Patent Publication Number: US-2022229501-A1

Title: Display panel, method for driving display panel, and display apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Chinese Patent Application No. 202210077655.3, filed on Jan. 24, 2022, the content of which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to the technical field of display, and in particular, to a display panel, a method for driving a display panel, and a display apparatus. 
     BACKGROUND 
     With the development of display technology, the application of styluses in the field of display has enriched human-computer interaction. Some electronic device manufacturers have proposed styluses for large-screen devices. There are two main types of styluses in the market, i.e., passive capacitive stylus and active capacitive stylus. The passive capacitive stylus uses the tip of the stylus to simulate the touch effect of the finger, has a tip made of a conductive material, and needs to be provided with a relatively wide tip. The active capacitive stylus uses an active electrical signal emitted by the stylus to simulate the effect of large-area contact. A touch detection circuit is integrated in the display apparatus, and the touch detection circuit cooperates with the stylus to realize a touch function. The current stylus has a large tip size and a low touch accuracy, which cause poor user experience. 
     SUMMARY 
     According to a first aspect, some embodiments of the present disclosure provide a display panel. The display panel includes at least one pixel circuit, at least one light-emitting device coupled to the pixel circuit, at least one data line, and a first voltage signal line. One pixel circuit of the at least one pixel circuit includes a data writing transistor and a photodiode. The data writing transistor includes a first electrode coupled to one of the at least one data line, and a second electrode coupled to a first electrode of the photodiode. The photodiode includes a second electrode coupled to the first voltage signal line. 
     According to a second aspect, some embodiments of the present disclosure further provide a method for driving a display panel. The display panel includes at least one pixel circuit, at least one light-emitting device coupled to the pixel circuit, at least one data line, and a first voltage signal line. One pixel circuit of the at least one pixel circuit includes a data writing transistor and a photodiode. The data writing transistor includes a first electrode coupled to one of the at least one data line, and a second electrode coupled to a first electrode of the photodiode. The photodiode includes a second electrode coupled to the first voltage signal line. The method includes: controlling the data writing transistor to be turned on, and detecting a voltage value on one data line of the at least one data line; and determining a position of an optical touch signal based on the voltage value. 
     According to a third aspect, some embodiments of the present disclosure further provide a display apparatus including a display panel. The display panel includes at least one pixel circuit, at least one light-emitting device coupled to the pixel circuit, at least one data line, and a first voltage signal line. One pixel circuit of the at least one pixel circuit includes a data writing transistor and a photodiode. The data writing transistor includes a first electrode coupled to one of the at least one data line, and a second electrode coupled to a first electrode of the photodiode. The photodiode includes a second electrode coupled to the first voltage signal line. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       To describe the technical solutions in the embodiments of the present disclosure or the related art more clearly, the following briefly describes the accompanying drawings required for describing the embodiments or the related art. The accompanying drawings in the following description show some embodiments of the present disclosure, and a person skilled in the art can still derive other drawings from these accompanying drawings. 
         FIG. 1  is a schematic circuit diagram of a display panel according to an embodiment of the present disclosure; 
         FIG. 2  is a sequence diagram of a pixel circuit according to an embodiment of the present disclosure; 
         FIG. 3  is a flowchart of a method for driving a display panel according to an embodiment of the present disclosure; 
         FIG. 4  is a flowchart of a method for driving a display panel according to an embodiment of the present disclosure; 
         FIG. 5  is a schematic circuit diagram of another display panel according to an embodiment of the present disclosure; 
         FIG. 6  is a schematic circuit diagram of another display panel according to an embodiment of the present disclosure; 
         FIG. 7  is a schematic circuit diagram of another display panel according to an embodiment of the present disclosure; 
         FIG. 8  is a schematic circuit diagram of another display panel according to an embodiment of the present disclosure; 
         FIG. 9  is a schematic circuit diagram of another display panel according to an embodiment of the present disclosure; 
         FIG. 10  is a schematic circuit diagram of another display panel according to an embodiment of the present disclosure; 
         FIG. 11  is a sectional view of another display panel according to an embodiment of the present disclosure; 
         FIG. 12  is a sectional view of another display panel according to an embodiment of the present disclosure; 
         FIG. 13  is a sectional view of another display panel according to an embodiment of the present disclosure; 
         FIG. 14  is a sectional view of another display panel according to an embodiment of the present disclosure; and 
         FIG. 15  is a schematic diagram of a display apparatus according to an embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In order to make technical solutions and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present disclosure. The described embodiments are some, rather than all of the embodiments of the present disclosure. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present disclosure shall fall within the protection scope of the present disclosure. 
     Terms in the embodiments of the present disclosure are merely used to describe the embodiments, and are not intended to limit the present disclosure. Unless otherwise specified in the context, words, such as “a”, “the”, and “this”, in a singular form in the embodiments of the present disclosure and the appended claims include plural forms. 
     The capacitive stylus in the related art simulates the touch effect of human hands to achieve the touch function. The tip of the stylus needs to have a large enough area. The actual contact area between the tip and the display is also large, resulting in low touch accuracy and failing to achieve pixel-level positioning of the touch position, which affects the user experience. Using the touch recognition method in the related art, the tip of the stylus needs to be in contact with the display screen. The tip of the stylus is usually made of metal, which will cause wear and tear on the screen after multiple touch operations. 
     An embodiment of the present disclosure provide a display panel, a pixel circuit of the display panel is improved, a photodiode is integrated in the pixel circuit, and an optical touch signal is detected by the pixel circuit, which can realize pixel-level positioning for the touch signal, increase the accuracy of touch detection, and improve the user experience. 
