Scan driving circuit and organic light emitting display using the same

This application claims the benefit of Korean Patent Application No. 2005-87426, filed on Sep. 20, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

1. Field of the Invention

The field of the present invention relates to an organic light emitting display, and more particular to a scan driving circuit used for a current programming type organic light emitting display.

2. Description of the Related Art

In general, an organic light emitting display electrically excites a phosphorous organic compound to emit light, and it voltage- or current-drives an array of organic light emitting cells to display images. Such an organic light emitting cell includes an anode of indium tin oxide (ITO), an organic thin film, and a cathode layer of metal.

The organic thin film has a multi-layer structure including an emitting layer (EML), an electron transport layer (ETL), and a hole transport layer (HTL) so as to maintain a balance between electrons and holes and to improve the light emitting efficiency, and further includes an electron injection layer (EIL) and a hole injecting layer (HIL).

Methods for driving the organic emitting cells include the passive matrix driving method, and the active matrix driving method using thin film transistors (TFTs) or metal oxide semiconductor field effect transistors (MOSFETs). The passive matrix display includes an array of cathode lines and anode lines which cross with each other. The active matrix display includes an array of pixels each having a TFT, a capacitor and an ITO pixel electrode to maintain a voltage across the capacitor.

Active matrix driving methods may be classified as voltage programming methods or a current programming methods, according to the type signal used to charge a voltage on a capacitor.

An active matrix type of organic light emitting display includes a display panel, a data driving circuit, a scan driving circuit, and a timing controller. The scan driving circuit receives a scan drive control signal from the timing controller, generates a scan signal, and sequentially provides the scan signal to scan lines of the display panel. That is, the scan driving circuit functions to sequentially generate the scan signal to be provided to the display panel in order to drive pixels included in the display panel.

FIG. 1 is a block diagram showing a conventional scan driving circuit. With reference to FIG. 1 , the conventional scan driving circuit includes a plurality of stages ST 1 to STn, which are coupled with a start pulse SP input line. The plurality of stages ST 1 to STn sequentially shifts a clock signal C in response to a start clock SP so as to generate output signals SO 1 to Son. Each of the second to n-th stages ST 2 to STn receives and shifts an output signal of a previous stage as a start pulse for the next stage. Accordingly, the stages generate output signals SO 1 to SOn in such a way that the start pulse is sequentially shifted, and provide the output signals for a matrix pixel array.

FIG. 2 is a circuit diagram of a stage in the scan driving circuit shown in FIG. 1 . FIG. 3 is an input/output waveform diagram of the stage shown in FIG. 2 . Referring to FIG. 2 and FIG. 3 , conventionally, each stage constituting a scan driving circuit uses a master-slave flip-flop. When a clock clk is at a low level, such a flip-flop continues to receive an input while maintaining the previous output. In contrast to this, when the clock clk is at high level, the flip-flop maintains an input IN received when the clock clk is at the low level, and outputs the received input, but no longer receives input.

In the aforementioned circuit, an inverter included in the flip-flop has disadvantages which include that a static current flows when the input thereof is at a low level. Furthermore, in the flip-flop, the number of inverters having received a low-level input is the same number as that of inverters having received a high-level input. Accordingly, the static current flows through half of all the inverters in the flip-flop, thereby causing excessive power consumption.

In addition, FIG. 2 shows an embodiment of the inverter circuit. According to this embodiment the high level output of the inverter is determined according to the ratio of resistance values of first and second PMOS transistors M 1 and M 2 . The low level output of the inverter is determined according to the threshold voltage of the first PMOS transistor M 1 .

Due to manufacturing variations, resistance and threshold parameters vary significantly from transistor to transistor. This is a significant problem because the transistors for organic light emitting displays often use transistors having high manufacturing variability. As a result, the performance of the circuit of FIG. 2 is uncertain. For example, threshold variation causes the low level output of each inverter to vary. As a result, when a low level output from a first inverter having an uncertain value is provided as the input to a second inverter, the second inverter may have a degraded high output level because the uncertain low value results in uncertain pull-up resistance in the first PMOS transistor of the second inverter.

Furthermore, in the inverter, when outputting a high level, a constant electric current flows through both the first and second PMOS transistors M 1 and M 2 . This results in constant power consumption. Also, the constant electric current flowing in the second PMOS transistor M 2 causes slower rise times for the inverter output signal.

Accordingly, it is an aspect to provide a scan driving circuit and an organic light emitting display using the same, which reduce power consumption by removing a current flow path of a static current from a stage of each unit, wherein the scan driving circuit includes a first scan driver for providing a selection signal and/or a boost signal, and a second scan driver for providing an emission signal, wherein the first scan driver includes a scan drive unit for outputting the selection signal, a first boost drive unit for outputting an odd-numbered boost signal, and a second boost drive unit for outputting an even-numbered boost signal.

One embodiment is a scan driving circuit coupled with an input signal line, and including a plurality of stages coupled with a two-phase clock signal input line. The circuit includes a first scan driver configured to sequentially output at least one of a selection signal and a boost signal through two or more of the plurality of stages, and a second scan driver configured to sequentially output an emission signal through two or more of the plurality of stages, where the first scan driver includes a scan drive unit configured to output the selection signal, a first boost drive unit configured to output an odd-numbered boost signal, and a second boost drive unit configured to output an even-numbered boost signal.

