JP6079115B2 - Organic EL display device and drive control method thereof - Google Patents

Description

The present invention relates to an organic EL display device and a drive control method thereof .

  Conventionally, an organic EL display device using an active matrix has been proposed in Patent Document 1, for example. In this prior art, a technique is described in which a voltage is held in a storage capacitor, a current flowing through the organic EL is controlled by the held voltage, and the organic EL emits light with a duty factor close to 100%.

JP-A-8-234683

  However, in the above conventional technique, the active drive in the organic EL display device is in a state close to DC drive. In the case of DC driving, there is a problem that even if the organic EL pixel is driven at a constant current, the luminance of the pixel changes greatly due to the change in environmental temperature.

  This will be described with reference to FIGS. First, as shown in FIG. 7, normally, in order to cause a pixel to emit light, a selection voltage is selected during 1H (horizontal scanning period) during 1V (vertical synchronization period), and the pixel voltage is reset by a reset voltage at time t1. Data is erased, and data is written with a write voltage at time t2. Thereby, the current I2 flowing through the light emitting element becomes Ia, and light emission is maintained during the period t3.

  Here, the amplitude of the light emission waveform differs greatly between high temperature and low temperature. That is, the luminance ratio Lha: Lla at high temperature and low temperature is increased. The inventors examined this cause in detail.

FIG. 8 shows the relationship of the luminance L [cd / m ² ] to the constant current I2 [μA / pixel] flowing through the light emitting element, that is, the IL characteristic at the time of DC driving. As shown in this figure, when the temperature is TH ° C., the luminance L of the pixel is Lha when the current Ia is passed as the constant current I2. On the other hand, when the temperature is TL ° C. lower than TH ° C., even if a current Ia having the same magnitude as the constant current I2 is passed, the luminance L becomes Lla smaller than Lha.

  That is, although the same current Ia is applied at both high and low temperatures, the luminance at high temperature is Lha, the luminance at low temperature is Lla, and the luminance change due to temperature increases per luminance used.

  In FIG. 8, I2 shows the vicinity of Ia where the current is low, but when looking up to the range near Ib where the current is large, the luminance at Ib is Lhb at a high temperature of TH ° C. as shown in FIG. At low temperature of TL ° C., it is Llb. In FIG. 9, the area surrounded by the alternate long and short dash line corresponds to FIG. Referring to FIG. 9, the luminance change rate due to the temperature change at the current Ib is Llb / Lhb. On the other hand, when FIG. 8 is seen, the luminance change rate by the temperature change at the time of the current Ia is Lla / Lha. When both luminance change rates are compared, the luminance change rate when the current is Ib is smaller than the luminance change rate when the current is Ia.

Therefore, in view of the above points, the present invention has an object to provide an organic EL display device and a drive control method thereof that can reduce a luminance change due to a temperature change.

  In order to achieve the above object, according to the first aspect of the present invention, a light emitting element (34) is formed at each intersection of a plurality of scanning lines (35) and a plurality of signal lines (36) arranged in a matrix. ing.

  Further, a writing process is performed in which a selection signal is input to one scanning line of the plurality of scanning lines (35) and a writing signal is input to one signal line that intersects one scanning line among the plurality of signal lines (36). As a result, a current is passed through one light emitting element formed at the intersection of one scanning line and one signal line to emit light, and a reset signal is input to one scanning line and a reset signal is input to one signal line. The control means (20, 40) for performing the normal control for stopping the current flowing through one light emitting element is provided.

  And it is an organic electroluminescence display which displays an image by making the light emitting element (34) of each intersection light-emit by a control means (20, 40), Comprising: The following points are characterized.

  That is, the control means (20, 40) causes the one light emitting element to emit light by performing a writing process on one light emitting element (34) at each intersection, and then causes the one light emitting element to emit light. Before performing the reset process on the light emitting element, by performing the reset process on the one light emitting element in synchronization with the reset process on the other light emitting element among the light emitting elements (34) at each intersection, a current is supplied to the one light emitting element. PWM control is performed to shorten the flowing period.