     The display panel provided by embodiments of the present disclosure includes a pixel circuit and a light-emitting device coupled to the pixel circuit. In some embodiments, the light-emitting device is an organic light emitting diode. In other embodiments, the light-emitting device is an inorganic light emitting diode. The photodiode is integrated in the pixel circuit. The photodiode is coupled to the data line through a data writing transistor. When the data writing transistor is turned on, the photodiode is controlled to operate under a reverse voltage. With irradiation, the carrier concentration in an anode region and a cathode region of the photodiode is improved to form a photocurrent, and the photocurrent will cause a voltage on the data line to change. Detection of the optical touch position can be implemented by detecting the change of the voltage signal on the data line. 
     The photodiode includes an anode and a cathode. When operating under a reverse voltage, the photodiode will generate a photocurrent after receiving light. In the embodiments of the present disclosure, a first electrode of the photodiode is coupled to the data line through the data writing transistor, and a second electrode of the photodiode is coupled to a first voltage signal line, so that when the data writing transistor is turned on, the photodiode can operate under a reverse voltage. In some embodiments, the first voltage signal line can be a signal line additionally provided in the display panel. In other embodiments, the first voltage signal line is coupled to the photodiode, and is also reused as a reset signal line or a power signal line in the display panel. 
     An optical touch function can be implemented through interaction between the laser pointer and the display panel. The laser pointer does not need to be in contact with the display panel, so that the optical touch function does not cause wear and tear of the display panel. After laser light emitted by the laser pointer is incident on the display panel, a bright spot will be formed on the display panel. In other words, whether a light-emitting device at a position irradiated by the laser pointer can emit light normally or not does not affect the overall display screen. 
     The present disclosure will be illustrated below through some embodiments. 
       FIG. 1  is a schematic circuit diagram of a display panel according to an embodiment of the present disclosure.  FIG. 2  is a sequence diagram of a pixel circuit according to an embodiment of the present disclosure. 
     As shown in  FIG. 1 , a pixel circuit  10  is coupled to a light-emitting device  20 . The pixel circuit  10  includes a drive transistor Tm, a data writing transistor T 1 , a threshold compensation transistor T 2 , a node reset transistor T 3 , an electrode reset transistor T 4 , a first light-emitting control transistor T 5 , a second light-emitting control transistor T 6 , and a storage capacitor Cst. 
     The display panel includes a data line Data, a first scanning signal line S 1 , a second scanning signal line S 2 , a reset signal line Ref, a light-emitting control line E, a first power signal line P 1 , and a second power signal line P 2 . 
     A control electrode of the drive transistor Tm is coupled to a first node N 1 , a first electrode of the drive transistor Tm is coupled to a second node N 2 , and a second electrode of the drive transistor Tm is coupled to a third node N 3 . A control electrode of the node reset transistor T 3  is coupled to the second scanning signal line S 2 , a first electrode of the node reset transistor T 3  is coupled to the reset signal line Ref, and a second electrode of the node reset transistor T 3  is coupled to the first node N 1 . A control terminal of the data writing transistor T 1  is coupled to the first scanning signal line S 1 , a first electrode of the data writing transistor T 1  is coupled to the data line Data, and a second electrode of the data writing transistor T 1  is coupled to the second node N 2 . The threshold compensation transistor T 2  is connected in series between the first node N 1  and the third node N 3 , and a control electrode of the threshold compensation transistor T 2  is coupled to the first scanning signal line S 1 . A control electrode of the electrode reset transistor T 4  is coupled to the first scanning signal line S 1 , a first electrode of the electrode reset transistor T 4  is coupled to the reset signal line Ref, and a second electrode of the electrode reset transistor T 4  is coupled to the fourth node N 4 . A control electrode of the first light-emitting control transistor T 5  and a control electrode of the second light-emitting control transistor T 6  are both coupled to the light-emitting control line E. A first electrode of the first light-emitting control transistor T 5  is coupled to the second power signal line P 2 , and a second electrode of the first light-emitting control transistor T 5  is coupled to the second node N 2 . A first electrode of the second light-emitting control transistor T 6  is coupled to the third node N 3 , and a second electrode of the second light-emitting control transistor T 6  is coupled to the fourth node N 4 . A first electrode of the light-emitting device  20  is coupled to the fourth node N 4 , and a second electrode of the light-emitting device  20  is coupled to the first power signal line P 1 ; one electrode plate of the storage capacitor Cst is coupled to the second power signal line P 2 , and another electrode plate of the storage capacitor Cst is coupled to the first node N 1 . 
     The light-emitting device  20  includes a first electrode, a light-emitting layer, and a second electrode. For example, if the first electrode of the light-emitting device  20  is an anode, the first power signal line P 1  is a cathode power signal line, and the second power signal line P 2  is an anode power signal line. In some embodiments, if the first electrode of the light-emitting device  20  is a cathode, the first power signal line P 1  is an anode power signal line, and the second power signal line P 2  is a cathode power signal line. 
     At least one pixel circuit  10  further includes a photodiode PD. A first electrode of the photodiode PD is coupled to the second electrode of the data writing transistor T 1 . In this case, the first electrode of the photodiode PD is coupled to the second node N 2 , and a second electrode of the photodiode PD is coupled to the first voltage signal line V 1 . In an embodiment of the present disclosure, the photodiode PD is coupled to the data line Data through the data writing transistor T 1 . In some embodiments, the first electrode of the photodiode PD is a cathode, and the second electrode of the photodiode PD is an anode. In other embodiments, the first electrode of the photodiode PD is an anode, and the second electrode of the photodiode PD is a cathode. In the following embodiments, an example where the first electrode of the photodiode PD being a cathode and the second electrode being an anode is taken for description. 
     An operation cycle of the pixel circuit  10  includes a reset phase t 1 , a data writing phase t 2 , and a light-emitting phase t 3 . The operation cycle of the pixel circuit  10  is described with reference to the sequence diagram shown in  FIG. 2 . 
