Patent Publication Number: US-11386834-B2

Title: Light-emitting diode (LED) display driver with programmable scan line sequence

Description:
BACKGROUND 
     The proliferation of electronic devices and integrated circuit (IC) technology has resulted in the commercialization of IC products. As new electronic devices are developed and IC technology advances, new IC products are commercialized. One example IC product for electronic devices is a light-emitting diode (LED) driver. In LED devices, there are some trends: the number of red-green-blue (RGB) LED pixels are increasing (e.g., up to 4K pixels and more than 15K LED drivers); the pitch between pixels is decreasing; and the refresh rate (e.g., up to 4 KHz) is increasing to account for increases in camera shutter speed (to avoid visibility of dimming lines in photography of LED signage). As an example, to achieve a 16-bit pulse-width modulation (PWM) with a 4 KHz refresh rate, a dock signal rate higher than 200 MHz is needed. Trends that increase the concentration of ICs, pins, and traces on a printed circuit board (PCB) for LED displays undesirably increase cost and complexity of LED display circuitry. 
     SUMMARY 
     In an example embodiment of the description, a light-emitting diode (LED) display driver circuit comprises: a set of scan lines, each scan line having a respective switch; a set of channels coupled to each scan line of the set of scan lines; and a scan line controller coupled to each respective switch of the set of scan lines, the scan line controller configured to provide a programmable sequence of control signals to respective switches of the set of scan lines. 
     In another example embodiment of the description, a system comprises: a LED display controller; and an LED display driver circuit coupled to the LED display controller and configured to receive LED data from the LED display controller. The LED display driver circuit including: a set of scan lines, each scan line having a respective switch; a set of channels coupled to each scan line of the set of scan lines; and a scan line controller coupled to each respective switch of the set of scan lines, the scan line controller configured to provide a programmable sequence of control signals to respective switches of the set of scan lines. 
     In another example embodiment of the description, a method comprising: receiving, by a LED display driver circuit, a scan line sequence code; generating, by the LED display driver circuit, a sequence of control signals based on the scan line sequence code; and using, by the LED display driver circuit, the sequence of control signals to control switches of a set of scan lines of the LED display driver circuit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a system in accordance with an example embodiment. 
         FIG. 2  is a diagram of part of a light-emitting diode (LED) display driver circuit in accordance with an example embodiment. 
         FIG. 3A  is a block diagram of a scan line sequence in accordance with a conventional technique. 
         FIG. 3B  is an image of photography with dimming lines due to the conventional scan line sequence of  FIG. 3A . 
         FIG. 4A  is a block diagram of a programmable scan line sequence in accordance with an example embodiment. 
         FIG. 4B  is a block diagram of a programmable scan line sequence in accordance with an example embodiment. 
         FIG. 4C  is an image of photography without dimming lines due to the programmable scan line sequence of  FIG. 4A  or  FIG. 4B . 
         FIG. 5A  is a table showing programmable scan line sequence information in accordance with an example embodiment. 
         FIG. 5B  is a table showing additional programmable scan line sequence information in accordance with an example embodiment. 
         FIG. 6A  is a table showing scan line sequence and memory information in accordance with a conventional technique. 
         FIG. 6B  is a table showing programmable scan line sequence memory and information in accordance with a conventional technique. 
         FIG. 7  is an LED display driver circuit layout in accordance with an example embodiment. 
         FIG. 8  is a diagram of outputs for a stackable pair of LED display driver circuits in accordance with an example embodiment. 
         FIG. 9A  is a diagram of a stackable pair of LED display driver circuits in accordance with a convention technique. 
         FIG. 9B  is a diagram of stackable pair of LED display driver circuits in accordance with an example embodiment. 
         FIG. 10  is a timing diagram of scan line operations and related parameters in accordance with an example embodiment. 
         FIG. 11  is a diagram of an LED display driver circuit in accordance with an example embodiment. 
         FIG. 12  is an LED display driver circuit method in accordance with an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Described herein is a light-emitting diode (LED) display driver circuit with programmable scan lines and related circuitry. In some example embodiments, an LED display driver circuit includes: a set of scan lines, each scan line having a switch; and a scan line controller configured to provide a programmable sequence of control signals to respective switches of the set of scan lines. In some example embodiments, the LED display driver circuit is an integrated circuit (IC). Also described herein are related systems or devices (e.g., LED signage) that use an LED display driver circuit. In an example system, a plurality of LED display driver circuits are coupled to an LED display controller, which provides LED data to each LED display driver circuit. In one example embodiment, the LED display controller is configured to provide a scan line sequence code to each LED display driver circuit, where each LED display driver circuit is configured to provide a sequence of control signals to respective switches of the set of scan lines based on the scan line sequence code. 
     As an example, the LED display controller may provide the scan line sequence code to each LED display driver circuit with the LED data. In such case, each LED display driver circuit is configured to decode or parse the scan line sequence code from the LED data for later use (e.g., to generate the sequence of control signals to respective switches of the set of scan lines). In other example embodiments, each LED display driver circuit is able to provide a programmable sequence of control signals to respective switches of the set of scan lines in another way (e.g., using a separate communication pin or time multiplexed communications to receive a scan line sequence code). 
