Scan driving circuit comprising a plurality of stages, each stage configured to receive multiple clocks

This application claims priority to and the benefit of Korean Patent Application No. 10-2006-0034959, filed on Apr. 18, 2006, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference.

1. Field of the Invention

The present invention relates to a scan driving circuit and an organic light emitting display using the same.

2. Discussion of Related Art

Recently, various flat panel displays devices with a small weight and volume compared with a cathode ray tube have been developed, and a flat panel display device arranges a plurality of pixels on a substrate in a matrix type to form a pixel unit, and connects scan lines and data lines to each pixel to selectively apply data signals to the pixels for displaying.

The flat panel display device is divided into a passive matrix type display device and an active matrix type display device in accordance with a driving scheme of a pixel. The active matrix type selectively lighting per the unit pixel has mainly been used in view of resolution, contrast and an operation speed.

Such a flat panel display device has been used as a display device of a portable information terminal such as a personal computer, a mobile telephone, a PDA, etc., or a monitor for various information equipments. A LCD using a liquid crystal panel, an organic electro luminescence display using organic light-emitting element and a PDP using a plasma panel, etc., have been known. In particular, the organic electro luminescence display, which is excellent in view of emission efficiency, brightness, view angle and has a rapid response speed, has been spotlighted.

In general, an active matrix type display device such as an organic light emitting display includes a pixel array arranged at crossings between data lines and scan lines in a matrix pattern.

Here, the scan lines include horizontal lines (i.e., row lines) of a matrix display region, and sequentially provide a predetermined signal, namely, a scan signal, from a scan driving circuit, to the pixel array.

One embodiment of the present invention is a scan driving circuit including a plurality of stages. The plurality of stages being for receiving three clocks, wherein each of the plurality of stages is configured to receive two of the three clocks, to receive and delay an input signal through an input terminal, and to output an output signal through an output terminal, wherein the input terminal of each of the plurality of stages is connected to the output terminal of a previous one of the stages. Each of the plurality of stages includes: a switch for turning on/off a connection of the input terminal according to a first clock among the three clocks, the first clock for inputting through a first clock terminal; a switch section for transferring a first voltage to the output terminal according to the first clock among the three clocks, and for preventing the first voltage from being transferred to the output terminal according to the input signal; and a storage section for maintaining a voltage of the output terminal for a predetermined time, and for transferring a voltage of a second clock among the three clocks to the output terminal according to the input signal, the second clock for inputting through the second clock terminal.

According to a second embodiment of the present invention, there is provided a scan driving circuit including: a plurality of stages, the plurality of stages being for receiving three clocks, wherein each of the plurality of stages is configured to receive two of the three clocks, to receive and delay an input signal through an input terminal, and to output an output signal through an output terminal, wherein the input terminal of each of the plurality of stages is connected to the output terminal of a previous one of the stages. Each of the plurality of stages includes: a first transistor for turning on/off a connection of the input terminal according to a first clock among the three clocks, the first clock for inputting through a first clock terminal; a switch section for transferring a first voltage to the output terminal according to the first clock among the three clocks; and a storage section for maintaining a voltage of the output terminal for a predetermined time, and for transferring a voltage of a second clock among the three clocks to the output terminal according to the input signal, the second clock for inputting through a second clock terminal.

In another embodiment of the invention, an organic light emitting display is provided. The device includes: a display region having a plurality of pixels for displaying an image; a scan driving circuit for transferring a scan signal to the display region; and a data driving circuit for transferring a data signal to the display region. The scan driving circuit includes a plurality of stages, the plurality of stages being for receiving three clocks, wherein each of the plurality of stages is configured to receive two of the three clocks, to receive and delay an input signal through an input terminal, and to output an output signal through an output terminal, wherein the input terminal of each of the plurality of stages is connected to the output terminal of a previous one of the stages. Each of the plurality of stages includes: a transistor for turning on/off a connection of the input terminal according to a first clock among the three clocks, the first clock for inputting through a first clock terminal; a switch section for transferring a first voltage to the output terminal according to the first clock among the three clocks, and for preventing the first voltage from being transferred to the output terminal according to the input signal; and a storage section for maintaining a voltage of the output terminal for a predetermined time, and for transferring a voltage of a second clock among the three clocks to the second clock terminal to the output terminal according to the input signal, the second clock for inputting through a second clock terminal.

