Light emitting device and method of driving the same

1. Field of the Invention

The present invention relates to a light emitting device and a method of driving the same, more particularly relates to a light emitting device for preventing cross-talk phenomenon and a method of driving the same.

2. Description of the Related Art

A light emitting device emits a light having a certain wavelength. Especially, an organic electroluminescent device as the light emitting device is self light emitting device.

FIG. 1 is a sectional view illustrating schematically pixel included in a common organic electroluminescent device. FIG. 2 is a view illustrating schematically a circuitry of a passive-matrix type organic electroluminescent device. FIG. 3 is a timing diagram illustrating a process of driving the organic electroluminescent device.

In FIG. 2 , the organic electroluminescent device includes a plurality of pixels 10 .

Each of the pixels 10 includes an anode electrode layer 2 , an hole transporting layer 3 , an emitting layer 4 , an electron transporting layer 5 and a cathode electrode layer 6 formed in sequence on an substrate 1 as shown in FIG. 1 .

The anode electrode layer 2 , the emitting layer 4 and the cathode electrode layer 6 are made up of transparent conductive material, organic material, and metal, respectively.

When a certain positive voltage and a negative voltage are provided to the anode electrode layer 2 and the cathode electrode layer 6 , respectively, the hole transporting layer 3 transports holes generated from the anode electrode layer 2 to the emitting layer 4 . In addition, the electron transporting layer 5 transports electrons generated from the cathode electrode layers 6 to the emitting layer 4 . Subsequently, the transported holes and the transported electrons are recombined in the emitting layer 4 , and so a light having a certain wavelength is emitted from the emitting layer 4 .

There are a passive-matrix type organic electroluminescent device and an active-matrix type organic electroluminescent device as the organic electroluminescent device.

Hereinafter, the passive-matrix type organic electroluminescent device of the organic electroluminescent device will be described in detail.

In FIG. 2 and FIG. 3 , the organic electroluminescent device includes a plurality of pixels 10 formed in cross areas of data lines D 1 to Dm and scan lines S 1 to Sn.

Scan signals SP 1 to SPn are provided to the scan lines S 1 to Sn, and so the scan lines S 1 to Sn are connected in sequence to a ground.

Data signals, i.e. data current Id synchronized with the scan signals SP 1 to SPn are provided to the data lines D 1 to Dm. As a result, pixels corresponding to a scan line connected to the ground emits a light having the brightness corresponding to the data current Id.

A cross-talk phenomenon is occurred in the organic electroluminescent device. This will be explained in detail with reference to the accompanying drawings.

FIG. 4 is a plan view illustrating a picture displayed on the organic electroluminescent device.

In FIG. 4 , a black picture is displayed on the center of the organic electroluminescent device, and a white picture is displayed on the other area thereof.

Hereinafter, a white picture area approximate to the black picture is assumed as a first white area A, and a white picture area over/under the first white area A is assumed as a second white area B.

Though data current having the same magnitude is provided to the first white area A and the second white area B so that light having the same brightness is emitted from the first white area A and the second white area B, the brightness of a light emitted from the first white area A is different from that of a light emitted from the second white area B. This is referred to as “Cross-talk phenomenon”. The cross-talk phenomenon will be described in more detail with reference to the accompanying drawing.

FIG. 5 is a timing diagram illustrating a process of driving the organic electroluminescent device.

As shown in FIG. 5 , since the first white area A displays the black picture, the amount of first precharge current provided to one data line in a second precharge time of a scan signal SP 2 provided to a N+1 scan line is smaller than that of second precharge current provided to the data line in a first precharge time of a scan signal SP 1 provided to a N scan line. In other words, the magnitude at a start point of a second luminescent time corresponding to the N+1 scan line is smaller than that at a start point of a first luminescent time corresponding to the N scan line.

Subsequently, data current having the same magnitude is provided to the data line during the first and second luminescent times so that the first white area A and the second white area B have the same brightness.

However, though the data current having the same magnitude is provided to the data line, a first pixel corresponding to the N+1 scan line and the data line has the brightness different from a second pixel corresponding to the N scan line and the data line because the amount of the first precharge current is different from that of the second precharge current. In other words, though the first white area A and the second white area B are preset to have the same brightness, the brightness of the first white area A is different from that of the second white area B. Accordingly, the display characteristics of the organic electroluminescent device might be deteriorated by the cross-talk phenomenon.