     One use of the programmable sequence of control signals is to increase (e.g., double or triple) the apparent refresh rate of an LED display driver circuit. In such case, the programmable sequence of control signals includes multiple partial sequences of control signals performed in order, each of the multiple partial sequences of control signals configured to skip over some of the switches of the set of scan lines. To double the apparent refresh rate, the multiple partial sequences includes a first partial sequence of control signals and a second partial sequence of control signals, the first partial sequence of control signals configured to skip over every other switch of the set of scan lines in order, and the second partial sequence of control signals configured to skip over switches related to the first partial sequence of control signals. Without limitation, if there are 20 scan lines, a first partial sequence of control signals is used to control scan lines 1, 3, 5, 7, 9, 11, 13, 15, 17, 19 in order. After the first partial sequence is complete, a second partial sequence is used to control scan lines 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 in order. Other partial sequences are possible. 
     The result of using these or other sets of partial sequences for control of scan lines of LED display driver circuits is that an LED display will have a faster apparent refresh rate. In reality, some of the scan lines are skipped for each partial sequence of each LED display driver circuit, but the skipped scan lines do not significantly affect the displayed image visible to the camera. When the refresh rate of an LED display is below a target shutter speed, photography of the LED display by a camera may include undesirable dimming lines. 
     By increasing the apparent refresh rate as described herein, the visible refresh rate is higher than a target camera shutter speed and photography of LED signage avoids dimming lines without increasing a system clock rate. Use of a programmable sequence of control signals for switches of a set of scan lines and use of a lower system clock rate facilitates the design of LED signage circuitry layout, which may use thousands of LED display driver circuits and related printed circuit boards (PCBs) and LED display controllers. To provide a better understanding, LED display driver circuits with a programmable sequence of control signals for scan line switches as well as related options and systems are described using the figures as follows. 
       FIG. 1  is a block diagram of a system  100  in accordance with an example embodiment. In some example embodiments, the system  100  is an LED display device (sometimes referred to as LED signage). As shown, the system  100  includes a computer  102  that provides the source of the graphics and communicates with a digital visual interface (DVI) graphics card  104 . In operation, the DVI graphics card  104  converts graphics source data and provides the data to a plurality of cabinets  106 A- 106 N, where each of the cabinets  106 A- 106 N includes a base board controller  108  and a plurality of LED modules  110 A- 110 N. In different examples, the DVI graphics card  104  provides the same graphics data or different graphics data to each of the cabinets  106 A- 106 N, where each of the cabinets  106 A- 106 N is associated with a different LED display. 
     In the example of  FIG. 1 , each of the plurality of LED modules  110 A- 110 N includes a plurality of LED submodules  114 A- 114 H, a switched-mode power supply (SMPS)  116 , and an on-board controller  118  (sometimes referred to herein as an LED display controller). In operation, each base board controller  108  is configured to receive graphics data from the DVI graphics card  104  and to provide LED data or related data to each LED module  110 A- 110 N. For example, each on-board controller  118  of each respective LED module  110 A- 110 N is configured to receive LED data or related data from a respective base board controller  108  and to provide a sub-set of the LED data or related data to each of the LED submodules  114 A- 114 H. 
     In operation, each of the LED submodules  114 A- 114 H is configured to manage the amount of current provided to respective pixels (e.g., red, green, blue pixels), where current flow to each pixel is a function of scan line operations as well as current source or current sink operations. As described herein, LED display driver circuits (e.g., the LED submodules  114 A- 114 H) use a programmable sequence of control signals to control switches of a set of scan lines. In some example embodiments, the same sequence of control signals is used for each of the LED submodules  114 A- 114 H of a respective cabinet. Also, each of the cabinets  106 A- 106 N may use the same sequence of control signals or a different sequence of control signals to control switches of a set of scan lines for respective LED submodules  114 A- 114 H. Regardless of the particular sequence of control signals in use for a particular cabinet, the sequence of control signals is programmable or adjustable. 
     One use of a programmable sequence of control signals for scan line switches is to increase (e.g., double or triple) the apparent refresh rate of each LED submodule  114 A- 114 H. In such case, the programmable sequence of control signals includes multiple partial sequences of control signals performed in order, each of the multiple partial sequences of control signals configured to skip over some of the switches of the set of scan lines. By increasing the apparent refresh rate, the visible refresh rate is higher than a target camera shutter speed and photography of LED signage avoids dimming lines without increasing a system clock rate. Use of a programmable sequence of control signals for switches of a set of scan lines and use of a lower system clock rate facilitates the design of LED signage circuitry layout, which may use thousands of LED display driver circuits along with related PCBs and LED display controllers. 
