Pixel driving circuit and display apparatus thereof

The present disclosure relates to a pixel driving circuit and a display apparatus thereof.

Display devices, such as liquid crystal display devices and organic electroluminescent (EL) display devices are widely used. These display devices include a plurality of pixel units. Each pixel unit corresponds to a pixel driving circuit. The pixel driving circuit includes a switching transistor, a drive transistor, a resetting transistor, a capacitor, and an organic light emitting diode (OLED). The pixel driving circuit sequentially operates in an initiating period, a compensation and writing period, and an emitting period. During the initiating period, the resetting transistor turns on for resetting the drive transistor and\or the OLED, thus an operation of writing data signals on a data line to the drive transistor is ensured. During the compensation and writing period, the switching transistor turns off based on an active signal on a scan line, such as high level voltage, the data signals on the data line is provided to the drive transistor and charges the capacitor. The drive transistor turns on. During the emitting period, the capacitor discharges, the drive transistor turns on, a current generated by the power source is providing to the OLED, and the OLED emits light. Due to a variation of a threshold voltage of the drive transistor, a variation of the current provided to the OLED may occur, thus a threshold voltage of the drive transistor needs to be compensated before the emitting period to prevent the current provided to the OLED from being effected by the variation threshold voltage. Due to a larger size of the display device with a high frequency driving, a time of the compensation and writing period corresponding to each pixel unit in a display frame becomes less, and the threshold voltage of the drive transistor is not fully compensated. Thus, there is room for improvement in the art.

Implementations of the present disclosure will now be described, by way of example only, with reference to the attached figures, wherein:

FIG. 1 is a plan view of an embodiment of a display apparatus with a pixel driving circuit.

FIG. 2 is a circuit diagram view of an embodiment of the pixel driving circuit of FIG. 1 , the pixel driving circuit operates an initiating period, a compensation period, a writing period, and an emitting period.

FIG. 3 is a cross-sectional view of the drive transistor of FIG. 2 .

FIG. 4 is a timing chart showing waveforms of a first embodiment of various signals of the pixel units of FIG. 1 .

FIG. 5 is a circuit diagram view of the pixel driving circuit of FIG. 2 , which operates in the initiating period, and the elements with a “X” mark are turned-off.

FIG. 6 is a circuit diagram view of the pixel driving circuit of FIG. 2 , which operates in the compensation period, and the elements with a “X” mark are turned-off.

FIG. 7 is a circuit diagram view of the pixel driving circuit of FIG. 2 , which operates in the writing period, and the elements with a “X” mark are turned-off.

FIG. 8 is a circuit diagram view of the pixel driving circuit of FIG. 2 , which operates in the emitting period, and the elements with a “X” mark are turned-off.

FIG. 9 is a diagram view of the voltage on the top gate electrode and a threshold voltage of the drive transistor.

FIG. 10 is a timing chart showing waveforms of a second embodiment of various signals of the pixel units of FIG. 1 .

It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. The drawings are not necessarily to scale and the proportions of certain parts may be exaggerated to better illustrate details and features. The description is not to be considered as limiting the scope of the embodiments described herein.

Several definitions that apply throughout this disclosure will now be presented.

The term “comprising” means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in a so-described combination, group, series, and the like.

The present disclosure is described in relation to a display apparatus with an improved image quality. The display apparatus includes a plurality of scan lines, a plurality of data lines, and a plurality of control lines. The scan lines and the data lines are arranged as a grid to define a plurality of pixel units at the crossed-line portions. Each pixel unit corresponds to one scan line, one data line, and two control lines. Each pixel unit further corresponds to a pixel driving circuit. The pixel driving circuit is a current type pixel driving circuit. The pixel driving circuit includes a first initiating transistor, a drive transistor, a resetting transistor, a controlling transistor, a second initiating transistor, a first storage capacitor, and a light emitting element. Due to a scan signal on the connected scan line is effective, such as a high level voltage, the first initiating transistor provides a bias voltage to the drive transistor. Due to a first control signal of one of the connected control lines is effective, the controlling transistor provides a voltage on the connected data line to the drive transistor. Due to a second control signal of the other of the connected control lines is effective, the resetting transistor resets an anode of the light emitting element. A cathode of the light emitting element is grounded. The pixel driving circuit further includes a second storage capacitor. The drive transistor is a dual gate transistor. The drive transistor includes a first gate electrode and a second gate electrode. The first gate electrode is electrically connected to a source electrode of the first initiating transistor. The second gate electrode is electrically connected to a source electrode of the controlling transistor. Two terminals of the first storage capacitor are respectively connected to the first electrode and a drain electrode of the drive transistor. Two terminals of the second storage capacitor are respectively connected to the second gate electrode and a source electrode of the second initiating transistor. Due to the second control signal, the second initiating transistor controls the second storage capacitor to discharge through the light emitting element, and resets the anode of the light emitting element during an initiating period.

