any row driver may determine its phase to use based on how many rows are located before the row. The rows may be numbered in a top-to-bottom or bottom-to-top order. Furthermore, the row drivers and column driver tasks may be reversed and all discussion related to rows may refer to columns and vice versa. Thus, the columns may be driven at different emission levels or times based on time, as discussed herein.
 
     As previously discussed, a data update and the emission phase may be performed at different times due to the pixel data buffers in the microdrivers.  FIG. 9  illustrates a timing diagram  1030  that illustrates an emission phase and its related data update. The timing diagram  1030  shows an emission state for each row when the duty cycle is relatively high (e.g., solid white) and four phases. A first cycle of a first phase  1032  is used at rows 1, 5, 9, 13, and 17, a first cycle of a second phase  1034  is used at rows 2, 6, 10, 14, and 18, a first cycle of a third phase  1036  is for rows 3, 7, 15, and 19; and a first cycle of a fourth phase  1038  is used for rows 4, 8, 16, and 20. Once a cycle (e.g., 16 milliseconds for a 60 Hz refresh rate) has been completed, the phases repeat. For example, a second cycle of the first phase  1040  begins for rows 1, 5, 9, 13, and 17 at the beginning of the new cycle and, a second cycle of the second phase  1042  begins for rows after 1/N of the cycle has been completed when N is the number of phase base clocks used. 
     The timing diagram  1030  also illustrates data updates  1044 ,  1046 ,  1048 ,  1050 ,  1052 ,  1054 ,  1056 , and  1058  used to update pixel data to the microdrivers. The data update may be updated prior to emission of the data via the emission clock phases. For example, the data update  1044  includes an update for rows using the first cycle  1034  of the phase 1 signals, and the data update  1046  includes an update for rows using the first cycle  1036  phase 2 signals, the data update  1048  includes an update for rows using the first cycle  1038  of the phase 3 signals, the data update  1050  includes an update for rows using the phase 0 signal second cycle  1040 , the data update  1052  includes an update for rows using the phase 1 signal second cycle  1042 , the data update  1054  includes an update for rows using a second cycle of the phase 2 signal, the data update  1056  includes an update for rows using a second cycle of the phase 3 signal, and the data update  1058  includes an update for rows using a third cycle of the phase 3 signal. Thus, the data update may be provided before emission of the data provided in the update. 
     By distributing emission and data updates, IR drop may be distributed and smoothed from row to row. In other words, luminance drops between rows may be eliminated or reduced. Furthermore, such distribution may be completed using a relatively low number of clock phases (e.g., 4 or 6 phases), but the distribution may be more complete with more clock phases. Since rows and columns are selectable, the illustrated distribution may be implemented on local passive matrices by programming shift registers to behave differently by shifting emission for adjacent rows. 
       FIG. 10  illustrates a timing diagram  1060  with an emission distribution using 6 phases. The timing diagram illustrates a first clock phase  1062  used by rows 1, 7, 13, 19, 25, and so on; a second clock phase  1064  used by rows 2, 8, 14, 20, 26, and so on; a third clock phase  1066  used by rows 3, 9, 15, 21, 27, and so on; a fourth clock phase  1068  used by rows 4, 10, 16, 22, 28, and so on; a fifth clock phase  1070  used by rows 5, 11, 17, 23, 29, and so on; and a sixth clock phase  1072  used by rows 6, 12, 18, 24, 30, and so on. Data updates also occur at T=1/N (e.g., 1/6) of a period  1073  of an emission scan. For example, at OT, a first data update  1074  is sent to rows (2, 8, 14, 20, 26, and so on) using the phase 1 clock  1064 ; a second data update  1076  is sent to rows using the phase 2 clock  1066  at 1/6T, a third data update  1078  is sent to rows using the phase 3 clock  1068  at 1/3T, a fourth data update  1078  is sent to rows using the phase 4 clock  1068  at 1/2T, a fifth data update  1080  is sent to rows using the phase 5 clock  1070  at 2/3T, and a sixth data update  1082  is sent to rows using the phase 0 clock  1072  at 5/6T. After a period T has elapsed, the emission sequence and data update pattern begin again. 