     During the reset phase t 1 , the second scanning signal line S 2  provides an enable signal to control the node reset transistor T 3  to turn on and write a reset signal provided by the reset signal line Ref into the first node N 1 , so as to reset the first node N 1 , that is, to reset the control electrode of the drive transistor Tm. 
     During the data writing phase t 2 , the first scanning signal line S 1  provides an enable signal to control the data writing transistor T 1 , the threshold compensation transistor T 2 , and the electrode reset transistor T 4  to turn on. After being turned on, the electrode reset transistor T 4  writes the reset signal provided by the reset signal line Ref into the fourth node N 4 , to reset the fourth node N 4 , that is, to reset the first electrode of the light-emitting device  20 . 
     When no light is incident on the photodiode PD, after the data writing transistor T 1  is turned on, the cathode of the photodiode PD is connected to the data line Data, and a voltage value of a voltage signal provided by the first voltage signal line V 1  is controlled to be lower than a voltage value of a data signal provided by the data line Data. Although the photodiode PD works under a reverse voltage, a dark current generated by the photodiode PD is extremely low because there is no light, and the impact of the dark current on the voltage of the data line Data is also small. In the data writing phase t 2 , after the data writing transistor T 1  and the threshold compensation transistor T 2  are turned on, the data signal provided by the data line Data is written into the first node N 1 , and a threshold voltage of the drive transistor Tm is self-checked and compensated, to complete the data writing process. 
     When light is incident on the photodiode PD, the irradiation causes a large increase in the carrier concentration in the anode region and the cathode region of the photodiode PD; the photodiode PD operates under a reverse voltage, and the reverse saturated leakage current increases, forming a photocurrent. Because the cathode of the photodiode PD is connected to the data line Data, the photocurrent generated by the photodiode PD will cause the voltage on the data line Data to change. The position of the optical touch can be determined by detecting the voltage change on the data line Data, thereby realizing the optical touch detection. Because the cathode of the photodiode PD is coupled to the second node N 2 , the photocurrent will cause a potential of the second node N 2  to change. In the data writing phase t 2 , the threshold compensation transistor T 2  will also be turned under the control of the enable signal, and will also complete the data writing process, except that the data signal actually written into the first node N 1  in this case is greatly different from an expected data signal (that is, an expected value of the data signal). 
     It can be understood that, the irradiation referred to in the description of the operating process of the data writing phase t 2  refers to laser light irradiation in the application. It can be understood that, in use of the display panel, there can be ambient light incident on the photodiode PD. However, due to a relatively low intensity, the ambient light cannot cause the photodiode PD in a reverse bias state to generate a photocurrent that can be used for optical touch detection. 
     During the light-emitting phase t 3 , the light-emitting control line E provides an enable signal to control the first light-emitting control transistor T 5  and the second light-emitting control transistor T 6  to turn on; after being turned on under the voltage control of the first node N 1 , the drive transistor Tm generates a driving current, and provides the driving current to the light-emitting device  20  to control the light-emitting device  20  to emit light. 
     When no light is incident on the photodiode PD, the data signal written into the first node N 1  in the data writing phase t 2  is the expected data signal; therefore, in the light-emitting phase t 3 , light-emitting brightness of the light-emitting device  20  is the expected brightness. 
     When there is light incident on the photodiode PD, because the data signal written into the first node N 1  in the data writing phase t 2  is greatly different from the expected data signal, the brightness of the light-emitting device  20  in the light-emitting phase t 3  is greatly (i.e., appreciably) different from the expected brightness. 
     In other words, when there is light incident on the photodiode PD, the data line Data and the cathode of the photodiode PD can be connected to each other by using an enable state of the data writing transistor T 1 , to set the photodiode PD to a reverse bias state, thereby detecting a voltage change on the data line Data. The position of the optical touch signal is determined based on the voltage change on the data line Data, thereby implementing optical touch detection. When the photodiode PD generates a photocurrent, a normal data signal (that is, the expected data signal) cannot be written into the pixel circuit  10  where the photodiode PD is located, which finally results in abnormal brightness of the light-emitting device  10  coupled to the pixel circuit  20 . The optical touch function is realized using interaction between the laser pointer and the display panel in actual application. After laser light emitted by the laser pointer is incident on the display panel, a bright spot will be formed on the display panel. That is, even if the brightness of the light-emitting device is abnormal at the position irradiated by the laser pointer, the overall visual effect will not be affected. 
     In the display panel provided by the embodiments of the present disclosure, the photodiode PD is integrated in the pixel circuit  10 , and the photodiode PD is coupled to the data line Data through the data writing transistor T 1 . When the photodiode PD does not receive light, the pixel circuit  10  sequentially executes the reset phase t 1 , the data writing phase t 2 , and the light-emitting phase t 3 , to drive the light-emitting device  20  to emit light to reach the expected brightness. When the photodiode PD receives light, the pixel circuit  10  executes the data writing phase t 2 , and the photodiode PD works under a reverse voltage to generate a photocurrent, which will cause the voltage on the data line Data to change. The position of an optical touch can be detected by detecting a voltage change on the data line, to realize pixel-level positioning for the optical touch signal, thereby improving the accuracy of touch detection and improving the user experience. During an optical touch operation, a laser pointer does not need to be in contact with the display panel, which avoids wear and tear of the display panel. In the embodiments of the present disclosure, by integrating the photodiode PD in the pixel circuit  10 , it is unnecessary to additionally arrange a touch detection circuit in the display panel, which can simplify the wiring in the display panel and increase the degree of integration. 
     In some embodiments, the display panel further includes a touch determining module. The touch determining module is coupled to the data line Data, and is configured to detect a voltage value on the data line Data when the data writing transistor T 1  is turned on, and to determine a position of an optical touch signal according to a voltage value. In the embodiments of the present disclosure, the optical touch signal can be acquired in the data writing phase t 2 , and then the touch determining module processes the optical touch signal. The acquisition process of the optical touch signal does not affect the working sequence of the pixel circuit  10 . 
