Patent Publication Number: US-10319295-B2

Title: Driving apparatus, driving method and display apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Section 371 National Stage Application of International Application No. PCT/CN2016/088370, filed on Jul. 4, 2016 which claims priority to the Chinese Patent Application No. 201511021518.4, filed on Dec. 31, 2015, entitled “DRIVING APPARATUS, DRIVING METHOD AND DISPLAY APPARATUS” which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to the display technology, and more particularly, to a driving apparatus, a driving method, and a display apparatus, which can control turn-on/turn-off of a light-emitting element using a multi-level control signal, to enhance accuracy of a driving current, thereby improving display quality. 
     BACKGROUND 
     Active Matrix Organic Light Emitting Diodes (AMOLEDs) are one of the hot spots in the research field of today&#39;s flat panel displays. Compared with Liquid Crystal Displays (LCDs), Organic Light Emitting Diodes (OLEDs) have advantages such as low power consumption, a low production cost, self-luminosity, a wide angle of view and a fast response etc. At present, in the display field such as mobile phones, Personal Digital Assistants (PDAs), digital cameras etc., the conventional LCD display screens have began to be replaced by OLED display screens. Pixel driving is the core technical content for AMOLED displays, and has important research significance. 
     Unlike Thin Film Transistor-Liquid Crystal Displays (TFT-LCDs) that use a stable voltage to control luminance, the OLEDs are driven by a current and require a constant current to control light emission. As shown in  FIG. 1 , a pixel driving circuit of the conventional AMOLED uses a 2T1C pixel driving circuit. The circuit is only comprised of one Driving Thin Film Transistor (DTFT), a switch thin film transistor T 1  and a storage capacitor C. An OLED and the DTFT are connected in series to a driving power supply voltage ELVDD, and a gate of the DTFT is connected to a data line which provides a data signal Vdata through the switch thin film transistor T 1 . A scanning line is connected to a gate of the switch thin film transistor T 1  to gate a row.  FIG. 2  illustrates an operation timing diagram of the pixel driving circuit shown in  FIG. 1 , which shows a timing relationship between a scanning signal provided by the scanning line and a data signal provided by the data line. 
     When the scanning line gates (i.e., scans) a certain row, in phase t 1 , the scanning signal Gate(n) is a low level signal, T 1  is turned on, and the data signal V data  is written into the storage capacitor C. After the row is completely scanned, in phase t 2 , Gate(n) transitions to a high level signal, T 1  is turned off, and a gate voltage stored on the storage capacitor C drives the DTFT to generate a current which drives the OLED to emit light. 
     According to the characteristics of the DTFT, a current passing through the DTFT is 
                 I   D     =       1   2     ⁢   μ   ⁢           ⁢     C   OX     ⁢     W   L     ⁢       (       V   GS     -     V   TH       )     2         ,         
where V GS  is a gate-source voltage of the DTFT, V TH  is a threshold voltage of the DTFT, C OX  is a capacitance of an oxide layer of the DTFT, W and L are a channel width and a channel length of the DTFT respectively, μ is a mobility, and V GS =V data -ELV DD . By substituting V GS  into the above equation,
 
               I   D     =       1   2     ⁢     μ   n     ⁢     C   OX     ⁢     W   L     ⁢       (       V   data     -     ELV   DD     -     V   TH       )     2             
is derived. Therefore, in the driving circuit of the OLED, the driving current and the data signal V data  outputted by the source driving circuit are in a quadratic function relationship.
 
       FIG. 3  illustrates a relationship between a driving current and luminance of an organic light emitting diode. As can be seen from  FIG. 3 , the luminance of the organic light emitting diode increases as a current density increases, and becomes darker as the current density decreases. 
     For an OLED display with certain luminance, a current range provided to the OLED is determined. As shown in  FIG. 3 , when a display in a luminance range of 0˜20000 cd/m 2  uses an EFF50 EL material, a driving current range is 0˜37 mA/cm 2 , and when the display uses an EFF80 EL material with higher efficiency, only 0˜24 mA/cm 2  is required. Thus, as the efficiency of the material increases, it is required to reduce the driving current, which reduces power consumption while requiring improved accuracy of the driving current under the same grayscale (8 bits correspond to 256 grayscales). 
