CN113053306B - Light emitting diode display and driving method thereof - Google Patents

Abstract

The invention discloses a driving method of a light emitting diode display, which is suitable for the light emitting diode display capable of changing the update rate and reducing the change of brightness due to the variation of the update rate. The method comprises the following steps: an organic light emitting diode of the light emitting diode display is controlled by a transmitting signal with a plurality of frame periods, wherein each of the frame periods is provided with a pulse width modulation part, the pulse width modulation part is provided with a duty ratio, whether a change exists in the update rate of the light emitting diode display is detected, and when the change is detected, a compensation procedure is executed, wherein the compensation procedure compensates a brightness difference of the organic light emitting diode by adjusting the duty ratio of the pulse width modulation part, and the brightness difference is caused by the change in the update rate. The invention also discloses a light-emitting diode display.

Description

Light emitting diode display and driving method thereof

Technical Field

The present invention relates to a light emitting diode (LED) display with a changeable refresh rate and a driving method thereof, and in particular to a light emitting diode display and a driving method thereof for reducing brightness variation caused by refresh rate variation.

Background Art

With the demand for display devices that can frequently change the refresh rate according to different uses (such as movies, file browsing, games, etc.), the change in brightness caused by the variation in refresh rate has become an annoying problem for users, so more and more display manufacturers are eager to solve this problem for market reasons. The reason why the brightness changes when the refresh rate of an LED display (such as an organic light emitting diode display) changes is that the length of the programming portion of the transmission signal (which can be understood as the vertical blanking interval) usually changes in response to the refresh rate variation. That is, the programming portion corresponding to a frame displayed just after the refresh rate changes is usually longer or shorter than the previous programming portion corresponding to the last frame displayed before the change.

Specifically, due to the difference in length of the programming parts and the fact that the time period of each frame remains constant, the pulse width modulation (PWM) part of the transmission signal (which can be understood as the data enable period) is also shortened or increased. Therefore, when the PWM part corresponding to the frame displayed after the update rate changes is longer than the PWM part corresponding to the last frame displayed before the change in response to the increase in the programming part, the length of the last enabled period of the PWM part after the update rate changes will inevitably be shorter than the length of the last enabled period of the PWM part before the update rate changes, and vice versa. Therefore, since the total time for the light-emitting diode receiving the transmission signal to emit light is changed, the last enabled period of the PWM part that is shortened or lengthened due to the change in the update rate causes a change in brightness.

Summary of the invention

In view of the above, the present invention provides a light emitting diode whose brightness is reduced due to update rate variation and a driving method thereof to meet the above needs.

An embodiment of the present invention discloses a driving method of a light emitting diode display, which is applicable to a light emitting diode display capable of changing the refresh rate. The driving method comprises: controlling an organic light emitting diode of the light emitting diode display with a transmission signal having a plurality of frame periods, wherein each of the frame periods has a pulse width modulation part, and the pulse width modulation part has a duty cycle; detecting whether there is a change in the refresh rate of the light emitting diode display; and when the change is detected, executing a compensation procedure, wherein the compensation procedure compensates for a brightness difference of the organic light emitting diode caused by the change in the refresh rate by adjusting the duty cycle of the pulse width modulation part.

A driving method for a light emitting diode display is applicable to a light emitting diode display capable of changing its refresh rate. The method comprises: controlling an organic light emitting diode of the light emitting diode display with an emission signal having a plurality of frame periods, wherein each of the frame periods has a pulse width modulation portion, and the pulse width modulation portion has a duty cycle; and when there is a change in the refresh rate of the light emitting diode display, changing the duty cycle from an initial duty cycle to a final duty cycle.

A light-emitting diode display capable of changing its refresh rate comprises: a light-emitting diode panel having a plurality of pixels; and a controller electrically connected to the pixels, wherein the controller generates an emission signal having a plurality of frame periods and transmits the emission signal to one of the pixels, wherein the frame periods each have a pulse width modulation portion, the pulse width modulation portion having a duty cycle, and wherein when there is a change in the refresh rate of the light-emitting diode display, the controller changes the duty cycle from an initial duty cycle to a final duty cycle.