       FIG. 11  illustrates the timing diagram  1060  with a relatively low duty cycle (e.g., low gray level). In other words, the emission period for each row in the emission scan is a relatively small portion of a possible emission period.  FIG. 12  illustrates an emission pattern  2000  using 6 phases for a display and a duty cycle of 75% for a single period. Rows  2002  using phase 0 clocks begin at 1/12T, rows  2004  using phase 1 clocks begin at 1/4T, rows  2006  using phase 2 clocks begin at 5/12T, rows  2008  using phase 3 clocks begin at 7/12T, rows  2010  using phase 4 clocks begin at 3/4T, and rows  2012  using phase 5 clocks begin at 11/12T.  FIG. 13  illustrates the emission pattern  2000  with 6 phases and a relatively low duty cycle of 35%. As can be seen, a higher duty cycle results in more overlap of the emission period of the pixels of the rows. 
       FIG. 14  illustrates a combined content emission pattern  2010 . The content emission pattern  2010  uses 6 phases. Rows  2012  using phase 0 clocks begin at 1/12T, rows  2014  using phase 1 clocks begin at 1/4T, rows  2016  using phase 2 clocks begin at 5/12T, rows  2018  using phase 3 clocks begin at 7/12T, rows  2020  using phase 4 clocks begin at 3/4T, and rows  2014  using phase 5 clocks begin at 11/12T. A lower portion  2026  of the content includes relatively high gray levels (e.g., 75% duty cycle), and an upper portion  2028  of the content includes relatively low gray levels (e.g., 5% duty cycle). 
       FIG. 15  illustrates a graph  2030  of normalized pixel luminance for the combined content emission pattern  2010  of  FIG. 14 . As the graph  2030  illustrates, the luminance of the pixels is generally consistent in a lower flatter region  2032  that includes rows 0 to 300. At row 300, the luminance encounters a luminance spike  2034  as the content transitions from lighter to darker values. Below the luminance spike  2034  on the display, the luminance of the pixels settles into a consistent higher flatter region  2036 . Although the lower flatter region  2032  and the upper flatter region  2036  appear primarily flat, some vertical variance appears in a lower plateau region  2038  and an upper plateau region  2040 .  FIG. 16  illustrates a scaled view of the lower plateau region  2038  accentuating an luminance drop  2042  that may be at least partially attributed to IR drop due to digital switching using traditional emission scanning. The example luminance drop includes a drop in luminance of about 12%. 
       FIG. 17  illustrates a graph  2050  of luminance drops resulting from the spatially varying emission scan discussed herein. The graph  2050  includes four luminance drop graphs all having the same number of phases (e.g., 6), but each graph has a different current and duty cycle combination. For instance, a first line  2054  corresponds to a luminance drop with a first current in the microdriver and a related duty cycle (e.g., 72%). A second line  2056  corresponds to a half-duty cycle (e.g., 36%) and double current. A third line  2058  corresponds to a quarter duty cycle (e.g., 18%) and quadruple the current. A fourth line  2060  corresponds to an eighth duty cycle (e.g., 9%) and eight times the current. As illustrated, the fourth line  2060  with the highest current has the greatest luminance drop  2062 , but the remaining lines  2054 ,  2056 , and  2058  substantially share a luminance drop  2064 . A region of interest  2066  is re-scaled in  FIG. 18 .  FIG. 18  is a re-scaled and zoomed view of the graph  2050  illustrating the differences between lines  2054 ,  2056 , and  2058 . As illustrated, the line  2054  (with the largest duty cycle and lowest current) includes a relatively low luminance drop  2070 , the line  2056  (with the medium duty cycle and medium current) corresponds to a medium luminance drop  2072 , and the line  2058  (with the smallest duty cycle and highest current) corresponds to a relatively high luminance drop  2074 . Thus, the overall luminance drop is related to duty cycle and microdriver current. 