In another embodiment of the invention, an organic light emitting display is provided. The device includes: a display region having a plurality of pixels for displaying an image; a scan driving circuit for transferring a scan signal to the display region; and a data driving circuit for transferring a data signal to the display region. The scan driving circuit includes a plurality of stages, the plurality of stages being for receiving three clocks, wherein each of the plurality of stages is configured to receive two of the three clocks, to receive and delay an input signal through an input terminal, and to output an output signal through an output terminal, wherein the input terminal of each of the plurality of stages is connected to the output terminal of a previous one of the stages. Each of the plurality of stages includes: a transistor for turning on/off a connection of the input terminal according to a first clock among the three clocks, the first clock for inputting through a first clock terminal; a switch section for transferring a first voltage to the output terminal according to the first clock among the three clocks; and a storage section for maintaining a voltage of the output terminal for a predetermined time, and for transferring a voltage of a second clock among the three clocks to the output terminal according to the input signal, the second clock for inputting through a second clock terminal.

These and/or other embodiments and features of the invention will become apparent and more readily appreciated from the following description of certain exemplary 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. 2A is a circuit diagram of one of the inverters shown in FIG. 2 ;

FIG. 3 is a timing diagram of the stage shown in FIG. 2 ;

FIG. 4 is a block diagram showing an organic light emitting display according to an embodiment of the present invention;

FIG. 5 is a block diagram showing a construction of a scan driving circuit according to an embodiment of the present invention;

FIG. 6 is a circuit diagram showing a first embodiment of a stage of the scan driving circuit shown in FIG. 5 ;

FIG. 7 is a timing diagram showing a first embodiment of an input/output waveform of the stage shown in FIG. 6 ;

FIG. 8 is a circuit diagram showing a second embodiment of a stage of the scan driving circuit shown in FIG. 5 ;

FIG. 9 is a circuit diagram showing a third embodiment of a stage of the scan driving circuit shown in FIG. 5 ;

FIG. 10A and FIG. 10B are timing diagrams showing a second embodiment and a third embodiment, respectively, of input/output waveforms of the stages shown in FIG. 8 and FIG. 9 , respectively;

FIG. 11 is a circuit diagram showing a fourth embodiment of a stage of the scan driving circuit shown in FIG. 5 ; and

FIG. 12 is a timing diagram of the stage shown in FIG. 11 .

Hereinafter, certain exemplary embodiments according to the present invention will be described with reference to the accompanying drawings. Here, when a first element is described as being connected to a second element, the first element may be not only directly connected to the second element but may also be indirectly connected to the second element via a third element. Further, elements that are not essential to the complete understanding of the invention are omitted for clarity. Also, like reference numerals refer to like elements throughout.

FIG. 1 is the 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 dependently connected with a start pulse SP input line. The plurality of stages ST 1 to STn sequentially shift a clock signal C in response to a start pulse SP to generate output signals SO 1 to SOn, respectively. In this case, each of second to n-th stages ST 2 to STn receives and shifts an output signal of a previous stage as a start pulse.

Accordingly, the stages generate output signals S 01 to SOn in such a way that the start pulse is sequentially shifted, and provide the output signals to the pixel array.

FIG. 2 is a circuit diagram of a stage in the scan driving circuit shown in FIG. 1 . FIG. 3 is a timing diagram of the stage shown in FIG. 2 . Referring to FIG. 2 and FIG. 3 , conventionally, each stage of 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 and maintains a previous output.

In contrast to this, when the clock CLK is at a high level, the flip-flop maintains an input received at an input terminal In received when the clock CLK is at the low level, and outputs the received input but no longer receives the input shown.