  According to this, the display which reduced the apparent brightness | luminance of the light emitting element (34) by PWM control can be performed. For this reason, the brightness | luminance change by the temperature change of a light emitting element (34) can be made small.

According to the first aspect of the present invention, the temperature range of a pixel constituted by one light emitting element is TL ° C. to TH ° C., and the luminance of the pixel at TL ° C. is Llc and Let the luminance change rate when the luminance of the pixel is Lhc be Llc / Lhc. The current flowing through one light-emitting element is set so that the luminance change rate Llc / Lhc is equal to or less than the allowable luminance change rate Llc / Lhc in the range of TH ° C to TL ° C. The duty k is set so that the apparent brightness of Lhc / k becomes . When switching the image display from the image in which the light emitting pixels and the non-light emitting pixels are mixed before the image display switching, the control means (20, 40) switches the image display for the plurality of light emitting elements (34). It is characterized in that normal control is performed before, PWM control is performed after switching of the image display, and normal control is returned after a predetermined time has elapsed from switching of the image display .

Thereby, in the pixel, the luminance change rate due to the temperature change can be suppressed to an allowable amount or less.
Although the organic EL display device has been described above, the same effect as described above can be obtained with the drive control method for the organic EL display device according to claim 2 .

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim shows the correspondence with the specific means as described in embodiment mentioned later.

1 is a block diagram of an organic EL display device according to a first embodiment of the present invention. It is the figure which showed the circuit which drives the light emitting element in an organic electroluminescent panel. It is a timing chart for demonstrating the operation | movement which carries out PWM control synchronizing with the reset process which concerns on another light emitting element. It is a figure for demonstrating the duty ratio which concerns on 2nd Embodiment of this invention. In 2nd Embodiment, it is the figure which showed the relationship between the electric current which flows into a light emitting element, and the brightness | luminance by the difference in temperature. In 2nd Embodiment, it is the figure which showed the relationship between a light control rate and a duty ratio. It is a figure for demonstrating a subject. It is a figure for demonstrating a subject. It is a figure for demonstrating a subject.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the organic EL display device includes a power supply circuit 10, a drive circuit 20, an organic EL panel 30, and a control circuit 40.

  The power supply circuit 10 generates a constant voltage for driving the drive circuit 20 and the control circuit 40, respectively. In other words, the power supply circuit 10 generates a constant voltage required by the drive circuit 20 and the control circuit 40 from the voltage input from the external power supply, and outputs it to the drive circuit 20 and the control circuit 40, respectively.

  The drive circuit 20 performs image display on the organic EL panel 30 based on a command input from the control circuit 40, and includes a column driver 21 that supplies a predetermined signal to the organic EL panel 30 and a row driver that supplies a predetermined signal. 22 is provided. The drive circuit 20 drives and displays one frame at a predetermined cycle.

  The organic EL panel 30 serves as a screen for image display, and performs image display by driving the column driver 21 and the row driver 22 of the drive circuit 20. The organic EL panel 30 has a plurality of signals arranged in a matrix (for example, M × N: M, N is an integer of 2 or more, M is the number of scanning lines, and N is the number of signal lines). A light emitting element is formed at each intersection of the line and the scanning line. A signal is supplied from the row driver 22 to the scanning line, and a signal is supplied from the column driver 21 to the signal line.

  As shown in FIG. 2, one pixel in the organic EL panel 30 includes a first transistor 31 (T1), a second transistor 32 (T2), a capacitor 33 (C), and a light emitting element 34 (OLED). Yes.

  Each of the first transistor 31 and the second transistor 32 is a P-type MOS transistor. The gate of the first transistor 31 is connected to the scanning line 35 (Vscan1), the source (S) is connected to the signal line 36 (Vsig), and the drain (D) is connected to the gate (G) of the second transistor 32. Yes.

  The source of the second transistor 32 is connected to the power supply (Vcc), and the drain is connected to the light emitting element 34. The light emitting element 34 is connected to a cathode voltage (Vcath). The capacitor 33 is connected between the gate and source of the second transistor 32.