     The touch determining module can be integrated in a display driver chip. After determining the optical touch position according to the optical touch signal, the touch determining module can feedback optical touch position information to a main board of the electronic device through the display driver chip. The main board controls the display panel according to the optical touch position information, thereby implementing a human-computer interaction process of the optical touch function. 
     In the application, the optical touch operation on the display panel can be implemented using the laser pointer. Light emitted by the laser pointer is incident on a partial region of the display panel. The photodiode PD of the pixel circuit  10  in the partial region receives the light. When the pixel circuit  10  operates in the data writing phase t 2 , the photodiode PD receiving the light works under a reverse voltage to generate a photocurrent. The photocurrent affects the voltage on the data line Data. The position of the optical touch is detected by detecting the change of the voltage signal on the data line Data. Then, the optical touch is fed back according to the position of the optical touch, to control an operating state of the display panel. 
     In some application scenarios, the laser pointer can have some functions of a mouse. For example, if there is a cursor on a display screen, the left button of the mouse is clicked to move the cursor in the related art. With the display panel provided by the embodiments of the present disclosure, the laser pointer can be used to move the cursor, and the position irradiated by the laser pointer is the optical touch position. After the optical touch position is detected, the system moves the cursor to the optical touch position. 
     In some application scenarios, such as presentations, it is necessary to mark parts of the text by, for example, underlining or circling them. With the display panel provided by the embodiments of the present disclosure, the text can be marked using the irradiation of the laser pointer. The position irradiated by the laser pointer is the optical touch position. When multiple optical touch positions are detected, the brightness of the light-emitting device at the optical touch positions is controlled to form an underline marker or a circle marker during display. 
     The pixel circuit  10  in  FIG. 1  is merely shown schematically. The pixel circuit in the embodiments of the present disclosure can be any pixel circuit including a data writing transistor in the related art. Transistors of the pixel circuit  10  shown in  FIG. 1  are p-type transistors. In other embodiments, transistors of the pixel circuit  10  are n-type transistors. In other embodiments, the pixel circuit  10  includes n-type transistors and p-type transistors. 
       FIG. 1  schematically illustrates that the control terminal of the electrode reset transistor T 4  and the control terminal of the data writing transistor T 1  are coupled to a same scanning signal line. In other embodiments, the control terminal of the electrode reset transistor T 4  and the control terminal of the node reset transistor T 3  are coupled to a same scanning signal line. In this case, the process of resetting the control electrode of the drive transistor Tm and the process of resetting the first electrode of the light-emitting device  20  are performed at the same time. 
       FIG. 1  schematically illustrates that the first electrode of the electrode reset transistor T 4  and the first electrode of the node reset transistor T 3  are coupled to a same reset signal line 
     Ref. In other embodiments, the first electrode of the electrode reset transistor T 4  and the first electrode of the node reset transistor T 3  are coupled to different reset signal lines. That is, the reset voltage for resetting the control electrode of the drive transistor Tm and the reset voltage for resetting the first electrode of the light-emitting device  20  have different values. 
     Based on a same concept, some embodiments of the present disclosure further provide a method for driving a display panel, to drive the display panel provided by the embodiments of the present disclosure. The method provided by the embodiments of the present disclosure can be referred to the embodiment shown in  FIG. 1 .  FIG. 3  is a flowchart of a method for driving a display panel according to an embodiment of the present disclosure. As shown in  FIG. 3 , the method includes step S 101  and step S 102 . 
     At step S 101 , a data writing transistor T 1  is controlled to be turned on, and a voltage value on a data line Data is detected. At step S 102 , a position of an optical touch signal is determined according to the voltage value. 
     When the method provided by the embodiments of the present disclosure is used for driving the display panel, after the data writing transistor T 1  is controlled to be turned on, a cathode of a photodiode PD can be connected to the data line Data, to apply a voltage on the data line Data to the cathode of the photodiode PD. An anode of the photodiode PD is coupled to a first voltage signal line V 1 , and the first voltage signal line V 1  provides a transmitted voltage signal to the anode of the photodiode PD. Therefore, after the data writing transistor T 1  is controlled to be turned on, the photodiode PD in the pixel circuit  10  can be reversely biased. 
     When receiving light and being reversely biased, the photodiode PD can generate a photocurrent. The photocurrent generated by the photodiode PD will affect the voltage on the data line Data coupled thereto. In this case, by detecting the voltage value on the data line Data, it can be determined whether a photocurrent is generated by the photodiode PD. The position where the optical touch signal is generated can be determined according to the position of the pixel circuit  10  to which the photodiode PD belongs in the display panel. In the embodiments of the present disclosure, the optical touch position is determined according to the position of the pixel circuit  10 , thereby achieving pixel-level positioning detection for the optical touch. 
       FIG. 4  is a flowchart of a method for driving a display panel according to an embodiment of the present disclosure. In some embodiments, as shown in  FIG. 4 , the method includes the following steps: step S 201 , step S 202 , and step S 203 . 
     At step S 201 , a data writing transistor T 1  is controlled to be turned on and to provide a data signal to a data line Data, and a voltage value on the data line Data is detected. 
     At step S 202 , when an absolute value of a difference between the voltage value and a voltage value of the data signal is greater than a preset voltage value, it is determined that a photodiode PD corresponding to the data signal generates a photocurrent. 
     At step S 203 , a position of an optical touch signal is determined according to a position of the photodiode PD that generates the photocurrent. 
