This application claims priority to Chinese Patent Application No. 201410584117.9, filed on Oct. 27, 2014. The present application claims priority to and the benefit of the above-identified application and is incorporated herein in its entirety. 
     TECHNICAL FIELD OF THE DISCLOSURE 
     The present disclosure relates to a driving circuit for a pixel compensation circuit of an AMOLED and a method used for the driving circuit. 
     BACKGROUND 
     With rapid progress of display technologies, a display apparatus with touch function is becoming welcomed by more and more people due to its advantages such as visualized operation and so on. Existing display apparatuses with touch function can typically be classified into on-cell touch panels and in-cell touch panels in terms of different relative positions between the touch panel and the display panel. Compared with the on-cell touch panel, the in-cell panel is thinner and has higher light transmittance. 
     As for existing display apparatuses, the OLED (Organic Light Emitting Diode) as a current-type light emitting device is applied to the high performance display area more and more due to its advantages such as self luminescence, rapid response, wide angle of view, capability of being fabricated on a flexible substrate, and so on. OLED display apparatus can be classified into a PMOLED (Passive Matrix Driving OLED) type and an AMOLED (Active Matrix Driving OLED) type in terms of different driving manners. Since the AMOLED display has advantages such as low manufacturing cost, high response speed, low power consumption, capability of being used in direct current driving of portable devices, large range of operating temperature and so on, the AMOLED display potentially becomes a new flat display of next generation for replacing the LCD (Liquid Crystal Display). In existing AMOLED display panels, every OLED is driven to emit light by a pixel driving circuit consisting of multiple TFTs (Thin Film Transistors) within one pixel unit on the array substrate to realize display. The pixel driving circuit directly decides the quality of light emitting and displaying of the OLED; therefore, the design of the pixel driving circuit is a key technology of the AMOLED. 
     It is very hard to achieve consistency of the threshold voltages of TFTs in a large area due to the manufacturing technologies and the material characteristics of TFTs. In the AMOLED display panel, the OLEDs are current sensitive devices and are driven by TFTs to control the light emitting intensity; therefore, if the threshold voltages of the TFTs vary in the display area, the brightness uniformity of the whole picture will be influenced largely, which influences the picture quality. 
     SUMMARY 
     In order to reduce the number of chips to be used while enabling the 4T2C pixel compensation circuit to use conventional gate driving chips to reduce the development cost, the present disclosure provides a driving circuit for the 4T2C pixel compensation circuit and a method for the driving circuit, wherein it is possible for the 4T2C pixel compensation circuit to use conventional gate driving chips and to reduce the number of driving chips to be used by one third with a group of control units. When GOA (Gate driver On Array) driving is used, it is possible to reduce the number of GOA units by one third and raise the reliability. 
     According to one aspect of embodiments of the present disclosure, there is provided a control unit which receives pulses, the control unit comprises a first module and a second module, and input terminals of the first module and the second module are connected with a first control voltage and the pulses, wherein the first module converts the received pulses into a first group of pulses and outputs them under the control of a first group of control signal lines; and the second module converts the received pulses into a second group of pulses and outputs them under the control of a second group of control signal lines. 
     Optionally, the first module comprises a first control transistor and a second control transistor; the second module comprises a third control transistor and a fourth control transistor; the first group of control signal lines comprises a first control signal line and a second control signal line; and the second group of control signal lines comprises a third control signal line and a fourth control signal line; and wherein a control terminal of the first control transistor is connected to the first control signal line, a first terminal of the first control transistor is connected with the first control voltage, a second terminal of the first control transistor is connected to a second terminal of the second control transistor; a control terminal of the second control transistor is connected to the second control signal line, a first terminal of the second control transistor is connected with the received pulses; a control terminal of the third control transistor is connected to the third control signal line, a first terminal of the third control transistor is connected with the received pulses, a second terminal of the third control transistor is connected to a second terminal of the fourth control transistor; a control terminal of the fourth control transistor is connected to the fourth control single line, a first terminal of the fourth control transistor is connected with the first control voltage; and wherein the second terminals of the first control transistor and the second control transistor output the first group of pulses, and the second terminals of the third control transistor and the fourth control transistor output the second group of pulses. 