  Although two light emitting elements 34 are shown in FIG. 2, the light emitting elements 34 are actually formed at the intersections of the scanning lines 35 and the signal lines 36 arranged in a matrix as described above.

  At the time of driving the organic EL panel 30 as described above, the M scanning lines are periodically scanned by the row driver 22 in the driving circuit 20, and the desired signal line among the N signal lines is transferred to the driving circuit 20. An image is displayed by applying a voltage signal from the column driver 21 and causing the light emitting elements 34 formed at the intersections of the scanning lines and the signal lines to emit light.

  The control circuit 40 is a circuit that processes image data input from the outside and outputs a drive command for the organic EL panel 30 to the drive circuit 20. Further, when the control circuit 40 operates the drive circuit 20 to cause the light emitting element 34 of the organic EL panel 30 to emit light, the control circuit 40 performs PWM control while increasing the current value in order to reduce the luminance change due to the temperature change of the light emitting element 34. To do. As a result, the apparent luminance of the light emitting element 34 is lowered to reduce the luminance change due to the temperature change. The control circuit 40 is composed of, for example, a microcomputer.

  The above is the overall configuration of the organic EL display device according to the present embodiment. The organic EL panel 30, the drive circuit 20, the control circuit 40, and the power supply circuit 10 are modularized, for example.

  Next, an operation for causing the light emitting element 34 of one pixel to emit light will be described with reference to FIGS. The light emitting operation of the light emitting element 34 is performed based on a command received from the control circuit 40 by the drive circuit 20 of FIG. Further, the current I2 flowing through the second transistor 32 is Ib. Here, the current Ib is set so that Lhb / k = Lha. Further, the time between the time points Ti (i = 0, 1,...) And Ti + 1 in FIG.

First, the reset voltage (V2) and the write voltage (V′3) are applied to the signal line 36 (Vsig) at a predetermined cycle. For example, from time T0 to time T1 by applying a reset voltage (V2), it is from time T1 to time T2 to apply a write voltage (V '3), repeating this. Further, when the selection voltage is applied to the scanning line 35 (Vscan), the reset voltage / writing voltage applied to the signal line 36 (Vsig) becomes effective. Hereinafter, the reset voltage is also referred to as a reset signal. The write voltage is also referred to as a write signal.

  First, the light emitting element 34 related to the scanning line 35 of Vscan1 is caused to emit light. At time T0, a selection voltage (0 [V]) is applied to the scanning line 35 (Vscan1) with respect to the light emitting element. As a result, the first transistor 31 is turned on, and the data stored in the capacitor 33 is reset. Further, since the voltage difference between the gate and the source of the second transistor 32 becomes small, the second transistor 32 is turned off, and the current I2 flowing through the light emitting element 34 related to Vscan1 becomes I2 = 0. The cathode voltage (Vcath) is 0 [V], for example, and V2 is the same voltage as Vcc, for example.

  Subsequently, when a write voltage (V′3) is applied to the signal line 36 (Vsig) at time T <b> 1, the write voltage (V′3) is written to the capacitor 33 as data. Further, the second transistor 32 is turned ON, and a current of I2 = Ib flows through the light emitting element 34. Thereby, the light emission waveform has a predetermined luminance. As described above, the process of causing the light emitting element 34 to emit light by inputting a selection signal to one scanning line and inputting a writing signal to one signal line is a writing process.

  Thereafter, the non-selection voltage (V1) is applied to the scanning line 35 (Vscan1) related to the light emitting element 34 at time T2. Accordingly, the first transistor 31 is turned off, while the second transistor 32 is continuously turned on, so that the light emitting element 34 continues to emit light. A period from time T0 to time T2 is 1H (horizontal scanning period). Note that V′3 is, for example, 0 [V] ≦ V′3 ≦ Vcc [V], and V1 is, for example, the same voltage as Vcc.

