Patent Publication Number: US-2023156880-A1

Title: Driving circuit and voltage modulation method

Description:
CROSS - REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Application Serial No. 63/264,046, filed Nov. 15, 2021, which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Field of Invention 
     The present invention relates to a driving circuit and a voltage modulation method. More particularly, the present invention relates to a driving circuit and a voltage modulation method both able to modulate a power voltage. 
     Description of Related Art 
     For most display devices on the market, the driver integrated circuits (IC) that control the currents passing through the light emitting diodes (LEDs) in the display device need a common bus system in order to communicate information about whether the driving voltage is large enough to drive the LEDs. In this approach, extra pins are required for all driver ICs in order to communicate through the common bus system, and thus the cost and complexity to manufacture the driver ICs increase. 
     SUMMARY 
     The present disclosure provides a driving circuit, coupled to a light emitting diode and a power supply circuit and configured to control the power supply circuit to provide power to the light emitting diode. The driving circuit includes a comparator, a serial input interface, and an integrating unit. The comparator is coupled to the light emitting diode and configured to determine whether a voltage at the light emitting diode’s cathode is lower than a threshold value and to generate a monitoring data. The serial input interface is configured to receive a serial input data from a previous driving circuit. The integrating unit is coupled to the comparator and the serial input interface and configured to integrate the monitoring data and the serial input data to generate an output data. The output data is transmitted to a following driving circuit or feedbacked to the power supply circuit in order to modulate a power voltage provided by the power circuit provides to the light emitting diode. 
     The present disclosure also provides a voltage modulation method, including determining whether a cathode voltage of a light emitting diode is lower than a threshold value and generating a monitoring data; receiving a serial input data from a previous driving circuit; integrating the monitoring data and the serial input data to generate an output data; and transmitting the output data to a following driving circuit or feeding back the output data to a power supply circuit in order to modulate a power voltage that the power circuit provides to the light emitting diode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows: 
         FIG.  1    is a circuit diagram of a display device in accordance with some embodiments of the present disclosure. 
         FIG.  2    is a circuit diagram of a driving circuit in accordance with some embodiments of the present disclosure. 
         FIG.  3 A  is a time sequence diagram of signals that a driving circuit transmits and receives in accordance with some embodiments of the present disclosure. 
         FIG.  3 B  is a time sequence diagram of signals that a driving circuit transmits and receives in accordance with some embodiments of the present disclosure. 
         FIG.  3 C  is a time sequence diagram of signals that a driving circuit transmits and receives in accordance with some embodiments of the present disclosure. 
         FIG.  3 D  is a time sequence diagram of signals that a driving circuit transmits and receives in accordance with some embodiments of the present disclosure. 
         FIG.  3 E  is a time sequence diagram of signals that a driving circuit transmits and receives in accordance with some embodiments of the present disclosure. 
         FIG.  4    is a circuit diagram of a driving circuit in accordance with some embodiments of the present disclosure. 
         FIG.  5    is a circuit diagram of a driving circuit in accordance with some embodiments of the present disclosure. 
         FIG.  6    is a flowchart of a voltage modulation method in accordance with some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments of the present disclosure, examples of which are described herein and illustrated in the accompanying drawings. While the disclosure will be described in conjunction with embodiments, it will be understood that they are not intended to limit the disclosure to these embodiments. On the contrary, the disclosure is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the disclosure as defined by the appended claims. It is noted that, in accordance with the standard practice in the industry, the drawings are only used for understanding and are not drawn to scale. Hence, the drawings are not meant to limit the actual embodiments of the present disclosure. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts for better understanding. 
     Please refer to  FIG.  1   .  FIG.  1    is a circuit diagram of a display device  100  in accordance with some embodiments of the present disclosure. The display device  100  includes multiple driving circuits  110 , a power supply circuit  120 , a control unit  130 , and multiple light emitting diodes (LEDs)  140  coupled between the power supply circuit  120  and the corresponding driving circuits  110 . In one embodiment, the display device  100  is a display panel, a touch panel, a television or a smart television including a LED backlight module or a colored LED panel. 