     According to another aspect of embodiments of the present disclosure, there is provided a driving circuit for a display panel, the driving circuit comprises gate drivers at two sides which output driving pulses in a manner of row-wise shifting, wherein the driving circuit further comprises a control section connected to output terminals of the gate driver at a first side; the control section comprises multiple control units each of which is a control unit as described in the above, and the received pulses are each row of pulses output by the gate driver at the first side. 
     Optionally, the gate driver at a second side outputs a third group of pulses. 
     Optionally, the gate drivers are gate drivers using GOA. 
     According to another aspect of embodiments of the present disclosure, there is provided a driving method for a driving circuit as described in the above, comprising, for each row of pixel circuits in a display panel, performing the following operations for each row of pulse output by the gate driver at the first side and the corresponding control unit of the control section:
         before a reset phase, setting pulses output by the gate driver at the first side as the first control voltage, the first control signal line applying a fourth control voltage, the second control signal line applying a third control voltage, the third control signal line applying the third control voltage, and the fourth control signal line applying the fourth control voltage;   at the reset phase, a compensation phase and a data loading phase, setting pulses output by the gate driver at the first side as a second control voltage, the second control signal line applying the fourth control voltage and the first control signal line applying the third control voltage when the first group of pulses are needed to output the second control voltage, and the third control signal line applying the fourth control voltage and the fourth control signal line applying the third control voltage when the second group of pulses are needed to output the second control voltage; and   at a light emitting phase, setting pulses output by the gate driver at the first side as the first control voltage, the first control signal line applying the fourth control voltage, the second control signal line applying the third control voltage, the third control signal line applying the third control voltage, and the fourth control signal line applying the fourth control voltage.       

     Optionally, the first control voltage is a voltage capable of turning off transistors in the pixel circuit, the second control voltage is a voltage capable of turning on transistors in the pixel circuit, the third control voltage is a voltage capable of turning off transistors in the control unit, and the fourth control voltage is a voltage capable of turning on transistors in the control unit. 
     Optionally, the driving method further comprises:
         before the reset phase, setting pulses output by the gate driver at the first side as the first control voltage, the first control signal line applying the fourth control voltage, the second control signal line applying the third control voltage; the third control signal line applying the third control voltage, and the fourth control signal line applying the fourth control voltage;   at the reset phase, setting pulses output by the gate driver at the first side as the second control voltage, the third control signal line applying the fourth control voltage, and the fourth control signal line applying the third control voltage, at the first half of the reset phase, the first control signal line still applying the fourth control voltage and the second control signal line still applying the third control voltage, at the second half of the reset phase, the second control signal line applying the fourth control voltage and the first control signal line applying the third control voltage;   at the compensation phase and the data loading phase, setting pulses output by the gate driver at the first side as the second control voltage, the second control signal line applying the fourth control voltage, the first control signal line applying the third control voltage, the third control signal line applying the third control voltage, and the fourth control signal line applying the fourth control voltage; and   at the light emitting phase, setting pulses output by the gate driver at the first side as the first control voltage, the first control signal line applying the fourth control voltage, the second control signal line applying the third control voltage, the third control signal line applying the third control voltage, and the fourth control signal line applying the fourth control voltage.       

     Optionally, the driving method further comprises:
         before the reset phase and at the reset phase and the compensation phase, setting each row of pulses output by the gate driver at a second side as the second control voltage;   at the data loading phase, setting each row of pulses output by the gate driver at the second side as the first control voltage; and   at the light emitting phase, setting each row of pulses output by the gate driver at the second side as the second control voltage.       

     According to another aspect of the present disclosure, there is provided a display panel comprising pixel circuits and a pixel driving circuit used to supply driving signals for the pixel circuits, wherein the pixel driving circuit is a driving circuit as described above. 
     According to another aspect of the present disclosure, there is provided a display apparatus comprising the display panel. 