     As can be known from the driving current 
               I   D     =       1   2     ⁢     μ   n     ⁢     C   OX     ⁢     W   L     ⁢       (       V   data     -     ELV   DD     -     V   TH       )     2             
of the DTFT, when the driving current range decreases, if an W/L ratio of the DTFT does not change, it is required to reduce a voltage range of V data , which requires improved accuracy of a voltage V data  output by a source driving circuit. The accuracy of the voltage output by the source driving circuit can now achieve 5 mV/grayscale. If the efficiency is then doubled, it needs to achieve 3 mV/grayscale, which has exceeded the process capability of the source driving circuit. Of course, the accuracy of V data  may also be reduced by reducing the W/L value of the DTFT. However, with the increase of resolution, in a limited pixel space, it is difficult to further increase the channel length of the DTFT.
 
     Therefore, there is a need for an apparatus and method which can improve the accuracy of the driving current and thereby improve the display quality. 
     SUMMARY 
     The present disclosure proposes a driving apparatus, a driving method, and a display apparatus, which can divide a light emission phase of the light-emitting element into at least two sub-phases, i.e., providing a dual-level driving in the light emission phase of the light-emitting element, wherein one level enables the light-emitting element to emit light normally, and the other level enables the light-emitting element not to emit light. In a case that the luminance is maintained to be unchanged, the driving current of the light-emitting element during light emission is enhanced by reducing a duty ratio between two levels, so as to improve the accuracy of the driving current. 
     According to a first aspect of the present disclosure, there is provided a driving apparatus for driving a light-emitting element, comprising: 
     a source driving circuit configured to generate a row scanning signal required for driving the light-emitting element and a data signal, wherein the data signal is written into a driving control circuit for the light-emitting element when the row scanning signal is valid; the driving control circuit configured to write a parameter of a driving element for the light-emitting element while writing the data signal when the row scanning signal is valid, wherein the driving control circuit is further configured to receive a level control signal and provide a driving voltage to the driving element according to the data signal, the parameter of the driving element and the level control signal in a light emission phase of the light-emitting element; and the driving element configured to convert the driving voltage provided by the driving control circuit into a driving current, and provide the driving current to the light-emitting element, so that the light-emitting element emits light under the driving of the driving current provided by the driving element; wherein the level control signal is configured to comprise a high level and a low level, one of which causes the driving voltage not to be sufficient enough to drive the driving element, and the other of which causes the driving control circuit to provide the driving voltage to the driving element according to the data signal and the parameter of the driving element to cause the light-emitting element to emit light. 
     Preferably, the level control signal is a power supply signal of the light-emitting element, wherein when the level control signal is at a high level, the driving control circuit provides the driving voltage to the driving element according to the data signal and the parameter of the driving element to drive the light-emitting element to emit light by the driving element, and when the level control signal is at a low level, the provided driving voltage is unable to drive the driving element and thereby the light-emitting element does not emit light. 
     Preferably, a high level power supply signal and a low level power supply signal are generated by a voltage selector, wherein the voltage selector comprises a high level voltage power supply for outputting the high level power supply signal and a low level voltage power supply for outputting the low level power supply signal, and the voltage selector receives a selection signal, and selects output of a power supply signal at one of a high level and a low level according to the selection signal. 
     Preferably, one of the high level power supply signal and the low level power supply signal is set as a power supply signal for causing the light-emitting element to emit light normally, and when the other of the high level power supply signal and the low level power supply signal is set as a power supply signal and the power supply signal is applied, driving elements are all in a cut-off state under all the data signals. 
     Preferably, the selection signal is generated by the source driving circuit or an external circuit. 
     Preferably, the voltage selector is comprised in the source driving circuit. 
     Preferably, the level control signal is input to a control terminal of the driving element, wherein the level control signal at one of the high level and the low level causes the driving element to be driven normally, and the level control signal at the other of the high level and the low level causes the driving element to be in a cut-off state or in a slight turn-on state. 
     Preferably, the level control signal is generated by the source driving circuit or an external circuit. 
     Preferably, the level control signal is synchronous with the row scanning signal. 
     Preferably, a duty ratio between the high level and the low level of the level control signal is adjustable. 
     Preferably, the voltage selector comprises a first transistor having a gate configured to receive the selection signal of the driving voltage control circuit, a source configured to receive a high level power supply signal, and a drain connected to a gate of a second transistor; the second transistor having a source configured to receive the high level power supply signal, and a drain connected to an output terminal; a first resistor having one end connected to the gate of the second transistor and the other end connected to the ground; a third transistor having a gate connected to a source of a fourth transistor, a source configured to receive a low level power supply signal, and a drain connected to the output end; the fourth transistor having a gate configured to receive the selection signal of the driving voltage control circuit and a drain connected to the ground; and a second resistor having one end connected to the source of the third transistor and the other end connected to the gate of the third transistor. 