       FIG. 19  illustrates an emission pattern  2080  corresponding to the line  2058 . The emission pattern  2080  includes six phases causing six emission periods  2082 ,  2084 ,  2086 ,  2088 ,  2090 , and  2092 . As illustrated, current draw is substantially consistently distributed throughout the display during the emission phase.  FIG. 20  illustrates an emission pattern  2100  corresponding to a similar display of content using double current and half-duty cycle compared to the emission pattern  2080  of  FIG. 19 . The emission pattern  2100  includes six phases causing six emission periods  2102 ,  2104 ,  2106 ,  2108 ,  2110 , and  2112 . In contrast to the emission pattern  2080 , the emission pattern  2100  includes current-less periods  2114  of no current being drawn by any rows and relatively high current periods  2116  with relatively high levels of current being drawn. These strong contrasts (and the resultant switching) may increase likelihood of apparent artifacts resulting from IR drop. 
       FIG. 21  illustrates a process  2120  for reducing IR drop artifacts by distributing emission periods throughout the display and distributing the emission periods over time. The process  2120  includes receiving, at an nth row driver out of number of row drivers, multiple emission clock phases from a timing controller (block  2122 ). A microdriver in a row corresponding to the row driver receives a data update for pixels (block  2124 ). In some embodiments, the data update may be received from a column driver for the pixels. The row driver sends, after the data update, an n modulo i clock phase to cause the receiving microdriver to send a pixel in the row into an emission state where n is the row and i is the number of clock phases available (block  2126 ). For example, when there are six emission clock phases, the seventh row may use the first emission clock phase while the tenth row may use the fourth emission clock phase. 
     Since row driving is distributed in time and space, some time-multiplexing may be used to drive more pixels using a single microprocessor without substantially increasing hardware in the microprocessor.  FIG. 22  illustrates an embodiment of a process  2200  for operating a display. The process  2200  includes receiving pixel data at a microdriver (block  2202 ). The pixel data may be received from a row driver or column driver to be stored in the microdriver for display via one or more pixels controlled by the microdriver during an emission period for the pixels. The microdriver then drives a first set of pixels in a first row to an emission state during a first period (block  2204 ). After the first period, the microdriver drives a second set of pixels in a second row to the emission state during a second period (block  2206 ). 
       FIG. 23  illustrates an embodiment of a timing diagram  2250 . As illustrated, four emission scans are initiated per period T. For example, scans  2252 ,  2254 ,  2256 , and  2258  are initiated within a first period of scanning, and scans  2260 ,  2262 ,  2264 , and  2266  are performed in a second period of scanning. As illustrated, the rows alternate between odd and even. If the refresh rate is 60 Hz frame, each of these sub-frames are initiated at a rate of 240 Hz. Thus, a new scan is performed every 1/4T, and a single line is scanned every 1/2T. For example, the first odd line is scanned at 0 time, 1/2T, T, and so forth. This emission is evenly distributed over space and time to reduce dynamic artifacts and IR drop (analog and digital). Using the foregoing timing diagram. Two neighboring rows do not emit at the same time thereby enabling a single microdriver to control emission of the pixels in a first row and a neighboring second row using time multiplexing since the two rows do not emit at the same time. This reuse of hardware reduces pin and area usage thereby reducing manufacturing costs of the electronic device. The microdriver may use a single set of emission control logic with (double pixel data buffers), a single current driver, and/or single set of emission clocks (one of each phase). This method works as long as the duty cycle is limited to less than or equal to 50%. 
       FIG. 24  illustrates an embodiment of a pixel driving system  2300 . The pixel driving system  2300  includes a microdriver that drives and controls pixels  2304 ,  2306 ,  2308 ,  2310 ,  2312 ,  2314 ,  2316 , and  2318  using time-multiplexing. Although the illustrated embodiment includes driving eight pixels in a four-column, two-row configuration, the eight pixels may be driven in a different configuration, such as a two-row, four-column configuration. Furthermore, the microdriver may drive more or less pixels with corresponding restrictions. For example, the microdriver may instead drive four rows of five pixels, each row limited to a 25% duty cycle and each pixel having a 5% duty cycle. 