The above description of the contents of the present disclosure and the following description of the embodiments are used to demonstrate and explain the spirit and principle of the present invention, and to provide further explanation of the claims of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a light emitting diode display capable of reducing brightness variation caused by refresh rate variation according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a light emitting diode display according to an embodiment of the present invention.

FIG. 3 is a voltage diagram of a plurality of signals transmitted to a pixel of a light emitting diode display according to an embodiment of the present invention.

FIG. 4 is a flow chart of a driving method for reducing brightness variation caused by refresh rate variation according to an embodiment of the present invention.

FIG. 5A is a voltage diagram of a transmission signal when the duty cycle of a PWM part is reduced according to an embodiment of the present invention.

FIG. 5B is a voltage diagram of a transmission signal when the duty cycle of the PWM part increases according to an embodiment of the present invention.

FIG. 6 is a block diagram of an LED display capable of reducing brightness variation caused by refresh rate variation according to another embodiment of the present invention.

FIG. 7A is a voltage diagram of a transmission signal when the duty cycle of a PWM part gradually decreases according to an embodiment of the present invention.

FIG. 7B is a voltage diagram of a transmission signal when the duty cycle of a PWM part gradually increases according to an embodiment of the present invention.

8A and 8B are voltage diagrams of a transmit signal when a pre-driving processor is not applied according to an embodiment of the present invention.

Wherein, the reference numerals are:

1 processing unit

2 Controller

21 Pre-driver processor

22 driver processor

3 Data Drivers

4 gate drivers

5Display Panel

51 pixels

IN input signal

DE data enable signal

PI image signal

DATA frame data signal

EM emission signal

VST1, VST2, VST4 signals

T1～T5 transistors

C _S capacitor

LED Organic Light Emitting Diode

Pf frame period

L Length of the programming part before _PG1

L Length of the programming section after _PG2

L Length of the PWM section before _PWM1

L Length of the PWM section after _PWM2

Pff front frame period

Pfl post-frame period

Pfm frame period

D _ONF , D _ON1 , D _ONL , D _ON2 enable period

SI information signal

DETAILED DESCRIPTION

The detailed features and advantages of the present invention are described in detail in the following embodiments, and the contents are sufficient to enable any person skilled in the art to understand the technical content of the present invention and implement it accordingly, and according to the contents disclosed in this specification, the scope of the patent application and the drawings, any person skilled in the art can easily understand the relevant purposes and advantages of the present invention. The following examples further illustrate the viewpoints of the present invention in detail, but do not limit the scope of the present invention in any viewpoint.

Please refer to FIG. 1 and FIG. 2. FIG. 1 is a block diagram of a light emitting diode (LED) display (e.g., an OLED display) capable of reducing brightness variation due to refresh rate variation according to an embodiment of the present invention. FIG. 2 is a circuit diagram of the light emitting diode display shown in FIG. In the display of this embodiment, a processing unit 1, a controller 2, a data driver 3, a gate driver 4, and a display panel 5 are included. The processing unit 1 receives an input signal IN and controls the data driver 3 and the gate driver 4 through the controller 2 so that the display panel 5 can display multiple frames in the input signal IN.