In the aforementioned circuit, an inverter included in the flip-flop shown in FIG. 2A has a problem in that a static current flows when an input thereof is at a low level. Furthermore, in the flip-flop, the number of inverters having received a high-level input is the same number as that of inverters having received a low-level input. Accordingly, the static current flows through a half of all the inverters M 1 ′ and M 2 ′ in the flip-flop, thereby causing power consumption to be increased.

In addition, in the circuit of FIG. 2A , a voltage value due to a ratio of resistance (i.e., the transistors M 1 ′ and M 2 ′) connected between a power supply VDD and a ground GND determines a high level of an output voltage out. Low level of the output voltage out is set to be greater than that of the ground GND by a threshold voltage of the transistor M 2 ′.

By way of example, due to characteristic deviations of the transistors, since levels of an input voltage are different according to respective stages, in the case where the circuits of FIGS. 2 and 2A are used, the deviation occurs when the output voltage is at a high level, with the result that the circuit may be erroneously operated.

Moreover, the deviation in a low level of the output voltage causes a deviation in on-resistance of an input transistor of an inverter included in the circuit of FIG. 2 to occur, thereby weighting a deviation in a high level of the output voltage. In particular, since a panel of an organic light emitting display uses a transistor having a great characteristic deviation, such a problem is more serious.

Further, in the inverter, an electric current flows through an input transistor to charge an output terminal, whereas the electric current flows through a load transistor to discharge the output terminal. Upon a charge of the output terminal, a source-gate voltage of the load transistor is gradually reduced, and a discharge current is accordingly reduced rapidly. This causes the discharge efficiency to be deteriorated.

FIG. 4 is a block diagram showing an organic light emitting display according to an embodiment of the present invention. With reference to FIG. 4 , the organic light emitting display includes a display region 30 , a scan driving circuit 10 , a data driving circuit 20 , and a timing controller 50 .

The display region 30 includes a plurality of pixels 40 formed at crossing areas of scan lines S 1 to Sn, and data lines D 1 to Dm. The scan driving circuit 10 drives the scan lines S 1 to Sn. The data driving circuit 20 drives the data lines D 1 to Dm. The timing controller 50 controls the scan driving circuit 10 and the data driving circuit 20 .

The timing controller 50 generates a data drive control signal DCS and a scan drive control signal SCS according to externally supplied synchronous signals. The data drive control signal DCS generated by the timing controller 50 is provided to the data driving circuit 20 , and the scan drive control signal SCS is provided to the scan driving circuit 10 . Furthermore, the timing controller 50 provides externally supplied data Data to the data driving circuit 20 .

The data driving circuit 20 receives the data drive control signal DCS from the timing controller 50 . Upon the receipt of the data drive control signal DCS, the data driving circuit 20 generates data signals, and provides the generated data signals to the data lines D 1 to Dm. In this embodiment, the data driving circuit 20 provides the generated data signals to the data lines D 1 to Dm every one horizontal period.

The display region 30 receives a first power from a first power supply ELVDD and a second power from a second power supply ELVSS from an exterior source, and provides them to the pixels 40 . Upon the receipt of the first power and the second power, the pixels 40 control an amount of current that flows into the second power supply ELVSS from the first power supply ELVDD through a light emitting element corresponding to the data signal, thus generating light corresponding to the data signal.

The scan driving circuit 10 generates a scan signal in response to a scan drive control signal SCS from the timing controller 50 , and sequentially provides the generated scan signal to the scan lines S 1 to Sn. That is, the scan driving circuit 10 sequentially generates the scan signal to drive the plurality of pixels, and provide the scan signal to the display region 10 .

Hereinafter, a construction and an operation of the scan driving circuit of an organic light emitting display according to an embodiment of the present invention will be explained.

FIG. 5 is a block diagram showing a configuration of a scan driving circuit according to an embodiment of the present invention. Referring to FIG. 5 , the scan driving circuit in one embodiment of the present invention includes n stages that are dependently connected with a start pulse input line so as to drive an m×n pixel array.