In an embodiment, a threshold voltage of the drive transistor linearly varies in accordance with a voltage of the second gate electrode of the drive transistor.

In an embodiment, the pixel driving circuit sequentially operates under a first frame and subsequent frames, which are after the first frame. During the first frame, the pixel driving circuit sequentially operates under the initiating period and a compensation period during the first frame. During the initiating period, the drive transistor and the light emitting element are initiating. During the compensation period, a first threshold of the drive transistor is stored in the first storage capacitor.

In an embodiment, when the signal of the scan line and the first control signal are effective, and the second control signal is ineffective, such as a low level voltage, the pixel driving circuit is in the initiating period. During the initiating period, the first initiating transistor, the controlling transistor, the resetting transistor, and the drive transistor turn on. The bias voltage is provided to the first gate electrode, and a first reference voltage on the data line is provided to the second gate electrode. A second reference voltage is provided to the source electrode of the drive transistor for resetting the drive transistor. The second initiating transistor turns off, the second storage capacitor discharges through the light emitting element until the voltage of the anode of the light emitting element is a cut-off voltage. When the signal of the scan line and the second control signal are effective, and the first control signal is ineffective, the pixel driving circuit is in the compensation period. During the compensation period, the first initiating transistor, the second initiating transistor, and the drive transistor turn on. The controlling transistor and the resetting transistor turn off. A first threshold voltage of the driving voltage is stored on the first storage capacitor.

In an embodiment, during the frames after the first frame, the pixel driving circuit sequentially operates under a writing period and an emitting period. During the writing period, a data voltage of the data line is provided to the second gate electrode. The second storage capacitor stores a second threshold voltage and the data voltage. During the emitting period, the light emitting element emits light. The data voltage is larger than the first reference voltage.

In an embodiment, when the signal of the scan line is ineffective, the first control signal and the second control signal are effective, the pixel driving circuit is in the writing period. During the writing period, the first initiating transistor turns off. The second initiating transistor, the controlling transistor, the resetting transistor, and the drive transistor turn on. The data voltage is provided to the second gate electrode. The second storage capacitor stores the second threshold voltage and the data voltage. When the signal on the scan line and the first control signal are effective, and the second control signal is ineffective, the pixel driving circuit is in the emitting period. During the emitting period, the first initiating transistor, the controlling transistor, and the resetting transistor turn off. The second initiating transistor and the drive transistor turn on for driving the light emitting element based on the data voltage.

In an embodiment, the pixel driving circuit sequentially operates under a blanking frame, a first subsequent frame after the blanking frame, and subsequent frames after the first frame. During the blanking frame, the pixel driving circuit resets the source electrode of the drive transistor. During the first frame, the pixel driving circuit sequentially operates under an initiating period and the compensation period. During the initiating period, the first gate electrode is set at the bias voltage, and the first reference voltage is provided by the data line. During the compensation period, the first storage capacitor stores the first threshold voltage. During other frame, the pixel driving circuit sequentially operates under a writing period and an emitting period. During the writing period, the data voltage of the data line is provided to the second gate electrode. The second storage capacitor stores a second threshold voltage and the data voltage. During the emitting period, the light emitting element emits light.

The detail description of the embodiment as below.