     The driving circuit and the driving method provided by embodiments of the present disclosure enable the 4T2C pixel compensation circuit to use conventional gate driving chips and reduce the number of driving chips to be used by one third with a group of control units. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to describe the solutions of embodiments of the present disclosure more clearly, the figures of the embodiments are introduced briefly in the following. Obviously, the figures described in the following are only part of embodiments of the present disclosure without limiting the present disclosure. In the figures, same reference numerals indicate same elements. 
         FIG. 1  is a circuit diagram of a conventional inside-pixel compensation circuit using 4T2C. 
         FIG. 2  is a time sequence diagram of key signals in a driving method of the 4T2C inside-pixel compensation circuit shown in  FIG. 1 . 
         FIG. 3  is a structural block diagram of a driving circuit for a display panel consisting of the 4T2C inside-pixel compensation circuits shown in  FIG. 1  provided by an embodiment of the present disclosure. 
         FIG. 4  is a circuit diagram of a control unit in the driving circuit provided by an embodiment of the present disclosure. 
         FIG. 5  is a time sequence diagram for key signals of the driving circuit shown in  FIG. 3  provided by an embodiment of the present disclosure. 
         FIG. 6  is a schematic diagram for output signals output by the driving chip. 
     
    
    
     DETAILED DESCRIPTION 
     To the knowledge of the inventor, a 4T2C inside-pixel compensation circuit is used currently, that is, each pixel is driven by 4 TFTs and 2 capacitors, so that the working current flowing through the light emitting device is not influenced by the threshold voltage of the driving TFTs. 
       FIG. 1  is a circuit diagram of a normal inside-pixel compensation circuit using 4T2C.  FIG. 2  is a time sequence diagram of key signals in the driving method of the inside-pixel compensation circuit shown in  FIG. 1 . 
     As shown in  FIG. 2 , the operation of each row of pixel circuits is divided into 4 phases. P 1  is a reset phase, P 2  is a compensation phase, P 3  is a data loading phase, and P 4  is a light emitting phase. Through the operations of the 4 phases, the voltage difference between the gate and the source of the driving TFT T 1  can be made to Vgs=V N1 −V N2 , which avoids the influence of the threshold voltage of T 1  on the working current flowing through the light emitting device. 
     However, the above method typically needs a specially designed gate driving chip. Each row of pixels correspond to 3 gate driving lines, i.e., S 1 , S 2  and S 3  as shown in  FIG. 1  and  FIG. 2 . Each row of pixels need the driving chip to output 3 signals. This means that the number of the output channels of a chip with the same size is reduced to one-third of its original number, and thus more chips are needed. If 1200 rows of pixels need to be driven, three conventional chips each of which has 1200 output channels are needed, and the layout design is difficult. A specially designed driving chip of 1200 channels with the same size can only support driving of 400 rows; therefore, if 1200 rows of pixels need to be driven, 3 such chips are needed too. 
     In the following, the technical solutions in embodiments of the present disclosure will be clearly and completely described in connection with the drawings. Obviously, the described embodiments are only part of the employments of the disclosure, but not all the employments. All other embodiments obtained by those skilled in the art based on the embodiments in the present disclosure without creative work fall into the protection scope of the present disclosure. 
       FIG. 3  is a structural block diagram of a driving circuit for a display panel consisting of the 4T2C inside-pixel compensation circuits shown in  FIG. 1  provided by an embodiment of the present disclosure. The inside-pixel compensation circuit as shown in  FIG. 1  comprises: a first transistor T 1 , a second transistor T 2 , a third transistor T 3 , a fourth transistor T 4 , a first capacitor C 1 , a second capacitor C 2  and a light emitting device L. 