       FIG. 2  is a diagram of part of an LED display driver circuit  200  (part of each LED submodule  114 A- 114 H in  FIG. 1 ) in accordance with an example embodiment. As shown, the LED display driver circuit  200  includes a circuit  210  (e.g., part of an IC) with a plurality of scan lines  211 A- 211 N with respective scan lines switches S 0 -S N−1 . For each of the scan lines  211 A- 211 N, there is a set of channels  201 A- 201 N that are active when switches S 0 -S N−1  are closed and that are inactive when S 0 -S N−1  are open. In the example of  FIG. 2 , there is a separate set of pixels  202  for each of the scan lines  211 A- 211 N and each of the channels  201 A- 201 N, where each set of pixels  202  includes a red pixel  204 , a green pixel  206 , and a blue pixel  208 . By controlling the scan lines switches S 0 -S N−1  and respective current sinks  212 A- 212 N,  214 A- 214 N, and  216 A- 216 N, pixel color and brightness levels are controlled for each pixel. More specifically, the scan lines switches S 0 -S N−1  are controlled by a programmable sequence of control signals SL 0 -SL N , and the current sinks  212 A- 212 N,  214 A- 214 N, and  216 A- 216 N are controlled by color/brightness control signals  218 . 
     One option for the programmable sequence of control signals SL 0 -SL N-1  is to increase (e.g., double or triple) the apparent refresh rate of the LED display driver circuit  200  as described herein. In one example, the programmable sequence of control signals SL 0 -SL N-1  includes multiple partial sequences of control signals performed in order, each of the multiple partial sequences of control signals configured to skip over some of the switches S 0 -S N−1 . Without limitation, a first partial sequence of control signals is used to operate even numbered scan line switches (e.g., S 0 , S 2 , etc.) in order. After the first partial sequence of control signals is complete, a second partial sequence of control signals is used to control odd numbered scan line switches (e.g., S 1 , S 3 , etc.) in order. In this manner, the apparent refresh rate of the LED display driver circuit  200  is doubled without increasing a system clock rate. One example strategy is to increase the apparent refresh rate so that the visible refresh rate is higher than a target camera shutter speed and thus avoid dimming lines in LED signage photography without increasing a system clock rate. Also, use of a programmable sequence of control signals SL 0 -SL N-1  for scan line switches S 0 -S N−1  can facilitate the layout of LED signage circuitry, which may use thousands of LED display driver circuits along with related PCBs and LED display controllers. 
       FIG. 3A  is a block diagram of a scan line sequence  300  in accordance with a conventional technique. In the scan line sequence  300 , the scan lines are scanned in order from scan line 0 (e.g., scan line  211 A in  FIG. 2 ) to scan line N−1 (e.g., scan line  211 N in  FIG. 2 ) starting at time t START  and ending at time t END . The result of the scan line sequence  300  is represented in  FIG. 3B , which shows an image  310  of photography with dimming lines  312  due to the refresh rate of LED display driver circuits being less than a target camera shutter speed. 
       FIG. 4A  is a block diagram of a programmable scan line sequence  400  in accordance with an example embodiment. In the scan line sequence  400 , the scan lines are scanned in a programmable order (e.g., using SL 0 -SL N-1  of  FIG. 2  in a programmable order) starting at time t START  and ending at time t END . One option for the programmable scan line sequence  400  doubles the apparent refresh rate of an LED display driver circuit (e.g., each of the LED submodules  114 A- 114 F in  FIG. 1 , or the LED display driver circuit  200  in  FIG. 2 ) as described herein. To double the apparent refresh rate of an LED display driver circuit, the programmable scan line sequence  400  includes multiple partial sequences of control signals performed in order, where each of the multiple partial sequences of control signals is configured to skip over some of the scan line switches. Without limitation, a first partial sequence of control signals of the programmable scan line sequence  400  controls even numbered scan line switches (e.g., S 0 , S 2 , etc., in  FIG. 2 ) in order. After the first partial sequence of control signals is complete, a second partial sequence of control signals of the programmable scan line sequence  400  controls odd numbered scan line switches (e.g., S 1 , S 3 , etc., in  FIG. 2 ) in order. This programmable scan line sequence with even and odd partial sequences is represented by the programmable scan line sequence  410  in  FIG. 4B . In this manner, the apparent refresh rate of an LED display driver circuit is doubled without increasing a system clock rate. 
     In other example embodiments, the programmable scan line sequence  400  is used to triple the apparent refresh rate of an LED display driver circuit (e.g., using three partial sequences of control signals). In other example embodiments, the programmable scan line sequence  400  is customized to facilitate outputting scan line signals of an LED display driver circuit to a PCB or otherwise facilitate layout of LED display driver circuits and/or other LED display circuitry on a PCB. 
       FIG. 4C  is an image  420  of photography without dimming lines due to the programmable scan line sequence  400  of  FIG. 4A  (e.g., the programmable scan line sequence  410  of  FIG. 4B ) doubling or tripling the apparent refresh rate of LED display driver circuits of an LED display. Use of the programmable scan line sequence  400  for switches of a set of scan lines and use of a lower system clock rate facilitates the design of LED signage circuitry layout, which may use thousands of LED display driver circuits along with related PCBs and LED display controllers. 
