JP2009204757A - Organic el display device and method of driving the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL display device capable of maintaining high display quality even when adjusting a beam attenuation rate, and to provide a method of driving the same. <P>SOLUTION: The organic EL display device includes: an organic EL panel 1 of a dot matrix type; scanning switch means 61 to 6m which allow scanning lines S1 to Sm to freely connect to a first potential or second potential; drive switch means 71 to 7n which allow drive lines D1 to Dn to freely connect to a drive current source 70 or off potential; and a control means 8 which allows the scanning switch means 61 to 6m to connect the scanning lines S1 to Sm to the first potential to successively select the scanning lines S1 to Sm, controls the connection state of the drive switch means 71 to 7n, and adjusts the beam attenuation rate of light emitting pixels E11 to Emn. The control means 8 changes a drawing frame frequency for successively selecting the scanning lines according to the beam attenuation rate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an organic EL display device having a dot matrix type organic EL panel having a plurality of anode lines and a plurality of cathode lines, and a driving method thereof.

  Conventionally, various dot matrix type organic EL panels have been proposed, and for example, disclosed in Patent Document 1. In such an organic EL panel, a plurality of anode lines (hereinafter referred to as drive lines) made of a conductive transparent film such as ITO are formed in a stripe shape on a translucent substrate, and an organic layer is formed on the back surface of the drive lines. A plurality of cathode lines (hereinafter referred to as scanning lines) made of a metal vapor deposition film such as aluminum are formed on the back surface of the organic layer so as to be orthogonal to the drive lines. A light-emitting pixel (organic EL element) is formed by sandwiching layers, and has attracted attention as a display capable of reducing power consumption, high display quality, and thickness in place of a liquid crystal display.

  The organic EL display device includes an organic EL panel 1, a cathode drive circuit 2, an anode drive circuit 3, a control unit 4, and a reset circuit 5 (see FIG. 4). The organic EL panel 1 has light emitting pixels E11 to Emn arranged in a matrix. The light emitting pixels E11 to Emn are provided at intersections between a plurality of scanning lines S1 to Sm provided in the vertical direction and drive lines D1 to Dn provided in the horizontal direction so as to be orthogonal to the scanning lines S1 to Sm. ing. The light emitting pixels E11 to Emn are represented by an equivalent circuit including a diode and a capacitor arranged in parallel (see FIG. 5). However, in order to prevent the drawing from becoming complicated, in FIG. 4, the light emitting pixels E <b> 11 to Emn are illustrated only by diodes.

  The cathode drive circuit 2 includes a plurality of scan switches 21 to 2m corresponding to the scan lines S1 to Sm. The scanning switches 21 to 2m selectively connect the scanning lines S1 to Sm to the non-selection potential Vb or the ground potential (0V) based on the control signal of the control unit 4. The period in which each of the scanning lines S1 to Sm is sequentially selected once is referred to as “drawing frame period”, and the reciprocal of the drawing frame period is referred to as “drawing frame frequency”.

  The anode drive circuit 3 makes it possible to connect the drive currents from the constant current sources 30 to the drive lines D1 to Dn, and to supply the drive currents individually to the drive lines D1 to Dn. It comprises drive switches 31 to 3n. Switching of each of the drive switches 31 to 3n is determined based on a control signal from the control unit 4.

  The control unit 4 outputs control signals to the cathode drive circuit 2 and the anode drive circuit 3, respectively, and scan switches corresponding to the scan lines S1 to Sm and the drive lines D1 to Dn necessary for causing the light emitting pixels E11 to Emn to emit light. 21 to 2m and drive switches 31 to 3n are selectively turned on / off.

  The reset circuit 5 includes a plurality of reset switches 50 respectively connected to the drive lines D1 to Dn. The reset switch 50 connects the drive lines D1 to Dn to the ground potential while any of the scan lines S1 to Sm is selected after the scan switches 21 to 2m are selected. The electric charges charged in the light emitting pixels E11 to Emn are discharged. The period during which the charges charged in the light emitting pixels E11 to Emn by the reset circuit 5 are discharged is referred to as “reset period”. In the reset period, not only the drive lines D1 to Dn but also the scan lines S1 to Sm are connected to the ground potential.