     In some embodiments, the power supply circuit  120  is configured to provide a power voltage VLED to anodes of the light emitting diodes  140 . In one embodiment, the power supply circuit  120  is a DC-to-DC converter or a low-dropout (LDO) regulator. 
     In some embodiments, one of the driving circuits  110  (e.g., the latest driving circuits  110   c  in the embodiment shown in  FIG.  1   ) is coupled with the power supply circuit  120  and the driving circuit  110   c  is configured to generate a feedback control signal SFB to the power supply circuit  120  for modulating the power voltage VLED provided by the power supply circuit  120 . 
     Each driving circuit  110  electrically connects to a plurality of LEDs  140 . In the embodiment shown in  FIG.  1   , each driving circuit  110  connects to two columns of LEDs  140 . As shown in  FIG.  1   , the driving circuit  110   a  connects to the LED columns A and B, the driving circuit  110   b  connects to the LED columns C and D, and the driving circuit  110   c  connects to the LED columns E and F. It should be noted that the number of the LED columns is merely exemplary. In some embodiments, the driving circuits  110  electrically connect to an array of LEDs  140  that consists of more than six columns of LEDs  140 . 
     In one embodiment, the control unit  130  includes a data driver for providing display data DD to be displayed on the array of LEDs  140  in the display device  100  and also a time controller (TCON) configured to transmit clock signals to the driving circuits  110 . 
     In some embodiments, the driving circuits  110  are configured to control driving currents passing through the LEDs  140  according to the display data DD. Specifically, the control unit  130  generates the display data DD and passes it to the driving circuits  110   a ,  110   b , and  110   c  through a serial transmission. According to such display data DD, the driving circuit  110   a  controls the currents of the LEDs  140  in the LED columns A and B, the driving circuit  110   b  controls the currents of the LEDs  140  in the LED columns C and D, and the driving circuit 110c controls the currents in the LEDs  140  of the LED columns E and F. 
     In the embodiment shown in  FIG.  1   , there are only three driving circuits  110 , i.e., the driving circuits  110   a ,  110   b ,  110   c . It should be noted that the number of the driving circuits  110  in the display device  100  is merely exemplary, and person having ordinary skills in the art can modify such number according to actual needs or design. 
     In some embodiments, the display data DD generated by the control unit  130  contain data about the images that will be displayed through the LEDs  140 . For example, the display data DD transmitted to the driving circuit  110   a  can define the brightness of the LEDs  140  in the LED columns A and B. In some embodiments, the display data DD carry a series of brightness codes, e.g., [0, 155, 30, 34, 50, 70], and the codes correspond to the LED columns A, B, C, D, E, and F. Specifically, the driving circuit  110   a  will receive the codes [0, 155] and control the brightness of the LED columns A and B correspondingly, the driving circuit  110   b  will receive the codes [30, 34] and control the brightness of the LED columns C and D correspondingly, and the driving circuit  110   c  will receive the codes [50, 70] and control the brightness of the LED columns E and F correspondingly. In other words, the display data DD represent the brightness of the LEDs  140 . In some embodiments, the display data DD are about the image frame to be displayed through the LED array. 
     The power supply circuit  120  is configured to drive the LEDs  140  in the display device  100 . Specifically, the power supply circuit  120  generates the power voltage VLED and provides it to the anode of the topmost LED  140  in each LED column, such as the LED  140   b   1  in the LED column C. When the power voltage VLED is large enough to create sufficient voltage difference between the two ends of each LED columns A, B, C, D, E, and F, all LEDs  140  in the display device  100  can operate properly. Specifically, one LED  140  is able to operate in light-emitting when the voltage difference between its anode and cathode is greater than or equal to the forward voltage (Vf) of that LED  140 , so in order to drive multiple LEDs  140  coupled in series in one LED column, e.g., the LEDs  140   b   1 ~ 140   bn  in the LED column C, the power voltage VLED has to be equal to or greater than n*Vf. 
     Because the forward voltages (Vf) for each of the LEDs  140  can be slightly different due to a manufacturing bias or a temperature conduction, if the power voltage VLED provided by the power supply circuit  120  is fixed, the fixed power voltage VLED may not be high enough to light up all LEDs  140  in every LED column. However, if the power supply circuit  120  provides the power voltage VLED with a relatively higher level that is way over a required level needed by the LED array, it will cost extra power consumption and be not power efficient. In some embodiments, the driving circuits  110  are able to detect cathode voltages on these LED columns and generate the feedback control signal SFB to the power supply circuit  120  for modulating the power voltage VLED (e.g., raising a voltage level of the power voltage VLED). 