Another embodiment is a scan driving circuit coupled with an input signal line and including a plurality of stages coupled with a two-phase clock signal input line. The circuit includes a first scan driver configured to sequentially output at least one of a selection signal and a boost signal through two or more of the plurality of stages, and a second scan driver configured to output an emission signal through two or more of the plurality of stages, where the first scan driver includes a first scan/boost drive unit configured to output odd-numbered selection and boost signals, and a second scan/boost drive unit configured to output even-numbered selection and boost signals.

Another embodiment is an organic light emitting display including a pixel portion having a plurality of pixels coupled to selection signal lines, data lines, emission signal lines, and boost signal lines. The display also includes a data driving circuit configured to provide a data signal to the data lines, and a scan driving circuit coupled with an input signal line, and including a plurality of stages coupled with a two-phase clock signal input line. The scan driving circuit includes a first scan driver configured to sequentially output at least one of a selection signal and a boost signal through two or more of the plurality of stages, and a second scan driver configured to sequentially output an emission signal through two or more of the plurality of stages, where the first scan driver includes a scan drive unit configured to output the selection signal, a first boost drive unit configured to output an odd-numbered boost signal, and a second boost drive unit configured to output an even-numbered boost signal.

Another embodiment is an organic light emitting display including a pixel portion having a plurality of pixels coupled to selection signal lines, data lines, emission signal lines, and boost signal lines. The display also includes a data driving circuit configured to provide a data signal to the data lines, and a scan driving circuit coupled with an input signal line and including a plurality of stages coupled with a two-phase clock signal input line. The scan driving circuit includes a first scan driver configured to sequentially output at least one of a selection signal and a boost signal through two or more of the plurality of stages, and a second scan driver configured to output an emission signal through two or more of the plurality of stages, where the first scan driver includes a first scan/boost drive unit configured to output odd-numbered selection and boost signals, and a second scan/boost drive unit configured to output even-numbered selection and boost signals.

These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a block diagram showing a conventional scan driving circuit;

FIG. 2 is a circuit diagram of a stage in the scan driving circuit shown in FIG. 1 ;

FIG. 3 is an input/output waveform diagram of the stage shown in FIG. 2 ;

FIG. 4 is a block diagram showing an organic light emitting display according to one embodiment;

FIG. 5 is a circuit diagram showing an example of a pixel circuit arranged at each pixel region of the organic light emitting display shown in FIG. 4 ;

FIG. 6 is a waveform diagram of selection, emission, and boost signals that are supplied to the pixel circuit shown in FIG. 5 ;

FIG. 7 is a block diagram showing a configuration of a first scan driver of a scan driving circuit according to an embodiment;

FIG. 8 is a circuit diagram of a stage in a first scan driver of the scan driving circuit according to a first embodiment;

FIG. 9 is an input/output waveform diagram of the stage shown in FIG. 8 ;

FIG. 10 is a block diagram showing a configuration of a first scan driver of a scan driving circuit according to an embodiment;

FIG. 11 is a circuit diagram of a stage in a first scan driver of the scan driving circuit according to another embodiment;

FIG. 12 is an input/output waveform diagram of the stage shown in FIG. 11 ;

FIG. 13 is a block diagram showing a configuration of a first scan driver of a scan driving circuit according to another embodiment;

FIG. 14 is a circuit diagram of a stage in a first scan driver of the scan driving circuit according to another embodiment;

FIG. 15 is an input/output waveform diagram of the stage shown in FIG. 14 ;

FIG. 16 is a block diagram showing a configuration of a first scan driver of a scan driving circuit according to another embodiment;

FIG. 17 is a circuit diagram of a stage in a first scan driver of the scan driving circuit according to another embodiment;

FIG. 18 is an input/output waveform diagram of the stage shown in FIG. 17 .

Hereinafter, certain inventive aspects will be described with reference to the accompanying drawings. Here, when a first element is connected to a second element, the first element may be directly connected to the second element or may be indirectly connected to the second element via a third element. Further, irrelative elements are omitted for clarity. Also, like reference numerals refer to like elements throughout.

FIG. 4 is a block view showing an organic light emitting display according to one embodiment;

As shown in FIG. 4 , the organic light emitting display according to one embodiment includes an organic light emitting display panel (referred to as ‘display panel’ hereinafter) 100 , a data driving circuit 200 , and a scan driving circuit. The scan driving circuit includes a first scan driver 310 and a second scan driver 320 . The first scan driver 310 provides a selection signal and/or a boost signal. The second scan driver 320 provides an emission signal.

The first scan driver 310 may be configured to be divided into a scan drive unit and a boost drive unit for outputting the selection signal and the boost signal, respectively. In this case, the boost drive unit can be further divided into odd- and even-numbered boost signals.

The display panel 100 includes a plurality of data lines D 1 through Dn, a plurality of signal lines S 1 to Sm, E 1 to Em, B 1 to Bm, and a plurality of pixel circuits 11 . The plurality of data lines D 1 through Dn are arranged in a column direction. The plurality of signal lines S 1 to Sm and E 1 to Em are arranged in a row direction. The plurality of pixel circuits 11 are arranged in an array.