  The control unit 4 sequentially turns on the scanning switches 21 to 2m, sequentially selects the scanning lines S1 to Sm, and turns on / off each of the drive switches 31 to 3n, thereby causing the organic EL panel 1 to have characters, figures, and the like. Is displayed. The driving method of the organic EL panel 1 as described above is called “simple matrix method” or “passive matrix method”.

  PWM (Pulse Width Modulation) is known as a method for adjusting the dimming rate of the organic EL panel 1. PWM adjusts the light attenuation rate according to the pulse width of the drive waveform, that is, the duty ratio of the drive waveform. For example, the pulse width W2 of the drive waveform is changed to the pulse width at the light attenuation rate of 0% (maximum luminance). If it is set to 20% of W1, the light attenuation rate becomes 80% (see FIG. 6). According to PWM, the dimming rate of the organic EL panel 1 can be changed in a range of about 0 to 99%.

As another method, Patent Document 2 provides a lighting frame that causes the light emitting pixels E11 to Emn to emit light according to the light attenuation rate and a thinning frame that does not cause the light emitting pixels E11 to Emn to emit light. A method of intermittently thinning out is disclosed.
JP-A-11-311978 JP 2006-64980 A

  However, when driving the light-emitting pixels E11 to Emn, which are organic EL elements, a waveform rounding phenomenon occurs at the rise of the drive voltage waveform as shown in FIG. This is caused by the impedance in the organic EL panel or the connection part of the wiring and the electrostatic capacitance of the light emitting pixels E11 to Emn itself, and the degree (time) varies depending on the design conditions. When performing dimming control by PWM, there is a problem that the ratio of the rounded portion to the light emission time is large, and the rounding is different depending on the number of pixels to be lit, so that the user perceives display unevenness. . In addition, in the method of intermittently thinning the light emission of the light emitting pixels E11 to Emn by providing a thinning frame, it takes a long time for the non-light emitting state to continue, which may cause display flickering and impair display quality. There was a problem. The present invention has been made in view of the above problems, and provides an organic EL display device capable of maintaining high display quality even when adjusting the light attenuation rate, and a driving method thereof. Objective.

  In order to solve the above problems, the present invention provides a dot matrix type organic EL panel having a plurality of scanning lines and a plurality of drive lines and having light emitting pixels provided in a matrix, and the scanning lines are connected to a first potential. Alternatively, the scan switch means that can be connected to the second potential, the drive switch means that allows the drive line to be connected to a drive current source or an off potential, and the scan switch means to connect the scan line to the first potential. A control means for sequentially selecting the scanning lines and controlling a connection state of the drive switch means, and adjusting a dimming rate of the light-emitting pixels, wherein the control The means is characterized by changing a drawing frame frequency for sequentially selecting the scanning lines in accordance with the light attenuation rate.

  The control means may change the drawing frame frequency by changing a source oscillation frequency.

  The control means may change the drawing frame frequency by changing the number of source oscillations counted in one frame.

  Further, the control means adjusts the light attenuation rate by changing a duty ratio of a drive waveform.

  The present invention includes a dot matrix type organic EL panel having a plurality of scanning lines and a plurality of drive lines and having light emitting pixels provided in a matrix, and connecting the scanning lines to a first potential or a second potential. The drive line can be freely connected to a drive current source or an off-potential, the scan line is connected to the first potential, the scan line is sequentially selected and the connection state of the drive line is controlled, A driving method of an organic EL display device that adjusts a light attenuation rate of the light emitting pixels, wherein a drawing frame frequency for sequentially selecting the scanning lines is changed according to the light attenuation rate.

  Further, the drawing frame frequency is changed by changing a source oscillation frequency.

  The drawing frame frequency is changed by changing the number of source oscillations counted in one frame.

  Further, the dimming rate is adjusted by changing the duty ratio of the driving waveform.