     According to a second aspect of the present disclosure, there is provided a method for driving a light-emitting element applied in the driving apparatus according to the present disclosure, comprising: providing a row scanning signal on a row scanning line; providing a data signal on a data line; providing a level control signal; writing a parameter of a driving element for the light-emitting element into a driving control circuit while writing the data signal when the row scanning signal is valid; and providing a driving voltage to the driving element according to the data signal, the parameter of the driving element and the level control signal in a light emission phase of the light-emitting element; wherein the level control signal is configured to comprise a high level and a low level, one of which causes the driving voltage not to be sufficient enough to drive the driving element, and the other of which causes the driving voltage to be provided to the driving element according to the data signal and the parameter of the driving element to cause the light-emitting element to emit light. 
     Preferably, the level control signal is a power supply signal of the light-emitting element. 
     Preferably, the level control signal is applied to a control terminal of the driving element, wherein the level control signal at one of the high level and the low level causes the driving element to be driven normally, and the level control signal at the other of the high level and the low level causes the driving element to be in a cut-off state or in a slight turn-on state. 
     Preferably, the level control signal is synchronous with the row scanning signal. 
     According to a third aspect of the present disclosure, there is provided a display apparatus, comprising: the driving apparatus according to the present disclosure; and light-emitting elements each configured to emit light according to the driving current provided by the driving apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other purposes, features and advantages of the present disclosure will be more clear with illustration of preferable embodiments of the present disclosure in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a structural diagram of a pixel driving circuit in the prior art; 
         FIG. 2  is an operation timing diagram of a pixel driving circuit in the prior art; 
         FIG. 3  is a diagram of a relationship between a driving current and luminance of an OLED; 
         FIG. 4  is a structural diagram of a conventional display apparatus; 
         FIG. 5  is an operation timing diagram of a driving apparatus in a conventional display apparatus; 
         FIG. 6  is a structural diagram of a driving apparatus according to an embodiment of the present disclosure; 
         FIG. 7  is a structural diagram of a display apparatus according to an embodiment of the present disclosure; 
         FIG. 8  is an operation timing diagram of a driving apparatus in a display apparatus according to an embodiment of the present disclosure; 
         FIG. 9  illustrates a diagram of a voltage selector according to an embodiment of the present disclosure; 
         FIG. 10  illustrates a structural diagram of a display apparatus according to another embodiment of the present disclosure; 
         FIG. 11  illustrates a structural diagram of a display apparatus of an 8.4-inch flat panel; 
         FIG. 12  illustrates an operation timing diagram of a driving apparatus in the display apparatus shown in  FIG. 11 ; 
         FIG. 13  is a structural diagram of a display apparatus according to an embodiment of the present disclosure; 
         FIG. 14  is an operation timing diagram of a driving apparatus in a display apparatus according to an embodiment of the present disclosure; 
         FIG. 15  illustrates a structural diagram of a display apparatus according to another embodiment of the present disclosure; 
         FIG. 16  illustrates an operation timing diagram of a driving apparatus in the display apparatus shown in  FIG. 15 ; and 
         FIG. 17  illustrates a flowchart of a driving method for a driving apparatus according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In the following description, some specific embodiments are merely provided for the purpose of description and should not be construed as limiting the present disclosure, but are merely examples of the present disclosure. Conventional structures or configurations will be omitted when the understanding of the present disclosure may be confused. 
       FIG. 4  is a structural diagram of a conventional display apparatus. As shown in  FIG. 4 , the display apparatus comprises a source driving circuit  400 , driving control circuits, driving elements, and light-emitting elements arranged in b rows*a columns. The source driving circuit  400  provides row scanning signals G 1 -Gb and provides data signals S 1 -Sa. It is to be noted that, although it is only illustrated in  FIG. 4  that the source driving circuit provides the data signals S 1 -Sa, the source driving circuit also provides the scanning signals G 1 -Gb. This is also applicable to the illustrations shown below. For an 8-bit display, 2 8 =256 grayscale voltages may be provided. For a 10-bit display, 2 10 =1024 grayscale voltages are required to be provided. ELV DD  represents a voltage of a power supply signal. 