Here, the signal lines S 1 to Sm and E 1 to Em include a plurality of selection signal lines S 1 to Sm for transferring a selection signal to select a pixel row, a plurality of emission signal lines E 1 to Em for transferring an emission signal to control an emission period of a pixel row, and a plurality of boost signal lines B 1 to Bm for transferring a boost signal to set a gate voltage of the drive thin film transistors in a pixel row.

Further, pixel circuits 11 are formed at a pixel region defined by the data lines D 1 through Dn, the selection signal lines S 1 to Sm, the emission signal lines E 1 to Em, and boost signal lines B 1 to Bm.

The data driving circuit 200 applies a data current I DATA to the data lines D 1 through Dn. The first scan driver 310 of the scan driving circuit 300 sequentially applies a selecting signal for selecting a pixel circuit 11 to the selection signal lines S 1 to Sm. Further, the data driving circuit 200 sequentially applies a boost signal to the boost signal lines B 1 to Bm to set a gate voltage of the drive thin film transistors of each pixel row.

Further, the second scan driver 320 of the scan driving circuit 300 applies an emission signal for controlling a luminance of the pixel circuit 11 to the emission signal lines E 1 to Em.

FIG. 5 is a circuit diagram showing an example of a pixel circuit arranged shown in FIG. 4 . However, in order to help understanding of the pixel circuit, only a pixel circuit connected to a j-th data line Dj and i-th signal lines Si and Ei is shown in FIG. 5 .

As shown in FIG. 5 , the pixel circuit according to one embodiment includes an organic light emitting diode OLED, transistors m 1 to m 4 , and first and second capacitors C 1 and C 2 . Here, although PMOS transistors are used for each of the transistors m 1 to m 4 , NMOS and CMOS implementations are also possible.

A first transistor m 1 is coupled between a power supply VDD and an organic light emitting diode OLED, and controls an electric current through the organic light emitting diode OLED. In detail, a source of the first transistor m 1 is coupled with the power supply VDD, and a drain thereof is coupled with a cathode of the organic light emitting diode OLED through a third transistor m 3 .

Furthermore, in response to a selection signal from the selection signal line Si, the second transistor m 2 passes a voltage from the data line Dj to a gate of the first transistor m 1 . A fourth transistor m 4 diode-connects the first transistor m 1 in response to the selection signal.

Moreover, the first capacitor C 1 is coupled between a gate and a source of the first transistor m 1 , and is charged with a voltage corresponding to the gate voltage of the first transistor m 1 when sourcing the data current I DATA to the data line Dj. A third transistor m 3 passes an electric current flowing through the first transistor m 1 to the organic light emitting diode OLED in response to an emission signal from the emission signal line Ei.

Further, the second capacitor C 2 is coupled between the gate of the first transistor m 1 and the boost signal line Bj.

Here, a voltage of the second capacitor C 2 is increased by a voltage increase magnitude ΔV B of a boost signal on the boost signal line Bj, and thus an increase magnitude ΔV G of a gate voltage V G of the first transistor m 1 is generated. V G may be approximated by the following equation 1.

As indicated by equation 1, by increasing the voltage of the boost signal by ΔV B , the gate voltage V G is increased by ΔV G according to the capacitances of the first and second capacitors. Parasitic capacitances of the transistors m 1 , m 2 , and m 4 , and the interconnects will also affect ΔV G . The parasitic capacitances decrease ΔV G by an amount related to the amount of parasitic capacitance relative to the sum of the first and second capacitors. Accordingly, the current I OLED supplied to an organic light emitting diode OLED can be set at the desired value.

FIG. 6 is a timing diagram of selection, emission, and boost signals that are supplied to the pixel circuit shown in FIG. 5 .

Referring to FIG. 5 and FIG. 6 , while the first, second, and fourth transistors m 1 , m 2 , and m 4 are turned-on and the data current I DATA is being sourced by the first transistor m 1 , the third transistor m 3 is turned-off. While in this state, the first transistor is effectively diode connected by the second and fourth transistors m 2 and m 4 . Accordingly, the gate voltage of the first transistor m 1 , goes to a value corresponding to the data current I DATA , and is stored in the capacitor C 1 .

As shown in FIG. 6 , by generating a pulse end of an emission signal of an emission signal line Ei so as to be generated after a pulse end of selection signal line Si, the third transistor m 3 is not turned on while the second transistor m 2 is on.

That is, in the embodiment of FIGS. 5 and 6 , the selection signal is applied in such a manner that a pulse of a low level of the selection signal ends before horizontal period by approximately 2 μs. Also shown in FIG. 6 , the emission signal is applied in such a way that the pulse width of a high level of the emission signal spans the pulse width of the low level of the selection signal.

Moreover, when the pulse end of a boost signal from the boost signal line Bi is generated after the pulse end of the selection signal, when a node voltage of the second capacitor C 2 is increased, programming of the data current I DATA is complete, and thus the effect of increasing a node voltage of the second capacitor C 2 is removed. Therefore, in this embodiment, as shown in FIG. 6 , by controlling a pulse end of a selection signal transferred to the selection signal line Sn to be generated before the pulse end of a boost signal transferred to the boost signal line Bn, a node voltage of the second capacitor C 2 is increased after a programming of the data current I DATA .