     In a reverse bias state of the photodiode PD, when ambient light is incident on the photodiode PD, although the ambient light is much weaker than light emitted by the laser pointer, the ambient light also affects the photodiode PD in certain degree to cause the photodiode PD to generate a small leakage current. It can be understood that the small leakage current will also affect the voltage on the data line Data. In the methods of the present disclosure, a preset voltage value is set, and when a voltage variation on the data line Data is greater than the preset voltage value, it is determined that there is an optical touch signal. In other words, it is determined that the voltage variation on the data line Data is caused by an optical touch operation only when the voltage variation reaches a certain value, which can improve the accuracy of optical touch detection. 
     In some embodiments, the method includes: controlling an operation cycle of the pixel circuit  10  to include a data writing phase t 2 . Reference can be made to the description about the operation cycle of the pixel circuit  10  in the embodiment shown in  FIG. 2 . In the data writing phase t 2 , the data writing transistor T 1  is controlled to turn on, and the voltage value on the data line Data is detected. In the embodiment, an acquisition process of the optical touch signal is integrated in the operation cycle of the pixel circuit  10 , and does not affect the operating sequence of the pixel circuit  10 . 
     In some embodiments, as shown in  FIG. 1 , the anode of the photodiode PD is directly connected to the first voltage signal line V 1 . In this case, the voltage signal provided by the first voltage signal line V 1  can be directly transmitted to the anode of the photodiode PD. Generally, the light-emitting device can display brightness of different grayscales, and each grayscale corresponds to one data voltage. Therefore, multiple different grayscales correspond to one data voltage range, and the data voltage range includes a minimum data voltage and a maximum data voltage. 
     A voltage value of the voltage signal provided by the first voltage signal line V 1  is designed to be smaller than a voltage value of the minimum data voltage. In this case, when the pixel circuit  10  operates in the data writing phase and the data writing transistor T 1  is turned on, the data signal is written into the cathode of the photodiode PD, so that the photodiode PD is reversely biased. When the photodiode PD does not receive light, the photodiode PD generates a small dark current, and the dark current has small impact on the voltage of the data line Data. The pixel circuit  10  can execute the normal data writing process to write the data signal provided by the data line Data into the first node N 1 , and can control the light-emitting device  20  to emit light normally in the subsequent light-emitting phase. When the photodiode PD receives light, the photocurrent generated by the photodiode PD causes the voltage on the data line Data to change. Upon detection that a voltage variation on the data line Data is greater than the preset voltage value, it is determined that there is an optical touch signal at the position of the pixel circuit  10 , thereby determining the position of the optical touch signal and also determining the position of the optical touch. By integrating the photodiode PD of the pixel circuit  10 , pixel-level detection for the optical touch signal is achieved. 
     In some embodiments, the photodiode PD is coupled to the first voltage signal line V 1  through a transistor.  FIG. 5  is a schematic circuit diagram of another display panel according to an embodiment of the present disclosure. As shown in  FIG. 5 , the pixel circuit  10  further includes a first transistor M 1 , and the photodiode PD is coupled to the first voltage signal line V 1  through the first transistor M 1 .  FIG. 5  schematically shows that a control electrode of the first transistor M 1  is coupled to the first scanning signal line S 1 , that is, the control electrode of the first transistor M 1  and the control electrode of the data writing transistor T 1  are coupled to the same scanning signal line. When the first scanning signal line Si provides an enable signal, the first transistor M 1  and the data writing transistor T 1  can be controlled to turn on at the same time. After the first transistor M 1  is turned on, the signal provided by the first voltage signal line V 1  is written into the anode of the photodiode PD. After the data writing transistor T 1  is turned on, the data signal provided by the data line Data is written into the cathode of the photodiode PD, and the photodiode PD is reversely biased. When no light is incident on the photodiode PD, the photodiode PD only generates a small dark current under a reverse voltage, and the dark current has a small impact on the voltage of the data line Data. The pixel circuit  10  sequentially executes the data writing phase t 2  and the light-emitting phase t 3 , and controls the light-emitting device  20  to emit light based on expected brightness in the light-emitting phase t 3 . When there is light incident on the photodiode PD, the photodiode PD works under a reverse voltage to generate a photocurrent. The photocurrent causes the voltage on the data line Data to change. The position of the optical touch can be detected by detecting the change of the voltage signal on the data line Data, thereby implementing pixel-level positioning for the optical touch signal and improving the accuracy of optical touch detection. When the photocurrent causes the voltage on the data line Data to change, the pixel circuit  10  can still sequentially execute the data writing phase t 2  and the light-emitting phase t 3 , except that the data signal written into the first node N 1  in the data writing phase t 2  is greatly different from the expected data signal, making the brightness of the light-emitting device in the light-emitting phase t 3  greatly different from the expected brightness. In addition, when the laser pointer is used to irradiate the display panel in the application, a bright spot will be formed on the display panel. Therefore, even if the brightness of the light-emitting device at the position irradiated by the laser pointer is greatly different from the expected brightness, the overall display effect will not be affected. 
     In some implementations, in the operation cycle of the pixel circuit  10 , a period during which the control electrode of the first transistor M 1  receives the enable signal is not later than a period during which the control electrode of the data writing transistor T 1  receives the enable signal. In some embodiments of the present disclosure, the photodiode PD and the data line Data are electrically connected when the data writing transistor T 1  is turned on, so that the data line Data is used to detect whether the photodiode PD generates a photocurrent. In this case, it can be ensured that the photodiode PD can operate under a reverse voltage in the data writing transistor T 1 .  FIG. 5  schematically shows that the control electrode of the first transistor M 1  is coupled to the first scanning signal line S  1 . In the embodiment shown in  FIG. 5 , the control electrode of the first transistor M 1  and the control electrode of the data writing transistor T 1  receive the enable signal during the same period, so that the photodiode PD is reversely biased when the data writing transistor T 1  is turned on. In another embodiment, the control electrode of the first transistor M 1  is coupled to the second scanning signal line S 2 . It can be seen from the sequence diagram in  FIG. 2  that, in the operation cycle of the pixel circuit  10 , a period during which the second scanning signal line S 2  provides the enable signal is earlier than a period during which the first scanning signal line S 1  provides the enable signal. Therefore, a period during which the control electrode of the first transistor M 1  receives the enable signal is earlier than a period during which the control electrode of the data writing transistor T 1  receives the enable signal. In this implementation, a voltage signal is first applied to the anode of the photodiode PD, and then the photodiode PD is reversely biased after the data writing transistor T 1  is turned on. 
