KR20030004774A - Driving circuit in display element of current driving type - Google Patents

Abstract

In particular, the present invention relates to a driving circuit of a current-driven display device, and more particularly, a scan driver driven by a scan signal, a constant current source for pixels on / off controlled by a data enable signal, and an organic EL pixel emitting light when the scan driver is turned on. N (N is a natural number) organic EL driving units configured in parallel are provided in each of the organic EL driving units by separately configuring a precharge unit for precharging the organic EL pixels immediately before a data enable signal is activated. Not only can the amount of current applied to the organic EL pixel be reduced, but also the desired luminance can be easily obtained by adjusting the response time of the organic EL pixel.

Description

Driving circuit of current-driven display device {Driving circuit in display element of current driving type}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit of a current driving type display element, and more particularly to a driving circuit of a current driving type display element which obtains low power consumption by separately providing a precharge constant current source.

Recently, in the field of flat panel display, rapid progress has been made.

In particular, current-driven flat panel displays, which started to emerge as the leading liquid crystal displays (LCDs), have recently surpassed the Cathode Ray Tube (CRT), which has been the most used in the display field for decades. Many developments are being made such as (Visual Fluorescent Display), FED (Field Emission Display), LED (Light Emitting Diode), EL (Electroluminescence).

Such current-driven display devices are not only good in visibility and color, but also have a simple manufacturing process, thereby expanding their applications in many areas.

In particular, the organic EL display panel has recently been attracting attention as a flat panel display panel with less space occupancy due to the enlargement of the display device.

In the organic EL display panel, a data line and a scan line cross each other in a matrix form, and a light emitting layer is formed on each pixel that crosses each other. That is, the organic EL display panel is a display device in which the light emission state is determined according to the voltages applied to the data line and the scan line.

The light emission of each pixel is sequentially selected from the first line to the last line of the scan line during one frame through the scan driver, and selectively inputs power to the data line through the data driver during the same frame to scan lines. The pixel which intersects and the data line emits light.

The current-emitting characteristics of such an organic EL display panel have little temperature dependence, but the current-voltage characteristics move toward higher voltage when the temperature is lowered. Therefore, when the organic EL element is voltage driven, it is difficult to obtain stable operation. Therefore, a constant current driving method is adopted for driving the organic EL element.

1 is a diagram showing an organic EL driving circuit according to the prior art.

1, the constant current Idd is supplied to the anode of the organic EL pixel 103 through the constant current source 101 and the switch 102 for pixels. The constant current source 101 controls the amount of current applied to the anode of the organic EL pixel 103. At this time, the time for which the current output from the constant current source 101 is applied to the anode of the organic EL pixel 103 is controlled by the pixel switch 102. That is, the current output from the constant current source 101 is applied to the anode of the organic EL pixel 103 while the pixel switch 102 is turned on to emit the organic EL pixel 103. In this case, the on / off of the pixel switch 102 is controlled by a pulse width modulation (PWM) waveform output from a data driver (not shown).

Hereinafter, the PWM waveform that controls the on / off of the pixel switch 102 is referred to as a data enable signal for convenience of description. Therefore, the gray level of the organic EL pixel 103 that emits light varies according to the pulse width of the data enable signal.

The scan driver 104 driven by the scan signal is composed of NMOS, the drain of the NMOS is connected to the cathode of the organic EL pixel 103, and the source is connected to another power supply voltage, Vss.

At this time, the organic EL pixel 103 does not emit light immediately even when a current is applied through the pixel switch 102. That is, it emits light with a constant response time. This is due to the time when voltage is occupied by the internal capacitance (not shown) of the organic EL pixel 103.

However, due to this reason, gray division is difficult and luminance is not good, and a large amount of current is required in the organic EL pixel 103 due to the time when the voltage is occupied by the capacitance.

As described above, as the size of the display panel increases, the current driving display elements consume more current in the display and the driving circuit. In addition, the higher the resolution, the less time is required to drive the display due to the physical quantity of the display, which requires more current to achieve the desired brightness.

This large amount of current is a disadvantage for handheld devices, and also results in poor display lifetime.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a driving circuit of a current driven display device which reduces the amount of current applied to an organic EL pixel by using a precharge structure. Is in.