Furthermore, by controlling a pulse start of the boost signal so as to be generated before a pulse start of the selection signal, while a voltage is programming in the first capacitor C 1 , a voltage of the first capacitor C 1 varies due to a drop of a node voltage of the second capacitor C 2 . As noted previously, when the voltage of the first capacitor C 1 changes, a voltage programming operation of the first capacitor C 1 should be again performed, and thus a time of programming a voltage in the first capacitor C 1 is needed. Accordingly, as shown in FIG. 6 , by controlling a start of the selection signal transferred to the selection signal line Sn to be generated after a start of the boost signal transferred to the boost signal line Bn, a programming operation of the data current I DATA is performed after a node voltage of the second capacitor C 2 drops.

Due to a difference between a load connected to the boost signal line Bn and a load connected to the emission signal line En, a pulse end of the emission signal is generated prior to a pulse end of the boost signal, during a time period between the pulse end of the emission signal and the pulse end of the boost signal, an electric current before an increase in a node voltage of the second capacitor C 2 flows through an organic light emitting diode OLED, thereby occurring stress in the organic light emitting diode OLED. When such an operation repeats, the lifetime of the organic light emitting diode OLED may be shortened. Consequently, as shown in FIG. 6 , by generating a pulse end of the boost signal transferred to the boost signal line Bn before a pulse end of the emission signal transferred to the emission signal line En, an electric current flows through the organic light emitting diode OLED after a node voltage of the second capacitor C 2 has been increased.

Furthermore, if a pulse start of the emission signal is generated after a pulse start of the boost signal, during a time period between the pulse start of the emission signal and the pulse start of the boost signal, an electric current due to a drop in a node voltage of the second capacitor C 2 flows through an organic light emitting diode OLED, thereby resulting in stress in the organic light emitting diode OLED. When such an operation repeats, the lifetime of the organic light emitting diode OLED may be shortened. Consequently, as shown in FIG. 6 , by generating the pulse start of the emission signal ahead of the pulse start of the boost signal, a node voltage of the second capacitor C 2 drops after the third transistor m 3 has been turned-off.

That is, in this embodiment, the boost signal is applied in such a manner that a pulse width of a low level of the boost signal spans a pulse width of a low level of the selection signal and is less than that of a high level of the emission signal.

As seen from FIG. 4 , the selection signal, the boost signal, and the emission signal are output through a first scan driver 310 and a second scan driver 320 , which are provided to a panel.

A construction and an operation of a scan driving circuit of one embodiment for outputting selection and boost signals having waveforms as shown in FIG. 6 will now be given.

That is, only the first scan driver of the scan driving circuit will be described. Since a description of the second scan driver can be easily obtained from the description of the first scan driver, no further detailed description will be provided.

FIG. 7 is a block diagram showing a configuration of a first scan driver of a scan driving circuit according to one embodiment.

Here, the first scan driver 310 according to one embodiment is divided into a scan drive unit 312 and boost drive units 314 and 316 , so that the scan drive unit 312 and the boost drive units 314 and 316 output a selection signal and a boost signal, respectively. Further, the boost drive unit includes a first boost drive unit 314 and a second boost drive unit 316 for separately outputting odd- and even-numbered boost signals.

The scan drive unit 312 , the first and second boost drive units 314 and 316 include n stages that are dependently coupled with input signal IN 1 , IN 2 , IN 3 lines thereof, respectively.

First output lines of the first n stages of the scan drive unit 312 are coupled with first n row lines S 1 to Sn included in the pixel array, and provide a selection signal to respective pixels defining the pixel array. Second output lines of the second n stages of the boost drive units 314 and 316 are coupled with second n row lines B 1 to Bn included in the pixel array, and provide a boost signal to respective pixels defining the pixel array.

Here, a first input signal IN 1 is supplied to a first stage included in the scan drive unit 312 , a first input signal IN 2 is supplied to a first stage included in the first boost drive unit 314 , and a first input signal IN 3 is supplied to a first stage included in the second boost drive unit 316 . Output signals of first to (n−1) th stages are supplied to respective next stages as input signals.

Further, each stage of the scan drive unit 312 includes a first clock terminal CLKa and a second clock terminal CLKb. First and second phase inverted clock signals CLK 1 and CLK 2 in which parts of high levels overlap with each other, are supplied to the first clock terminal CLKa and the second clock terminal CLKb, respectively. A first clock signal CLK 1 is supplied to the first clock terminal CLKa of odd-numbered stages in the first scan driver 310 , and a second clock signal CLK 2 is supplied to the second clock terminal CLKb. In contrast to this, the second clock signal CLK 2 is supplied to a first clock terminal CLKa of even-numbered stages, and the first clock signal CLK 1 is supplied to a second clock terminal CLKb of the even-numbered stages.

That is, when each stage receives the first input signal IN 1 or an output voltage gi of a previous stage, and the first and second clock signals CLK 1 and CLK 2 , it sequentially outputs a low-level signal through an output lines thereof at time intervals as the first and second clock signals overlap with each other at high level.

In the same manner as above, respective stages of the first boost drive unit 314 and the second boost drive unit 316 include first and second clock terminals CLKa and CLKb. Third and fourth clock signals CLK 3 and CLK 4 whose phases are inverted and in which parts of high level overlap with each other, and fifth and sixth clock signals CLK 5 and CLK 6 , are provided to the first and second clock terminals CLKa and CLKb.