Specifically, the processing unit 1 can receive an input signal IN to generate an image signal PI and a data enable signal DE based on the input signal IN. The image signal PI includes the content of a frame to be displayed by the display panel 5. The data enable signal DE is used to sequentially enable a plurality of pixels 51 of the display panel 5. The pixels 51 described below can each represent a single-color pixel or a sub-pixel of a multi-color pixel. The controller 2 (which can be a timing controller of a general display device) is coupled to the processing unit 1 and receives the image signal PI and the data enable signal DE transmitted by the processing unit 1, and the controller 2 is further coupled to the data driver 3 and the gate driver 4 respectively. Based on the image signal PI and the data enable signal DE, the controller 2 controls the data driver 3 and the gate driver 4 to generate and transmit a plurality of signals to the display panel 5 coupled to the data driver 4 and the gate driver 4. With respect to the pixels 51 of the display panel 5, each pixel 51 in the present embodiment has a 5T1C (5 transistors T1-T5 and a capacitor Cs) structure as shown in FIG. 2, and emits light of the color of a frame of pixels with its organic light emitting diode LED. The structure of each pixel is not limited in the present embodiment, so when a pixel 51 having a structure different from 5T1C is used, the multiple signals transmitted to the display panel 5 may be different. To provide each pixel with a different structure, the signal transmitted to each pixel 51 may still include the frame data signal DATA from the data driver 3 and the emission signal EM from the gate driver 4. Specifically, through this 5T1C structure, in addition to the emission signal EM for normally operating the pixel 51, the gate driver 4 further transmits the signal VST1, the signal VST2, and the signal VST4 to each pixel 51. In operation, once the pixel 51 receives signals from the data driver 3 and the gate driver 4, the pixel 51 can emit light through the frame data signal DATA that controls the amount of light emitted by a corresponding one of the pixels 51, and through the emission signal EM for determining the enabling time period of each pixel 51.

Please refer to FIG. 3 , which is a voltage diagram of a plurality of signals including the emission signal EM and transmitted to the pixel 51 to provide a better understanding of the operation. In the present invention, the emission signal EM includes a plurality of frame periods Pf, which are provided for a plurality of frames to be displayed by the display panel 5, and each frame period Pf is divided into a programming portion and a pulse width modulation (PWM) portion. The programming portion is used to set the pixel 51 to be ready to emit light, and the PWM portion has a duty ratio to actuate the pixel 51 to emit light during an on-duration of the PWM portion. Specifically, in the operation of the light-emitting diode display, when the refresh rate is changed, the length of the programming portion is also changed accordingly; that is, the length of the programming portion corresponds to the refresh rate of the light-emitting diode display. Since the total length of the programming portion and the PWM portion (i.e., the length of the frame period Pf) remains constant, the variation in the length of the programming portion caused by the change in the refresh rate thus causes a variation in the length of the PWM portion. The present invention applies the following driving method, which can suppress the difference in the amount of light emitted by the pixel 51 during the PWM portion before and after the refresh rate variation.

Please refer to FIGS. 1, 2 and 4, wherein FIG. 4 is a flow chart of a driving method for reducing brightness variation caused by update rate variation according to an embodiment of the present invention. In step S1, the emission signal EM having the frame periods Pf controls the organic light emitting diode LED of the light emitting diode display through the controller 2, and the PWM part has an initial duty cycle, which can be understood as the duty cycle before the compensation process in response to the update rate variation. In step S2, based on the image signal PI and the data enable signal DE, the controller 2 detects whether there is a change in the update rate of the light emitting diode display. Specifically, if there is such a change, the update rate before the change is defined as the first update rate, and the update rate with such a change is defined as the second update rate. In step S3, when the controller 2 detects the change in the update rate, a compensation process is executed. This compensation process is implemented to compensate for the brightness difference of the organic light emitting diode LED caused by the update rate variation by adjusting the initial duty cycle of the PWM part to the final duty cycle, wherein the final duty cycle can be understood as the duty cycle after the compensation process.

In order to suppress the brightness change caused by the update rate variation, the variation of the length of the programming part and the adjustment of the duty cycle are preferably (but not limited to) positively correlated, so that the adjustment of the duty cycle can compensate for the brightness difference of the organic light emitting diode LED. Specifically, please refer to Figures 5A and 5B, which are voltage diagrams of the emission signal EM before and after the compensation process. Hereinafter, for the convenience of subsequent description, the programming part before the compensation process will be referred to as the front programming part; the PWM part before the compensation process will be referred to as the front PWM part; the programming part after the compensation process will be referred to as the post-programming part; and the PWM part after the compensation process will be referred to as the post-PWM part. In addition, the front programming part and the front PWM part are both in a front frame period Pff, and the post-programming part and the post-PWM part are both in a post-frame period Pfl.