       FIG. 5  is an operation timing diagram of a driving apparatus in a conventional display apparatus. Here, PMOS transistors will be described as an example. That is, a low level is a valid level. When an m th  row of scanning signal Gm is at a low level, the entire m th  row of light-emitting elements are selected, in which case a data signals S 1 -Sa are written into driving control circuits for the m th  row of a light-emitting elements respectively. When the m th  row of scanning signal ends, an (m+1) th  row is turned on, and similarly, a data signals S 1 -Sa are written into the driving control circuits for the (m+1) th  row of a light-emitting elements respectively, and so on. After the m th  row of data signals are written into corresponding driving control circuits, each of the driving control circuits provides a driving voltage corresponding to a respective data signal to a corresponding driving element, and the driving element converts the driving voltage into a driving current to drive a corresponding light-emitting element. In general, ELV DD  is a constant voltage. 
       FIG. 6  is a structural diagram of a driving apparatus  600  according to an embodiment of the present disclosure. 
     As shown in  FIG. 6 , according to the embodiment of the present disclosure, the driving apparatus  600  comprises: a source driving circuit  610  configured to generate a row scanning signal and a data signal according to an input video signal; a driving control circuit  620  configured to write a parameter of a driving element for a light-emitting element while writing the data signal when the row scanning signal is valid, wherein the driving control circuit is further configured to receive a level control signal and generate a driving voltage according to the row scanning signal, the data signal and the level control signal of the source driving circuit in a light emission phase of the light-emitting element; and the driving element  630  configured to convert the driving voltage provided by the driving control circuit into a driving current.  FIG. 6  further illustrates the light-emitting element  640 , configured to emit light according to the driving current provided by the driving apparatus  600 , specifically, the driving current provided by the driving element  630 . The level control signal is configured to comprise a high level and a low level, one of which causes the driving voltage not to be sufficient enough to drive the driving element, and the other of which causes the driving control circuit to provide the driving voltage to the driving element according to the data signal and a parameter of the driving element, wherein the driving voltage can compensate for the parameter of the driving element and cause the light-emitting element to emit light normally. 
       FIG. 7  is a structural diagram of a display apparatus according to an embodiment of the present disclosure. The display apparatus shown in  FIG. 7  uses the driving apparatus  600  according to the embodiment of the present disclosure shown in  FIG. 6 .  FIG. 8  is an operation timing diagram of a driving apparatus in a display apparatus according to an embodiment of the present disclosure. 
     As shown in  FIG. 7 , a high level voltage ELVH and a low level voltage ELVL are provided to the display apparatus, and a voltage selector is provided to the display apparatus. That is, the level control signal is a power supply signal of the light-emitting element. 
     As shown in  FIG. 7 , the voltage selector receives a dual-level signal, i.e., a high level power supply signal and a low level power supply signal. The source driving circuit  600  outputs a selection signal EL C  to the voltage selector, to cause the voltage selector to selectively output one of the high level power supply signal and the low level power supply signal. When the level control signal is the high level power supply signal, the driving control circuit provides the driving voltage to the driving element according to the data signal and the parameter of the driving element to drive the light-emitting element to emit light by the driving element, and when the level control signal is the low level power supply signal, the provided driving voltage is unable to drive the driving element and thereby the light-emitting element does not emit light. 
     As shown in  FIG. 8 , the selection signal EL C  outputted by the source driving circuit is a pulse control signal having a duty ratio of D. This pulse has the same period as a period of the row scanning signal of the display apparatus, and is divided into a high level and a low level within the period of the row scanning signal, so that the voltage ELV DD  of the power supply signal output by the voltage selector is also correspondingly divided into a high level and a low level, which represent a light emission sub-phase and a non-light emission sub-phase of the light-emitting element, respectively. 
     When the voltage ELV DD  of the provided power supply signal is alternatively at a high level and a low level, the data signal cannot be written when the voltage of the power supply signal is at a low level since the signal written at this time is no longer a data voltage corresponding to the data signal. As a result, the row scanning signal Gm is correspondingly adjusted so that a gating time thereof is the same as duration of the high level power supply signal. That is, the level control signal is synchronous with the row scanning signal. The duty ratio between the high level and the low level of EL C  may be correspondingly adjusted to achieve a desired driving current density. However, a minimum duty ratio of EL C  needs to ensure a data write time. 