       FIG. 5A  is a table  500  showing programmable scan line sequence information in accordance with an example embodiment. In table  500 , 32 scan lines are assumed and the columns of table  500  include a register column, a register length column, a default sequence column, and a programmed sequence column. The register column of table  500  identifies the registers program_order_0 to program_order_31 used to store programmable sequence information. The register length column of table  500  identifies the length of each register identified in the register column. Since there are 32 scan lines in this example, the register length for each register is 5 bits, which enables the numbers 0 (00000) to 31 (11111) to be stored or updated to identify a programmed sequence. The default sequence column for table  500  identifies a default scan line sequence (e.g., Line_0 to Line_31, or 00000 to 11111 in sequential order). The programmed sequence column for table  500  Identifies a programmed sequence of scan lines. To double the apparent refresh rate of an LED display driver circuit as described herein, the programmed sequence may include a first partial sequence of even scan lines in order (e.g., Line_0, Line_2, Line_4, etc.) followed by a second partial sequence of odd scan lines in order (e.g., Line_1, Line_3, Line_5, etc.). In some example embodiments, an LED display driver circuit includes a set of registers and/or other storage elements to store information such as the information in table  500 , which is used to generate a default sequence or programmable sequence of control signals for scan line switches of the LED display driver circuit. 
       FIG. 5B  is a table  510  showing additional programmable scan line sequence information in accordance with an example embodiment. In table  510 , 32 scan lines are assumed and the columns of table  510  include a register column, a max_scan_line #column, a default sequence column, and a status column. The register column of table  510  identifies the registers program_order_0 to program_order_31 used to store programmable sequence information. The max_scan_line #column of table  510  identifies the maximum number of active scan lines, which is 20 in this example. The default sequence column for table  510  identifies a default scan line sequence (e.g., Line_0 to Line_19, or 00000 to 10011 in sequential order) up to the maximum number of active scan lines. In table  510 , the registers program_order_20 to program_order_31 are inactive and are thus not applicable (N/A) to the default sequence. The status column of table  510  identifies which scan lines are active versus inactive. In table  510 , Line_0 to Line_19 are active, while Line_20 to Line_31 are inactive. In some example embodiments, an LED display driver circuit includes a set of registers and/or other storage elements to store information such as the information in table  510 , which is used to generate a default sequence or programmable sequence of control signals for scan line switches of the LED display driver circuit that accounts for a maximum scan line limitation and/or active versus inactive scan line options. 
       FIG. 6A  is a table  600  showing scan line sequence and memory information in accordance with a conventional technique. In table  600 , 32 scan lines are assumed and the columns of table  600  include a physical line #column, a scan sequence column, and a static random-access memory (SRAM) read sequence column. The physical line #column of table  600  identifies the physical scan line Line_0 to Line_31, the scan line sequence column of table  600  identifies a conventional scan sequence for the scan lines (e.g., sequential from Line_0 to Line_31), and the SRAM read sequence of table  600  identifies an SRAM read sequence related to providing a sequence of control signals for scan line switches related to Line_0 to Line_31 in order. If an LED display driver circuit includes a set of registers and/or other storage elements to store information such as the information in table  600 , the resulting scan sequence will be sequential, which results in dimming lines in photography if the refresh rate of an LED display driver circuit is less than a target shutter speed. This is because the vertical distribution of LED rows that are lit up by a sequential sequence of scan line control signals within a target time interval (faster than new camera shutter rates) does not cover the entire distribution of LED rows (leaving a block of sequential LED rows unlit for LED display photography). In should be noted that visibility of LED displays by the human eye is not the issue. Rather, the described solutions are to ensure that camera photography captured by cameras with reduced shutter speeds show LED display images without dimming lines (due to the refresh rate relative to the camera shutter speed). Also, with a sequential scan line sequence, the layout complexity of LED display driver circuits and/or other circuitry on an LED display PCB may increase. In particular, a fixed pin layout and a fixed sequential scan line sequence results in more overlapping traces with stacked LED display driver circuits as described for  FIG. 9A . Using programmable scan line sequencing to avoid overlapped PCB traces simplifies PCB layout as described for  FIG. 9B . 
       FIG. 6B  is a table  610  showing scan line sequence and memory information in accordance with an example embodiment. In table  610 , 32 scan lines are assumed and the columns of table  610  include a physical line #column, a programmed scan sequence column, and a static random-access memory (SRAM) read sequence column. The physical line #column of table  610  identifies the physical scan line Line_0 to Line_31, the programmed scan line sequence column of table  610  identifies a programmed scan sequence for the scan lines (e.g., a reverse sequence from Line_31 to Line_0), and the SRAM read sequence of table  610  identifies an SRAM read sequence related to providing a programmed sequence of control signals to scan line switches related to Line_31 to Line_0 in reverse order. If an LED display driver circuit includes a set of registers and/or other storage elements to store information such as the information in table  610 , the resulting scan sequence may be used to reduce layout complexity of LED display driver circuits and/or other circuitry on an LED display PCB. The layout complexity is due to a fixed pin layout and a fixed sequencing order, which results in overlapping PCB traces when LED display driver circuits are stacked as described in  FIG. 9A . In some examples, reverse sequencing may be combined with other programmed sequences to increase the apparent refresh rate of an LED display driver circuit as described herein. 