     The mechanism for modulating the power voltage VLED is discussed below. Please refer to  FIG.  1    and  FIG.  2   .  FIG.  2    is a circuit diagram of the driving circuit  110   b  in accordance with some embodiments of the present disclosure. Here, the driving circuit  110   b  shown in  FIG.  1    is used as an example for explanatory purpose. The other driving circuit  110 , such as the driving circuit  110   a , can have the same components as the driving circuit  110   b  shown in  FIG.  2   . 
     The driving circuit  110   b  includes a comparator  111 , a serial input interface  112 , and an integrating unit  113 . As shown in  FIG.  1    and  FIG.  2   , the driving circuit  110   b  is coupled to the driving circuit  110   a  and the driving circuit  110   c . For the purpose of simplicity, in the embodiment shown in  FIG.  2   , only the LED column C couples to the driving circuit  110   b , and the LED column D shown in  FIG.  1    is omitted here. Thus, in the embodiment shown in  FIG.  2   , the driving circuit  110   b  is coupled to the LED column C (not shown in  FIG.  1   ), specifically to the LED 140bn. 
     The comparator  111  is coupled to the LED  140   bn  and configured to determine whether the cathode voltage of the LED  140   bn  (i.e., the voltage at the node N) is lower than a threshold value and to generate a monitoring data Dmon. Specifically, the comparator  111  receives the voltage at the node N and compares it with the predetermined threshold value, in order to determine whether a higher voltage should be provided to the LED  140   bn  (i.e., whether the power voltage VLED configured to drive all LEDs  140  in the display device  100   needs to be stepped up). In one embodiment, the threshold value is predetermined by the designer or manufacturer of the display device  100 . 
     In one embodiment, when the comparator  111  determines that the voltage at the node N is lower than the threshold value, the monitoring data Dmon has a first level, while when the comparator  111  determines that the voltage at the node N is higher than the threshold value, the monitoring data Dmon has a second level. The monitoring data Dmon having the first level indicates that the power voltage VLED needs to be stepped up, and the monitoring data Dmon having the second level indicates that the power voltage VLED is large enough and does not need to be raised. In one embodiment, the monitoring data is a digital data, the first level is high logic level, and the second level is low logic level. In one embodiment, the monitoring data is an analog data, the first level is a higher voltage level, and the second level is lower voltage level. 
     The serial input interface  112  is configured to receive a serial input data SDI from a previous driving circuit, i.e., the driving circuit  110   a  in the embodiment shown in  FIG.  2   . The serial input data SDI include both the display data DD generated by the control unit  130  as shown in  FIG.  1    and the data about the cathode voltages of the LEDs  140  that are monitored by the driving circuit  110   a . As previously discussed, the driving circuit  110   a  has the same components as the driving circuit  110   b  and thus the driving circuit  110   a  includes the comparator  111  configured to monitor cathode voltages of the LEDs  140  coupled to it. How the display data DD and the data about the voltage of the LEDs  140  monitored by the driving circuit  110   a  are transmitted through the serial input data SDI in different time periods will be discussed in later paragraphs. Below first discuss how the data about the voltage of the LEDs  140  monitored by the driving circuit  110   a  and the data about the voltage of the LEDs  140  monitored by the driving circuit  110   b  are integrated. 
     The integrating unit  113  is coupled to the comparator  111  and the serial input interface  112  and configured to integrate the monitoring data Dmon and the serial input data SDI to generate an output data SDO. The output data SDO is then transmitted to a following driving circuit, which is the driving circuit  110   c  in this embodiment. The monitoring data Dmon indicate that whether the power voltage VLED is sufficiently large to drive the LED column C, and the serial input data SDI indicate that whether the power voltage VLED is sufficiently large to drive the LEDs  140  coupled to the driving circuit  110   a  (e.g., the LEDs  140  of the LED columns A and B in  FIG.  1   ). Thus, the integrating unit  113  is configured to combine the information about the cathode voltages monitored by the driving circuits  110   a  and  110   b  and pass such information to the driving circuit  110   c . 