     The control terminal of the first transistor T 1  is connected to a second terminal of the second transistor T 2  and a first terminal N 1  of the first capacitor C 1 , a first terminal of the first transistor T 1  is connected to a second terminal of the fourth transistor T 4 , a second terminal of the first transistor T 1  is connected to a first terminal of the light emitting device L, a second terminal N 2  of the first capacitor C 1  and a first terminal of the second capacitor C 2 . The control terminal of the second transistor T 2  is connected with a first driving signal S 1 , and a first terminal of the second transistor T 2  is connected to a data line DATA. The control terminal of the third transistor T 3  is connected with a second driving signal S 2 , a first terminal of the third transistor T 3  is connected with a second voltage Vsus, and a second terminal of the third transistor T 3  is connected to the second terminal N 2  of the first capacitor C 1 . The control terminal of the fourth transistor T 4  is connected with a third driving signal S 3 , and a first terminal of the fourth transistor T 4  is connected with a first voltage ELVDD. A second terminal of the second capacitor C 2  is connected to a second terminal of the light emitting device L. The second terminal of the light emitting device L is connected with a third voltage ELVSS. 
     In the embodiments of the present disclosure, the light emitting device L can be various current-driven light emitting devices in known technological solutions including LED (Light Emitting Diode) or OLED. In embodiments of the present disclosure, description is made by taking the OLED as an example. 
     As shown in  FIG. 3 , the driving circuit provided by an embodiment of the present disclosure uses conventional gate driving chips at the left and right sides which outputs driving pulses in a manner of row-wise shifting. The gate driver at a second side outputs pulses S 3   n  for driving the fourth transistor T 4  in each row of inside-pixel compensation circuits. The control section is added to connect to the output terminals of the gate driver at a first side. The control section consists of multiple control units each of which converts each row of pulse Gn output by the gate driver at the first side into two groups of pulses S 1   n  and S 2   n  according to control signals SEL 1 -SEL 4 . The two groups of pulses S 1   n  and S 2   n  are used to drive the second transistors T 2  and the third transistors T 3  of each row of inside-pixel compensation circuits respectively. 
       FIG. 4  is a circuit diagram of the control unit in the driving circuit provided by an embodiment of the present disclosure. As shown in  FIG. 4 , the control unit comprises four transistors T 5 -T 8 . A control terminal of the first control transistor T 5  is connected to the first control signal line SEL 1 , a first terminal of the first control transistor T 5  is connected with the first control voltage VGL 1 , a second terminal of the first control transistor T 5  is connected to a second terminal of the second control transistor T 6 ; a control terminal of the second control transistor T 6  is connected to the second control signal line SEL 2 , a first terminal of the second control transistor T 6  is connected with the pulse Gn output by the gate driver at the first side; a control terminal of the third control transistor T 7  is connected to the third control signal line SEL 3 , a first terminal of the third control transistor T 7  is connected with the pulse Gn output by the gate driver at the first side, a second terminal of the third control transistor T 7  is connected to a second terminal of the fourth control transistor T 8 ; a control terminal of the fourth control transistor T 8  is connected to the fourth control single line SEL 4 , a first terminal of the fourth control transistor T 8  is connected with the first control voltage VGL 1 ; and the second terminals of the first control transistor T 5  and the second control transistor T 6  output the pulses S 1   n  for driving the second transistors T 2  of each row of inside-pixel compensation circuits, and the second terminals of the third control transistor T 7  and the fourth control transistor T 8  output the pulses S 2   n  for driving the third transistors T 3  of each row of inside-pixel compensation circuits. 
     Optionally, the above gate drivers are gate drivers using GOA. 
       FIG. 5  is a time sequence diagram for key signals of the driving circuit shown in  FIG. 3 . The first control voltage VGL 1  is a voltage capable of turning off TFTs in the inside-pixel compensation circuit shown in  FIG. 1 , the second control voltage VGH 1  is a voltage capable of turning on TFTs in the inside-pixel compensation circuit, the third control voltage VGL 2  is a voltage capable of turning off TFTs in the control unit shown in  FIG. 4 , and the fourth control voltage VGH 2  is a voltage capable of turning on TFTs in the control unit. In the following, a driving method for the control unit shown in  FIG. 4  according to an embodiment of the present disclosure will be described in connection with  FIG. 4  and  FIG. 5 . The method comprises the following steps. 
