JP2005091717A - Display device and driving method of display panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control light emission luminance with sufficient accuracy as preventing poor light emission, to improve luminescence life and to further prevent electrode short circuit at an element insulation part. <P>SOLUTION: Organic EL elements E(1, 1) to E(m, n) are arranged to each intersection of scanning lines A(1) to A(m) and signal lines B(1) to B(n) like a matrix. A scanning driver IC8 sequentially connects the selected scanning lines A to a ground and switches unselected scanning lines A to the side of reverse bias voltage Vcc 1. A signal driver IC4 connects a signal line B to which an EL element E made to emit light is connected to a current source 6 and connects other signal lines B to the ground. Each frame is provided with a period for switching all scanning switches 9 to the side of the reverse bias voltage Vcc, switching all driving switches 5 to the ground side and impressing the reverse bias voltage Vcc to all the EL elements E. Bias voltage Vcc 1 is set to be almost equal to voltage which the EL elements are constantly burdened when drive current is supplied from the current source 6 to the EL elements E. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a display device that displays an image on a display panel including a plurality of light emitting elements arranged in a matrix, and a display panel driving method.

  FIG. 13 shows a display panel driving apparatus using a conventional organic EL (Electro Luminescence) element. In the display panel 1, each intersection of a plurality of scanning lines A (1) to A (m) (m is 64, for example) and a plurality of signal lines B (1) to B (n) (n is 128, for example). The organic EL elements E (1,1) to E (m, n) are arranged in a matrix with the scanning line A side as a cathode and the signal line B side as an anode. An equivalent circuit of the EL element E can be represented by using a light emitting element having diode characteristics and a parasitic capacitance connected in parallel to the light emitting element. In FIG. 13, the EL element E is represented by a diode symbol.

  The scanning driver IC 2 switches the scanning switches 3 (1) to 3 (m) provided for the scanning lines A (1) to A (m) at a constant period, and in the non-selected state, the scanning driver IC 2 moves to the reverse bias voltage Vcc side. The connected scanning lines A (1) to A (m) are sequentially connected to the ground side. In addition, the signal driver IC 4 sequentially switches the drive switches 5 (1) to 5 (n) provided for the signal lines B (1) to B (n) in synchronization with the scanning, so that the EL element E emits light. / Signal lines B (1) to B (n) are connected to current sources 6 (1) to 6 (n) or ground, respectively, according to non-light emission. With this configuration, it is possible to cause the EL element E at an arbitrary intersection point to emit light.

  For example, when the EL element E (1,2) and the EL element E (1, n-1) are caused to emit light, the scanning switch 3 (1) is switched to the ground side as shown in FIG. Switches 3 (2) -3 (n) are switched to the reverse bias voltage Vcc side. The drive switches 5 (1) and 5 (n-1) are switched to the current sources 6 (1) and 6 (n-1), respectively, and the drive switches 5 (2) to 5 (n-2), 5 Switch (n) to the ground side. As a result, only the EL elements E (1,1) and E (1, n-1) are supplied with a drive current to emit light. By performing such scanning at high speed, the EL element E at an arbitrary position is caused to emit light, and the human eye can visually recognize that a plurality of EL elements E are simultaneously emitting light, thereby causing the display panel 1 to display image data. Can be displayed.

FIG. 14 shows voltage waveforms of the scanning lines A (1), A (2), A (m−1), and A (m). The reason why such a voltage waveform is used will be described below.
The light emitting panel 1 has a configuration in which an anode, a light emitting layer, and a cathode are sequentially laminated on a transparent substrate. And if there is a part where the thickness of the light emitting layer is thin or a part where the light emitting layer does not exist and the anode and the cathode are in contact with each other due to dust adhesion in the manufacturing process, a leak current is generated and flows to another normal light emitting layer. There is a problem that the current decreases and the luminance of the entire light emitting panel 1 decreases.

  In order to solve this problem of light emission failure, Patent Document 1 provides a period HB after scanning through the scanning lines A (1) to A (m), and all the EL elements E (1, 1) are provided in this period. ) To E (m, n), a driving method is shown in which a voltage in the direction opposite to the voltage applied during light emission (the above-described reverse bias voltage Vcc) is applied. According to this driving method, in the period HB, the leak current concentrates and flows in the defective portion due to the reverse bias voltage Vcc, and the cathode is bent or further bent and bent due to the expansion pressure that the light emitting layer is vaporized. Such a cathode portion does not emit light but does not generate a leakage current, so that it is possible to prevent light emission defects in other normal light emitting layers.

  Further, since the EL element E has the parasitic capacitance as described above, when the scanning line A is switched, the EL element E emits light from the switching due to the influence of the charge accumulated in the parasitic capacitance of the EL element E. There is also a problem that the rising speed is reduced and high-speed scanning cannot be performed. In order to solve this problem, Patent Document 2 discloses that all scanning lines are included in the reset periods R1 to Rm after each scanning of the scanning lines A (1) to A (m) is finished and before the next scanning is started. A technique is shown in which A (1) to A (m) and signal lines B (1) to B (n) are connected to the ground to discharge charges accumulated in the parasitic capacitance.