In FIG. 5A , due to the update rate variation, the length L _PG2 of the rear programming section is smaller than the length L _PG1 of the front programming section, and thus the length L _PWM2 of the rear PWM section is larger than the length L _PWM1 of the front PWM section. Therefore, in the compensation procedure, the controller 2 adjusts the duty cycle of the PWM section from the initial duty cycle of the front PWM section to the final duty cycle of the rear PWM section, and the final duty cycle is smaller than the initial duty cycle. By the final duty cycle smaller than the initial duty cycle, although the last enable period D _ON2 of the rear PWM section is longer than the last enable period D _ON1 of the front PWM section, each of the remaining enable periods D _ONL of the rear PWM section is shorter than each of the remaining enable periods D _ONF of the front PWM section, so the increase in light quantity caused by the longer last enable period of the rear PWM section can be compensated by the decrease in light quantity caused by the shorter remaining enable periods. Similarly, in FIG. 5B , due to the update rate variation, the length L _PG2 of the rear programming section is greater than the length L _PG1 of the front programming section, and thus the length L _PWM2 of the rear PWM section is less than the length L _PWM1 of the front PWM section. In the compensation procedure, the controller 2 adjusts the duty cycle of the PWM section from the initial duty cycle of the front PWM section to the final duty cycle of the rear PWM section, and the final duty cycle is greater than the initial duty cycle. Thus, the decrease in light quantity caused by the shorter last enable period D _ON2 of the rear PWM section can be compensated by the increase in light quantity caused by the longer remaining enable period D _ONL . In theory, the driving method of the present invention compensates the increase/decrease in light quantity caused by the longer/shorter last enable period D _ON2 of the rear PWM section as much as possible with the decrease/increase in light quantity caused by the shorter/longer remaining enable period D _ONL .

In particular, it can be understood that the PWM portion can be divided into a plurality of fractions, and each of the plurality of enabled periods of the PWM portion occupies a portion of the fractions, and the duty cycle of the PWM portion can be expressed as a ratio of the number of fractions of an enabled period to the number of fractions of the entire cycle of the PWM portion (i.e., the total number of enabled periods and off periods). In the compensation process of the present invention, in some cases, because the number of increases or decreases in the fractions of the rear PWM portion cannot be divided by the number of its enabled periods, the variation of the length of the programming portion cannot be evenly distributed in each enabled period. In these cases, through the compensation process, the difference between the variation of the length of the programming portion and the total amount of changes in the enabled periods due to the adjustment of the duty cycle does not exceed the product of the number of enabled periods and the time period of the fraction. Specifically, in an ideal case, the total amount of changes in the enabled periods due to the adjustment of the duty cycle is equal to the variation of the length of the programming portion of the shorter/longer last enabled period of the rear PWM portion, that is, the increase or decrease in the number of fractions of the rear PWM portion can be divided by the number of enabled periods. In other words, under this ideal condition, the variation of the length of the programming portion is equal to the total amount of changes in the enable periods caused by the adjustment of the duty cycle.

In addition, in order to quickly adjust the duty cycle of the enable period when the update rate variation occurs (as shown in FIG. 6 ), the controller 2 may have a pre-driving processor 21 and a driving processor 22. The pre-driving processor 21 is electrically connected to the processing unit 1 to receive the image signal PI and the data enable signal DE to detect whether the update rate changes. The driving processor 22 is coupled to the pre-driving processor 21, the processing unit 1, the data driver 3, and the gate driver 4. During operation, the pre-driving processor 21 receives the image signal PI and the data enable signal DE at a first time point earlier than the driving processor 22, and when the change of the update rate is detected, the pre-driving processor 21 calculates the required final duty cycle based on the image signal PI and the data enable signal DE and generates an information signal SI having the final duty cycle information. The driving processor 22 receives the image signal PI, the data enable signal DE, and the information signal SI at a second time point at least one frame time later than the first time point, and performs a compensation process to generate its output to the data driver 3 and the gate driver 4. Thus, although the outputs to the data driver 3 and the gate driver 4 are slightly delayed, the signal generated by the drive processor 22 can quickly respond to variations in the length of the programmed portion within the same frame period Pf and change the duty cycle to accurately minimize brightness variations caused by refresh rate variations as shown in FIGS. 5A and 5B .