       FIG. 6  is a schematic circuit diagram of another display panel according to an embodiment of the present disclosure. In some embodiments, as shown in  FIG. 6 , the first voltage signal line V 1  is reused as a reset signal line Ref, and the first voltage signal line V 1  is configured to provide a reset signal to the pixel circuit  10 . The first electrode of the node reset transistor T 3  and the first electrode of the electrode reset transistor T 4  are both coupled to the first voltage signal line V 1 . In an embodiment, the first voltage signal line V 1  provides a voltage signal to the second electrode of the photodiode PD; at the same time, the first voltage signal line 
     V 1  also provides a reset signal to the pixel circuit  10 . By reusing the first voltage signal line V 1 , the number of signal lines in the display panel can be reduced, thereby saving the wiring space in the display panel. 
       FIG. 6  schematically shows that the node reset transistor T 3  and the electrode reset transistor T 4  are coupled to the same reset signal line. In some implementations, the display panel includes a first reset signal line and a second reset signal line, where the first reset signal line and the second reset signal line provide voltage signals having different voltage values. The first electrode of the node reset transistor T 3  is coupled to the first reset signal line, and the first electrode of the electrode reset transistor T 4  is coupled to the second reset signal line. In an embodiment, the first voltage signal line V 1  is reused as the first reset signal line. In this case, the first electrode of the node reset transistor T 3  and the anode of the photodiode PD are both coupled to the first voltage signal line V 1 . In another embodiment, the first voltage signal line V 1  is reused as the second reset signal line. In this case, the first electrode of the electrode reset transistor T 4  and the anode of the photodiode PD are both coupled to the first voltage signal line V 1 . 
       FIG. 7  is a schematic circuit diagram of another display panel according to an embodiment of the present disclosure. In some embodiments, as shown in  FIG. 7 , the first transistor M 1  is reused as the electrode reset transistor T 4 , the first electrode of the first transistor M 1  is coupled to the first voltage signal line V 1 , and the second electrode of the first transistor M 1  is coupled to the light-emitting device  20  and the second electrode of the photodiode PD. That is, the second electrode of the photodiode PD is coupled to the first voltage signal line V 1  through the electrode reset transistor T 4 , and the first voltage signal line V 1  is reused as the reset signal line Ref. In this embodiment, when the electrode reset transistor T 4  is turned on, the second electrode of the photodiode PD is connected to the reset signal line Ref; when the data writing transistor T 1  is turned on, the first electrode of the photodiode PD is connected to the data line Data, so that the photodiode PD is reversely biased. Moreover, at the moment when the first electrode of the photodiode PD is connected to the data line Data, it is detected whether the voltage on the data line Data changes. Upon detection that the voltage on the data line Data changes, it can be determined that the photodiode PD has generated a photocurrent, that is, the presence of an optical touch signal can be determined. The optical touch position in the display panel can be determined according to the pixel circuit  10  in which the photodiode PD is located, thereby realizing pixel-level positioning for the optical touch signal. 
     As shown in  FIG. 7 , the control electrode of the first transistor M 1  and the control electrode of the data writing transistor T 1  are both coupled to the first scanning signal line S 1 , that is, the control electrodes of the two transistors are coupled to the same scanning signal line. When the first scanning signal line S 1  provides an enable signal, the first transistor M 1  and the data writing transistor T 1  are controlled to turn on at the same time. The first electrode of the photodiode PD is connected to the data line Data. At the same time, the second electrode of the photodiode PD is connected to the reset signal line Ref, so that the photodiode PD is reversely biased in this phase. When the photodiode PD receives light, the photodiode PD will generate a photocurrent under the effect of a reverse voltage, thus affecting the voltage on the data line Data. The pixel-level positioning detection for the optical touch signal is implemented by detecting the voltage change on the data line Data. 
       FIG. 8  is a schematic circuit diagram of another display panel according to an embodiment of the present disclosure. In some embodiments, as shown in  FIG. 8 , the control electrode of the first transistor M 1  and the control electrode of the node reset transistor T 3  are both coupled to the second scanning signal line S 2 , that is, the control electrodes of the two transistors are coupled to the same scanning signal line. When the pixel circuit  10  operates in the reset phase t 1 , the second scanning signal line S 2  provides an enable signal to control the first transistor M 1  and the node reset transistor T 3  to be turned on. After the node reset transistor T 3  is turned on, the reset signal provided by the first voltage signal line V 1  (that is, the reset signal line Ref) is written into the first node N 1 , to reset the first node N 1 . After the first transistor M 1  is turned on, the reset signal provided by the first voltage signal line V 1  is written into the fourth node N 4  to reset the fourth node N 4 , and the second electrode of the photodiode PD is coupled to the fourth node N 4 . In this case, it is equivalent to writing the voltage signal into the second electrode of the photodiode PD. When the pixel circuit  10  works in the data writing phase t 2 , the first scanning signal line S 1  provides an enable signal to control the data writing transistor T 1  to turn on. After the data writing transistor T 1  is turned on, the first electrode of the photodiode PD is connected to the data line Data, so that the photodiode PD is reversely biased. In this implementation, the voltage signal is first written into the second electrode of the photodiode PD, to wait for the first electrode of the photodiode PD to be connected to the data line Data. When the first electrode of the photodiode PD is connected to the data line Data, the photodiode PD is reversely biased. 