     In some example embodiments of an LED display driver circuit, SRAM is implemented to achieve data transmission and image display simultaneously. For a fixed line sequence as in  FIG. 6A , the SRAM address is defined from Line 0 to Line N−1, and data is shifted in and out following the line&#39;s sequence. For a programmable line sequence as in  FIG. 6B , users do not need to adjust the SRAM data sequence according to the programmed line sequence. Instead, the LED display driver circuit will modify the SRAM read sequence automatically. 
       FIG. 7  is an LED display driver circuit pin layout  700  (e.g., each driver circuit  700  represents an LED submodules  114 A- 114 H in  FIG. 1 , the LED display driver circuit  200  of  FIG. 2 , or the LED display driver circuit  1100  in  FIG. 11 ) in accordance with an example embodiment. As shown, the LED display driver circuit layout  700  includes programmable scan line circuitry  702 . Example components of the programmable scan line circuitry  702  include: a decoder to decode a scan line sequence code; storage elements to store the scan line sequence code or related information (e.g., a programmable scan line sequence such as the programmable scan line sequence  400  in  FIG. 4A , the information in table  500  of  FIG. 5A , the information in table  610  of  FIG. 6B , etc.); storage elements to store active/inactive scan line information (e.g., the information in table  510  of  FIG. 5B ); a scan line controller configured to generate control signals for scan line switches responsive to the scan line sequence code, related information, and/or active/inactive scan line information. 
     As shown, the LED display driver circuit layout  700  also includes a ground  704  as well as plurality of pins or contacts 1-76 (as used herein, pins and contacts may mean, for example, ball bonds, pins, leads, terminals, or other form of contacts for providing an electrical, physical or thermal connection to a packaged semiconductor device). More specifically, there are respective pins (pins 1-6, 10-18, and 21-57) for red-blue-green (RGB) pixels of 16 channels (R0-R16, G0-B15, B0-B15). There are also respective pins (pins 7-9, 19-20, and 48-51) for a supply voltage (VCC), a red output supply voltage (VR), a blue output supply voltage (VB), a green output supply voltage (VG), GND, and a reference current (IREF). There are also respective pins (pins 58-60) for a data output (SOUT), a data input (SIN), and a clock signal (SCLK) for communications in accordance with a protocol such as serial peripheral interface (SPI). There are also respective pins (pins 61-76) for 16 scan line outputs (Line0-Line15). In different examples, the LED display driver circuit layout  700  is used with common cathode LEDs or common anode LEDs. In either case, programmable scan line sequencing may be used to increase the apparent refresh rate of Line0-Line15 to avoid dimming lines in LED display photography as described herein. Additionally or alternatively, the scan line sequencing of Line0-Line15 can be programmed (e.g., reversed) to avoid overlapping PCB traces as described in  FIGS. 9A and 9B . In some example embodiments, the same advantages could be achieved by customizing the 
       FIG. 8  is a diagram of outputs for a stackable pair of LED display driver circuits  804 A and  804 B (e.g., two of the LED submodules  114 A- 114 H, or two of the LED display driver circuits  200 , or two LED display driver circuits related to the layout  700  of  FIG. 7 ) in accordance with an example embodiment. As shown, each of the LED display driver circuits  804 A and  804 B includes RGB outputs for 16 channels as well as 16 scan line outputs. In the example of  FIG. 8 , the stackable LED display driver circuits  804 A and  804 B support 32 total lines and 32 total RGB channels (twice as many pixel sets  802  are supported by the stackable pair of LED display driver circuits  804 A and  804 B compared to a pair of non-stackable LED display driver circuits). In some example embodiments, stackable LED display driver circuits are used with scan lines that are strictly center aligned to minimize the parasitic inductance impact. With a fixed or sequential scan line sequence, the layout of the scan lines for a pair of stackable LED display driver circuits includes some complex connections (e.g., overlapping connections) as shown in  FIG. 9A . With a programmable scan line sequence, the layout of the scan lines for a pair of stackable LED display driver circuits is simpler (no overlapping connections) and the two LED display driver circuits are symmetrical. 
       FIG. 9A  is a diagram of a stackable pair of LED display driver circuits  902 A and  902 B without programmable scan line circuitry in accordance with a conventional technique. In the example of  FIG. 9A , some of the traces  904  extending from scan line outputs of the LED display driver circuit  902 B cross over each other when using the stackable pair of LED display driver circuits  902 A and  902 B together resulting in a high complexity PCB payout. 
       FIG. 9B  is a diagram of stackable pair of LED display driver circuits  912 A and  912 B with programmable scan line circuitry (e.g., the programmable scan line circuitry  702  in  FIG. 7 ) in accordance with an example embodiment. In the example of  FIG. 9A , programmable scan line circuitry is used to adjust the scan line outputs so that the traces  914  extending from scan line outputs of the LED display driver circuit  902 B do not cross over each other when using the stackable pair of LED display driver circuits  912 A and  912 B together resulting in a lower complexity PCB payout compared to the arrangement of  FIG. 9A . 