Another method based on the above structure is shown in FIG. 7A and FIG. 7B. As shown in FIG. 7A and FIG. 7B, among the frame periods Pf, there is a middle frame period Pfm between the previous frame period Pff and the next frame period Pfl, and the middle frame period Pfm has a PWM portion with a middle duty cycle, wherein the middle duty cycle is between the initial duty cycle and the final duty cycle. That is, the duty cycle is gradually adjusted during the compensation process. Although FIG. 7A and FIG. 7B only show one middle frame period between the previous frame period Pff and the next frame period Pfl, there may be more than one middle frame period Pfm between the two, wherein the middle duty cycle of the PWM portion of these middle frame periods Pfm gradually increases or decreases from the initial duty cycle to the final duty cycle.

Furthermore, in order to perform the driving method of the present invention, the above-mentioned structure in which the controller 2 has the pre-driving processor 21 and the driving processor 22 is only used as an embodiment of the present invention, and the present invention is not limited thereto. Specifically, in the embodiment in which the controller 2 does not have the pre-driving processor 21, when the change of the update rate occurs, the driving processor 22 detects the change of the update rate based on the image signal PI and the data enable signal DE and performs the compensation procedure. In this embodiment, the driving processor 22 can still start the compensation procedure early enough so that the emission signal EM has a waveform as shown in Figures 5A, 5B, 7A and 7B, for example, starting the compensation procedure during the programming part of the rear frame period. The situation may occur when the driving processor 22 detects the change of the update rate during the previous frame period Pff, or even during the programming part of the rear frame period Pfl of Figures 5A and 5B, or during the middle frame period Pfm of Figures 7A and 7B. However, in this embodiment, since the controller 2 does not have a pre-driving processor 21 to calculate the final duty cycle before the PWM portion of the rear frame period Pfl shown in Figures 5A and 5B or the mid-frame period Pfm shown in Figures 7A and 7B begins, there may be a mid-frame period Pfm with a PWM portion having an initial duty cycle as shown in Figures 8A and 8B. Figures 8A and 8B show that the driving processor 22 detects the change in the update rate during the mid-frame period Pfm, and starts the compensation process in the next frame period Pf of the mid-frame period Pfm, so that the PWM portion of the next frame period Pf of the mid-frame period Pfm (e.g., the rear frame period Pfl of Figures 8A or 8B) can have a final duty cycle in response to the update rate variation. Similarly, although Figures 8A and 8B only show that the duty cycle is quickly adjusted from the initial duty cycle to the final duty cycle, there may still be more than two mid-frame periods Pfm for gradual adjustment of the duty cycle between the front frame period Pff and the rear frame period Pfl.

In summary, by implementing the driving method disclosed in the present invention, the change in light quantity due to the variation in the update rate can be compensated by adjusting the duty cycle of the PWM portion of the frame period Pf, thereby minimizing the brightness change due to the variation in the update rate. In addition, this driving method can be implemented not only by a controller having two driving processors including a pre-driving processor, but also by a controller without a pre-driving processor.