First output lines of the first n stages are connected with first n row lines corresponding to the scan lines S 1 to Sn included in the pixel array. A start pulse SP is supplied to a first stage. Output signals of first to n−1th stages are provided to next stages as a start pulse, respectively. Each stage receives and operates according to a first clock CLK 1 and a second clock CLK 2 , the second clock CLK 2 and a third clock CLK 3 or the first clock CLK 1 and the third clock CLK 3 . Each stage includes a first clock terminal ck 1 and a second clock terminal ck 2 . In the embodiment shown, the first clock CLK 1 and the second clock CLK 2 are supplied to the first clock terminal ck 1 and the second clock terminal ck 2 of a (3k−2)-th stages. The second clock CLK 2 and the third clock CLK 3 are supplied to the first clock terminal ck 1 and the second clock terminal ck 2 of a (3k)-th stages. The first clock CLK 1 and the third clock CLK 3 are supplied to the second clock terminal ck 2 and the first clock terminal ck 1 of a (3k−2)-th stages. Here, k is a natural number.

That is, each stage operates in response to two clocks selected from the first clock CLK 1 , the second clock CLK 2 and the third clock CLK 3 , but does not operate in response to merely one clock.

Further, when the first stage outputs a signal in response to the first and second clocks, the second stage receives and operates according to the second and third clocks. When the second stage outputs a signal in response to the second and third clocks, the third stage receives and operates according to the third and first clocks. That is, the first, second, and third stages sequentially output the signal to sequentially drive a display region of an organic light emitting display by scan lines.

An external control circuit (not shown) provides the input signals of the driving circuit, that is, a start pulse SP, the first clock, the second clock and the third clock, CLK 1 , CLK 2 and CLK 3 , and a supply voltage VDD.

FIG. 6 is a circuit diagram showing a first embodiment of a stage of the scan driving circuit shown in FIG. 5 . FIG. 7 is a timing diagram showing a first embodiment of an input/output waveform of the stage shown in FIG. 6 .

As shown in FIG. 6 , in this embodiment of the present invention, transistors included in each stage are all PMOS transistors, and sequentially send a low level output through the scan driving circuit. Namely, the scan driving circuit of the present invention outputs a high level signal to a display region of an active matrix type display device such as an organic light emitting display for most of the time, and sequentially outputs a low level pulse through a plurality of stages as shown in FIGS. 6 and 7 .

Referring to FIG. 6 , the stage 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 , a fifth PMOS transistor M 5 , and a first capacitor C 1 . The first PMOS transistor M 1 includes a gate connected with a first clock terminal ck 1 , receives an output voltage Si of a previous stage or a first start pulse SP, and selectively transfers the output voltage Si of a previous stage or the first start pulse SP to a first node N 1 . The second PMOS transistor M 2 includes a gate connected to the first node N 1 , and is connected between the second clock terminal ck 2 and a second node N 2 . The third PMOS transistor M 3 includes a gate connected to the first clock terminal ck 1 , and is connected between a ground voltage source and a third node N 3 . The fourth PMOS transistor M 4 includes a gate connected to the first node N 1 , and is connected between the first clock terminal ck 1 and the third node N 3 . The fifth PMOS transistor M 5 includes a gate connected to the third node N 3 , and is connected between a power supply VDD and the second node N 2 . The first capacitor C 1 is connected between the first node N 1 and the second node N 2 , and maintains a predetermined voltage.

Although it is shown that the ground voltage source VSS is embodied by a ground GND, it can be either ground or a negative voltage power supply.

Hereinafter, through a circuit arrangement of the (3k−2)-th stage among the stages shown in FIG. 5 , the operation of the stages will be explained.