     According to an embodiment of the present disclosure, the voltage selector is provided outside the source driving circuit. According to another embodiment, the voltage selector may be included in the source driving circuit. The voltage selector comprises a high level voltage power supply for outputting a high level power supply signal and a low level voltage power supply for outputting a low level power supply signal. According to an embodiment, the selection signal EL C  is generated by the source driving circuit or an external circuit. 
       FIG. 9  illustrates a diagram of a voltage selector according to an embodiment of the present disclosure. As shown in  FIG. 9 , the voltage selector  900  comprises a first transistor T 1  having a gate configured to receive a selection signal of the driving voltage control circuit, a source configured to receive the high level power supply signal, and a drain connected to a gate of a second transistor T 2 ; the second transistor T 2  having a source configured to receive the high level power supply signal, and a drain connected to an output terminal; a first resistor R 1  having one end connected to the gate of the second transistor T 2  and the other end connected to the ground; a third transistor T 3  having a gate connected to a source of a fourth transistor T 4 , a source configured to receive the low level power supply signal, and a drain connected to the output end; the fourth transistor T 4  having a gate configured to receive the selection signal of the driving voltage control circuit and a drain connected to the ground; and a second resistor R 2  having one end connected to the source of the third transistor T 3  and the other end connected to the gate of the third transistor T 3 . 
     When the selection signal EL C  selects the high level signal EL VDDH , the transistors T 1  and T 4  are turned on, T 3  is turned off, and T 2  is turned on. Therefore, the voltage EL VDD  of the output power supply signal is equal to EL VDDH  minus a turn-on voltage of T 1 , and as a result, the output voltage is a power supply signal which is approximately equal to EL VDDH . When the selection signal EL C  selects the low level signal EL VDDL , T 1  and T 4  are turned off, T 2  is turned off, and T 3  is turned on. The voltage EL VDD  of the output power supply signal is equal to EL VDDL  minus a turn-on voltage of T 3 , and as a result, the output voltage is a power supply signal which is approximately equal to EL VDDL . Therefore, the high level power supply signal and low level power supply signal can be selectively output by controlling the selection signal EL C . 
     Obviously, in the voltage selector illustrated in  FIG. 9 , PMOS transistors will be described as an example. However, it is to be noted that NMOS transistors or other transistors, or even other connection manners, may be used as well, as long as the high level signal EL VDDH  and the low level signal EL VDDL  are input, and the output power supply signal selectively outputs a high level power supply signal and a low level power supply signal according to the selection signal. 
     According to an embodiment of the present disclosure, the voltage selector may also be integrated into the source driving circuit.  FIG. 10  illustrates a structural diagram of a display apparatus according to another embodiment of the present disclosure. In the display apparatus according to the embodiment of the present disclosure, the source driving circuit receives a high level power supply signal and a low level power supply signal, selectively outputs one of the high level power supply signal and the low level power supply signal to the driving element during scanning of each row, wherein the high level power supply signal drives the light-emitting element to emit light, and the low level power supply signal cannot drive the light-emitting element to emit light. 
     In the above-described embodiment, the density of the driving current can be adjusted by adjusting the driving voltage provided in the light emission phase of the light-emitting element, thereby improving the display quality. 
       FIG. 11  illustrates a structural diagram of a display apparatus of an 8.4-inch flat panel.  FIG. 12  illustrates an operation timing diagram of a driving apparatus in the display apparatus shown in  FIG. 11 . 
     As shown in  FIG. 12 , an operation timing of the display apparatus shown in  FIG. 11  is as follows: 
     1) During a reset phase t 1 , a driving control signal EM and a scanning signal Gate are at a high level, a transistor T 5  and a transistor T 6  are turned off, a transistor T 3  and a transistor T 4  are also turned off, a reset signal Reset is at a low level, and a capacitor C 1  is reset through a transistor T 7  And a transistor T 1 , that is, a voltage across the capacitor C 1  is ELV DD  and Vint, respectively. 
     2) During a data write phase t 2 , the driving control signal EM and the reset signal Reset are at a high level, T 5 , T 6 , T 1  and T 7  are turned off, the scanning signal Gate is at a low level, and T 4  and T 2  are turned on. As in the reset phase, a negative potential of Vint is written into a point N 2  of the capacitor C 1 , and T 3  is turned on, T 3  writes a level of ELV DD -V th  into N 2  through T 2 , while Data writes a data signal data into a point N 1  of C 1  through T 4 . The voltage across C 1  is ELV DD -V th -V data . 