  Here, in the case of light emission under normal control, the current flowing through the light emitting element (34) is stopped at a time T (2M) when a fixed time has elapsed from time T2, that is, when 1 V (vertical synchronization period) has elapsed since time T0, stop. In this case, a selection signal is input to one scanning line and a reset signal is input to one signal line. The reset process at this time T (2M) is the reset process of the normal control.

  Similarly, the light emitting element 34 related to the scanning line 35 of Vscan2 is caused to emit light. At time T2, by applying a selection voltage (0 [V]) to the scanning line 35 (Vscan2) with respect to the light emitting element 34, the first transistor 31 related to Vscan2 is turned on, and the data of the capacitor 33 is reset. . At time T3, the second transistor 32 is turned on by applying the write voltage (V′3) to the signal line 36 (Vsig) and writing data to the capacitor 33, and the light emitting element 34 related to Vscan2 has I2 = Ib. Current flows. Thereby, the light emitting element 34 emits light.

  Thereafter, by applying a non-selection voltage (V1) to the scanning line 35 of Vscan2 at time T4, the first transistor 31 related to Vscan2 is turned OFF and the second transistor 32 is kept ON, so that light emission related to Vscan2 is emitted. The element 34 continues to emit light. In FIG. 3, the current waveform and the light emission waveform of the light emitting element 34 according to Vscan2 are omitted.

  When displaying an image on the organic EL panel 30 by causing a large number of pixels to emit light, the screen of the organic EL panel 30 is input by inputting desired signals to the plurality of scanning lines 35 and the plurality of signal lines 36 respectively at desired timings. The desired image is displayed throughout.

  Next, in the operation of causing each light emitting element 34 to emit light as described above, when one light emitting element 34 emits light, the brightness of the one light emitting element 34 is synchronized with the reset of the other light emitting element 34. The operation of dropping the image will be described.

  As described above, after the light emitting element 34 related to the scanning line 35 of Vscan1 emits light, the scanning line of Vscan1 is synchronized with resetting of the other light emitting elements 34 from time T (2j) to time T (2j + 1). A selection voltage (0 [V]) is applied to 35. Thereby, at the time T (2j), the first transistor 31 is turned on by the selection voltage (0 [V]), the data of the capacitor 33 is reset, and the second transistor 32 is turned off. For this reason, after the time T (2j), no current flows through the light emitting element 34 related to Vscan1, and the light emission waveform becomes zero as shown in FIG.

  Thus, before performing the normal control for the light emitting element 34 related to Vscan1, that is, the reset process at time T (2M) when 1 V (vertical synchronization period) has elapsed, Vscan1 is synchronized with the reset process of the other light emitting elements 34. The light emitting element 34 according to the above is reset. With such advance reset processing, PWM control that shortens the period during which current flows through the light emitting element 34 can be performed.

  Here, the light emission of the light emitting element 34 according to Vscan1 is maintained from time T2 to time T (2j). That is, this reset operation is an operation for PWM control of the light emitting element 34, and the apparent luminance is set to {T (2j) -T1} / {T (2M) -T1 by PWM control while driving the light emitting element 34 with a large current. }. Here, if {T (2M) −T1} / {T (2j) −T1} is represented by k, the luminance is reduced to 1 / k by this reset operation. According to such a driving method, the time during which the light emitting element 34 is allowed to emit light is shortened, so that the luminance change due to the temperature change can be reduced. That is, since the luminance ratio between the high-temperature luminance Lhb and the low-temperature luminance Llb of the light-emitting element 34 is Lhb: Llb, the apparent luminance is Lhb / k: Llb / k. When the conventional light emitting method that emits most of 1V so that the current Ia flows in the organic EL is used, the luminance change when changing from TH ° C. to TL ° C. is Lha: Lla. When Lhb / k (= Lha): Llb / k of the present invention is compared with Lha: Lla of the conventional method, a relative luminance change with respect to the same temperature change can be reduced.