With reference to FIGS. 6 and 7 , each stage of the scan driving circuit may divide one period into a precharge period, an evaluation period, and a quiescent period according to the first clock CLK 1 , the second clock CLK 2 , and the third clock CLK 3 . During the precharge period, the first clock CLK 1 of a low level is inputted to a first clock terminal ck 1 of the stage, the second clock CLK 2 of a high level is inputted to the second clock terminal ck 2 . Further, a start pulse SP or a scan signal Si of a previous stage is inputted to the input clock terminal In. At this time, the first PMOS transistor M 1 and the third PMOS transistor M 3 are turned-on in response to a first clock to maintain the first node N 1 and the third node N 3 at a low level voltage. When the first node N 1 becomes a low level, the second PMOS transistor M 2 and the fourth PMOS transistor M 4 are turned-on. When the second PMOS transistor M 2 is turned-on, the capacitor C 1 is charged with a voltage corresponding to a difference between voltages of the first node N 1 and the second node N 2 . Further, when the fourth transistor M 4 is turned-on, a voltage of the first clock CLK 1 is inputted to the third node N 3 . Consequently, the fifth PMOS transistor M 5 is turned-on to output a drive voltage to an output terminal out.

During the evaluation period, a first clock CLK 1 of a high level is inputted to the first clock terminal ck 1 , and a second clock CLK 2 of a low level is inputted to the second clock terminal ck 2 . At this time, the first PMOS transistor M 1 is turned-on and becomes a floating-state, so that the first node N 1 maintains a previous voltage by the capacitor C 1 . Accordingly, the second PMOS transistor M 2 and the fourth PMOS transistor M 4 are turned-on. When the fourth PMOS transistor M 4 is turned-on, the first clock CLK 1 transferred to the first clock terminal ck 1 becomes a high level, with the result that the fifth PMOS transistor M 5 is turned-off. Further, when the second PMOS transistor M 2 is turned-on, a voltage of the second node N 2 is varied according to a voltage of the second clock CLK 2 , with the result that a voltage of the output terminal has the same waveform as that of the second clock CLK 2 . In addition, since a drive voltage from a power supply VDD is not transferred to the output terminal out by the fifth PMOS transistor M 5 , a voltage of the output terminal changes according to a voltage of the second node N 2 .

Finally, the quiescent period indicates when the third clock CLK 3 has a low level. During the quiescent period, a first clock CLK 1 and a second clock CLK 2 of high level are transferred to the stage, whereas the third clock CLK 3 is not transferred thereto. At this time, the output terminal maintains a high level voltage.

Moreover, when the second clock CLK 2 again becomes a low level, the first node N 1 has a high level voltage by a capacitor, and the output terminal also maintains a high level voltage. Furthermore, in a state that the start pulse SP or the scan signal Si of a previous stage are not transferred through an input terminal In, when the first and second clocks of low level are transferred, the first node N 1 maintains a high level voltage, and the second PMOS transistor M 2 and the fifth PMOS transistor M 5 are turned-off. Accordingly, a voltage of the output terminal depends on a voltage of the second node N 2 , and the second PMOS transistor M 2 is turned-off, so that a voltage of the second node N 2 maintains a high level without variation.

Consequently, when a low level signal is not inputted to an input terminal In of each stage, the output terminal out maintains a high level signal, so that each stage receives an output low level signal of the previous stage and outputs a low level signal that results in a sequential output of the scan signal.

FIG. 8 is a circuit diagram showing a second embodiment of a stage of the scan driving circuit shown in FIG. 5 . Referring to FIG. 8 , the second embodiment of the stage 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 , a fifth PMOS transistor M 5 , and a capacitor C 1 .

The first PMOS transistor M 1 transfers an input signal to the first node N 1 in response to the second clock CLK 2 , and the second PMOS transistor M 2 transfers the third clock CLK 3 to the second node N 2 corresponding to a voltage of the first node N 1 . The third PMOS transistor M 3 transfers a ground voltage to a gate of the fifth transistor PMOS M 5 in response to the first clock CLK 1 . A gate of the fourth PMOS transistor M 4 is connected to the output terminal out, and the fourth transistor M 4 transfers the first clock CLK 1 to a gate of the fifth PMOS transistor M 5 corresponding to a voltage of the output terminal out. Further, the fifth PMOS transistor M 5 transfers a voltage of a power supply VDD to the output terminal corresponding to a voltage of a gate thereof. Moreover, the capacitor C 1 is connected between the first node N 1 and the second node N 2 , and maintains a predetermined voltage.