     Specifically, in one embodiment, the integrating unit  113  sets the output data SDO as the first level when the monitoring data Dmon has the first level or the serial input data SDI has the first level. That is, when either of the monitoring data Dmon and the serial input data SDI has the first level, the output data SDO generated by the integrating unit  113  has the first level. In other words, when either of the driving circuit  110   a  and the driving circuit  110   b  determines that the power voltage VLED is not sufficient to drive the LEDs  140  coupled to them and that the power voltage VLED needs to be stepped up, the output data SDO is set as the first level. The output data SDO generated by the integrating unit  113  with the first level is configured to trigger the power supply circuit  120  to raise the power voltage VLED. On the other hand, in one embodiment, the integrating unit  113  sets the output data SDO as the second level when both the monitoring data Dmon and the serial input data SDI have the second level. In other words, when both of the driving circuit  110   a  and  110   b  determine that the power voltage VLED is sufficient to drive the LEDs  140  coupled to them and that the power voltage VLED does not need to be stepped up, the output data is set as the second level. The output data SDO generated by the integrating unit  113  with the second level is configured to trigger the power supply circuit  120  to maintain the power voltage VLED. These two embodiments can also be understood through the embodiments in  FIGS.  3 A,  3 B,  3 C,  3 D, and  3 E . More details will be discussed in later paragraphs. 
     In one embodiment, the serial input data SDI and/or the output data SDO is a digital data, the first level is high logic level, and the second level is low logic level. In one embodiment, the serial input data SDI and/or the output data SDO is an analog data, the first level is a higher voltage level, and the second level is lower voltage level. 
     In one embodiment, the output data SDO is transmitted to a serial output interface  114  as shown in  FIG.  2   , and the serial output interface  114  transmits the output data SDO to the driving circuit  110   c . Therefore, through the combination and operation of the components of the driving circuit  110   b , the information about the voltage of the LEDs  140  coupled to the driving circuit  110   a  (which is contained in the serial input data SDI) and the information about the voltage of the LEDs  140  coupled to the driving circuit  110   b  (which is contained in the monitoring data Dmon) can be integrated together and passed to the driving circuit  110   c  in the form of the output data SDO. In some embodiments, the output data SDO can be referred to as a multi-chip communication signal, which contains the information collected by more than one chip (i.e., the driving circuit  110  in the present disclosure). 
     Please refer to  FIG.  2    and  FIG.  3 A .  FIG.  3 A  is a time sequence diagram of the signals that the driving circuit  110   b  transmits and receives in accordance with some embodiments of the present disclosure. As pointed out in the paragraphs above, the display data DD is also contained in the serial input data SDI. To be more specific, in one embodiment, the integrating unit  130  integrates the monitoring data Dmon and the serial input data SDI in a time-dividing manner, in which the integrating unit  130  bypasses the display data DD carried in the serial input data SDI as the output data SDO during a first period P1 and combines the monitoring data Dmon with the serial input data SDI as the output data SDO during a second period P 2 . The first period P 1  and the second period P 2  do not overlap. 
     The serial input data SDI in  FIG.  3 A  are the data received by the serial input interface  112  of the driving circuit  110   b  as shown in  FIG.  2   , the monitoring data Dmon in  FIG.  3 A  are the data monitored by the comparator  111  and transmitted to the integrating unit  113  as shown in  FIG.  2   , and the output data SDO in  FIG.  3 A  are the data generated by the integrating unit  113  as shown in  FIG.  2   . The control signal Scon in  FIG.  3 A  is configured to control the driving circuit  110   b  to operate in the first period P 1  or the second period P 2 . In one embodiment, the control signal Scon is provided by the control unit  130  as shown in  FIG.  1   . In the embodiment shown in  FIG.  3 A , the display data DD is a square wave during the first period P 1 . It is worth noted that the square wave of the display data DD shown in  FIG.  3 A  is merely exemplary, and that the display data DD can have a waveform other than the square wave. During the first period P 1 , the control signal Scon has a low logic level and the driving circuit  110   b  operates in the first period P 1 . During the second period P 2 , the control signal Scon has a high logic level and the driving circuit  110   b  operates in the second period P 2 . 