       FIG. 9  is a schematic circuit diagram of another display panel according to an embodiment of the present disclosure. In some embodiments, as shown in  FIG. 9 , the first transistor M 1  is reused as the node reset transistor T 3 . The first electrode of the first transistor M 1  is coupled to the first voltage signal line V 1 , the second electrode of the first transistor M 1  is coupled to the first node N 1 , and the control electrode of the drive transistor Tm and the second electrode of the photodiode PD are both coupled to the first node N 1 . The first voltage signal line V 1  is reused as the reset signal line Ref. In this implementation, when the pixel circuit  10  works in the reset phase t 1 , the second scanning signal line S 2  provides an enable signal to control the first transistor M 1  to turn on. After the first transistor M 1  is turned on, a reset signal provided by the first voltage signal line V 1  is written into the first node N 1 , to reset the first node N 1 . At the same time, after the first transistor M 1  is turned on, the first voltage signal line V 1  is connected to the second electrode of the photodiode PD. In this case, it is equivalent to writing the voltage signal into the second electrode of the photodiode PD. When the pixel circuit  10  operates in the data writing phase t 2 , the first scanning signal line S 1  provides an enable signal to control the data writing transistor T 1  to be turned on. After the data writing transistor T 1  is turned on, the first electrode of the photodiode PD is connected to the data line Data, so that the photodiode PD is reversely biased. In this implementation, the voltage signal is first written to the second electrode of the photodiode PD, to wait for the first electrode of the photodiode PD to be connected to the data line Data. When the first electrode of the photodiode PD is connected to the data line Data, the photodiode PD is reversely biased. 
       FIG. 10  is a schematic circuit diagram of another display panel according to an embodiment of the present disclosure. In other embodiments, as shown in  FIG. 10 , the second electrode of the photodiode PD is coupled to the first voltage signal line V 1 , and the first voltage signal line V 1  is reused as the first power signal line P 1 . The light-emitting device  20  includes a first electrode, a light-emitting layer, and a second electrode. The first electrode is coupled to the pixel circuit  10 , that is, the first electrode is coupled to the fourth node N 4 . The second electrode is coupled to the first voltage signal line V 1 . In this implementation, the first voltage signal line V 1  is reused, which can simplify the wiring manner in the display panel. The second electrode of the photodiode PD is constantly connected to the first voltage signal line V 1 . In this case, during detection of the optical touch, it is necessary to wait for the data writing transistor T 1  to be turned on to connect the first electrode of the photodiode PD to the data line Data, so that the photodiode PD is reversely biased. 
       FIG. 11  is a sectional view of another display panel according to an embodiment of the present disclosure. In some embodiments, as shown in  FIG. 11 , the display panel includes a substrate  010 , a transistor layer  020  located at a side of the substrate, and a light-emitting device layer  030 . Transistors of the pixel circuit  10  are located in the transistor layer  020 , and the light-emitting device  20  is located in the light-emitting device layer  030 . The light-emitting device  20  includes a first electrode  21 , a light-emitting layer  22 , and a second electrode  23  that are stacked together. Second electrodes  23  of multiple light-emitting devices  20  are interconnected to form a second electrode layer  23   c . The second electrode of the photodiode PD is coupled to the first voltage signal line V 1  through the second electrode layer  23   c . In this implementation, the first voltage signal line V 1  is a voltage signal provided by the second electrode layer  23   c . The display panel includes a display region AA and a non-display region BA, where the first voltage signal line V 1  is located in the non-display region BA. The second electrode layer  23   c  extends from the display region AA to the non-display region BA, and is electrically connected to the first voltage signal line V 1  in the non-display region.  FIG. 11  schematically shows a film position of the first voltage signal line V 1  in the display panel, which is not intended to limit the present disclosure. 
       FIG. 11  further schematically shows the data writing transistor T 1  and the drive transistor Tm in the pixel circuit  10 . The photodiode PD is coupled to the data writing transistor T 1 . 
     As shown in  FIG. 11 , the photodiode PD includes a p-type semiconductor layer  41 , an intrinsic layer  42 , and an n-type semiconductor layer  43  that are stacked together. That is, the photodiode PD includes a PIN junction, and the intrinsic layer  42  has a low doping and a high resistance. In other embodiments, the photodiode PD includes a PN junction, that is, the photodiode PD includes a p-type semiconductor layer and an n-type semiconductor layer that are stacked together. 
     In the embodiment shown in  FIG. 11 , the n-type semiconductor layer  43  is the first electrode of the photodiode PD, and the p-type semiconductor layer  41  is the second electrode of the photodiode PD. 
     In some embodiments, as shown in  FIG. 11 , both the photodiode PD and the light-emitting device  20  are located at a side of the transistor layer  020  facing away from the substrate  010 , and the photodiode PD is located between adjacent light-emitting devices  20 . In this implementation, the arrangement of the photodiode PD does not increase the thickness of the display panel. The light-emitting device layer  030  further includes a pixel defining layer  031 , and the pixel defining layer  031  is used for separating adjacent light-emitting devices  20 . The photodiode PD can be connected to the second electrode layer  23   c  through a via in the pixel defining layer  031 , so that the second electrode of the photodiode PD is coupled to the first voltage signal line V 1  through the second electrode layer  23   c . The photodiode PD is arranged between two light-emitting devices  20 . Laser light emitted by the laser pointer can reach the photodiode PD through few films, thereby reducing the optical loss of the laser light, which improves the accuracy of the optical touch detection. 