The stage having the construction as described above receives and operates according to the first clock and the second clock CLK 1 and CLK 2 among the first clock, the second clock and the third clock, CLK 1 , CLK 2 and CLK 3 shown in FIG. 7 . When the first clock CLK 1 is low, the stage operates in a precharge mode. When the second clock CLK 2 is low, the stage operates in an evaluation mode. When the third clock CLK 3 is low, the stage operates in a quiescent mode.

FIG. 9 is a circuit diagram showing a third embodiment of a stage of the scan driving circuit shown in FIG. 5 . In the stage shown in FIG. 9 , the stage has substantially the same functions as that of FIG. 8 . The difference between the stage of FIG. 9 from that of the stage of FIG. 8 is that the first clock CLK 1 is transferred to a source and a gate of the third PMOS transistor M 3 . Accordingly, when the first clock CLK 1 has a low level, the fifth PMOS transistor M 5 is turned-on. Since all other components of the stage in FIG. 9 are arranged in substantially the same manner as the corresponding components of FIG. 8 , they will not be described in detail.

FIG. 10A and FIG. 10B are timing diagrams showing a second embodiment and a third embodiment, respectively, of input/output waveforms of the stages shown in FIG. 8 and FIG. 9 , respectively. FIG. 10A and FIG. 10B show operations of the stage when at least two of the first clock, the second clock and the third clock, CLK 1 , CLK 2 and CLK 3 overlap with each other by external influences. FIG. 10A indicates an operation of the stage when the first clock and the second clock, CLK 1 and CLK 2 overlap with each other. FIG. 10B indicates an operation of the stage when the first clock, the second clock and the third clock, CLK 1 , CLK 2 and CLK 3 overlap with each other.

In the case of FIG. 10A , when the first clock and the second clock, CLK 1 and CLK 2 overlap with each other due to an erroneous operation of the second clock CLK 2 , they do not overlap with the third clock CLK 3 of a normal operation. Accordingly, since the first clock and the second clock, CLK 1 and CLK 2 overlap with each other, a start part of a scan signal that a first stage outputs is distorted. However, because the second clock and the third clock, CLK 2 and CLK 3 overlap with each other, a second stage outputs a scan signal, which is not distorted. Further, the third clock CLK 3 and a first clock CLK 1 of the second time do not overlap with each other, in the event that a third stage outputs a scan signal, which is not distorted.

In the case of FIG. 10B , when the first clock and the second clock, CLK 1 and CLK 2 overlap with each other, and the second clock and the third clock, CLK 2 and CLK 3 overlap with each other, the third clock CLK 3 and a first clock CLK 1 of the second time do not overlap with each other. Accordingly, the start parts of output scan signals of the first stage and the second stage are distorted, whereas an output scan signal of the third stage is not distorted.

As a result, the scan signal appears to have a normal waveform periodically, so that a difference between a waveform of a scan signal inputted to a first scan line and a waveform of a scan signal inputted to a second scan line is not great.

FIG. 11 is a circuit diagram showing a fourth embodiment of a stage of the scan driving circuit shown in FIG. 5 . FIG. 12 is a timing diagram of the stage shown in FIG. 11 . With reference to FIG. 11 , the stage is formed of NMOS transistors. The fourth embodiment of the stage includes a first NMOS transistor M 6 , a second NMOS transistor M 7 , a third NMOS transistor M 8 , a fourth NMOS transistor M 9 , a fifth NMOS transistor M 10 and a capacitor C 1 . Each stage of FIG. 11 and FIG. 12 has similar construction to that of FIG. 6 , and operates to have a precharge period, an evaluation period and a quiescent period.

Since the scan driving circuit and an organic light emitting display using the same in exemplary embodiments according to the present invention switch an output voltage from a positive source voltage to a negative source voltage, an operation speed may be increased. Furthermore, even if a clock transferred to the scan driving circuit is erroneously operated, a change of a waveform of a scan signal may be not great.

Although exemplary 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 these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.