Here, as shown, a third clock signal CLK 3 or a fifth clock signal CLK 5 is supplied to the first clock terminal CLKa of odd-numbered stages, and a fourth clock signal CLK 4 or a sixth clock signal CLK 6 is supplied to the second clock terminal CLKb thereof.

In contrast to this, the fourth clock signal CLK 4 or the sixth clock signal CLK 6 is supplied to a first clock terminal CLKa of even-numbered stages, and the third clock signal CLK 3 or the fifth clock signal CLK 5 is supplied to a second clock terminal CLKb of the even-numbered stages.

That is, when each stage receives the first input signal IN 2 or IN 3 , or an output voltage gi of a previous stage, and the third and fourth clock signals CLK 3 and CLK 4 , or the fifth and sixth clock signals CLK 4 and CLK 6 , it sequentially outputs a low-level signal to respective odd- and even-numbered boost signal lines through an output line thereof at time intervals in which the third and fourth clock signals CLK 3 and CLK 4 , or the fifth and sixth clock signals CLK 4 and CLK 6 overlap with each other at high level.

As seen from FIG. 6 , the boost signal is output in such a manner that a pulse width of a low level of the boost signal spans a pulse width of a low level of the selection signal and is less than that of a high level of the emission signal. Further, the selection having a pulse width of a low level less than that of a horizontal period is output.

Namely, in this embodiment, in order to set a pulse width of the boost signal greater than that of the horizontal period, the boost drive unit is configured to be divided into an odd-numbered output unit 314 and an even-numbered output unit 316 .

FIG. 8 is a circuit diagram of an embodiment of a stage in the scan driving circuit shown in FIG. 7 , which shows a detailed circuit arrangement of odd-numbered stages of the scan drive unit, first and second boost drive units. FIG. 9 is an input/output waveform diagram of the stage shown in FIG. 8 .

With reference to FIG. 8 and FIG. 9 , each odd-numbered stage of the scan drive unit, first and second boost drive units is precharged to first and second input clock signals CLK 1 and CLK 2 , CLK 3 and CLK 4 , or CLK 5 and CLK 6 during the first time period having phases inverted to each other. The odd-numbered stage performs an evaluation operation during a second period having a phase inverted to a phase of the first period to sequentially output a low-level pulse at overlapped time intervals of the clock signal at a high level.

Namely, the odd-numbered stage outputs a high-level signal during a precharge period, and outputs a signal corresponding to an input received during the precharge period during an evaluation period.

Moreover, the evaluation period of the odd-numbered stages is designated to coincide with the precharge period of even-numbered stages,

Hereinafter, operation of stages will be explained in detail by reference to a circuit arrangement of an odd-numbered stage shown in FIG. 8 .

PMOS thin film transistors will be now described as an example of transistors included in the stages. However, other implementations are also possible, such as NMOS or CMOS embodiments.

Referring to FIG. 8 , an odd-numbered stage 400 according to one embodiment includes a first PMOS transistor M 1 , a second PMOS transistor M 2 , a third PMOS transistor M 3 , a fourth PMOS transistor M 4 , and a fifth PMOS transistor M 5 . The first PMOS transistor M 1 receives an output voltage gi of a previous stage or a first input signal N 1 or N 2 . A gate terminal of the first PMOS transistor M 1 is coupled with a first clock terminal. The second PMOS transistor M 2 is coupled with a second clock terminal and an output line OUT, and a gate terminal thereof is coupled with an output terminal of the first PMOS transistor M 1 . The third PMOS transistor M 3 is coupled between a second power supply VSS and a first node N 1 , a gate terminal thereof is coupled with the first clock terminal. The fourth PMOS transistor M 4 is coupled between the first clock terminal and the first node N 1 , and a gate terminal thereof is coupled with an output terminal of the first PMOS transistor M 1 . The fifth PMOS transistor M 5 is coupled between a first power supply VDD and the output line OUT, and a gate terminal thereof is coupled with the first node N 1 .

The scan driving circuit further includes a first capacitor C 1 that is coupled between an output terminal of the first PMOS transistor M 1 and the output line OUT.

As shown, when the stage is an odd-numbered stage of the scan drive unit, a first clock signal CLK 1 is supplied to the first clock terminal, and a second clock signal CLK 2 is supplied to the second clock terminal. On the contrary, when the stage is an even-numbered stage 322 of the scan drive unit, the second clock signal CLK 2 is supplied to the first clock terminal, and the first clock signal CLK 1 is supplied to the second clock terminal.

In contrast to this, as shown, when the stage is an odd-numbered stage of the first boost drive unit 314 , a third clock signal CLK 3 is supplied to the first clock terminal, and a fourth clock signal CLK 4 is supplied to the second clock terminal. On the contrary, when the stage is an even-numbered stage of the first boost drive unit, the fourth clock signal CLK 4 is supplied to the first clock terminal, and the third clock signal CLK 3 is supplied to the second clock terminal.

Further, as shown, when the stage is an odd-numbered stage of the second boost drive unit 316 , a fifth clock signal CLK 5 is supplied to the first clock terminal, and a sixth clock signal CLK 6 is supplied to the second clock terminal. On the contrary, when the stage is an even-numbered stage of the second boost drive unit 316 , the sixth clock signal CLK 6 is supplied to the first clock terminal, and the fifth clock signal CLK 5 is supplied to the second clock terminal.