       FIG. 12  is a sectional view of another display panel according to an embodiment of the present disclosure. In some embodiments, as shown in  FIG. 12 , in a direction e perpendicular to a pane of the substrate  010 , the photodiode PD is located between the transistor layer  020  and the light-emitting device  20 .  FIG. 12  schematically shows that the second electrode of the photodiode PD is electrically connected to the first electrode  21  of the light-emitting device  20 . Based on the circuit diagram shown in  FIG. 7 , the first electrode  21  of the light-emitting device  20  is also coupled to the fourth node N 4 , so that the first electrode  21  is coupled to the second electrode of the electrode reset transistor T 4  and the second electrode of the second light-emitting control transistor T 6 .  FIG. 12  merely schematically shows the film position of the photodiode PD in the display panel, while other details are simplified. Therefore,  FIG. 12  does not show a via through which the first electrode  21  of the light-emitting device  20  is connected to the fourth node N 4 . The photodiode PD is manufactured between the transistor layer  020  and the light-emitting device  20 , without changing the arrangement manner of original transistors in the pixel circuit  10 , thereby simplifying the manufacturing process of the transistor layer  020 . The second electrode of the photodiode PD is electrically connected to the first electrode  21  of the light-emitting device. In this case, the second electrode of the photodiode PD is coupled to the electrode reset transistor T 4  through the first electrode  21 , so as to be coupled to the first voltage signal line V 1  through the electrode reset transistor T 4 . In this way, the wiring in the transistor layer  020  can be simplified. 
       FIG. 13  is a sectional view of another display panel according to an embodiment of the present disclosure. In some embodiments, as shown in  FIG. 13 , the photodiode PD is located in the transistor layer  020 . The second electrode of the photodiode PD is coupled to the second electrode of the data writing transistor T 1 . In this implementation, the photodiode PD is integrated in the pixel circuit  10 , to implement pixel-level detection for the optical touch position. The photodiode PD is located in the transistor layer  020 , so that the arrangement of the photodiode PD does not increase the thickness of the display panel. 
     In some embodiments, as shown in  FIG. 12 , in the direction e perpendicular to the plane of the substrate  010 , at least a part of the photodiode PD does not overlap with the light-emitting device  20 . In the operation cycle of the pixel circuit  10 , the photodiode PD is reversely biased and generates a photocurrent only when light is received. The photocurrent will affect the voltage on the data line Data. Therefore, the detection of the optical touch position is implemented by detecting the voltage change on the data line Data. At least a part of the photodiode PD does not overlap with the light-emitting device  20 , so that more light at the position irradiated by the laser pointer can be received by the photodiode PD, thereby improving the sensitivity of the photodiode PD and improving the accuracy of the optical touch detection. 
       FIG. 14  is a sectional view of another display panel according to an embodiment of the present disclosure. In some embodiments, as shown in  FIG. 14 , the display panel further includes a black matrix  50  located at a side of the light-emitting device  20  facing away from the substrate  010 . The black matrix  50  has multiple openings  51 , and one opening  51  corresponds to one light-emitting device  20 . In the direction e perpendicular to the plane of the substrate  010 , the photodiode PD overlaps with the light-emitting device  20 . The display panel further includes a filtering unit  60  and an encapsulation layer  70 . The encapsulation layer  70  is located at a side of the light-emitting device  20  that is away from the substrate  010 . The encapsulation layer  70  is configured to provide encapsulation protection for the light-emitting device  20 , to isolate the light-emitting device  20  from water and oxygen, thus prolonging the service life of the light-emitting device  20 . At least a part of the filtering unit  60  is located in the openings  51 . The coordination of the filtering unit  60  and the black matrix  50  can reduce ambient light reflected by the display panel and improve the user experience. The black matrix  50  can shield light, and in application, laser light emitted by the laser pointer will also be shielded by the black matrix  50 . In the implementation, light emitted by the laser pointer penetrates the light-emitting device  20  to be incident on the photodiode PD. The photodiode PD is designed to overlap with the light-emitting device  20  to ensure that the photodiode PD can receive laser light, thereby achieving the optical touch detection. 
     In some embodiments, the size of the photodiode PD is not larger than the size of the light-emitting device  20 . The size is calculated based on an area of orthographic projection on the substrate  010 . The orthographic projection of the photodiode PD on the substrate  010  is a first projection, the orthographic projection of the light-emitting device  20  on the substrate  010  is a second projection, and the area of the first projection is smaller than or equal to the area of the second projection. In the embodiment in which the photodiode PD is located between adjacent light-emitting devices  20 , for example, in the embodiment corresponding to  FIG. 11 , the size of the photodiode PD is not larger than the size of the light-emitting device  20 , thereby ensuring the aperture ratio of the display panel. In the embodiment in which the photodiode PD is located at a side of the light-emitting device  20  that is close to the substrate  010 , for example, in the embodiment corresponding to  FIG. 12  or  FIG. 13 , the size of the photodiode PD is not larger than the size of the light-emitting device  20 , so that the photodiode PD is not excessively large in size to affect the arrangement of other structures in the display panel. 
     Based on the same concept, some embodiments of the present disclosure further provide a display apparatus.  FIG. 15  is a schematic diagram of a display apparatus according to an embodiment of the present disclosure. As shown in  FIG. 15 , the display apparatus includes the display panel  100  provided in any embodiment of the present disclosure. The structure of the display panel  100  has been described in the foregoing embodiments, and details are not repeated herein. The display apparatus provided by the embodiments of the present disclosure can be, for example, any device having a display function, such as a mobile phone, a tablet computer, a notebook computer, an electronic paper book, a television, or an intelligent watch. 
     The above merely illustrates some embodiments of the present disclosure, and is not intended to limit the present disclosure. Any modifications, equivalent replacements, improvements, and like made within the principle of the present disclosure shall fall within the scope of the present disclosure. 
     Finally, it should be noted that the foregoing embodiments are merely intended to describe and not to limit the technical solutions of the present disclosure. Although the present disclosure has been described in detail with reference to the foregoing embodiments, persons skilled in the art should understand that they can still make modifications to the technical solutions described in the foregoing embodiments or make equivalent replacements to some or all of the technical features thereof. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present disclosure.