  Further, in the conventional driving method, when the same display is displayed on the organic EL panel 30 for a long time, the temperature of the light emitting pixel rises, and the temperature differs from the temperature of the non-light emitting pixel. When the display is switched after entering such a state, among the light-emitting elements that should shine with the same luminance after switching, pixels whose temperature is high due to the display before switching brightly shines, and pixels whose temperature is low due to the display before switching are displayed. It glows dark. However, if the driving method according to the present embodiment is used, the difference in luminance due to the temperature change of the light emitting element 34 can be reduced.

  Then, after the time point T (2j + 1), the current waveform of the light emitting element 34 related to the scanning line 35 of Vscan2 is set to 0 by resetting the data of the capacitor 33 in synchronization with the resetting of the other light emitting elements 34. . In this manner, the PWM control is also performed on the light emitting element 34 related to Vscan2.

  For example, when the entire scanning line 35 is M = 480 lines and the reset operation after the start of light emission of the first row is synchronized with the reset period from time T (240) to time T (241), that is, light emission of the 122th row. When synchronized with the pre-start reset operation, k = (960-1) / (240-1) ≈4.0. Of course, this is only an example, and the timing at which the reset is synchronized may be set as appropriate.

  As for the correspondence between the description of the present embodiment and the description of the claims, the drive circuit 20 and the control circuit 40 correspond to “control means” of the claims.

(Second Embodiment)
In the present embodiment, parts different from the first embodiment will be described. In the present embodiment, when the same display is performed on the organic EL panel 30 for a long time and the image display is switched thereafter, the control for the plurality of light emitting elements 34 is temporarily changed to PWM control at the moment when the image display is switched. . “Switching image display” means changing the display from the currently displayed image to another image. Thereby, the brightness | luminance change by a temperature change can be made small.

  Then, when a predetermined time has elapsed since the image display switching, the normal control that is not synchronized with the reset of the other light emitting elements 34 is restored. In other words, when a current flows through the light emitting element 34 and the temperature of the light emitting element 34 becomes constant, the control method is switched from PWM control to normal control.

  In this example, “normal control” refers to the following control. That is, the current flowing through the light emitting element 34 in the period t3 is set to Ia = Ib / k, and the selection voltage (0 [V]) is applied between time T (2j) and time T (2j + 1) in the scan signal Vscan1. The control method is as shown in FIG. The PWM control is the same as the method described in the first embodiment.

  In this case, the control circuit 40 counts a predetermined time, and when the predetermined time is reached, the control method for the drive circuit 20 is switched. Thereby, display unevenness after display switching can be prevented, and power can be saved.

(Third embodiment)
In the present embodiment, parts different from the first and second embodiments will be described. In this embodiment, the duty ratio k (see FIG. 4) of PWM control when the dimming rate is 100% is determined as shown in FIGS.

First, the duty ratio k is a ratio of a non-zero period with respect to one cycle. As shown in FIG. 4, assuming that one period is A and a period that is not zero in the period A is B, the duty ratio k is B / A. That is, B in one cycle A is a pulse width.

As shown in FIG. 5, assuming that the rate of change in luminance allowed in the range of TH ° C. to TL ° C. is Rac, when the current I2 [μA / pixel] flowing through the light emitting element 34 is Ic, Ic is Rac = The current value is Llc / Lhc. Further, as shown in FIG. 6, when Lr the target display luminance when the dimming ratio of 100%, de Yuti ratio k limit Bc / Ac becomes Bc / Ac = Lr / Lhc.

  As described above, when the current flowing through the light emitting element 34, the target display luminance, and the duty ratio of PWM control when the dimming rate is 100% are determined, the dimming rate lower than that is decreased. This can be achieved, and the display unevenness after the display switching in the organic EL panel 30 can be prevented at all dimming rates of 0 to 100%. Further, the change in luminance due to temperature can be made equal to or less than the allowable luminance change rate.

(Other embodiments)
The configuration of the organic EL display device described in each of the above embodiments is an example, and the present invention is not limited to the configuration described above, and may be another configuration that can realize the present invention. For example, the control circuit 40 and the drive circuit 20 can perform normal control as described above, but may perform only PWM control.