Furthermore, a negative supply voltage may be applied to the second power supply VSS, but the second power supply VSS may be grounded as shown in FIG. 8 . In one embodiment, it is shown that the second power supply VSS is embodied to be grounded.

Each stage includes a transfer unit, an inversion unit, and a buffer unit. The transfer unit is composed of first PMOS transistor M 1 , second PMOS transistor M 2 , and first capacitor C 1 . The inversion unit is composed of first, third, and fourth PMOS transistors M 1 , M 3 , and M 4 . The buffer unit is composed of a fifth PMOS transistor M 5 .

Assuming that the stage is an odd-numbered stage 312 of the first scan driver, a time period when the first clock signal CLK 1 has a low level but the second clock signal CLK 2 has a high level becomes a precharge period. A time period when the first clock signal CLK 1 has a high level but the second clock signal CLK 2 has a low level becomes an evaluation period. The odd-numbered stage 312 of the first scan driver outputs a high-level signal during the precharge period, and outputs a signal corresponding to an input received during the precharge during the evaluation period.

In this embodiment, as shown, first and second clock signals, third and fourth clock signals, or fifth and sixth clock signals as input signals of each stage are each provided so as to overlap each other at a part of a high level.

Each stage outputs a pair of clock signals CLK 1 and CLK 2 , CLK 3 and CLK 4 , or CLK 5 and CLK 6 so as to have time intervals corresponding to an overlapped time of the first and second clock signals CLK 1 and CLK 2 at a high level. The reason to have predetermined time intervals between output signals of each stage is for guaranteeing a margin for a clock skew or delay.

An operation of the odd-numbered stage will be explained with reference to FIG. 8 and FIG. 9 . First, during the precharge period, namely, while the first clock signal CLK 1 of a low level and a second clock signal CLK 2 of a high level are inputting thereto, the first and third transistors M 1 and M 3 are turned-on, whereby an input signal IN 1 is transferred to gate terminals of the second and fourth transistors M 2 and M 4 .

Accordingly, since an output voltage of a previous stage or an input signal IN 1 is stored in the first capacitor C 1 as an input signal, and a first node N 1 is charged with a second clock signal CLK 2 or a low-level signal from the second power supply VSS, the fifth transistor M 5 is turned-on, with the result that a first power supply VDD of a high level is output through an output terminal OUT.

That is, during the precharge period, an output of the buffer unit of the stage becomes a high level. Moreover, during the evaluation period, the first transistor M 1 is turned-off, thereby blocking an input signal IN 1 and the third and fourth transistors M 3 and M 4 are accordingly turned-off.

When a signal received during the precharge period, namely, an output voltage of a previous stage or an input signal IN 1 is at a high level, the received signal maintains a level of a signal precharged during the precharge period, whereby the buffer unit outputs a high-level signal unchanged.

In contrast to this, when the signal received during the precharge period, namely, an output voltage of a previous stage or an input signal IN 1 is at a low level, the second transistor M 2 is turned-on according to the low-level signal stored in the first capacitor C 1 . Accordingly, in the transfer unit, as the second transistor M 2 is turned-on, a second clock signal CLK 2 of a low level is output through an output terminal OUT.

That is, during the evaluation period, when a signal received during the precharge period, namely, an output voltage of a previous stage or an input signal IN 1 is at a low level, the stage outputs a low-level signal. When the received signal is at a high level, the stage outputs a high-level signal.

As noted previously, first and second clock signals as input signals of each stage are provided to overlap each other at a part of a high level as shown in FIG. 9 .

In a case that the first and second clock signals CLK 1 and CLK 2 are at high level, when a previous period is a precharge period, first and third transistors M 1 and M 3 controlled by the first clock signal CLK 1 are all turned-off, and a voltage of a capacitor C 1 remains unchanged, thereby maintaining a previous output.

In contrast to this, when the previous period is an evaluation period, the first and third transistors M 1 and M 3 are turned-off, a second transistor M 2 maintains a previous state. When the second transistor M 2 is turned-off, the stage receives a high-level signal, with the result that a high-level output is remained by a fifth transistor M 5 .

On the contrary, when the evaluation transistor M 3 is turned-on, since the stage receives a low-level signal, namely, a gate terminal of the second transistor M 2 is in a floating state, a voltage of the capacitor C 1 remains unchanged, and thus the second transistor M 2 continues to be turned-on that causes a second clock signal of high level to be output as an output signal.

As is seen from the foregoing description, in a case that the first and second clock signals CLK 1 and CLK 2 are at high level, when a previous period is a precharge period, an output maintains a previous state. When the previous period is an evaluation period, an output has a high level. Consequently, a time interval may be reduced between output pulses of adjacent stages by an overlapped time in high levels of the first and second clock signals CLK 1 and CLK 2 .