It is a feature of the present invention to provide a light emitting device for preventing cross-talk phenomenon and a method of driving the same.

A light emitting device according to one embodiment of the present invention includes a plurality of pixels and a scan driving circuit. The pixels are formed in cross areas of data lines and scan lines. The scan driving circuit couples at least one scan line to a first voltage source having a first voltage during a first time, couples the scan line to a second voltage source having a second voltage during a second time, and couples the scan line to a third voltage source having a third voltage during a third time. Here, the second voltage is a voltage between the first voltage and the third voltage.

An organic electroluminescent device according to one embodiment of the present invention includes a plurality of pixels, a precharging circuit, a data driving circuit and a scan driving circuit. The pixels are formed in cross areas of data lines and scan lines. The precharging circuit provides precharge current to the data lines during a precharge time. The data driving circuit provides data current to the data lines during a luminescent time. The scan driving circuit couples one scan line to a first voltage source having a first voltage during the precharge time, couples the scan line to a second voltage source having a second voltage during a delay time, and couples the scan line to a third voltage source having a third voltage during the luminescent time. Here, the delay time is a time between the precharge time and the luminescent time.

A method of driving a light emitting device having a plurality of pixels formed in cross areas of data lines and scan lines according to one embodiment of the present invention includes coupling one scan line to a first voltage source having a first voltage during a precharge time; coupling the scan line to a second voltage source having a second voltage during a delay time; and coupling the scan line to a third voltage source having a third voltage during a luminescent time. Here, the second voltage is a voltage between the first voltage and the third voltage.

As described above, a light emitting device and a method of driving the same according to one embodiment of the present invention discharge data lines to the same level as data current irrespective of precharge current, and thus cross-talk phenomenon is not occurred to the light emitting device.

The above and other features and advantages of the present invention will become readily apparent by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a sectional view illustrating schematically pixel included in a common organic electroluminescent device;

FIG. 2 is a view illustrating schematically a circuitry of a passive-matrix type organic electroluminescent device;

FIG. 3 is a timing diagram illustrating a process of driving the organic electroluminescent device;

FIG. 4 is a plan view illustrating a picture displayed on the organic electroluminescent device;

FIG. 5 is a timing diagram illustrating a process of driving the organic electroluminescent device;

FIG. 6 is a block diagram illustrating a light emitting device according to one embodiment of the present invention;

FIG. 7 is a view illustrating schematically a circuitry of a scan driving circuit according to one embodiment of the present invention;

FIG. 8 is a timing diagram illustrating controlling signals provided to switches of FIG. 7 ;

FIG. 9 is a view illustrating a circuitry of a scan driving circuit according to another embodiment of the present invention;

FIG. 10 is a timing diagram illustrating controlling signals provided to switches of FIG. 9 ;

FIG. 11 is a timing diagram illustrating a process of driving the light emitting device according to one embodiment of the present invention; and

FIG. 12A and FIG. 12B are timing diagrams illustrating a method of setting the delay time and the luminescent time according to one embodiment of the present invention.

Hereinafter, the preferred embodiments of the present invention will be explained in more detail with reference to the accompanying drawings.

FIG. 6 is a block diagram illustrating a light emitting device according to one embodiment of the present invention. FIG. 7 is a view illustrating schematically a circuitry of a scan driving circuit according to one embodiment of the present invention. FIG. 8 is a timing diagram illustrating controlling signals provided to switches of FIG. 7 . FIG. 9 is a view illustrating a circuitry of a scan driving circuit according to another embodiment of the present invention. FIG. 10 is a timing diagram illustrating controlling signals provided to switches of FIG. 9 .

The light emitting device according to one embodiment of the present invention includes an organic electroluminescent device, a plasma display panel, a liquid crystal display, and others. Hereinafter, the organic electroluminescent device will be described as an example of the light emitting device for convenience of the description.

In FIG. 6 , the light emitting device of the present invention includes a panel 60 , a controller 61 , a scan driving circuit 63 , a precharging circuit 64 and a data driving circuit 65 .