     3) During a light emission phase t 3 , the reset signal Reset and the scanning signal Gate are all at a high level, T 1 , T 7 , T 2  and T 4  are turned off, and the driving control signal EM is at a low level. In this case, T 5  and T 6  are turned on, T 3  is also turned on, a level of ELV DD ′ is clamped to the terminal N 1  of C 1  through T 5 , and a level at the point N 2  becomes ELV DD ′+ELV DD -V th -V data . 
     During a light emission phase t 3 , the driving current of T 3  is 
               I   D     =       1   2     ⁢     μ   n     ⁢     C   OX     ⁢     W   L     ⁢       (       ELV   DD   ′     -     V   data       )     2             
wherein, a function of ELV DD ′ is to reduce the effects of a resistance voltage drop, and is used as a reference level.
 
     It can be seen that the driving current has no relation to the voltage ELV DD  of the power supply signal. Generally, ELV DD ′ is a single-level signal. 
       FIG. 13  is a structural diagram of a display apparatus according to an embodiment of the present disclosure. As shown in  FIG. 13 , the driving apparatus of the display apparatus according to the embodiment of the present disclosure further comprises a reference voltage control circuit configured to generate a high level reference voltage and a low level reference voltage. 
     Specifically, the reference voltage control circuit of the driving apparatus according to the embodiment of the present disclosure is configured to generate a high level reference voltage and a low level reference voltage. The driving control circuit is configured to provide a high/low level signal to a control terminal of the driving element according to the reference voltage. A signal at one of the high level and the low level causes the driving element to be driven normally; and a signal at the other of the high level and the low level causes the driving element to be in a cut-off state or in a slight turn-on state. 
     The high level reference voltage and the low level reference voltage are generated by the reference voltage control circuit. Generally, voltage amplitude may be adjusted through programming. 
       FIG. 14  is an operation timing diagram of a driving apparatus in a display apparatus according to an embodiment of the present disclosure. 
     In combination with  FIGS. 11, 13 and 14 , an operation timing of the driving apparatus in the display apparatus shown in  FIG. 13  is as follows: 
     1) During a reset phase t 1 , a driving control signal EM and a scanning signal Gate are at a high level, a transistor T 5  and a transistor T 6  are turned off, a transistor T 3  and a transistor T 4  are also turned off, a reset signal Reset is at a low level, and a capacitor C 1  is reset through a transistor T 7  and a transistor T 1 , that is, a voltage across the capacitor C 1  is ELV DD  and Vint, respectively. 
     2) During a data write phase t 2 , the driving control signal EM and the reset signal Reset are at a high level, T 5 , T 6 , T 1  and T 7  are turned off, the scanning signal Gate is at a low level, and T 4  and T 2  are turned on. As in the reset phase, a negative potential of Vint is written into a point N 2  of the capacitor C 1 , and T 3  is turned on, T 3  writes a level of ELV DD -V th  into N 2  through T 2 , while Data writes a data signal data into a point N 1  of C 1  through T 4 . The voltage across C 1  is ELV DD -V th -V data . 
     3) During a light emission phase t 3 , alternate light emission sub-phase t 4  and non-light emission sub-phase t 5  are included. The reset signal Reset and the scanning signal Gate are at a high level, T 1 , T 7 , T 2  and T 4  are turned off, and the driving control signal EM is at a low level. In this case, T 5  and T 6  are turned on, T 3  is also turned on, a level of Vref is clamped to the terminal N 1  of C 1  through T 5 , and the level at the point N 2  becomes Vref+ELV DD -V th -V data . During a phase t 4 , Vref is a low level reference voltage VrefL, that is, a level which can control T 3  to be turned on normally to cause the light-emitting element to emit light. During a phase t 5 , Vref becomes a high level reference voltage VrefH, and as the level of Vref increases, the level at the terminal N 2  of C also increases, and thereby T 3  is cut off and the light-emitting element does not emit light. 
     In this embodiment, the emission luminance of the light-emitting element, that is, the current density of the light-emitting element, can be adjusted by adjusting a duty ratio between VrefL and VrefH. 
       FIG. 15  illustrates a structural diagram of a display apparatus according to another embodiment of the present disclosure. 