Although, described above were results on the odd-numbered state of the first scan driver, the same results were obtained on an odd-numbered stage of the first boost drive unit or the second boost drive unit

Accordingly, when the first boost drive unit 314 and the second boost drive unit 316 of FIG. 7 receive third and fourth clock signals CLK 3 and CLK 4 , and an input signal IN 2 ; and fifth and sixth clock signals CLK 5 and CLK 6 , and an input signal IN 3 , respective, they sequentially output a low-level pulse at overlapped time intervals of a pair of clock signals CLK 3 and CLK 4 or CLK 5 and CLK 6 at a high level.

As shown in FIG. 9 , third and fourth clock signals CLK 3 and CLK 4 , or fifth and sixth clock signals CLK 5 and CLK 6 are input to have longer overlapped time, precharge period, and evaluation period as compared with first and second clock signals CLK 1 and CLK 2 . Further, input signals IN 1 and IN 3 respectively input to the first and second boost drive units have low level of greater width in comparison with that of an input signal IN 1 input to the scan drive unit.

In addition, the fifth and sixth clock signals CLK 5 and CLK 6 , and an input signal IN 2 are input to a stage of the second boost drive unit 316 to be delayed by approximately one horizontal period in comparison with the third and fourth clock signals CLK 3 and CLK 4 and the input signal IN 3 input to a stage of the first boost drive unit 314 .

As seen from FIG. 6 , this operation is performed to cause the boost signal to be greatly applied in such a way that a pulse width of a high level of the boost signal contains the pulse width of a low level of a corresponding selection signal.

That is, in one embodiment, in order to make the output boost signal to have a pulse width greater than that of a corresponding selection signal, the boost drive unit is configured to be divided into an odd-numbered output unit and an even-numbered output unit. Time periods of clock signals CLK 3 , CLK 4 , CLK 5 , and CLK 6 applied to respective boost drive units and low-level widths of the input signals IN 1 and IN 2 are adjusted.

FIG. 10 is a block diagram showing a configuration of a first scan driver of a scan driving circuit according to another embodiment.

However, a description of the same construction and operation of the second embodiment as those of the first embodiment shown in FIG. 7 is omitted.

In the same manner as in the first embodiment shown in FIG. 7 , a first scan drive of the first embodiment is configured to be divided into a scan drive unit and a boost drive unit for outputting a selection signal and a boost signal, respectively. In particular, the boost drive unit is composed of a first boost drive unit and a second boost drive unit for separating outputting an odd-numbered boost signal and an even-numbered boost signal.

However, besides clock signals CLK 3 , CLK 4 , CLK 5 , and CLK 6 , and input signals IN 2 and IN 3 , control signals D 1 , D 2 , D 3 , and D 4 are applied to the first and second boost drive units to adjust a swing of an output pulse.

The first and third control signals D 1 and D 3 are input to odd-numbered stages of the first and second boost drive units, whereas the second and fourth control signals D 2 and D 4 are input to even-numbered stage of the first and second boost drive units.

FIG. 11 is a circuit diagram of an embodiment of a stage in a first scan driver of the scan driving circuit, which shows a detailed circuit arrangement of odd-numbered stages of the scan drive unit, first and second boost drive units shown in FIG. 10 . FIG. 12 is an put/output waveform diagram of the stage shown in FIG. 11 .

A portion of a stage 400 of a scan drive unit shown in FIG. 11 , and the timing chart of signals input thereto are identical with those of the first embodiment shown in FIG. 9 , and thus a description thereof is omitted.

However, in a case of the first and second boost drive units, a sixth PMOS thin film transistor M 6 and a seventh PMOS thin film transistor M 7 are further provided in the construction of the first embodiment shown in FIG. 8 . Further, the control signals B 1 , B 2 , B 3 , and B 4 are input to an input terminal of a sixth transistor M 6 in order to adjust a swing of an output boost signal.

Here, first and second control signals D 1 and D 2 are respectively input to odd- and even-numbered stages of the first boost drive unit, whereas third and fourth control signals D 3 and D 4 are respectively input to odd- and even-numbered stages of the second boost drive unit.

In a detailed description, as shown in FIG. 11 , an odd-numbered stage 500 of a boost drive unit includes first to fifth transistors M 1 to M 5 , a sixth PMOS transistor M 6 , and a seventh PMOS transistor M 7 . The sixth PMOS transistor M 6 is coupled to a control signal D 1 or D 3 input line and a boost signal output line BST, and a gate terminal thereof is coupled to an output terminal of the first transistor M 1 . The seventh PMOS transistor M 7 is coupled between a first power supply VDD and the boost signal output line BST.

As noted previously, the sixth and seventh PMOS transistors M 6 and M 7 are further included. As a control signal is applied through the sixth PMOS transistor M 6 , a difference between high and low levels in a boost signal output from each stage, namely, a swing of an output pulse is controlled by the control signal.

That is, similar to the first embodiment, the same signal is output through an output terminal of a stage to be input to a next stage. However, a corresponding boost signal is output through a boost signal output line BST of each stage depending on a swing level of the control signal.

As shown in FIG. 12 , the first and second control signals D 1 and D 2 are applied to the first boost drive unit with a less difference of high and low levels as compared with that of the third and fourth clock signals CLK 3 and CLK 4 applied to the first boost drive unit. That is, the first and second control signals have a swing less than that of the third and fourth corresponding clock signals CLK 3 and CLK 4 .

Similar to that described above, the boost signal is output through a stage of a boost drive unit shown in FIG. 11 as a pulse width greater than that of a corresponding selection signal, and as a pulse having a small difference of high and low levels by the control signal.