Another object of the present invention is to provide a driving circuit of a current-driven display device that controls the amount of current required in the precharge structure and adjusts the precharge timing to control the power of the entire system.

1 is a driving circuit diagram of a current driven display device according to the prior art;

2 is a driving circuit diagram of a current driven display device according to the present invention;

3 (a) to 3 (e) are operation waveform diagrams of respective portions by the rising sink according to the present invention, and show a case where the precharge level is maximum.

4 (a) to 4 (e) are operation waveform diagrams of respective parts by the polling sink according to the present invention, and show a case where the precharge level is maximum.

5A to 5E are operation waveform diagrams of respective parts by the rising sink according to the present invention, and show a case where the precharge level is intermediate.

6 (a) to 6 (e) are operation waveform diagrams of respective parts by the polling sink according to the present invention, and show a case where the precharge level is intermediate.

Explanation of symbols for main parts of the drawings

201: organic EL driver 201a: constant current source for precharge

201b: current controller 201c: precharge switch

202: organic EL driver 202a: constant current source for pixels

202b: current controller 202c: pixel switch

202d: Organic EL Pixel 202e: Scan Driver

The driving circuit of the current-driven display device according to the present invention for achieving the above object includes a scan driver driven by a scan signal, a constant current source for pixels whose on / off is controlled by a data enable signal and the scan N (N is a natural number) organic EL driving units including organic EL pixels emitting light when the driving unit is turned on are provided, and each of the organic EL driving units precharges the organic EL pixels immediately before a data enable signal is activated. It is characterized in that the pre-charge portion to be configured separately.

The precharge unit may be configured by a precharge constant current source that is turned on by a precharge signal that controls a precharge time in an organic EL pixel and supplies a current for precharge to the organic EL pixel.

The amount of current output from the precharge constant current source is controlled by adjusting a bias of the precharge constant current source from the outside.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

A preferred embodiment of a driving circuit of a current driving display device according to the present invention will be described with reference to the accompanying drawings.

2 is a view showing a driving circuit of the current driven display device according to the present invention.

2, the precharge unit 201 is further provided in the organic EL driver 202 as shown in FIG. The precharge unit 201 and the organic EL driver 202 are provided as many as the number of pixels arranged at a position where a data line and a scan line of the organic EL display panel intersect.

In this case, the organic EL driver 202 is turned on / off according to a constant current source 202a for controlling the luminance of the organic EL pixel and a data enable signal to apply the current of the constant current source to the organic EL pixel. 202c, an organic EL pixel 202d that emits light by applying current through the pixel switch 202c, and a scan driver 202e. At this time, the constant current source 202a is provided with a current controller 202b for controlling the amount of current of the constant current source 202a. Here, the data enable signal is the positive width of the PWM waveform. That is, the high period of the data enable signal corresponds to the duty of the PWM waveform. Therefore, the longer the high period of the data enable signal, the higher the gray scale.

The precharge unit 201 controls a constant current source 201a for controlling the precharge current and a current amount of the constant current source 201a to adjust the response time of the organic EL pixel 202d. 201b, and a precharge switch 201c for controlling the on / off of the precharge to apply the current of the constant current source 201a to the organic EL pixel 202d. At this time, the on / off time of the precharge switch 201c may be controlled to control the time precharged in the organic EL pixel 202d. That is, the total power can be adjusted by controlling the precharged time.

Here, one of the constant current sources 201a and 202a of the precharge unit 201 and the organic EL driver 202 is commonly connected to the power supply voltage Vdd. One of the precharge unit 201 and the switches 201c and 202c of the organic EL driver 202 is commonly connected to the anode of the organic EL pixel 202d.

In addition, the current controllers 201b and 202b may control the bias using a resistor or control the digital / analog converter (DAC) outside the IC. That is, the precharge current Ipd applied to the organic EL pixel 202d can be controlled by adjusting the bias of the constant current source 201a by using a resistor or a DAC outside the IC.

The cathode of the organic EL pixel 202b is connected to a cathode circuit, which is connected to another power supply voltage Vss, and is not shown in the present invention.

Also, the precharge start time is different depending on the time point at which the organic EL pixel 202d is turned on. That is, in the case of rising sync, the precharge is started at the start point of the scan signal, and in the case of the falling sync, the precharge is started before the data enable starts.

