Scan driver and organic light emitting display device having the same
A scan driver having no shift register and an organic light emitting display device having the same are disclosed. The scan driver includes a latch unit and a NAND gate instead of a shift register, thereby reducing the area occupied by the driver in a display panel. The scan driver uses only a clock signal and a start pulse, thereby reducing the number of driving lines and transistors and reducing power loss.
1 . A scan driver comprising a plurality of scan signal generating circuits configured to output a plurality of scan signals, the plurality of the scan signal generating circuits comprising a first scan signal generating circuit which comprises:
a first latch unit comprising a first input, a second input, and an output, the first input being configured to receive an immediately preceding scan signal, the second input being configured to receive an immediately succeeding scan signal; and
a first NAND gate comprising a first input, a second input, and an output, the first input being connected to the output of the first latch unit, the second input being configured to receive a first clock signal, the output being configured to output a first scan signal.
2 . The scan driver of claim 1 , wherein the plurality of scan signal generating circuits comprise odd-numbered scan signal generating circuits and even-numbered scan signal generating circuit, the odd-numbered scan signal generating circuits being configured to receive one of two clock signals having a phase difference of half a cycle, the even-numbered scan signal generating circuits being configured to receive the other of the two clock signals, and wherein the first scan signal generating circuit is one of the odd or even-numbered circuits.
3 . The scan driver of claim 1 , wherein the plurality of scan signal generating circuits further comprise a second scan signal generating circuit, and wherein the second scan signal generating circuit comprises:
a second latch unit comprising a first input, a second input, and an output, the first input being connected to the output of the first NAND gate, the second input being configured to receive an immediately succeeding scan signal; and
a second NAND gate comprising a first input, a second input, and an output, the first input being connected to the output of the second latch unit, the second input being configured to receive a second clock signal, the second clock signal having a phase difference of half a cycle with respect to the first clock signal, the output being connected to the second input of the first latch unit, the output being configured to output a second scan signal.
4 . The scan driver of claim 1 , wherein the first latch unit comprises:
an input unit configured to receive the immediately preceding scan signal and the immediately succeeding scan signal and to selectively output a positive power supply voltage to the output of the first latch unit depending on the scan signals; and
a negative voltage transmission unit configured to receive the positive power supply voltage from the input unit and to selectively output a negative power supply voltage to the output of the first latch unit depending on the scan signals.
5 . The scan driver of claim 4 , wherein the input unit comprises:
a first transistor having a source connected to a positive power supply source, a drain connected to the output of the first latch unit, and a gate connected to the first input of the first latch unit; and
a second transistor having a source connected to the positive power supply source, a drain connected to the negative voltage transmission unit, and a gate connected to the second input of the first latch unit.
6 . The scan driver of claim 5 , wherein the negative voltage transmission unit comprises:
a third transistor having a source connected to a negative power supply source, a drain connected to the drain of the second transistor, and a gate connected to the drain of the first transistor; and
a fourth transistor having a source connected to the negative power supply source, a drain connected to the drain of the first transistor, and a gate connected to the drain of the second transistor.
7 . The scan driver of claim 6 , wherein the first and second transistors have a different conductivity type from that of the third and fourth transistors.
8 . The scan driver of claim 1 , wherein the NAND gate comprises:
a positive voltage transmission unit configured to selectively output a scan signal having a positive power supply voltage level depending on an output signal of the first latch unit and the first clock signal; and
a negative voltage transmission unit configured to selectively output a scan signal having a negative power supply voltage level depending on the output signal of the first latch unit and the first clock signal.
9 . The scan driver of claim 8 , wherein the positive voltage transmission unit comprises two transistors connected in parallel between a positive power supply voltage source and the output of the first NAND gate, one of the transistors having a gate connected to the output of the first latch unit, the other of the transistors having a gate configured to receive the first clock signal; and
wherein the negative voltage transmission unit comprises two transistors connected in series between a negative power supply voltage source and the output of the first NAND gate, one of the transistors having a gate connected to the output of the first latch unit, the other of the transistors having a gate configured to receive the first clock signal.
10 . The scan driver of claim 9 , wherein the transistors of the positive voltage transmission unit have a conductivity type different from that of the transistors of the negative voltage transmission unit.
11 . The scan driver of claim 1 , wherein the first scan signal generating circuit further comprises a buffer unit having an input connected to the output of the first NAND gate and an output configured to supply the first scan signal.
12 . A display device comprising the scan driver of claim 1 .
13 . The display device of claim 12 , wherein the display device comprises an organic light emitting display device.
14 . The display device of claim 12 , further comprising:
an array of pixels; and
an emission control driver configured to supply an emission control signal to the pixels,
wherein the scan driver is configured to supply the plurality of scan signals to the pixels.
15 . A scan driver comprising a plurality of scan signal generating circuits configured to output a plurality of scan signals, the plurality of the scan signal generating circuits comprising: a first scan signal generating circuit configured to generate a first scan signal; a second scan signal generating circuit configured to generate a second scan signal; and a third scan signal generating circuit configured to generate a third scan signal, wherein the second scan signal generating circuit comprises:
means for receiving the first scan signal and the third scan signal and generating a second output signal such that the second output signal has a high-level from a falling edge of the first scan signal to a falling edge of the third scan signal; and
means for logically combining the second output signal and one of two clock signals having a phase difference of half a cycle, thereby generating the second scan signal.
16 . The scan driver of claim 15 , wherein the first scan signal, the second scan signal, and the third scan signal are sequentially output.
17 . The scan driver of claim 15 , wherein the first scan signal generating circuit comprises:
means for receiving a start pulse signal and the second scan signal and generating a first output signal such that the first output signal has a high-level from a falling edge of the start pulse signal to a falling edge of the second scan signal; and
means for conducting a NAND operation on the first output signal and the other of the two clock signals, thereby generating the first scan signal.
18 . The scan driver of claim 15 , wherein the plurality of the scan signal generating circuits comprise a fourth scan signal generating circuit configured to generate a fourth scan signal, and wherein the third scan signal generating circuit comprises:
means for receiving the second scan signal and the fourth scan signal and generating a third output signal such that the third output signal has a high-level from a falling edge of the second scan signal to a falling edge of the fourth scan signal; and
means for conducting a NAND operation on the third output signal and the other of the two clock signals, thereby generating the third scan signal.
19 . A display device comprising the scan driver of claim 15 .
20 . A method of generating a plurality of scan signals for a display device, the method comprising:
generating a first scan signal;
generating a second scan signal; and
generating a third scan signal,
wherein generating the second scan signal comprises:
receiving the first scan signal and the third scan signal;
generating a second output signal based on the first scan signal and the third scan signal such that the second output signal has a high-level from a falling edge of the first scan signal to a falling edge of the third scan signal;
conducting a NAND operation on the second output signal and one of two clock signals having a phase difference of half a cycle, thereby generating the second scan signal.
21 . The method of claim 20 , wherein generating the third scan signal comprises:
receiving the second scan signal and an immediately succeeding scan signal;
generating a third output signal based on the second scan signal and the immediately succeeding scan signal such that the third output signal has a high-level from a falling edge of the second scan signal to a falling edge of the immediately succeeding scan signal;
conducting a NAND operation on the third output signal and the other of the two clock signals, thereby generating the third scan signal.