FIG. 1 illustrates an embodiment of a display apparatus 1 . In at least one embodiment, the display apparatus 1 is, for example, an organic light emitting diode (OLED) device. The display apparatus 1 defines a display region 11 and a non-display region 13 surrounding the display region 11 . The display region 11 a plurality of scan lines S 1 -Sn, a plurality of data lines D 1 -Dm, a plurality of control lines EM 1 -EM( 2 n ). The scan lines S 1 -Sn extending along a first direction X and the data lines D 1 -Dm extending along a second direction Y perpendicular to the first direction X as a grid define a plurality of pixel units 10 . In other embodiments, the scan lines S 1 -Sn, the control lines EM 1 -EM( 2 n ), and the data lines D 1 -Dm can be arranged in an angled manner, but not limited. The display apparatus 1 further includes a gate driving circuit 20 , a source driving circuit 30 , and a control circuit 40 , which are located in the non-display region 103 . Each pixel unit 10 is electrically connected to the gate driving circuit 20 through one of the scan lines S 1 -Sn, is electrically connected to the source driving circuit 30 through one of the data lines D 1 -Dm, and further electrically connected to the control circuit 40 through two adjacent of the control lines EM 1 -EM( 2 n ). In an embodiment, the gate driving circuit 20 , the source driving circuit 30 , and the control circuit 40 are formed on a chip-on-glass (COG) through a tape-automated bonding manner, or formed on a display panel through a gate-in-panel (GIP) manner. In other embodiment, the gate driving circuit 20 , the source driving circuit 30 , and the control circuit 40 are embedded on the display panel. The display apparatus 1 further includes a timing controller (not shown) in the non-display region 13 . The timing controller supplies various control signals (not shown) to the gate driving circuit 20 for driving the display apparatus to display images, and further supplies data signals to the source driving circuit 30 . The various control signals may include a vertical synchronization (Vsync) signal, a horizontal synchronization (Hsync) signal, a clock (CLK) signal, and a data enable (DE) signal, but is not limited thereto. Each pixel unit 10 corresponds to the pixel driving circuit 300 (as shown in FIG. 2 ). The display apparatus 1 further includes a first frame f 1 and a plurality of other subsequent frames f 2 -fn after the first frame f 1 (as shown in FIG. 4 ).

FIG. 2 illustrates a first embodiment of the driving circuit 300 corresponding to a pixel driving circuit 10 . The pixel driving circuit 300 corresponds to the scan line Sn, the data line Dm, and two control lines EM( 2 n −1)-EM 2 n . The pixel driving circuit 300 is a current type pixel driving circuit.

The pixel driving circuit 300 includes a first initiating transistor M 1 , a drive transistor M 2 , a controlling transistor M 3 , a resetting transistor M 4 , a second initiating transistor M 5 , a first storage capacitor C 1 , a second storage capacitor C 2 , and a light emitting element EL. In the embodiment, the first initiating transistor M 1 , the drive transistor M 2 , the controlling transistor M 3 , the resetting transistor M 4 , and the second initiating transistor M 5 are a same type of transistors, such as N-type Metal Oxide Semiconductor (NMOS) transistors. In the pixel driving circuit 300 , the drive transistor M 2 is a dual gate transistor. The drive transistor M 2 includes a first gate electrode BG (as shown in FIG. 3 ), a second gate electrode TP (as shown in FIG. 3 ), a channel layer 54 (as shown in FIG. 3 ), a source electrode (not labeled), and a drain electrode (not labeled). A bottom gate type transistor is formed by the first gate electrode BG, the channel layer 54 , the source electrode, and the drain electrode. Further, a top gate type transistor is formed by the second gate electrode TP, the channel layer 54 , the source electrode, and the drain electrode. A threshold voltage of the drive transistor M 2 is linearly varied in accordance with a voltage of a second gate electrode of the drive transistor M 2 . In the first frame f 1 , the drive transistor M 2 corresponds a first threshold voltage Vth 1 due to a first reference Vref 1 , in the other frames f 2 -fn, the drive transistor M 2 corresponds a second threshold voltage Vth 2 due to a data voltage Vdata. The first reference voltage Vref 1 is less than the data voltage Vdata. The first threshold voltage Vth 1 is a breakover voltage for turning on the drive transistor M 2 during the first frame f 1 , and the second threshold voltage Vth 2 is a breakover voltage for turning on the drive transistor M 2 during the subsequent other frames f 2 -fn.