Claims (25)

1. A method for driving a light emitting diode display, applicable to a light emitting diode display capable of changing a refresh rate, characterized in that the method comprises: Controlling an organic light emitting diode of the light emitting diode display with a transmission signal having a plurality of frame periods, wherein each of the frame periods has a pulse width modulation portion, the pulse width modulation portion having a duty cycle, wherein the transmission signal is divided into the pulse width modulation portion and a programming portion, and a length of the programming portion corresponds to the refresh rate of the light emitting diode display; detecting whether there is a change in the refresh rate of the light emitting diode display; and A compensation process is executed when the change is detected, wherein the compensation process compensates for a brightness difference of the organic light emitting diode caused by the change of the refresh rate by adjusting the duty cycle of the pulse width modulation part. 2. The driving method of the light emitting diode display according to claim 1, characterized in that the change of the refresh rate causes a variation of the length of the programming portion, and the variation of the length of the programming portion is positively correlated with an adjustment of the duty cycle. 3. The driving method of a light emitting diode display according to claim 2 is characterized in that the pulse width modulation part has a plurality of enabling periods, each of the enabling periods includes a plurality of segments, and wherein the difference between the variation in the length of the programming part and a total amount of changes in the enabling periods caused by the adjustment of the duty cycle does not exceed the product of a number of the enabling periods and a period of the segment. 4 . The driving method of a light emitting diode display according to claim 3 , wherein the total amount of changes of the enabling periods caused by the adjustment of the duty cycle is equal to the variation of the length of the programming portion. 5. The driving method of the light emitting diode display according to claim 1 is characterized in that the update rate before detecting whether the update rate of the light emitting diode display has the change is a first update rate, the update rate with the change is a second update rate, the duty cycle before the compensation process is an initial duty cycle, and the duty cycle after the compensation process is a final duty cycle. 6. The driving method of the light emitting diode display according to claim 5 is characterized in that a middle frame period among the frame periods exists between a previous frame period and a subsequent frame period among the frame periods, and the previous frame period and the middle frame period both have a pulse width modulation portion with the initial duty cycle, and the subsequent frame period has a pulse width modulation portion with the final duty cycle. 7 . The driving method of a light emitting diode display according to claim 6 , wherein the compensation procedure starts during the mid-frame period. 8. The driving method of the light emitting diode display according to claim 5 is characterized in that a previous frame period among the frame periods is adjacent to a subsequent frame period among the frame periods, the previous frame period has a pulse width modulation portion with the initial duty cycle, and the subsequent frame period has a pulse width modulation portion with the final duty cycle. 9 . The driving method of a light emitting diode display according to claim 8 , wherein the compensation procedure starts during the programming portion of the subsequent frame period. 10. The driving method of the light emitting diode display according to claim 5, characterized in that a middle frame period among the frame periods is between a previous frame period and a next frame period among the frame periods, the previous frame period has a pulse width modulation portion with the initial duty cycle, the next frame period has a pulse width modulation portion with the final duty cycle, and the middle frame period has a pulse width modulation portion with a duty cycle between the initial duty cycle and the final duty cycle. 11 . The driving method of a light emitting diode display according to claim 10 , wherein the compensation procedure starts during the programming portion of the subsequent frame period. 12. The driving method of the light emitting diode display according to claim 1, characterized in that controlling the organic light emitting diode of the light emitting diode display comprises: transmitting an image signal and a data enable signal to a pre-driving processor at a first time point to selectively generate an information signal, transmitting the image signal and the data enable signal to a driving processor at a second time point at least one frame period later than the first time point, and generating the emission signal based on the image signal and the data enable signal, or generating the emission signal based on the image signal, the data enable signal and the information signal by the driving processor. 13. The driving method of the light emitting diode display according to claim 12, wherein the detection of whether the refresh rate of the light emitting diode display has the change is performed by the pre-driving processor, the compensation procedure is performed by the driving processor, and the information signal is generated when the change is detected. 14 . The driving method of the light emitting diode display according to claim 1 , wherein the emission signal is generated by a controller of the light emitting diode display and transmitted to a pixel of the light emitting diode display, wherein the pixel has the organic light emitting diode. 