3 to 6 show examples in which a precharge start point varies according to a turning on time point of the organic EL pixel. For comparison, two display element driving circuits as shown in FIG. 2 are provided, and two organic EL pixels are provided. Shows an example of driving each. 3A through 6A are scan waveforms input to the scan driver 202e, and b and c are organic ELs driven by a precharge signal corresponding to data 1 and a data enable signal. The pixels (d) and (e) show examples of organic EL pixels driven by a precharge signal corresponding to data 2 and a data enable signal.

That is, the switch 202c of each precharge unit 201 is turned on during the high periods of (b) and (d), and a current output from the constant current source 201a is applied to each organic EL pixel 202d. Free charge. Further, the pixel switch 202c of each organic EL driver 202 is turned on during the high period of (c) and (e), and at this time, the current output from the constant current source 202a is transferred to each organic EL pixel 202d. It is applied to light the organic EL pixel 202d. Here, the precharge signal for controlling the on / off of the precharge switch 201c and the data enable signal for controlling the on / off of the pixel switch 202c are PMW waveforms.

The response time of the organic EL pixel is determined according to the high period of the precharge signal, that is, the pulse width, and the gray level of the organic EL pixel that emits light is determined according to the high period of the data enable signal, that is, the pulse width.

First, Figs. 3A to 3E are operation waveform diagrams of respective parts by the rising sink according to the present invention, and show a case where the precharge level is maximum. In addition, the data enable signal of data 1 has a maximum pulse width (for example, 256 gray scale) as shown in FIG. 3 (c), and the data enable signal of data 2 has a pulse as shown in FIG. An example where the width is not maximum (eg 160 gray scale) is shown as an example.

3, it can be seen that precharging is started at the start of the scan waveform of (a). That is, the precharge signal turns high at the start of the scan waveform to turn on the precharge switch 201c. Then, the current output from the constant current source 201a during the high period of the precharge signal is applied to the anode of the organic EL pixel 202d through the switch 201c to pre-fill the internal capacitance of the organic EL pixel 202d. Take it up. Then, when the precharge signal turns low, the precharge switch 201c is turned off, so that the current of the precharge constant current source 201a is no longer applied to the organic EL pixel 202d.

That is, the precharge time of the data 1 and the data 2 both start at the same point as the start point of the scan signal, and at this time, the organic EL pixel 202d has only the amount of current set by the precharge constant current source 201a. Is applied. When the precharging is completed by the above-described process, the pixel switch 202c is turned on by the data enable signal. Then, the amount of current set by the pixel constant current source 202a turns on the pixel switch 202c. Through the organic EL pixel 202d. That is, after precharging is completed, the data enable signal turns high to turn on the pixel switch 202c. The high period of the data enable signal is determined by a preset gray level. At this time, since the organic EL pixel 202d is already precharged by the precharging unit 201, it emits light as soon as a current is applied from the pixel constant current source 202a. Therefore, the organic EL driver 202 does not need to consume current for the charge of the internal capacitance of the organic EL pixel 202d.

Then, when the data enable signal turns low, the pixel switch 202c is also turned off so that the current of the pixel constant current source 202a is no longer applied to the organic EL pixel 202d.

On the other hand, Fig. 4 (a) to (e) is an operation waveform diagram of each part by the polling sink according to the present invention, showing a case where the precharge level is the maximum. In the case of FIG. 4, the data enable signal of data 1 has a maximum pulse width (eg, 256 gray scale) as shown in FIG. 4C, and the data enable signal of data 2 corresponds to FIG. 4E. As shown in FIG. 2, the pulse width is not the maximum (eg, 160 gray scale).

Referring to FIG. 4, it can be seen that all data enable signals are terminated at the end of the scan waveform of (a). That is, the precharging start time varies according to the size of the data enable signal. This is because the data enable signals of data 1 and data 2 which turn on the organic EL pixels are different from each other, and thus the precharge starts at different points.