A gate electrode of the first initiating transistor M 1 is electrically connected to the corresponding scan line Sn, a source electrode of the first initiating transistor M 1 receives a bias voltage Vbias from a power line, and a drain electrode of the first initiating transistor M 1 is electrically connected to a first gate electrode BG of the drive transistor M 2 through a first node N 1 . A source electrode of the drive transistor M 2 is electrically connected to an anode of the light emitting element EL thorough a second node N 2 , a drain electrode of the drive transistor M 2 receives a power voltage VDD from a power line, a second electrode of the drive transistor M 2 is electrically connected to a source electrode of the controlling transistor M 3 through a third node N 3 . A gate electrode of the controlling transistor M 3 receives a first control signal from the control line EM( 2 n −1), a drain electrode of the controlling transistor M 3 is electrically connected to the data line Dm. A gate electrode of the resetting transistor M 4 receives the first control signal, a drain electrode of the resetting transistor M 4 receives a second reference voltage Vref 2 as a reset signal, and a source electrode of the resetting transistor M 4 is electrically connected between the source electrode of the drive transistor M 2 and the anode of the light emitting element EL. In other words, the source electrode of the resetting transistor M 4 is electrically connected to the second node N 2 . A gate electrode of the second initiating transistor M 5 receives the second control signal from the control line EM( 2 n ), a drain electrode of the second initiating transistor M 5 is electrically connected to the source electrode of the drive transistor M 2 through the second node N 2 , and a source electrode of the second initiating transistor M 5 is electrically connected the anode of the light emitting element EL through the fourth node N 4 . A first terminal of the first storage capacitor C 1 is electrically connected to the first gate electrode BG of the drive transistor M 2 by passing through the second node N 2 , and a second terminal of the first storage capacitor C 1 is electrically connected to the source electrode of the drive transistor M 2 . A first terminal of the second storage capacitor C 2 is electrically connected to the second gate electrode TG of the drive transistor M 2 by passing through the third node N 3 , and a second terminal of the second storing transistor C 2 is electrically connected to the source electrode of the second initiating transistor M 5 by passing through the fourth node N 4 . A cathode of the light emitting element EL is electrically connected to a ground voltage VSS. A parasitic capacitor Cel is formed, and two terminals of the parasitic capacitor Cel are respectively electrically connected to the anode and the cathode of the light emitting element EL. In the embodiment, the second reference voltage is less than the ground voltage VSS.

FIG. 3 illustrates a cross-sectional of the drive transistor M 2 . The drive transistor M 2 includes a substrate 50 , a first conductive layer 51 , an insulating layer 52 , a channel layer 54 , a second conductive layer 56 , a passivation layer 58 , and a third conductive layer 59 . The substrate 50 may be made of a transparent glass or a plastic material. In other embodiments, the substrate 50 may be made of one of Polycarbonate (PC), Polythylene terephthalate (PET), Polymethylmethacrylate (PMMA), Cyclic Olefin Copolymer (COC), or Polyether sulfone (PES). In other embodiments, the substrate 50 can be a flexible substrate. The first conductive layer 51 is disposed on the substrate 50 . The first conductive layer 51 is being patterned to form the first gate electrode BG. The insulating layer 52 is covered on a surface of the substrate 50 exposed from the first conductive layer 51 and a surface of the first conductive layer 51 away from the substrate 50 . The insulating layer 52 insulates the channel layer 54 from the first conductive layer 51 . The insulating layer 52 is capable of the deforming. The insulating layer 52 is made of a flexible material. In other exemplayer embodiment, the insulating layer 52 is a transparent material or a translucent material. The channel layer 54 is disposed on a surface of the insulating layer 52 away from the first conductive layer 51 . The channel layer 54 is patterned to form an semiconductor path of the drive transistor M 2 . A projector of the channel layer 54 on the first conductive layer 51 is at a center of the first conductive layer 51 . The second conductive layer 56 is disposed on the channel layer 54 away from the insulating layer 52 and the insulating layer 52 exposing from the channel layer 54 . The second conductive layer 56 covers a surface of the insulating layer 52 away from the first conductive layer 51 , a surface of the channel layer 54 away from the insulating layer 52 , and further covers a side surface of the channel layer 54 . The channel layer 54 is partially exposed from the second conductive layer 56 . The second conductive layer 56 is being patterned to form a source electrode and a drain electrode of the drive transistor M 2 . The passivation layer 58 is disposed on the second conductive layer 56 and the channel layer 54 . The third conductive layer 59 is disposed on the passivation layer 58 away from the second conductive layer 56 . The third conductive layer 59 is being patterned to form the second gate electrode TG. The second gate electrode TG is overlapped with the first gate electrode BG. A projector of the second gate electrode TG is at a center of the first conductive layer 51 . In the embodiment, the first conductive layer 51 , the second conductive layer 56 , and the third electrode layer 59 is made of metal material, such as, but not limited to, Ag, Cu, and Mo. In the embodiment, the first gate electrode and the second gate electrode overlap along a direction perpendicular to the substrate 50 . The voltages of the first gate electrode BG and the second gate electrode TP are related to the threshold voltage of the drive transistor M 2 .