  The present invention relates to an organic EL display device having a dot matrix type organic EL panel having a plurality of anode lines and a plurality of cathode lines, and a method for driving the organic EL display device. Display quality can be maintained.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. 1 to 3 show this embodiment. The organic EL display device includes an organic EL panel 1, a cathode drive circuit 6, an anode drive circuit 7, a control unit 8 (control means), and a reset circuit 5.

  The organic EL panel 1 has light emitting pixels E11 to Emn arranged in a matrix. The light emitting pixels E11 to Emn are provided at intersections between a plurality of scanning lines S1 to Sm provided in the vertical direction and drive lines D1 to Dn provided in the horizontal direction so as to be orthogonal to the scanning lines S1 to Sm. ing.

  The cathode driving circuit 6 includes a plurality of scanning switches 61 to 6m (scanning switch means) corresponding to the scanning lines S1 to Sm. Each of the scanning switches 61 to 6m includes a first transistor Tr1 that connects the scanning lines S1 to Sm to the ground potential (first potential), and a first transistor that connects the scanning lines S1 to Sm to the non-selection potential Vb (second potential). And a second transistor Tr2 (see FIG. 2). The first transistor Tr1 is an N-channel transistor, and the second transistor Tr2 is a P-channel transistor. In FIG. 1, in order to prevent the drawing from being complicated, one of the first transistor Tr1 and the second transistor Tr2 is shown for each of the scan switches 61 to 6m.

  The first transistor Tr1 and the second transistor Tr2 have gates Ga and Gb, sources Sa and Sb, and drains Da and Db, respectively. The source Sa of the first transistor Tr1 is connected to the ground potential, and the drain Da is connected to the scanning lines S1 to Sm. The first transistor Tr1 connects the scanning lines S1 to Sm to be selected to the ground potential based on the drive signal input from the gate Ga. The source Sb of the second transistor Tr2 is connected to the non-selection potential Vb, and the drain Db is connected to the scanning lines S1 to Sm. The second transistor Tr2 connects the unselected scanning lines S1 to Sm to the non-selection potential Vb based on the drive signal input from the gate Gb. The scanning lines S1 to Sm are sequentially selected by the scanning switches 61 to 6m.

  The reset circuit 5 includes a plurality of reset switches 50 respectively connected to the drive lines D1 to Dn. The reset switch 50 connects the drive lines D1 to Dn to the ground potential while any of the scan lines S1 to Sm is selected after the scan switches 61 to 6m are selected. The electric charges charged in the light emitting pixels E11 to Emn are discharged.

  The anode drive circuit 7 includes a constant current source 70 (drive current source) that individually supplies a drive current corresponding to each drive line D1 to Dn, and each drive line D1 to Dn based on a control signal from the control unit 8. Are selectively connected to a constant current source 70 or a ground potential (off potential).

  The control unit 8 includes a display controller. For example, when vehicle travel information is input by various sensors, the controller 8 performs predetermined calculation processing and displays various information such as vehicle speed, engine speed, and remaining fuel on the organic EL panel 1. In order to achieve this, a control signal is output to each of the cathode drive circuit 2 and the anode drive circuit 7, and the scan switches 61 corresponding to the scan lines S1 to Sm and the drive lines D1 to Dn necessary for causing the light emitting pixels E11 to Emn to emit light. The predetermined information is displayed on the organic EL panel 1 by selectively turning on and off ˜6 m and drive switches 71 to 7 n. The control unit 8 has a PWM circuit 8a, and adjusts the light attenuation rate by changing the duty ratio of the drive waveform by the PWM circuit 8a.