     As shown in  FIG.  3 A , the display data DD is transmitted through the serial input data SDI during the first period P 1 , and the monitoring data DmonA is transmitted through the serial input data SDI during the second period P 2 . The monitoring data DmonA refer to the monitoring data that the comparator  111  of the driving circuit  110   a  generates according to the cathode voltage of the LEDs  140  coupled to the driving circuit  110   a , and the monitoring data DmonA is transmitted to the driving circuit  110   b  from the serial output interface  114  of the driving circuit  110   a . The monitoring data DmonB refer to the monitoring data that the comparator  111  of the driving circuit  110   b  generates and transmits to the integrating unit  113  of the driving circuit  110   b . The output data SDO refer to the data that the integrating unit  113  of the driving circuit  110   b  generates by integrating the monitoring data Dmon and the serial input data SDI in the time-dividing manner mentioned above. 
     Specifically, in the embodiment shown in  FIG.  3 A , during the first period P 1 , the display data DD is transmitted through the serial input data SDI, and, although the integrating unit receives the monitoring data DmonB, because the integrating unit  113  does not combine the monitoring data Dmon with the serial input data SDI during the first period P 1 , the integrating unit  113  simply outputs the display data DD as the output data SDO. 
     During the second period P 2 , the monitoring data DmonA is transmitted through the serial input data SDI, and because the integrating unit  113  combines the monitoring data Dmon with the serial input data SDI as the output data SDO during the second period P 2 , the integrating unit  113  integrates the monitoring data DmonA and the monitoring data DmonB into the monitoring data DmonC in the second period P 2 . 
     In one embodiment, the serial input interface  112 , the integrating unit  113 , and the serial output interface  114  operate in the second period P 2  when the control signal Scon has the first level, and the serial input interface  112 , the integrating unit  113 , and the serial output interface  114  operate in the first period P 1  when the control signal Scon has the second level. In one embodiment, the first level is high logic level, and the second level is low logic level. 
     Please refer to  FIG.  3 B .  FIG.  3 B  is a time sequence diagram of the signals that the driving circuit  110   b  transmits and receives in accordance with some embodiments of the present disclosure. In one embodiment, the serial input data SDI during the second period P 2  (i.e., the monitoring data DmonA in  FIG.  3 A ) has a high voltage level, which indicates that according to the cathode voltage monitored by the comparator  111  of the driving circuit  110   a  the power voltage VLED needs to be stepped up; the monitoring Dmon has a low voltage level, which indicates that according to the cathode voltage monitored by the comparator  111  of the driving circuit  110   b  the power voltage VLED does not need to be stepped up. Therefore, the output data SDO during the second period P 2  (i.e., the monitoring data DmonC in  FIG.  3 A ) has a high voltage level as the output data SDO is generated by combining the serial input data SDI and the monitoring data Dmon during the second period P 2 . 
     Please refer to  FIG.  3 C .  FIG.  3 C  is a time sequence diagram of the signals that the driving circuit  110   b  transmits and receives in accordance with some embodiments of the present disclosure. In one embodiment, the serial input data SDI during the second period P 2  has a low voltage level, which indicates that according to the cathode voltage monitored by the comparator  111  of the driving circuit  110   a  the power voltage VLED does not need to be stepped up; the monitoring Dmon has a high voltage level, which indicates that according to the cathode voltage monitored by the comparator  111  of the driving circuit  110   b  the power voltage VLED needs to be stepped up. Therefore, the output data SDO during the second period P 2  has a high voltage level. 
     Please refer to  FIG.  3 D .  FIG.  3 D  is a time sequence diagram of the signals that the driving circuit  110   b  transmits and receives in accordance with some embodiments of the present disclosure. In one embodiment, both the serial input data SDI and the monitoring Dmon during the second period P 2  have high voltage levels. Therefore, the output data SDO during the second period P 2  has a high voltage level. 