       FIG. 10  is a timing diagram  1000  of scan line operations  1004 A- 1004 N and related parameters in accordance with an example embodiment. In the timing diagram  1000 , the scan line operations  1004 A- 1004 N are repeated for each of intervals  1002 A- 1002 N (labeled Sub0 to SubN−1), where the duration of each of the intervals  1002 A- 1002 N is based on the display refresh speed. As shown, the duration of each of the intervals  1002 A- 1002 N is less than a target shutter rate. The dimming or flickering issue is a common issue for a matrix of LED display driver circuits when taking photos with a high speed camera. To avoid this issue, the minimum refresh rate of an LED display should be at least 2 times higher than the target shutter speed of a camera in order to support doubling the apparent refresh rate to overcome dimming lines as described herein. 
     In some examples, the duration of each of the intervals  1002 A- 1002 N may be less than half of the target shutter speed to ensure the described technique avoids dimming lines in LED display photography as described herein. To support the scan line operations  1004 A- 1004 N for each of the intervals  1002 A- 1002 N, a clock signal (GCLK)  1006  is used. In some example embodiments, GCLK is a pulse-width modulated (PWM) clock signal and the rate of GCLK is selected to achieve a desired duration of the intervals  1002 A- 1002 N (e.g., a duration less than the target shutter rate). 
       FIG. 11  is a diagram of an LED display driver circuit  1100  (an example of each LED submodule  114 A- 114 H in  FIG. 1 , the LED display driver circuit  200  in  FIG. 2 , or the LED display driver circuit related to the LED display driver circuit layout  700  in  FIG. 7 ) in accordance with an example embodiment. As shown, the LED display driver circuit  1100  includes various pin or contacts for VCC, IREF, GND, SCLK, SIN, SOUT, GND, Line0-Line15, R0-R15, G0-G15, B0-B15, VB, VG, and VR. More specifically, the LED display driver circuit  1100  includes a VCC pin  1170 , an IREF pin  1172 , a GND pin  1174 , Line0-Line15 pins  1184 A- 1184 P, R0-R15 pins  1186 A- 1186 P, G0-G15 pins  1188 A- 1188 P, B0-B15 pins  1190 A- 1190 P, a VB pin  1192 , a VG pin  1194 , and a VR pin  1196 . 
     As shown, the VCC pin  1170  is coupled to an internal low-dropout regulator (LDO)  1128  and a bandgap voltage reference circuit  1126 . The IREF pin  1172  is coupled to a 3-bits brightness control circuit  1122  powered by the bandgap voltage reference circuit  1126 . The 3-bits brightness control circuit  1122  is coupled to a R/G/B 8-bits color control circuit  1124  configured to control channel drivers  1120  based on color control codes or related information. In the example of  FIG. 11 , the channel drivers  1120  are coupled to a channel control circuit  1112 , where the operations of the channels drivers  1120  are a function of signals from the channel control circuit  1112  and signals from the R/G/B 8-bits color control circuit  1124 . As shown, the channel drivers  1120  are coupled to channel circuitry  1160  including a set of current sources  1161  with current sources  1162 A- 1162 P powered by VR for R0-R15, current sources  1164 A- 1164 P powered by VG for G0-G15, and current sources  1166 A- 1166 P power by VB for B0-B15, where the outputs of the channel drivers  1120  determine the amount of current provided by each of the respective current sources current sources  1162 A- 1162 P, current sources  1164 A- 1164 P, and current sources  1166 A- 1166 P. In other example embodiments, when driving common anode LEDs instead of common cathode LEDs, the channel circuit  1160  includes current sinks instead of current sources. 
     In the example of  FIG. 11 , the LED display driver circuit  1100  also includes: a frequency multiplier circuit  1106  coupled to the SCLK pin  1176 ; and a decoder circuit  1108  and SRAM  1110  coupled to the SIN pin  1178 . As shown, the frequency multiplier  1106 , the decoder  1108 , and the SRAM  1110  are also coupled to a digital core  1102  configured to provide control signals for components of the LED display driver circuit  1100  based on SCLK and data received via the SIN pin  1178 . Example data received via the SIN pin  1178  includes color codes and a scan line sequence code, where the decoder  1108  operates to decode or parse the scan line sequence code from other data received via the SIN pin  1178 . In some example embodiments, the scan line sequence code or related information (e.g., the information in table  500  of  FIG. 5A , the information in table  510  of  FIG. 5B , and/or the information in table  610  of  FIG. 6B ) is stored by storage elements  1104  of the digital core  1102 . As needed, control signals from the digital core  1102  are provided to the channel control circuit  1112 , a frame control circuit  1114 , and/or a line control circuit  1116 . Responsive to the output of the line control circuit  1116 , line drivers  1118  coupled to the line control circuit  1116  control scan line switches (e.g., transistors M0-M15 in  FIG. 11 ). More specifically, each respective control terminal of M0-M15 is coupled to the line drivers  1118 , each respective first current terminal of M0-M15 is coupled to one of the Line0-Line15 pins  1184 A- 1184 N, and each respective second current terminal of M0-M15 is coupled to GND. In operation, M0-M15 selectively conduct current responsive to a programmable sequence of control signals from the line drivers  1118  as described herein, where Line0-Line15 pins  1184 A- 1184 P are coupled to LED anodes, while R0-R15 pins  1186 A- 1186 P, G0-G15 pins  1188 A- 1188 P, and B0-B15 pins  1190 A- 1190 P are coupled to LED cathodes. With common anode LEDs, current sinks are used instead of the current sources  1162 A- 1162 P,  1164 A- 1164 P, and  1166 A- 1166 N. On the other hand, with common cathode LEDs, the current sources  1162 A- 1162 P,  1164 A- 1164 P, and  1166 A- 1166 N are used. Also, in some example embodiments, the LED display driver circuit  1100  is stackable with programmable scan line outputs (see e.g.,  FIGS. 8 and 9B ). 