  Further, when adjusting the dimming rate, the control unit 8 changes the duty ratio of the drive waveform and also changes the drawing frame frequency for sequentially selecting the scanning lines S1 to Sm according to the dimming rate. For example, FIG. 3A shows a driving waveform in the case where the scanning lines S1 to Sm are sequentially selected at a light attenuation rate of 0% (maximum luminance) and a drawing frame frequency of 120 Hz. On the other hand, when it is determined to increase the light attenuation rate (decrease the light emission luminance), the control unit 8 decreases the duty ratio of the drive waveform as shown in FIG. 3B, for example. The drawing frame frequency is changed based on the dimming rate / drawing frame frequency control table. In FIG. 3B, the drawing frame frequency is 80 Hz. In this case, although the duty ratio of the drive waveform can be lowered in accordance with the adjustment of the dimming rate, the drawing frame cycle becomes longer by further lowering the drawing frame frequency, and the actual pulse width W4 of the driving waveform has a dimming rate of 0%. The pulse width W3 is longer than when the pulse width W3 is simply shortened at the drawing frame frequency at the time, and the ratio of the drive waveform rounding to the pulse width W4 can be suppressed, and display unevenness occurs due to the rounding of the drive waveform. This can be suppressed and high display quality can be maintained. Note that the drawing frame frequency with respect to the dimming rate is appropriately determined according to various conditions, and even if the drawing frame frequency is continuously changed by the dimming rate, it is changed in stages. It may be a thing.

  Further, the control unit 8 changes the drawing frame frequency by a method of changing the source oscillation frequency or a method of changing the number of source oscillations counted in one frame.

  As described above, according to the present embodiment and its driving method, when adjusting the dimming rate by changing the duty ratio of the driving waveform, the scanning lines S1 to Sm are sequentially arranged according to the adjusted dimming rate. By changing the drawing frame frequency to be selected, it is possible to maintain high display quality even when adjusting the light attenuation rate.

  Further, the conventional method of providing a thinned frame cannot change the non-lighting time itself, whereas the method of changing the drawing frame frequency of the present invention does not cause a flicker phenomenon (display flicker) to be not significant. The lighting time can be adjusted and high display quality can be maintained.

1 is a configuration diagram of an organic EL display device showing a first embodiment of the present invention. The circuit diagram of the scanning switch which shows embodiment same as the above. The drive waveform figure which shows embodiment same as the above. The block diagram of the organic electroluminescence display which shows a prior art example. Explanatory drawing of the equivalent circuit of the pixel which shows a prior art example same as the above. The drive waveform figure which shows a prior art example same as the above.

Explanation of symbols

1 Organic EL panel S1 to Sm Scan line D1 to Dn Drive line 61 to 6m Scan switch (scan switch means)
71-7n Drive switch (drive switch means)
8 Control unit (control means)
8a PWM circuit 70 Drive current source (constant current source)

Claims (8)

A dot matrix type organic EL panel having a plurality of scanning lines and a plurality of drive lines and having light emitting pixels provided in a matrix;
Scanning switch means for freely connecting the scanning line to a first potential or a second potential;
Drive switch means for freely connecting the drive line to a drive current source or an off-potential;
Control means for connecting the scan lines to the first potential by the scan switch means to sequentially select the scan lines, to control the connection state of the drive switch means, and to adjust the dimming rate of the light emitting pixels An organic EL display device comprising:
The organic EL display device, wherein the control means changes a drawing frame frequency for sequentially selecting the scanning lines in accordance with the light attenuation rate. The organic EL display device according to claim 1, wherein the control unit changes the drawing frame frequency by changing a source oscillation frequency. 2. The organic EL display device according to claim 1, wherein the control unit changes the drawing frame frequency by changing a source oscillation number to be counted in one frame. The organic EL display device according to claim 1, wherein the control unit adjusts the dimming rate by changing a duty ratio of a drive waveform. A dot matrix type organic EL panel having a plurality of scanning lines and a plurality of drive lines and having light emitting pixels provided in a matrix, the scanning lines being freely connectable to a first potential or a second potential, The drive line can be freely connected to a drive current source or an off-potential, the scan line is connected to the first potential, the scan lines are sequentially selected, and the connection state of the drive line is controlled. A driving method of an organic EL display device for adjusting a light attenuation rate,
A driving method of an organic EL display device, wherein a drawing frame frequency for sequentially selecting the scanning lines is changed according to the light attenuation rate. 6. The method of driving an organic EL display device according to claim 5, wherein the drawing frame frequency is changed by changing a source oscillation frequency. 6. The method of driving an organic EL display device according to claim 5, wherein the drawing frame frequency is changed by changing a source oscillation number to be counted in one frame. 6. The method of driving an organic EL display device according to claim 5, wherein the dimming rate is adjusted by changing a duty ratio of a driving waveform.

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