     Please refer to  FIG.  3 E .  FIG.  3 E  is a time sequence diagram of the signals that the driving circuit  110   b  transmits and receives in accordance with some embodiments of the present disclosure. In one embodiment, both the serial input data SDI and the monitoring Dmon during the second period P 2  have low voltage levels. Therefore, the output data SDO during the second period P 2  has a low voltage level, which indicates that according to the cathode voltages monitored by the comparators  111  of the driving circuits  110   a  and  110   b  the power voltage VLED does not need to be stepped up. 
     In one embodiment, one or all of the monitoring data Dmon, the serial input data SDI, and the output data SDO is digital data, which has a high logic level or a low logic level. In one embodiment, one or all of the monitoring data Dmon, the serial input data SDI, and the output data SDO is analog data, which can have different voltage level, e.g., 0V, 1V, 2V, 3V, and others alike. 
     Please refer to  FIG.  1    and  FIG.  4   .  FIG.  4    is a circuit diagram of the driving circuit  110   c  in accordance with some embodiments of the present disclosure. The driving circuit  110   c  includes the same components as the driving circuit  110   b  (i.e., the comparator  111 , the serial input interface  112 , the integrating unit  113 , and the serial output interface  114 ) and a feedback generator  115 . Detailed description of the previous embodiments can be referred to. The feedback generator  115  is configured to receive the output data SDO and generate the feedback control signal SFB to the power supply circuit  120 . In some embodiments, the feedback generator  115  is configured to extract the monitoring data DmonC in the second period P 2 , as shown in  FIG.  3 A , from the output data SDO. The monitoring data DmonC reflect whether the cathode voltages of the LEDs  140  coupled to the driving circuits  110  are lower than the threshold voltage. The feedback control signal SFB is generated to trigger the power supply circuit to raise or maintain the power voltage VLED. 
     In the embodiment shown in  FIG.  4   , the feedback controller  115  is included in the latest driving circuit  110   c , but the present disclosure is not limited thereto. In other embodiments, the functions of the feedback controller  115  can be integrated into the power supply circuit  120 , and the output data SDO are directly transmitted to the power supply circuit  120  from the driving circuit  110   c . 
     In some embodiments, the serial input data SDI and the output data SDO are transmitted among the driving circuits  110   a ,  110   b , and  110   c  through a serial transmission in a time-dividing manner. In other words, the serial input data SDI and the output data SDO can be transmitted through only one line, instead of two independent lines. 
     For most display devices on the market, the driver integrated circuits (IC) that control the currents passing through the light emitting diodes (LEDs) in the display device need a common bus system in order to communicate information about whether the driving voltage is large enough to drive the LEDs. In this approach, extra pins are required for all driver ICs in order to communicate through a common bus system that is different and independent from the driver ICs′ input/output interface, and thus the cost and complexity to manufacture the driver ICs increase. 
     Thus, the power voltage VLED can be modulated according to the output data SDO. It is worth noted that the configuration between the driving circuit  110   c  and the power supply circuit  120  does not intend to limit the present disclosure. Person having ordinary skills in the art can use different configuration between the driving circuit  110   c  and the power supply circuit  120  and still implement the disclosed driving circuits  110  configured to modulate the power voltage VLED. In the embodiment where the output data SDO is digital data, the feedback generator  115  can be further configured to transform the output data SDO into analog data for the purpose of modulating the power voltage VLED. 
     Please refer to  FIG.  5   .  FIG.  5    is a circuit diagram of the driving circuit  110   c  in accordance with some embodiments of the present disclosure. In one embodiment, the driving circuit  110   c  does not have the feedback generator  115  shown in  FIG.  4   , and the output data SDO is transmitted to a microcontroller unit (MCU)  150 . The microcontroller unit  150  determines whether the power voltage VLED needs to be stepped up according to the output data SDO and then transmits a raise control signal RCON to the power supply circuit  120 . The power supply circuit  120  raises or maintains the power voltage VLED based on the raise control signal RCON. 
     In conclusion, the driving circuits  110  in the various embodiments of the present disclosure can transmit the information regarding the monitored voltage of the corresponding LEDs  140  through the serial input interface  112  and the serial output interface  114 . The serial input interface  112  and the serial output interface  114  and others alike are normally included in most driving circuits, but in most cases they transmit only the display data DD configured to control the current of the LEDs coupled to the driving circuits. On the contrary, in the embodiments of the present disclosure, the serial input interface  112  and the serial output interface  114  are also configured to transmit the information regarding whether the power voltage VLED should be raised. 