     In the example of  FIG. 11 , various other components are included in the LED display driver circuit  1100  including protection circuitry  1150  such as an overcurrent protection circuit  1152  and a line clamp  1154 . The LED display driver circuit  1100  also includes LED management circuitry  1140  such as an LED short detection circuit  1142 , an LED open detection circuit  1144 , a pre-discharge circuit  1146 , and a low grayscale compensation circuit  1148 . The LED display driver circuit  1100  also includes: a thermal shutdown circuit  1132  configured to shut down the LED display driver circuit  1100  responsive to an overtemperature condition; and an undervoltage-lockout circuit  1130  configured to shut down the LED display driver circuit  1100  responsive to a low voltage condition (e.g., VCC dropping below a threshold). 
     In some example embodiments, an LED display driver circuit (e.g., each of the LED submodules  114 A- 114 H in  FIG. 1 , the LED display driver circuit  200  in  FIG. 2 , an LED display driver circuit related to the LED display driver circuit layout  700  in  FIG. 7 , or the LED display driver circuit  1100  in  FIG. 11 ) includes: a set of scan lines (e.g., scan lines  211 A- 211 N in  FIG. 2 , Line0-Line31 in  FIGS. 5A, 5B, 6B , scan line outputs Line0-Line 15 in  FIGS. 7, 8, and 11 ), each scan line having a respective switch (e.g., S 0 -S N−1  in  FIG. 2 , or M0-M15 in  FIG. 11 ); a set of channels (e.g., the set of channels  201 A- 201 N in  FIG. 2 , R0-R15, G0-G15, B0-B15 in  FIGS. 7 and 11 , or OUTR0-OUTR15, OUTG0-OUTG15, OUTB0-OUTB15 in  FIG. 8 ) coupled to each scan line of the set of scan lines; and a scan line controller (e.g., line driver  1118  and the digital core  1102 ) coupled to each respective switch of the set of scan lines, the scan line controller configured to provide a programmable sequence of control signals (e.g., SL 0 -SL N−1  in  FIG. 2 ) to respective switches of the set of scan lines. 
     In some example embodiments, the LED display driver circuit includes a communication node (e.g., the SIN pin in  FIGS. 7 and 11 ); and a decoder (e.g., decoder  1108  in  FIG. 11 ) coupled to the communication node and configured to decode a scan line sequence code from data received via the communication node, wherein the scan line controller is configured to use the scan line sequence code to provide the programmable sequence of control signals (e.g., a programmable sequence of SL 0 -SL N−1 ). In some example embodiments, the LED display driver circuit includes a storage element (e.g., the storage elements  1104  in  FIG. 11 ) coupled to the decoder and configured to store the scan line sequence code, wherein the scan line controller is configured to use the scan line sequence code stored in the storage element to provide the programmable sequence of control signals. 
     In some example embodiments, the sequence of control signals includes multiple partial sequences of control signals performed in order, each of the multiple partial sequences of control signals configured to skip over some of the switches of the set of scan lines. In some example embodiments, the multiple partial sequences includes a first partial sequence of control signals (e.g., SL 0 , SL 2 , etc.) and a second partial sequence of control signals (e.g., SL 3 , SL 3 , etc.), the first partial sequence of control signals configured to skip over every other switch of the set of scan lines in order, and the second partial sequence of control signals configured to skip over switches related to the first partial sequence of control signals. 
     In some example embodiments, the LED display driver circuit includes a storage element (e.g., the storage element  1104  in  FIG. 11 ) that stores active scan line information (see e.g., the information in table  510  in  FIG. 5B ), wherein the scan line controller is configured to use the active scan line information and the scan line sequence code to provide the programmable sequence of control signals to only some switches of the set of scan lines. In some example embodiments, the LED display driver circuit includes a storage element (e.g., the storage element  1104  in  FIG. 11 ) that stores inactive scan line information (see e.g., the information in table  510  in  FIG. 5B ), wherein the scan line controller is configured to use the inactive scan line information and the scan line sequence code to provide the programmable sequence of control signals to only some switches of the set of scan lines. In some example embodiments, the LED display driver circuit includes a set of scan line outputs (e.g., the scan lines outputs Line0-Line15 in  FIGS. 7, 8, and 11 ) coupled to the set of scan lines, the set of scan line outputs configured to support an additional set of channels (e.g., the set of channels  201 A- 201 N in  FIG. 2 ) external to the LED display driver circuit based on the scan line sequence code. 