     Before scanning to the n th  row of pixels, that is, before the time t 1  in  FIG. 5  (before phase P 1 ), pulse Gn output by the gate driver at the first side is set as the first control voltage VGL 1 , the first control signal line SEL 1  applies a fourth control voltage VGH 2 , the second control signal line SEL 2  applies a third control voltage VGL 2 , T 1  is turned on, T 2  is turned off, S 1   n  outputs the first control voltage VGL 1 ; the third control signal line SEL 3  applies the third control voltage VGL 2 , the fourth control signal line SEL 4  applies the fourth control voltage VGH 2 , T 4  is turned on, T 3  is turned off, and S 2   n  outputs the first control voltage VGL 1 . As shown in  FIG. 5 , at this time, S 1   n -S 2   n  before the time t 1  correspond to S 1 -S 2  before the time t 1  in  FIG. 2 . 
     When scanning to the n th  row of pixels, that is, at time t 1 -t 4  in  FIG. 5  (phases P 1 -P 3 ), pulse Gn output by the gate driver at the first side is set as a second control voltage VGH 1 ; when S 1   n  is needed to output the second control voltage VGH 1 , the second control signal line SEL 2  applies the fourth control voltage VGH 2 , the first control signal line SEL 1  applies the third control voltage VGL 2 , T 2  is turned on, and T 1  is turned off; when S 2   n  is needed to output the second control voltage VGH 1 , the third control signal line SEL 3  applies the fourth control voltage VGH 2 , the fourth control signal line SEL 4  applies the third control voltage VGL 2 , T 3  is turned on, and T 4  is turned off. As shown in  FIG. 5 , at this time, S 1   n -S 2   n  between time t 1  to t 4  (i.e. phases P 1 -P 3 ) correspond to S 1 -S 2  between time t 1  to t 4  (i.e. phases P 1 -P 3 ) in  FIG. 2 . 
     After the scanning of the n th  row of pixels is finished, that is, after the time t 4  in  FIG. 5  (phase P 4 ), pulse Gn output by the gate driver at the first side is set as the first control voltage VGL 1 , the first control signal line SEL 1  applies the fourth control voltage VGH 2 , the second control signal line SEL 2  applies the third control voltage VGL 2 , the third control signal line SEL 3  applies the third control voltage VGL 2 , and the fourth control signal line SEL 4  applies the fourth control voltage VGH 2  to turn on T 1  and T 4  again and turn off T 2  and T 3 . S 1   n  and S 2   n  output the first control voltage VGL 1 . As shown in  FIG. 5 , at this time, S 1   n -S 2   n  after time t 4  (i.e., phase P 4 ) correspond to S 1 -S 2  after time t 4  (i.e., phase P 4 ) in  FIG. 2 . 
     Optionally, the driving method for the control unit comprises:
         before the reset phase P 1 , setting pulse Gn output by the gate driver at the first side as the first control voltage VGL 1 , the first control signal line SEL 1  applying the fourth control voltage VGH 2 , the second control signal line SEL 2  applying the third control voltage VGL 2 , T 1  being turned on, T 2  being turned off, S 1   n  outputting the first control voltage VGL 1 ; the third control signal line SEL 3  applying the third control voltage VGL 2 , and the fourth control signal line SEL 4  applying the fourth control voltage VGH 2 , T 4  being turned on, T 3  being turned off, S 2   n  outputting the first control voltage VGL 1 ;   at the reset phase P 1 , setting pulse Gn output by the gate driver at the first side as the second control voltage VGH 1 , the third control signal line SEL 3  applying the fourth control voltage VGH 2 , and the fourth control signal line SEL 4  applying the third control voltage VGL 2 , T 3  being turned on, T 4  being turned off, S 2   n  outputting the second control voltage VGH 1 ; at the first half of P 1 , the first control signal line SEL 1  still applying the fourth control voltage VGH 2 , the second control signal line SEL 2  still applying the third control voltage VGL 2 , T 1  being turned on, T 2  being turned off, and S 1   n  outputting the first control voltage VGL 1 ; at the second half of P 1 , the second control signal line SEL 2  applying the fourth control voltage VGH 2 , the first control signal line SEL 1  applying the third control voltage VGL 2 , T 2  being turned on, T 1  being turned off, and S 1   n  outputting the second control voltage VGH 1 ;   at the compensation phase P 2  and the data loading phase P 3 , setting pulse Gn output by the gate driver at the first side as the second control voltage VGH 1 , the second control signal line SEL 2  applying the fourth control voltage VGH 2 , the first control signal line SEL 1  applying the third control voltage VGL 2 , T 2  being turned on, T 1  being turned off, and S 1   n  outputting the second control voltage VGH 1 ; the third control signal line SEL 3  applying the third control voltage VGL 2 , and the fourth control signal line SEL 4  applying the fourth control voltage VGH 2 , T 4  being turned on, T 3  being turned off, and S 2   n  outputting the first control voltage VGL 1 ; and   at the light emitting phase P 4 , setting pulse Gn output by the gate driver at the first side as the first control voltage VGL 1 , the first control signal line SEL 1  applying the fourth control voltage VGH 2 , the second control signal line SEL 2  applying the third control voltage VGL 2 , T 1  being turned on, T 2  being turned off, and S 1   n  outputting the first control voltage VGL 1 ; the third control signal line SEL 3  applying the third control voltage VGL 2 , and the fourth control signal line SEL 4  applying the fourth control voltage VGH 2 , T 4  being turned on, T 3  being turned off, and S 2   n  outputting the first control voltage VGL 1 .       

     An embodiment of the present disclosure also provides a driving method for the driving circuit shown in  FIG. 3 . In the following, the method will be described in connection with  FIGS. 3-5 . As shown in  FIG. 5 , for each row of pixels, the method comprises performing the above-described driving methods for the control unit for each row of pulse Gn output by the gate driver at the first side and the corresponding control unit of the control section, and setting each row of pulse S 3   n  output by the gate driver at the second side as follows:
         before the reset phase P 1  and at the reset phase P 1  and the compensation phase P 2 , setting each row of pulse S 3   n  output by the gate driver at the second side as the second control voltage VGH 1 ;   at the data loading phase P 3 , setting each row of pulse S 3   n  output by the gate driver at the second side as the first control voltage VGL 1 ; and   at the light emitting phase P 4 , setting each row of pulse S 3   n  output by the gate driver at the second side as the second control voltage VGH 1 .       

     S 3   n  of each phase in  FIG. 5  corresponds to S 3  of respective phase in  FIG. 2 . 
       FIG. 6  is a schematic diagram of shift pulses output by the driving IC. Conventional gate driving chips can output such signals. The driving chip can be in COF (Chip on Film) package or COG (Chip on Glass) package. 
     Likewise, the control unit shown in  FIG. 4  can be used in gate driving with GOA (Gate On Array), and it can realize driving for inside-pixel compensation circuits directly by normal GOA shift registers. 
     The present disclosure also provides a display panel comprising pixel circuits and a pixel driving circuit to supply driving signals for the pixel circuits, wherein the pixel driving circuit is a driving circuit as described above. 
     The present disclosure also provides a display apparatus comprising the above display panel. 
     The display apparatus herein can be electronic paper, a cell phone, a tablet, a TV set, a display, a notebook computer, a digital photo frame, a navigator, or any other product or devices with display function. 
     It can be noted that the above embodiments are only illustrative embodiments for illustrating the principle of the present disclosure, but the protection scope of the present disclosure is not limited to this. Those skilled in the art can devise various alternations or replacements which should be included within the protection scope of the present disclosure without departing from the spirit and essence of the present disclosure.
A control unit, driving circuit for a display panel and a driving method thereof, a display panel and a display apparatus are disclosed. The control unit comprises a first module and a second module, and input terminals of the first module and the second module are connected with a first control voltage and the pulses. The first module converts the received pulses into a first group of pulses and outputs them under the control of a first group of control signal lines, and the second module converts the received pulses into a second group of pulses and outputs them under the control of a second group of control signal lines. The number of driving chips to be used can be reduced by one third.