     Returning to  FIG. 25 , during a first period, the microdriver drives pixels  2304 ,  2306 ,  2308 , and/or  2310 , and during a second period, the microdriver drives pixels  2312 ,  2314 ,  2316 , and  2318 . Each pixel includes multiple sub-pixels. For example, pixel  2304  includes red sub-pixel  2320 , green sub-pixel  2322 , and blue sub-pixel  2324 . Similarly, pixel  2306  includes red sub-pixel  2326 , green sub-pixel  2328 , and blue sub-pixel  2330 ; pixel  2308  includes red sub-pixel  2332 , green sub-pixel  2334 , and blue sub-pixel  2336 ; pixel  2310  includes red sub-pixel  2336 , green sub-pixel  2338 , and blue sub-pixel  2340 ; pixel  2312  includes red sub-pixel  2342 , green sub-pixel  2344 , and blue sub-pixel  2346 ; pixel  2314  includes red sub-pixel  2348 , green sub-pixel  2350 , and blue sub-pixel  2352 ; pixel  2316  includes red sub-pixel  2354 , green sub-pixel  2356 , and blue sub-pixel  2358 ; and pixel  2318  includes red sub-pixel  2360 , green sub-pixel  2362 , and blue sub-pixel  2364 . 
       FIG. 25  illustrates a timing diagram  2366  that may be used to drive pixels  2304 - 2318  using eight-way time-multiplexing with 4 pixels in columns and 2 pixels in rows, every pixel in the microdriver may share resources thereby reducing hardware area and/or pin counts around the microdriver to reduce manufacturing overhead or provide additional display fidelity. It is important to note that although eight-way time multiplexing is discussed, 2, 3, 4, 5, 6, 7, or more-way multiplexing may be employed in some embodiments. Under such sharing, the duty cycle for each microled (e.g., pixel  2304 ) is limited to 1/4 of the overall duty cycle of a row for the microdriver. For example, when four pixels are driven in a row by the microdriver, each of the pixels has a maximum emission period of 12.5%. As illustrated, the pixel driving pattern includes skipping rows and columns such that a currently emitting pixel is not adjacent to a a previous or next emitting pixel. Thus, the emissions are distributed throughout the region to reduce IR drop appearance while enabling the pixel data to be time-multiplexed for all of the pixels connected to the microdriver  2302 . 
       FIG. 26  illustrates a process  2400  for operating a microdriver. The process  2400  includes limiting duty cycle of a row to 50% or less (block  2402 ). The process  2400  also includes receiving, at a microdriver, a first data update from a column driver for a first row of pixels (block  2404 ). The microdriver also receives a second data update from a column driver for a second row of pixels (block  2406 ). In some embodiments, these data updates may be time limited such that the first data is written and cleared before the second data update is received. In other words, a single buffer may be used to store the first and second data updates. However, in some embodiments, the received data updates may be stored in different buffers. The microdriver receives a first emission clock phase from a timing controller (block  2408 ). In response to the first emission clock phase, the microdriver drives the first first to enter an emission state (block  2410 ). For example, the microdriver  2302  may cause the pixels  2304 ,  2306 ,  2308 , and/or  2310  to emit light based on the received data update. 
     After or during emission via the first row of pixels, the microdriver receives a second emission clock phase from the timing controller (block  2414 ). In response to the second emission clock phase and when the first period has ended, drive the second row of pixels to enter the emission phase (block  2414 ). 
     The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure. Moreover, although the foregoing discusses row drivers that send data to microdrivers and column drivers that control which microdriver in a row receives the data, it should be appreciated that the foregoing discussion about row drivers may be applied to column drivers and vice versa merely by rotating orientation of the display. Thus, recitations of columns and rows may be interchangeable in meaning herein.