10 power supply circuit 20 drive circuit (control means)
30 Organic EL Panel 34 Light Emitting Element 35 Scanning Line 36 Signal Line 40 Control Circuit (Control Unit)

Claims (2)

A light emitting element (34) is formed at each intersection of a plurality of scanning lines (35) and a plurality of signal lines (36) arranged in a matrix,
Write processing for inputting a selection signal to one scanning line of the plurality of scanning lines (35) and inputting a writing signal to one signal line intersecting the one scanning line among the plurality of signal lines (36). By doing so, a current is caused to flow through one light emitting element formed at the intersection of the one scanning line and the one signal line, and the selection signal is input to the one scanning line and the reset signal is input to the one signal line. Control means (20, 40) for performing a normal control to stop the current flowing through the one light emitting element by performing a reset process.
An organic EL display device that displays an image by causing the light emitting element (34) at each intersection to emit light by the control means (20, 40),
The control means (20, 40) causes the one light emitting element to emit light by performing the writing process on one light emitting element among the light emitting elements (34) at each intersection, Before performing the reset process on one light emitting element, the one light emitting element is reset by synchronizing the reset process of the other light emitting elements among the light emitting elements (34) at each intersection. PWM control is performed to shorten the period during which current flows.
The temperature range of the pixel constituted by the one light emitting element is TL ° C. to TH ° C., the luminance of the pixel at the TL ° C. is Llc, and the luminance of the pixel at the TH ° C. is Lhc. If the luminance change rate at the time is Llc / Lhc,
The current flowing through the one light emitting element is set so that the luminance change rate Llc / Lhc is equal to or less than the allowable luminance change rate Llc / Lhc in the range of TH ° C to TL ° C. The duty k is set so that the actual apparent luminance is Lhc / k ,
When the image display is switched from an image in which light-emitting pixels and non-light-emitting pixels before image display switching are mixed, the control means (20, 40) performs the image on the plurality of light-emitting elements (34). The organic EL is characterized in that the normal control is performed before switching the display, the PWM control is performed after the switching of the image display, and the normal control is returned after a predetermined time has elapsed since the switching of the image display. Display device. A light emitting element (34) is formed at each intersection of a plurality of scanning lines (35) and a plurality of signal lines (36) arranged in a matrix,
Write processing for inputting a selection signal to one scanning line of the plurality of scanning lines (35) and inputting a writing signal to one signal line intersecting the one scanning line among the plurality of signal lines (36). By doing so, a current is caused to flow through one light emitting element formed at the intersection of the one scanning line and the one signal line, and the selection signal is input to the one scanning line and the reset signal is input to the one signal line. Control means (20, 40) for performing a normal control to stop the current flowing through the one light emitting element by performing a reset process.
A driving control method for an organic EL display device that performs image display by causing the light emitting element (34) at each intersection to emit light by the control means (20, 40),
The control means (20, 40) causes the one light emitting element to emit light by performing the writing process on one light emitting element among the light emitting elements (34) at each intersection, Before performing the reset process on one light emitting element, the one light emitting element is reset by synchronizing the reset process of the other light emitting elements among the light emitting elements (34) at each intersection. PWM control to shorten the period during which current flows in
The temperature range of the pixel constituted by the one light emitting element is TL ° C. to TH ° C., the luminance of the pixel at the TL ° C. is Llc, and the luminance of the pixel at the TH ° C. is Lhc. If the luminance change rate at the time is Llc / Lhc,
In the PWM control, the current flowing through the one light emitting element is set so that the luminance change rate Llc / Lhc is equal to or less than the allowable luminance change rate Llc / Lhc in the range of TH ° C. to TL ° C., and the duty is set to k. Then, the duty k is set so that the actual apparent luminance of the pixel is Lhc / k ,
When the image display is switched from an image in which light-emitting pixels and non-light-emitting pixels before image display switching are mixed, the control means (20, 40) performs the image on the plurality of light-emitting elements (34). The organic EL is characterized in that the normal control is performed before switching the display, the PWM control is performed after the switching of the image display, and the normal control is returned after a predetermined time has elapsed since the switching of the image display. A display device drive control method.

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