     The present disclosure also provides a voltage modulation method. Please refer to  FIG.  6   .  FIG.  6    is a flowchart of a voltage modulation method  600  in accordance with some embodiments of the present disclosure. The voltage modulation method  600  includes steps S 610 , S 620 , S 630 , and S 640 . These steps can be performed through the configurations shown in the previous embodiments of the present disclosure. 
     The step S 610  is to determine whether a cathode voltage of a light emitting diode is lower than a threshold value and generate a monitoring data. For example, in the embodiment shown in  FIG.  2   , the comparator  111  determines whether the cathode voltage of the LED  140   bn  is lower than the threshold value and generates the monitoring data Dmon accordingly. 
     In one embodiment, the monitoring data has a first level in response to the cathode voltage of the light emitting diode being lower than the threshold value, and the monitoring data has a second level in response to the cathode voltage of the light emitting diode being higher than the threshold value. Detailed description of the previous embodiments can be referred. 
     The step S 620  is to receive a serial input data from a previous driving circuit. For example, in the embodiment shown in  FIG.  2   , the serial input interface  112  receives the serial input data SDI from the driving circuit  110   a  and passes such data to the integrating unit  113 . 
     The step S 630  is to integrate the monitoring data and the serial input data to generate an output data. For example, in the embodiment shown in  FIG.  2   , the integrating unit  113  integrates the monitoring data Dmon and the serial input data SDI and then generates the output data SDO. 
     In one embodiment, the output data has the first level in response to the monitoring data having the first level or the serial input data having the first level, and the output data has the second level in response to the monitoring data having the second level and the serial input data having the second level. Detailed description of the previous embodiments can be referred. 
     The step S 640  is to transmit the output data to a following driving circuit or to feedback the output data to a power supply circuit in order to modulate a power voltage VLED that the power circuit provides to the light emitting diode. For example, in the embodiment shown in  FIG.  2   , the serial output interface  114  transmits the output data SDO to the driving circuit  110   c . In another example, as shown in  FIG.  4   , the feedback generator  115  feedbacks the output data SDO to the power supply circuit  120 . However, in the two examples, the goal is the same - to modulate the power voltage VLED that the power circuit  120  provides to the LEDs  140 . 
     In one embodiment, the voltage modulation method  600  further includes transmitting the output data to a microcontroller unit configured to determine whether the power voltage needs to be stepped up according to the output data and to transmit a raise control signal to the power supply circuit. For example, as in the embodiment shown in  FIG.  5   , the output data SDO is transmitted to the microcontroller unit  150 , and the microcontroller unit  150  transmits the raise control signal RCON to the power supply circuit  120 . Detailed description of the previous embodiments can be referred. 
     In one embodiment, the voltage modulation method  600  further includes receiving a display data from the previous driving circuit and transmitting the display data to the following driving circuit. The display data is configured to control a current passing through the light emitting diode in this embodiment. For example, as in the embodiments shown in  FIG.  2   ,  FIG.  4   , and  FIG.  5   , the serial input interface  112  receives the display data DD and transmits it to the serial output interface  114 . Detailed description of the previous embodiments can be referred. 
     In one embodiment, integrating the monitoring data and the serial input data to generate the output data further includes bypassing a display data carried in the serial input data as the output data during a first period and combining the monitoring data with the serial input data as the output data during a second period. The first period and the second period do not overlap. For example, as in the embodiments shown in  FIG.  2    and  FIG.  3 A , the integrating unit  113 , during the first period P 1 , bypasses the display data DD carried in the serial input data SDI as the output data SDO and, during the second period P 2 , combines the monitoring data Dmon (which is the monitoring data DmonB during the second period P 2 ) with the serial input data SDI(which is the monitoring data DmonA during the second period P 2 ) as the output data SDO (which is the monitoring data DmonC during the second period P 2 ). 
     In conclusion, through the voltage modulation method  600 , information about voltage of the LEDs coupled to different driving circuits can be combined together and passed to a power supply circuit of a display device so that the power supply circuit can modulate the driving voltage accordingly. 
     Although the present invention has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims.