OLED driving circuit and AMOLED display panel

1. An organic light-emitting diode (OLED) driving circuit, comprising an OLED, a switching thin film transistor (TFT) and a driving TFT, wherein a first terminal of the switching TFT receives a data voltage, a second terminal of the switching TFT is electrically connected to a gate of the driving TFT, a gate of the switching TFT receives a nth scan signal, and n is an integer greater than or equal to 2; a first terminal of the driving TFT receives a source voltage, a second terminal of the driving TFT is electrically connected to a positive electrode of the OLED, and a negative electrode of the OLED receives a low potential voltage; wherein, the OLED driving circuit further comprises an offset capacitor and an offset TFT set for offsetting variations of a driving current of the OLED caused by shifting of a threshold voltage of the driving TFT and a voltage drop of the source voltage;

wherein the offset capacitor comprises a first storage capacitor and a second storage capacitor, the first storage capacitor is serially connected with the second storage capacitor, a first electrode of the first storage capacitor is electrically connected to the gate of the driving TFT, a second electrode of the first storage capacitor is electrically connected to a first electrode of the second storage capacitor, and a second electrode of the second storage capacitor receives the source voltage;

wherein the offset TFT set comprises a third offset TFT, a fourth offset TFT, a fifth offset TFT and a sixth offset TFT; a first terminal of the third offset TFT is electrically connected to the second terminal of the switching TFT, a second terminal of the third offset TFT is electrically connected to the positive electrode of the OLED, and a gate of the third offset TFT receives a (n−1)th scan signal; a first terminal of the fourth offset TFT receives a reference voltage, a second terminal of the fourth offset TFT is electrically connected to the second terminal of the switching TFT, and a gate of the fourth offset TFT receives the (n−1)th scan signal; a first terminal of the fifth offset TFT receives the source voltage, a second terminal of the fifth offset TFT is electrically connected to the first electrode of the second storage capacitor, and a gate of the fifth offset TFT receives an enable signal; a first terminal of the sixth offset TFT is electrically connected to the first electrode of the second storage capacitor, a second terminal of the sixth offset TFT is electrically connected to the first terminal of the driving TFT, and a gate of the sixth offset TFT receives a reverse signal; wherein the reverse signal is reverse of the nth scan signal;

wherein a cycle of the OLED driving circuit comprises a reset period, a threshold voltage obtaining period, a writing period and an illuminating period; wherein,

in the reset period and the threshold voltage obtaining period, the fifth offset TFT is turned off, the third offset TFT, the fourth offset TFT and the sixth offset TFT are turned on, and the driving TFT is turned off until a voltage between the first terminal and the gate of the driving TFT is the same as the threshold voltage of the driving TFT;

in the writing period, the fourth offset TFT is turned off, the switching TFT is turned on, and the data voltage is transmitted to the gate of the driving TFT and stored in the first storage capacitor;

in the illuminating period, the fifth offset TFT and the sixth offset TFT are turned on, the driving TFT is turned on, the OLED illuminates, and a formula for calculating the driving current IOLED is:

I

OLED

=

K

⁡

[

C

1

C

1

+

C

2

×

(

Vdata

-

Vref

)

]

2

;

wherein, K is a current amplifying coefficient of the driving TFT, Vdata is the data voltage, and Vref is the reference voltage.

2. The OLED driving circuit according to claim 1 , wherein the switching TFT, the driving TFT, the third offset TFT, the fourth offset TFT, the fifth offset TFT and the sixth offset TFT are all N-type TFT's.

3. The OLED driving circuit according to claim 1 , wherein a difference between the source voltage and the reference voltage is greater than the threshold voltage of the driving TFT.

4. The OLED driving circuit according to claim 1 , wherein, in the writing period, a voltage between the first storage capacitor and the second storage capacitor is:

Vref

-

Vth

+

(

C

2

C

1

+

C

2

×

(

Vdata

-

Vref

)

)

;

wherein, Vref is the reference voltage, Vth is the threshold voltage of the driving TFT, C 1 is a capacitance of the first storage capacitor, C 2 is a capacitance of the second storage capacitor, and Vdata is the data voltage.

5. The OLED driving circuit according to claim 1 , wherein, in the illuminating period, a voltage of the gate of the driving TFT affected by coupling effect of the first storage capacitor is:

C

1

C

1

+

C

2

×

(

Vdata

-

Vref

)

+

VDD

+

Vth

;

wherein, C 1 is a capacitance of the first storage capacitor, C 2 is a capacitance of the second storage capacitor, Vdata is the data voltage, Vref is the reference voltage, VDD is the source voltage, and Vth is the threshold voltage of the driving TFT.

6. The OLED driving circuit according to claim 1 , wherein the first terminal is source and the second terminal is drain, or, the first terminal is drain and the second terminal is source.

7. An active matrix organic light-emitting diode (AMOLED) display panel, comprising an OLED driving circuit, wherein the OLED driving circuit comprises an OLED, a switching thin film transistor (TFT) and a driving TFT, a first terminal of the switching TFT receives a data voltage, a second terminal of the switching TFT is electrically connected to a gate of the driving TFT, a gate of the switching TFT receives a nth scan signal, and n is an integer greater than or equal to 2; a first terminal of the driving TFT receives a source voltage, a second terminal of the driving TFT is electrically connected to a positive electrode of the OLED, and a negative electrode of the OLED receives a low potential voltage; wherein, the OLED driving circuit further comprises an offset capacitor and an offset TFT set for offsetting variations of a driving current of the OLED caused by shifting of a threshold voltage of the driving TFT and a voltage drop of the source voltage;

wherein the offset capacitor comprises a first storage capacitor and a second storage capacitor, the first storage capacitor is serially connected with the second storage capacitor, a first electrode of the first storage capacitor is electrically connected to the gate of the driving TFT, a second electrode of the first storage capacitor is electrically connected to a first electrode of the second storage capacitor, and a second electrode of the second storage capacitor receives the source voltage;

wherein the offset TFT set comprises a third offset TFT, a fourth offset TFT, a fifth offset TFT and a sixth offset TFT; a first terminal of the third offset TFT is electrically connected to the second terminal of the switching TFT, a second terminal of the third offset TFT is electrically connected to the positive electrode of the OLED, and a gate of the third offset TFT receives a (n−1)th scan signal; a first terminal of the fourth offset TFT receives a reference voltage, a second terminal of the fourth offset TFT is electrically connected to the second terminal of the switching TFT, and a gate of the fourth offset TFT receives the (n−1)th scan signal; a first terminal of the fifth offset TFT receives the source voltage, a second terminal of the fifth offset TFT is electrically connected to the first electrode of the second storage capacitor, and a gate of the fifth offset TFT receives an enable signal; a first terminal of the sixth offset TFT is electrically connected to the first electrode of the second storage capacitor, a second terminal of the sixth offset TFT is electrically connected to the first terminal of the driving TFT, and a gate of the sixth offset TFT receives a reverse signal; wherein the reverse signal is reverse of the nth scan signal;

wherein a cycle of the OLED driving circuit comprises a reset period, a threshold voltage obtaining period, a writing period and an illuminating period; wherein,

in the reset period and the threshold voltage obtaining period, the fifth offset TFT is turned off, the third offset TFT, the fourth offset TFT and the sixth offset TFT are turned on, and the driving TFT is turned off until a voltage between the first terminal and the gate of the driving TFT is the same as the threshold voltage of the driving TFT;

in the writing period, the fourth offset TFT is turned off, the switching TFT is turned on, and the data voltage is transmitted to the gate of the driving TFT and stored in the first storage capacitor;

in the illuminating period, the fifth offset TFT and the sixth offset TFT are turned on, the driving TFT is turned on, the OLED illuminates, and a formula for calculating the driving current IOLED is:

I

OLED

=

K

⁡

[

C

1

C

1

+

C

2

×

(

Vdata

-

Vref

)

]

2

;

wherein, K is a current amplifying coefficient of the driving TFT, Vdata is the data voltage, and Vref is the reference voltage.

8. The AMOLED display panel according to claim 7 , wherein the switching TFT, the driving TFT, the third offset TFT, the fourth offset TFT, the fifth offset TFT and the sixth offset TFT are all N-type TFT's.

9. The AMOLED display panel according to claim 7 , wherein a difference between the source voltage and the reference voltage is greater than the threshold voltage of the driving TFT.

10. The AMOLED display panel according to claim 7 , wherein, in the writing period, a voltage between the first storage capacitor and the second storage capacitor is:

Vref

-

Vth

+

(

C

2

C

1

+

C

2

×

(

Vdata

-

Vref

)

)

;

wherein, Vref is the reference voltage, Vth is the threshold voltage of the driving TFT, C 1 is a capacitance of the first storage capacitor, C 2 is a capacitance of the second storage capacitor, and Vdata is the data voltage.

11. The AMOLED display panel according to claim 7 , wherein, in the illuminating period, a voltage of the gate of the driving TFT affected by coupling effect of the first storage capacitor is:

C

1

C

1

+

C

2

×

(

Vdata

-

Vref

)

+

VDD

+

Vth

;

wherein, C 1 is a capacitance of the first storage capacitor, C 2 is a capacitance of the second storage capacitor, Vdata is the data voltage, Vref is the reference voltage, VDD is the source voltage, and Vth is the threshold voltage of the driving TFT.

12. The AMOLED display panel according to claim 7 , wherein the first terminal is source and the second terminal is drain, or, the first terminal is drain and the second terminal is source.