At this time, when the precharge signal changes to high and the precharge switch 202c is turned on, the current set in the precharge constant current source 201a during the high period of the precharge signal is transmitted through the switch 202c. Is applied at 202d. Then, when the precharge signal turns low and the precharging is completed, the pixel switch 202c is turned on by the data enable signal, and the organic EL pixel 202d has a constant current source for the pixel during the high period of the data enable signal. The current set at 202a is applied through the switch 202c. At this time, regardless of the magnitude of the data enable signal, the time point at which all of the data enable signals end is the same as the end point of the scan waveform.

5A to 5E are operation waveform diagrams of the respective portions by the rising sink as shown in FIG. 3, which differs from FIG. 3 in that the precharge level is intermediate.

That is, the total precharge time coincides with the beginning of the scan time, but the start time of the precharge signal for turning on the actual precharge switch 201c becomes the middle part of the entire precharge time, not the beginning of the scan time. . Referring to FIGS. 5B and 5D, it can be seen that the time points at which the precharge signals of the data 1 and 2 change to high are all in the middle of the entire precharge signal.

As such, the total precharge time is the same as the start time of the scan waveform, but the on time of the switch 201c becomes a specific part of the total precharge time according to the magnitude of the precharge signal for turning on the switch 201c. For example, as the actual precharge time is longer, the on-time of the switch 201c corresponds to the front of the entire precharge time, and as the actual precharge time is shorter, the on-time of the switch 201c is to the rear of the overall precharge time. Yes.

Since the subsequent operation is the same as in FIG.

6 (a) to 6 (e) are operation waveform diagrams of the respective parts by the polling sink as shown in FIG. 4, and differ from FIG. 4 in that the precharge level is intermediate.

Similarly in Fig. 6, all data enable signals are terminated at the end of the scan time. The precharge is completed before the data enable signal goes high, that is, before the switch 202c starts on. At this time, since the data enable signals of data 1 and data 2 which turn on the organic EL pixels are different from each other, the precharge starts at different points.

In addition, the precharge signal for turning on the precharge switch 201c turns high from a predetermined portion of the entire precharge time and then maintains a high state for a preset precharge time.

At this time, when the precharge signal changes to high and the precharge switch 202c is turned on, the current set by the precharge constant current source 201a during the high period of the precharge signal is transmitted through the switch 202c. Is applied to the pixel 202d. Then, when the precharge signal turns low and the precharging is completed, the pixel switch 202c is turned on by the data enable signal, and the organic EL pixel 202d has a constant current source for the pixel during the high period of the data enable signal. The current set at 202a is applied through the switch 202c. At this time, regardless of the magnitude of the data enable signal, the time point at which all of the data enable signals end is the same as the end point of the scan waveform.

On the other hand, the present invention may be provided separately from the pre-charge constant current source, or by turning on a plurality of constant current sources made in the IC at the same time to control the total power during precharging by using as a pre-charge constant current source. have.

According to the driving circuit of the current-driven display element according to the present invention as described above, the organic EL pixel driving current and the pre-charging constant current source for precharging the pixel are separately provided. By controlling the driving of the EL pixel, not only the amount of current applied to the organic EL pixel can be reduced, but also the desired luminance can be easily obtained by adjusting the response time of the capacitance inside the pixel.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (6)

A scan driver driven by a scan signal, a constant current source for pixels controlled on / off by a data enable signal, and an organic EL driver composed of organic EL pixels emitting light when the scan driver is turned on, In the driving circuit of the current-driven display device provided with: And a precharge section for precharging the organic EL pixels immediately before a data enable signal is activated in each of the organic EL driver sections. The method of claim 1, wherein the precharge portion A drive of a current-driven display element comprising a constant current source for precharging which is turned on by a precharge signal for controlling the precharge time in an organic EL pixel and supplies a current for precharging to the organic EL pixel. Circuit. The method of claim 2, And controlling the amount of current output from the precharge constant current source by controlling a bias of the precharge constant current source from the outside. The method of claim 1, wherein the precharge portion And when the organic EL pixel is turned on at the rising sink, precharging of the organic EL pixel is started at a start point of a scan signal. The method of claim 1, wherein the precharge portion And a precharge is started before the data enable signal is activated when the organic EL pixel is turned on at the falling sync. The method of claim 1, wherein the precharge portion And a plurality of constant current sources designed for the organic EL driver are simultaneously turned on and used as a constant current source for purge charge.