FIG. 4 illustrates a first embodiment of waveforms of the various signals of the pixel units 10 . FIG. 4 only shows the waveforms of the various signals of the pixel units 10 corresponding to the scan lines S(n−1)-Sn. The first frame f 1 is an initiating frame, and the other frames f 2 -fn are display frames. In the first frame f 1 , all the pixel driving circuits 300 corresponding to the pixels 10 sequentially operates under an initiating period T 1 . After the pixel driving circuit 300 corresponding to the last pixel unit 10 completes the initiating operation, the pixel driving circuits 300 corresponding to the pixels 10 sequentially operate under a compensation period T 2 . After the pixel driving circuit 300 corresponding to the last pixel unit 10 has completed the compensation operation, the pixel driving circuits 300 corresponding to the pixels 10 sequentially operate under a writing period T 3 . After the pixel driving circuit 300 has completed the writing operation, the pixel driving circuit 300 operates under an emitting period T 4 .

The pixel units 10 arranged in one line are controlled by a same scan line Sn and two control lines EM( 2 n −1)-EM( 2 n ), and load different voltages from the data lines D 1 -Dm, such as a first reference voltage Vref 1 . The pixel units 10 arranged in one column load a same voltage from the data line Dm respectively, and are controlled by different scan lines S 1 -Sn and the different control lines EM 1 -EM( 2 n ). In the embodiment, the pixel units 10 in adjacent lines are sequentially scanned by the scan lines S 1 -Sn and the control lines EM 1 -EM( 2 n ). The pixel units 10 in adjacent columns are sequentially loaded the voltage of the data lines D 1 -Dm.

In detail, the driving method of the pixel driving circuit 300 receiving signals of the scan line Sn, the control lines EM( 2 n −1)-EM( 2 n ), and the data line Dm is described as below as an example.

Referring to FIGS. 4 and 5 , during the first frame f 1 , the pixel driving circuit 300 sets the first gate electrode BG of the drive transistor M 2 at the bias voltage Vbias and the anode of the light emitting element EL, discharges the second storage capacitor C 2 through the second initiating transistor M 5 , and further stores the first threshold voltage of the drive transistor M 2 on the first storage capacitor C 1 . During the first frame f 1 , the pixel driving circuits 300 sequentially operate under the initiating period T 1 and compensation period T 2 , the data line Dm provides a first reference voltage Vref 1 . During each of the other frames f 2 -fn, the pixel driving circuits 300 sequentially operate under the writing period T 3 and the emitting period T 4 , the data line Dm provides a data voltage Vdata. In the embodiment, the data voltage Vdata is larger than the first reference voltage Vref 1 . The operation of one of the pixel driving circuit 300 is described as below.