15. A method for driving a light emitting diode display, applicable to a light emitting diode display capable of changing a refresh rate, characterized in that the method comprises: controlling an organic light emitting diode of the light emitting diode display with a transmission signal having a plurality of frame periods, wherein each of the frame periods has a pulse width modulation portion, the pulse width modulation portion having a duty cycle, wherein the transmission signal is divided into the pulse width modulation portion and a programming portion, and a length of the programming portion corresponds to the refresh rate of the light emitting diode display; and When there is a change in the refresh rate of the light emitting diode display, the duty cycle is changed from an initial duty cycle to a final duty cycle. 16. The driving method of the light emitting diode display according to claim 15 is characterized in that there is a middle frame period among the frame periods between a previous frame period and a subsequent frame period among the frame periods, and the previous frame period and the middle frame period both have a pulse width modulation portion with the initial duty cycle, and the subsequent frame period has a pulse width modulation portion with the final duty cycle. 17. The driving method of the light emitting diode display according to claim 15 is characterized in that a previous frame period among the frame periods is adjacent to a subsequent frame period among the frame periods, the previous frame period has a pulse width modulation portion with the initial duty cycle, and the subsequent frame period has a pulse width modulation portion with the final duty cycle. 18. The driving method of the light emitting diode display according to claim 15 is characterized in that a middle frame period among the frame periods is between a previous frame period and a next frame period among the frame periods, the previous frame period has a pulse width modulation portion with the initial duty cycle, the next frame period has a pulse width modulation portion with the final duty cycle, and the middle frame period has a pulse width modulation portion with a duty cycle between the initial duty cycle and the final duty cycle. 19. A light emitting diode display capable of changing its refresh rate, characterized in that the light emitting diode display comprises: an LED panel having a plurality of pixels; and a controller electrically connected to the pixels, wherein the controller generates an emission signal having a plurality of frame periods and the controller transmits the emission signal to one of the pixels, the frame periods each having a pulse width modulation portion, the pulse width modulation portion having a duty cycle, and wherein when there is a change in the refresh rate of the light emitting diode display, the controller changes the duty cycle from an initial duty cycle to a final duty cycle, The transmitting signal is divided into the pulse width modulation part and a programming part, and a length of the programming part corresponds to the refresh rate of the light emitting diode display. 20. The light emitting diode display according to claim 19 is characterized in that a middle frame period among the frame periods exists between a previous frame period and a subsequent frame period among the frame periods, and the previous frame period and the middle frame period both have a pulse width modulation portion with the initial duty cycle, and the subsequent frame period has a pulse width modulation portion with the final duty cycle. 21. The light emitting diode display according to claim 19, wherein a previous frame period among the frame periods is adjacent to a subsequent frame period among the frame periods, the previous frame period has a pulse width modulation portion with the initial duty cycle, and the subsequent frame period has a pulse width modulation portion with the final duty cycle. 22. The light emitting diode display according to claim 19 is characterized in that a middle frame period among the frame periods is between a previous frame period and a next frame period among the frame periods, the previous frame period has a pulse width modulation portion with the initial duty cycle, the next frame period has a pulse width modulation portion with the final duty cycle, and the middle frame period has a pulse width modulation portion with a duty cycle between the initial duty cycle and the final duty cycle. 23. The light emitting diode display according to claim 19, wherein the controller comprises a pre-driving processor and a driving processor, the pre-driving processor is electrically connected to the driving processor, the driving processor is electrically connected to the pixels, and the pre-driving processor and the driving processor are both used to receive an image signal and a data enable signal. 24. The light emitting diode display according to claim 23 is characterized in that the pre-driving processor receives an image signal and a data enable signal at a first time point to selectively generate an information signal, and the driving processor receives the image signal and the data enable signal at a second time point that is at least one frame period later than the first time point, and generates the emission signal based on the image signal and the data enable signal, or generates the emission signal based on the image signal, the data enable signal and the information signal. 25. The light emitting diode display according to claim 23 is characterized in that the pre-driving processor detects whether the change of the refresh rate exists based on the image signal and the data enable signal, and generates an information signal when the change is detected, and when the driving processor receives the information signal, the duty cycle is changed from an initial duty cycle to a final duty cycle.