The panel 60 includes a plurality of pixels 60 formed in cross areas of the data lines D 1 to Dm and scan lines S 1 to Sn.

The controller 61 receives display data, e.g. RGB data from an outside device, and controls the scan driving circuit 63 and the data driving circuit 65 using the received display data. In addition, the controller 61 detects the gray scale of the display data, and reads precharge current data corresponding to the detected gray scale from a look-up table 62 . Then, the controller 61 generates controlling signals SEL 1 and SEL 2 corresponding to the precharge current data, and controls the precharging circuit 64 using the controlling signals SEL 1 and SEL 2 . Here, the first controlling signal SEL 1 is a signal for controlling the precharging circuit 64 so that precharge current corresponding to the precharge current data is provided to the data lines D 1 to Dm during a precharge time. However, the second controlling signal SEL 2 is a signal for controlling the precharging circuit 64 so that the precharge current is cut off after the precharge time, and then data current is provided to the data lines D 1 to Dm.

The look-up table 62 stores precharge current data corresponding to gray scale of the display data.

The precharging circuit 64 provides the precharge current to the data lines D 1 to Dm, thereby precharging the data lines D 1 to Dm.

The data driving circuit 65 provides data signals, i.e. data current corresponding to the display data to the precharged data lines D 1 to Dm under the control of the controller 61 .

The scan driving circuit 63 transmits in sequence scan signals to the scan lines S 1 to Sn under the control of the controller 61 . As a result, the scan lines S 1 to Sn are coupled in sequence to a third voltage source, e.g. a ground. Here, a scan signal (SPi: 1≦i≦n) provided to a scan line coupled to the third voltage source has a delay time which is a time between the precharge time and a luminescent time. In this case, the scan signal has a second level voltage which is a voltage between a first level voltage corresponding to high logic and a second level voltage corresponding to low logic. In particular, the scan driving circuit 63 includes a first voltage source VSCAN 1 for supplying a first level voltage to the scan lines S 1 to Sn, a second voltage source VSCAN 2 for supplying a second level voltage to the scan lines S 1 to Sn, and a third voltage source, e.g. a ground for supplying a third level voltage to the scan lines S 1 to Sn. Here, the second level voltage according to one embodiment of the present invention has the same magnitude as a driving voltage corresponding to the maximum brightness of a pixel in the light emitting device. Additionally, the scan driving circuit 63 further includes a first switch (+) Ts for switching connection between the scan lines S 1 to Sn and the first voltage source VSCAN 1 , a second switch Tds for switching connection between the scan lines S 1 to Sn and the second voltage source VSCAN 2 , and a third switch Ts for switching connection between the scan lines S 1 to Sn and the third voltage source, e.g. the ground.

The switches (+) Ts, Tds and Ts connect the scan lines S 1 to Sn to the first voltage source VSCAN 1 , the second voltage source VSCAN 2 , or the ground in accordance with an on-off controlling signal transmitted from a timing controller (not shown). Here, the switches (+) Ts, Tds and Ts are controlled by a first scan controlling signal CS 1 , a second scan controlling signal CS 2 , and a third scan controlling signal CS 3 , respectively as shown in FIG. 8 .

At least one of the switches (+) Ts, Tds and Ts according to one embodiment of the present invention has MOS transistor. For example, each of the switches (+) Ts, Tds has P-MOS transistor, the switch Ts has a N-MOS transistor.

In short, the light emitting device of the present invention discharges the data lines D 1 to Dm precharged by the precharge current during the delay time.

In other words, the light emitting device of the present invention discharges the precharged data lines D 1 to Dm during a delay time of the first scan signal SP 1 provided to the N scan line corresponding to the second white area B shown in FIG. 4 , and discharges the precharge data lines D 1 to Dm during a delay time of the second scan signal SP 2 provided to the N+1 scan line corresponding to the first white area A. Here, the data lines D 1 to Dm are discharged to the same level as following data current. Then, the data current is provided to the data lines D 1 to Dm during the luminescent time.

Hereinafter, a process of driving the light emitting device of the present invention will be described with reference to the accompanying drawings.