     According to an embodiment of the present disclosure, a high level reference voltage and a low level reference voltage are generated by an external circuit. According to an embodiment of the present disclosure, the driving apparatus comprises a source driving circuit, a driving control circuit, a driving element, and a light-emitting element. The source driving circuit outputs a selection signal to a reference voltage control circuit which receives the high level reference voltage and the low level reference voltage, to cause the reference voltage control circuit to selectively output one of the high level reference voltage and the low level reference voltage, so that the driving control circuit provides a high level driving voltage and a low level driving voltage. 
       FIG. 16  illustrates an operation timing diagram of a driving apparatus in the display apparatus shown in  FIG. 15 . The reference voltage selection circuit selectively outputs VrefH or VrefL according to a selection signal E on  output by the source driving circuit. 
     Although the driving apparatus is shown in  FIG. 6 , the display apparatuses are shown in  FIGS. 7, 10, 13, and 15 , and the voltage selector is shown in  FIG. 9 , it will be apparent to those skilled in the art that these circuits and apparatuses may use other structures. For example, the driving apparatus according to the embodiment of the present disclosure may be applied to a display apparatus having another structure, and the voltage selector according to the embodiment of the present disclosure may be applied to a driving apparatus having another structure. These figures are shown by way of example only. For example, the structure of the voltage selector shown in  FIG. 9  may not be limited to the illustrated structure. 
       FIG. 17  illustrates a flowchart of a driving method for a driving apparatus according to an embodiment of the present disclosure. 
     As shown in  FIG. 17 , the driving method for the driving apparatus according to an embodiment of the present disclosure comprises the following steps. In step S 1710 , a row scanning signal is provided on a row scanning line. In step S 1720 , a data signal is provided on a data line. In step S 1730 , a level control signal is provided. In step S 1740 , a parameter of a driving element for a light-emitting element is written into a driving control circuit while writing the data signal when the row scanning signal is valid. In step S 1750 , in a light emission phase of the light-emitting element, a driving voltage is provided to the driving element according to the data signal, the parameter of the driving element and the level control signal; wherein the level control signal is configured to comprise a high level and a low level, one of which causes the driving voltage not to be sufficient enough to drive the driving element, and the other of which causes the driving voltage to be provided to the driving element according to the data signal and the parameter of the driving element to cause the light-emitting element to emit light. 
     Steps S 1710 -S 1730  may be performed in parallel. In other words, the row scanning line is connected to a row scanning signal source, the data line is connected to a data source, and a source of the level control signal is connected to a line of the level control signal in advance. Then, steps S 1710 -S 1730  are performed so that the display apparatus enters a data write phase, i.e., the row scanning signal is valid while writing the data signal. In this case, in step S 1740 , the parameter of the driving element for the light-emitting element is written into the driving control circuit. Then, when the display apparatus enters the light-emission phase of the light-emitting element, in step S 1750 , the driving voltage is provided to the driving element according to the data signal, the parameter of the driving element, and the level control signal which have been written. 
     According to an embodiment of the present disclosure, the level control signal may be a power supply signal of the light-emitting element. That is, when the level control signal is at a high level, the driving control circuit provides the driving voltage to the driving element according to the data signal and the parameter of the driving element to drive the light-emitting element to emit light by the driving element; and when the level control signal is at a low level, the provided driving voltage is unable to drive the driving element and thereby the light-emitting element does not emit light. 
     According to an embodiment of the present disclosure, the level control signal may be applied to a control terminal of the driving element. The level control signal at one of a high level and a low level causes the driving element to be driven normally, and the level control signal at the other of the high level and the low level causes the driving element to be in a cut-off state or in a slight turn-on state. 
     According to an embodiment of the present disclosure, the level control signal is synchronous with the row scanning signal. That is, a gating time of the row scanning signal is the same as duration of the high level power supply signal so that the data signal is not written when the power supply signal is at a low level. 
     It should be noted that, in the foregoing description, the technical solutions of the present disclosure have been illustrated by way of example only, and are not intended to limit the present disclosure to the above-described steps and structures. Wherever possible, steps and structures can be adapted and selected as needed. Therefore, some steps and units are not elements necessary to implement the general inventive idea of the present disclosure. Accordingly, the requisite technical features of the present disclosure are limited only by the minimum requirements that can achieve the general inventive idea of the present disclosure, without being limited to the specific examples above. 
     The present disclosure has been described in combination with the preferable embodiments. It is to be understood that various other changes, substitutions and additions can be made by those skilled in the art without departing from the spirit and scope of the present disclosure. Accordingly, the scope of the present disclosure is not limited to the specific embodiments described above, but should be defined by the appended claims.