     In some example embodiments, a system (e.g., the system  100  in  FIG. 1 ) includes: an LED display controller (e.g., the base board controller  108  and/or each on-board controller  118 ); and an LED display driver circuit (e.g., each of the LED submodules  114 A- 114 H in  FIG. 1 , the LED display driver circuit  200  in  FIG. 2 , the LED display driver circuit related to the LED display driver circuit layout  700  in  FIG. 7 , or the LED display driver circuit  1100  in  FIG. 11 ) coupled to the LED display controller and configured to receive LED data from the LED display controller. The LED display driver circuit includes: a set of scan lines (e.g., scan lines  211 A- 211 N in  FIG. 2 , Line0-Line31 in  FIGS. 5A, 5B, 6B , scan line outputs Line0-Line 15 in  FIGS. 7, 8, and 11 ), each scan line having a respective switch (e.g., S 0 -S N−1  in  FIG. 2 , or M0-M15 in  FIG. 11 ); a set of channels (e.g., the set of channels  201 A- 201 N in  FIG. 2 , R0-R15, G0-G15, B0-B15 in  FIGS. 7, 8, and 11 ) coupled to each scan line of the set of scan lines; and a scan line controller (e.g., line driver  1118  and the digital core  1102 ) coupled to each respective switch of the set of scan lines, the scan line controller configured to provide a programmable sequence of control signals (e.g., SL 0 -SL N−1  in  FIG. 2 ) to respective switches of the set of scan lines. 
     In some example embodiments, the system also includes: a PCB (e.g., a PCB for each of the LED modules  110 A- 110 N), wherein the LED display controller and the LED display driver circuit are mounted to the PCB; and a graphics card (e.g., the DVI graphics card  104  in  FIG. 1 ) coupled to the PCB and configured to provide graphics data to the PCB, wherein the LED display controller is configured to generate LED data based on the graphics data, and the scan line sequence code is provided to LED display driver circuit with the LED data. In some example embodiments, the system includes a plurality of LED display driver circuits (e.g., each of the LED submodules  114 A- 114 H in  FIG. 1 , the LED display driver circuit  200  in  FIG. 2 , a plurality of the LED display driver circuit related to the LED display driver circuit layout  700  in  FIG. 7 , or a plurality of the LED display driver circuit  1100  in  FIG. 11 ) coupled to the LED display controller, each LED display driver circuit supporting a refresh rate of at least 4 KHz using a pulse width modulation clock signal at or below 80 MHz. 
       FIG. 12  is an LED display driver circuit method  1200  in accordance with an example embodiment. The method  1200  is performed by an LED display driver circuit (e.g., each LED submodule  114 A- 114 H in  FIG. 1 , the LED display driver circuit  200  in  FIG. 2 , the LED display driver circuit related to the LED display driver circuit layout  700  in  FIG. 7 , or the LED display driver circuit  1100  in  FIG. 11 ). As shown, the method  1200  includes receiving by an LED display driver circuit, a programmable scan sequence code at block  1202 . At block  1204 , the LED display driver circuit generates a sequence of control signal based on the programmable scan sequence code. At block  1206 , the LED display driver circuit uses the sequence of control signals to control switches of a set of scan lines of the LED display driver circuit. 
     In some example embodiments, generating a sequence of control signals at block  1204  involves generating multiple partial sequences of control signals performed in order, each of the multiple partial sequences of control signals configured to skip over some of the switches of the set of scan lines. In one example embodiment, the multiple partial sequences includes a first partial sequence of control signals and a second partial sequence of control signals, the first partial sequence of control signals configured to skip over every other switch of the set of scan lines in order, and the second partial sequence of control signals configured to skip over switches related to the first partial sequence of control signals. 
     In some example embodiments, the method  1200  also includes: storing, by the LED display driver circuit, the scan line sequence code and active scan line information; and generating, by the LED display driver circuit, the sequence of control signals based on the scan line sequence code and the active scan line information. In other example embodiments, the method  1200  includes storing, by the LED display driver circuit, the scan line sequence code and inactive scan line information; and generating, by the LED display driver circuit, the sequence of control signals based on the scan line sequence code and the inactive scan line information. In some example embodiments, the method  1200  also includes outputting, by the LED display driver circuit, scan line signals to support channels external to the LED display driver circuit based on the scan line sequence code. 
     In this description, the term “couple” may cover connections, communications, or signal paths that enable a functional relationship consistent with this description. For example, if device A generates a signal to control device B to perform an action: (a) in a first example, device A is coupled to device B by direct connection; or (b) in a second example, device A is coupled to device B through intervening component C if intervening component C does not alter the functional relationship between device A and device B, such that device B is controlled by device A via the control signal generated by device A. 
     Modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the claims.