FIG. 11 is a timing diagram illustrating a process of driving the light emitting device according to one embodiment of the present invention. FIG. 12A and FIG. 12B are timing diagrams illustrating a method of setting the delay time and the luminescent time according to one embodiment of the present invention.

One data line located in only white area of the data lines D 1 to Dm will be explained for the convenience of description. In addition, first data current I 1 provided to the data line during a first luminescent time lt 1 of the first scan signal provided to the N scan line is preset to have the same brightness as second data current I 2 provided to the data line during a second luminescent time lt 2 of the second scan signal provided to the N+1 scan line.

As shown in FIG. 11 , the data line is discharged by a discharging circuit (not shown) during a first discharge time dcha 1 in the first scan signal provided to the N scan line corresponding to the second white area B.

Subsequently, first precharge current is provided to the data line during a first precharge time pcha 1 , and so the discharged data line is precharged.

Then, the precharged data line is discharge to the same level as following first data current I 1 during a first delay time dt 1 .

Subsequently, the first data current is provided to the discharged data line during a first luminescent time lt 1 , and so a first pixel corresponding to the data line and the N scan line emits a light.

Then, the data line is discharged during a second discharge time dcha 2 in the second scan signal provided to the N+1 scan line corresponding to the first white area A.

Subsequently, second precharge current is provided to the data line during a second precharge time pcha 2 , and so the discharged data line is precharged.

Then, the precharged data line is discharged to the same level as following second data current I 2 during a second delay time dt 1 .

Subsequently, the second data current I 2 is provided to the discharged data line during a second luminescent time lt 2 , and thus a second pixel corresponding to the data line and the N+1 scan line emits a light.

As described above, the data line is discharged to the same level as the first data current I 1 during the first delay time dt 1 irrespective of the magnitude of the first precharge current. Moreover, the data line is discharged to the same level as the second data current I 2 during the second delay time dt 2 irrespective of the magnitude of the second precharge current. Here, since the data current I 1 and I 2 have the same magnitude, the pixels corresponding to the data line emit a light having the same brightness during the first luminescent time lt 1 and the second luminescent time lt 2 . In other words, the pixels emit the light having the same brightness during the first luminescent time lt 1 and the second luminescent time lt 2 irrespective of the magnitude of the first precharge current and the second precharge current. Accordingly, cross-talk phenomenon is not occurred to the light emitting device of the present invention.

Hereinafter, a process of setting the delay time and the luminescent time in the light emitting device of the present invention will be described in detail with reference to FIG. 12A and FIG. 12B .

In FIG. 12A , the delay time and the luminescent time of a scan signal employed in the light emitting device of the present invention have the same length as a luminescent time in Related Art. In other words, the light emitting device of the present invention has the luminescent time smaller than the light emitting device described in Related Art. This delay time and luminescent time may be set by adjusting the number of clock as shown in FIG. 12A . For example, one scan time corresponds to 27 clocks. In this case, the length of the luminescent time in Related Art corresponds to 24 clocks, whereas the length of the luminescent time in the present invention is set to 22 clocks. Here, the number of the reduced clocks, i.e. 2 clocks is set as the delay time in the present invention. Accordingly, the frame frequency in the present invention is substantially identical to that in Related Art because the clock number of the luminescent time and the delay time in the present invention is substantially identical to that of the luminescent time in Related Art.

In FIG. 12B , the scan time in the light emitting device according to another embodiment of the present invention is longer than in Related Art. In this case, the length of the luminescent time in the light emitting device of the present invention is identical to that of the luminescent time in Related Art. The increased scan time is set as the delay time in the present invention as shown in FIG. 12B .

A method of setting the delay time in the present invention may be variously modified. However, it will be immediately obvious to those skilled in the art that many modifications for setting the delay time do not have any effect to the scope of the present invention.

In addition, a method of driving the light emitting device according to one embodiment of the present invention may be applied to an active-matrix type light emitting device as well as the passive-matrix type light emitting device.

From the preferred embodiments for the present invention, it is noted that modifications and variations can be made by a person skilled in the art in light of the above teachings. Therefore, it should be understood that changes may be made for a particular embodiment of the present invention within the scope and the spirit of the present invention outlined by the appended claims.