When the signal on the connected scan line Sn and a first control signal of the control line EM( 2 n ) are effective, and the second control signal of the control line EM( 2 n −1) is ineffective, the pixel driving circuit 300 is in the initiating period T 1 . During the initiating period T 1 , the first initiating transistor M 1 , the drive transistor M 2 , the controlling transistor M 3 , and the resetting transistor M 4 turn on, and the second initiating transistor M 5 turns off. The bias voltage is provided to the first gate electrode BG of the drive transistor M 2 due to the first initiating transistor M 1 being turned on, and the first storage capacitor C 1 charges. The first reference voltage Vref 1 is provided to the second gate electrode TG of the drive transistor M 2 through the third node N 3 due to the controlling transistor M 3 being turned on. The second reference voltage Vref 2 is provided to the second node N 2 due to the resetting transistor M 4 being turned on, thus the source electrode of the drive transistor M 2 is being reset. The second storage capacitor C 2 discharges through the light emitting element EL, until the voltage of the fourth node N 4 is equal to a cut-off voltage of the light emitting element EL. The voltage stored on the second storage capacitor C 2 is equal to a difference between the first reference voltage Vref 1 and the cut-off voltage. Thus, the light emitting element EL stops emitting light. The cut-off voltage is related to a color of the light emitting element EL. In the embodiment, the cut-off voltage can be 2.5V.

When the signal on the connected scan line Sn and the second control signal of the control line EM( 2 n −1) are effective, and the first control signal of the control line EM( 2 n ) is ineffective, the pixel driving circuit 300 is in the compensation period T 2 . During the compensation period T 2 , the first initiating transistor M 1 , the drive transistor M 2 , and the second initiating transistor M 5 turn on, and the controlling transistor M 3 and the resetting transistor M 4 turn off. The voltage of the first gate electrode BG remains in the bias voltage due to the first initiating transistor M 1 being turned on. The voltage of the anode of the light emitting element EL and the voltage of the fourth node N 4 are respectively equal to the second reference voltage Vref 2 due to the second initiating transistor M 5 being turned on. The potential of the second node N 2 is changed to a difference between the bias voltage Vbias and the first threshold voltage Vth 1 . Due to keep the potential stored on the second storage capacitor C 2 to be constant, the potential of the third node N 3 is changed to Vbias−Vth 1 +Vref 1 −Vref 2 −Voff. The light emitting element EL remains the non-luminous state.

When the signal on the connected scan line Sn is ineffective, and the first control signal of the control line EM( 2 n ) and the second control signal of the control line EM( 2 n −1) are effective, the pixel driving circuit 300 is in the writing period T 3 . During the writing period T 3 , the first initiating transistor M 1 turns off, the drive transistor M 2 , the controlling transistor M 3 , the resetting transistor M 4 , and the second initiating transistor M 5 turn on. The potential of the second node N 2 is equal to the second reference voltage Vref 2 due to the resetting transistor M 4 being turned on. Due to keep the potential stored on the first storage capacitor C 1 , the potential of the first node N 1 is changed to Vbias−(Vbais−Vth 1 )+Vref 2 , which is equal to Vth 1 +Vref 2 . The data voltage Vdata on the data line Dm is provided to the second gate electrode TG of the drive transistor M 2 due to the controlling transistor M 3 being turned on, and the second storage capacitor C 2 further charges. The potential stored on the second storage capacitor C 2 is equal to a difference between the data voltage Vdata and the second reference voltage Vref 2 .

When the signal on the connected scan line Sn and a first control signal of the control line EM( 2 n ) are ineffective, and the second control signal of the control line EM( 2 n −1) is effective, the pixel driving circuit 300 is in the emitting period T 4 . During the emitting period T 4 , the first initiating transistor M 1 , the controlling transistor M 3 , and the resetting transistor M 4 turn off, and the drive transistor M 2 and the second initiating transistor M 5 turn on. The potential of the second node N 2 is changed to the emitting voltage Voled. Due to keep the potential stored on the first storage capacitor C 1 , the potential of the first node N 1 is changed to Vbias−(Vbais−Vth 1 )+Voled, which is equal to Vth 1 +Voled. Due to keep the potential stored on the second storage capacitor C 2 , the potential of the third node N 3 is changed to Vdata−Vref 2 +Voled.

The current provided to the light emitting element EL is calculated by the formula.

K represents a current amplified constant value related to the carrier mobility and a ratio between a width to a length of a channel of the drive transistor M 2 . Vth 1 represents the first threshold voltage of the drive transistor M 2 in the first frame f 1 . Vth 2 represents the second threshold voltage of the drive transistor M 2 in the other frames f 2 -fn, and is related to the data voltage Vdata.