That is, this embodiment has an advantage in that it may adjust a pulse swing of an output boost signal.

FIG. 13 is a block diagram showing a configuration of a first scan driver of a scan driving circuit according to another embodiment.

In the embodiments discussed above, the first scan driver is divided into a scan drive unit, and first and second boost drive units. In other embodiments the scan drive unit is configured to be divided into odd- and even-numbered scan drive units, and the odd- and even-numbered scan drive units are connected to the first and second boost drive units.

In other words, as shown in FIG. 13 , the first scan driver 310 includes a first scan/boost drive unit 318 and a second scan/boost drive unit 319 . The first scan/boost drive unit 318 outputs odd-numbered selection signal and boost signal. The second scan/boost drive unit 319 outputs even-numbered selection signal and boost signal.

In addition to clock signals CLK 7 , CLK 8 , CLK 9 , CLK 10 , input signals IN 4 , IN 5 , and control signals D 1 , D 2 , D 3 , D 4 for adjusting a swing of an output pulse, which have similar function to corresponding signals discussed above, selection control signals A 1 , A 2 , A 3 , and A 4 for sequentially outputting odd- and even-numbered selection signals are further applied to the first scan/boost drive unit 318 and the second scan/boost drive unit 319 .

First and third selection control signals A 1 and A 3 are input to odd-numbered stage of the first and second scan/boost drive units 318 and 319 , respectively. Second and fourth selection control signals A 2 and A 4 are input to even-numbered stage of the first and second scan/boost drive units 318 and 319 , respectively.

FIG. 14 is a circuitry diagram of a stage in a first scan driver of the scan driving circuit, which shows a detailed circuit arrangement of odd-numbered stages of first and second scan/boost drive units 318 and 319 shown in FIG. 13 . Further, FIG. 15 is an input/output waveform diagram of the stage shown in FIG. 14 .

As shown in FIG. 14 and FIG. 15 , a scan/boost drive unit is configured by adding an eighth PMOS transistor M 8 and a ninth PMOS transistor M 9 to an arrangement of the second embodiment shown in FIG. 11 . In order to sequentially output odd- and even-numbered selection signals, selection control signals A 1 , A 2 , A 3 , and A 4 are input to an input terminal of the eighth PMOS transistor M 8 .

Herein, first and second selection control signals A 1 and A 2 are input to odd- and even-numbered stages of the first scan/boost drive unit, respectively. Further, third and fourth selection control signals A 3 and A 4 are input to odd- and even-numbered stages of the second scan/boost drive unit, respectively.

As shown in FIG. 14 , an odd-numbered stage 600 of a scan/boost drive unit further includes first to seventh transistors M 1 to M 7 , a first capacitor C 1 , an eighth PMOS transistor M 8 , and a ninth PMOS transistor M 9 . The eighth PMOS transistor M 8 is coupled to a selection control signal A 1 or A 3 input line and a selection signal output line SEL, and a gate terminal thereof is coupled to an output terminal of the first transistor M 1 . The ninth PMOS transistor M 9 is coupled between a first power supply VDD and the selection signal output line SEL, and a gate terminal thereof is coupled to the first node N 1 .

As noted previously, the eighth and ninth PMOS transistors M 8 and M 9 are further included. As a selection control signal is applied through the eighth PMOS transistor M 8 , as shown in FIG. 15 , selection signals output from odd- and even-numbered stages may be output.

That is, this embodiment has advantages in that it may adjust a pulse width and a swing of a boost signal, and may reduce the number of drive units.

FIG. 16 is a block diagram showing a configuration of a first scan driver of a scan driving circuit according to another embodiment.

In this embodiment, it is unnecessary to input control signals D 1 , D 2 , D 3 , and D 4 in each stage.

FIG. 17 is a circuit diagram of a stage in a first scan driver of the scan driving circuit, which shows a detailed circuit arrangement of an odd-numbered stage of the first and second scan/boost drive units. FIG. 18 is an input/output waveform diagram of the stage shown in FIG. 17 .

As shown in FIG. 17 and FIG. 18 , scan/boost drive unit 600 has the same construction as that shown in FIG. 14 .

The difference is that a third power supply VL in place of control signals D 1 , D 2 , D 3 , and D 4 is applied to an input terminal of a sixth PMOS transistor M 6 . The third power supply VL supplies a negative voltage corresponding to a low level value of the control signal. In this case, as shown in FIG. 18 , the fourth embodiment can still obtain an output waveform similar to that of the third embodiment.

As apparent from the above description, in accordance with a scan driving circuit with a first scan driver for providing a selection signal and/or a boost signal, and a second scan driver for providing an emission signal, by freely adjusting a pulse width and a swing of the boost signal, an electric current I OLED supplied to an organic light emitting diode can be set at a desired value.

Furthermore, a flow path of a static current is removed from the scan driving circuit that allows power consumption to be reduced.

In addition, when the scan driving circuit outputs a high-level signal, an output terminal is not charged, thereby minimizing a leakage current. When the scan driving circuit outputs a low-level signal, a reduction of an electric current charging the output terminal is minimized to increase an operation speed.

Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes might be made in this embodiment without departing from the principles and spirit of the invention.