FIG. 9 illustrates the relation of the threshold voltage of the drive transistor M 2 and the voltage provided on the second gate electrode TG of the drive transistor. The threshold voltage of the drive transistor M 2 is linearly varied in accordance with a voltage of the second gate electrode TG of the drive transistor M 2 , and the relationship is calculated by the formula below.

Vth=a ( Vn 2− Vn 3)+ b   2)

Vn 2 represents a potential of the second node N 2 . Vn 3 represents a potential of the third node N 3 . Both a and b in the formula 2) represent a constant value.

The first threshold voltage Vth 1 of the drive transistor M 2 in the first frame f 1 is related to the first reference voltage Vref 1 , which can be calculated by the formula 2).

The second threshold voltage of the drive transistor M 2 in the other frames f 2 -fn is related to the data voltage Vdata, which can be calculated by the formula 2).

ΔV represents a difference voltage between the first reference voltage Vref 1 and the data voltage Vdata, which is a constant value.

Thus, the current of the light emitting element EL can be further represents as below.

As the above recited, the current on the light emitting element EL only relates with the second reference voltage Vref 2 and a difference voltage of the first reference voltage Vref 1 and the data voltage Vdata, and has no relationship with the threshold voltage of the drive transistor M 2 .

Based on the structure of the display apparatus 1 with pixel driving circuit 300 , during the first frame, the pixel driving circuit 300 only operates under the initiating period T 1 and the compensation period T 2 , which prevents the current of the light emitting element of the display apparatus 1 being effect by a difference of the threshold voltage of the drive transistor M 2 , thus a display performance of the display apparatus 1 is improved. The drive transistor M 2 with two gate electrodes can reduces an area of the pixel driving circuit 300 , which is suitable for a narrow border display apparatus 1 . A uniformity and brightness of the display apparatus 1 is improved by the current type pixel driving circuit 300 .

FIG. 10 illustrates a second embodiment of waveforms of the various signals of the pixel units 10 operated in different frames. FIG. 10 only shows the waveforms of the various signals of the pixel units 10 corresponding to the scan lines S 1 -S 3 . The display apparatus 1 further includes a blanking frame f 0 . During the blanking frame f 0 , the pixel driving circuit 300 resets the source electrode of the drive transistor M 2 . During the first frame f 1 , the anode of the light emitting element EL is reset. During the blanking frame f 0 , the pixel driving circuits 300 sequentially operates under the reset period T 0 . During the blanking frame f 0 , the signals of the scan lines S 1 -Sn and the second control signals are ineffective, and the first control signals are effective. During the first frame f 1 , all of the pixel driving circuits 300 simultaneously operate under an initiating period T 1 , and then further simultaneously operate under a compensation period T 2 when all of the pixel driving circuits 300 being initiating. During the first frame f 1 , each data line Dm provides the first reference voltage Vref 1 . During the other frames f 2 -fn, the pixel driving circuits 300 simultaneously operate under a writing period T 3 . Each pixel driving circuit 300 operates under an emitting period T 4 after the writing period. During the other frames f 2 -fn, each data line Dm provides a data voltage Vdata.

Based on the structure of the display apparatus 1 with the pixel driving circuit 300 , during the blanking frame, the pixel driving circuit 300 resets the drive transistor M 2 . During the first frame, the pixel driving circuit 300 only operates under the initiating period T 1 and the compensation period T 2 , which prevents the current of the light emitting element of the display apparatus 1 being effect by a difference of the drive transistor M 2 , thus a display performance of the display apparatus 1 is improved. Further, the pixel driving circuits 300 simultaneously operates in the initiating period T 1 , and then simultaneously operates in the compensation period T 2 . The drive transistor M 2 with two gate electrodes can reduces an area of the pixel driving circuit 300 , which is suitable for a narrow border display apparatus 1 . A uniformity and brightness of the display apparatus 1 is improved by the current type pixel driving circuit 300 .

The embodiments shown and described above are only examples. Even though numerous characteristics and advantages of the present technology have been set forth in the foregoing description, together with details of the structure and function of the present disclosure, the disclosure is illustrative only, and changes may be made in the detail, including matters of shape, size, and arrangement of the parts within the principles of the present disclosure, up to and including the full extent established by the broad general meaning of the terms used in the claims.