Furthermore, if the reverse bias Vcc applied to the EL element E is constant, there is a problem that the brightness adjustment range is narrowed and the linearity of gradation is deteriorated. To solve this problem, scanning during the light emission period occurs. Japanese Patent Application Laid-Open No. 2004-228688 discloses a technique that allows a reverse bias voltage value applied to a non-selected scanning line to be adjusted on a line A according to a pulse width or a current value for gradation control.
JP-A-11-305727 Japanese Patent Application Laid-Open No. 9-232074 JP 2000-200066 A

  In the case of adopting the means shown in Patent Document 1, the inventors of the present application need to set the reverse bias voltage Vcc to a value larger than a certain value in order to effectively prevent the light emission failure. It was clarified by experiment. FIG. 15 shows the experimental results showing the correlation between the reverse bias voltage Vcc and the occurrence probability of defective pixels. The probability of occurrence of defective pixels after 1000 hours of operation under each reverse bias voltage Vcc is shown. According to this, it is necessary to increase the reverse bias voltage Vcc to about 20 V in order to suppress the occurrence of light emission failure. However, a new problem occurs when the reverse bias voltage Vcc increases. This problem will be described below with reference to FIGS.

(1) Deterioration of gradation control characteristics FIGS. 16 and 17 show (a) the voltage of the scanning line A, (b) the current output from the current source 6 to the signal line B, (c ) A waveform of light emission luminance is shown. FIG. 16 shows a case where dimming is executed by controlling the pulse width of the driving current, and FIG. 17 shows a case where dimming is executed by controlling the magnitude of the driving current. In (b) current waveform and (c) light emission luminance waveform, the solid line indicates the waveform during high luminance light emission, and the broken line indicates the waveform during low luminance light emission.

  As shown in FIG. 16, for example, when the period RB is switched to the period H1 (see FIG. 14), the (instantaneous) light emission luminance of the EL element E rises sharply beyond the original target luminance, and thereafter, with time. It exhibits brightness characteristics that gradually settle to the target brightness. Since the light emission luminance of the EL element E is proportional to the drive current, the actual drive current flowing through the EL element E also has a waveform that approximates this. This phenomenon becomes more prominent as the reverse bias voltage Vcc is higher.

  This is because, when the period RB shifts to the period H1, for example, charge transfer occurs between the parasitic capacitances of 64 EL elements E connected to each signal line B, and the EL elements E that emit light are transiently excessive. This is because a voltage is applied. The current drive capability of the current source 6 does not have the capability to instantaneously settle such a transient phenomenon. Since the (instantaneous) emission brightness immediately after switching is high, even if the pulse width is reduced in order to reduce the average emission brightness (that is, the brightness that is visible to the human eye), the reduction rate of the pulse width The brightness does not decrease, a high dimming ratio of about 1/50 cannot be achieved, and linear gradation control becomes difficult.

  Such a problem also occurs when gradation control is performed by controlling the magnitude of the drive current as shown in FIG. That is, since the transient phenomenon immediately after the switching occurs regardless of the output current of the current source 6, even if the magnitude of the output current of the current source 6 is reduced, the light emission luminance of the EL element E immediately after the switching changes. Without reaching the target brightness, the target brightness is finally reduced when the transient state is finally settled. Therefore, also in this case, a high dimming ratio cannot be achieved, and the gradation control characteristics are deteriorated.

(2) Short-circuit between the cathode and the anode generated in the insulating portion When k of the m EL elements E connected to one signal line B are not emitting light, the non-emitting EL element E is in one frame. K−1 reverse bias pulses are applied to the EL element E that emits light, and k reverse bias pulses are applied in one frame. 18 and 19 show a cross-sectional structure of a gap portion between two adjacent EL elements E. FIG. An insulating portion is provided in the gap portion.

  The inventors of the present application have clarified that as the number of times the reverse bias pulse is applied increases, the damage to the insulating portion increases and the probability of occurrence of a short circuit between the cathode and the anode as shown in FIG. 19 increases. FIG. 20 shows experimental results showing the relationship between the number of reverse bias pulses applied in one frame and the occurrence probability of the short circuit. However, since the conditions for preventing the above-described deterioration of the gradation control characteristics and the conditions for preventing the short circuit between the cathode and the anode are contradictory, the conventional technology cannot realize driving that simultaneously solves these problems.

(3) Decrease in luminance half-life FIG. 21 shows the response characteristics (solid line) of the light emission luminance of the EL element E in the initial use of the display panel 1 and the response characteristics of light emission luminance after deterioration with time due to use (broken line). It shows. FIG. 22 shows the change over time of the light emission luminance of the EL element E, and the solid line shows the relative luminance when the above-described transient state at the time of switching does not occur (that is, when ideal constant current driving is performed). The broken line represents the relative luminance when the above-described transitional state at the time of switching occurs.

  In the EL element E, the light emission efficiency (current-luminance characteristics) deteriorates as the operation time elapses, and the light emission luminance with respect to the same drive current decreases. Therefore, even if the EL element E is driven at a constant current, a certain decrease in luminance is inevitable (see the solid line in FIG. 22). Furthermore, the resistance of the EL element E gradually increases as the light emission operation time elapses. When the transition state at the time of switching described above occurs, the EL element E is not in the constant current drive state but in the voltage drive state until the transient state is settled. (See broken lines in FIGS. 21 and 22). As a result, not only the luminous efficiency is decreased, but also directly affected by the increase in resistance, the luminance half-life is significantly decreased.

  The present invention has been made in view of the above circumstances, and its purpose is not only to accurately control the light emission luminance while preventing a light emission failure, but also to prevent a short circuit between the anode and the cathode in the insulating portion. Another object of the present invention is to provide a display device and a display panel driving method capable of extending the luminance half life by increasing the resistance of the EL element as much as possible.

  According to the means described in claims 1 and 20, there is provided a period for stopping the light emission of the light emitting element, and in the light emission stop period, the first reverse bias voltage is applied to the light emitting element, so that the light emitting layer is thin. Alternatively, leakage current concentrates and flows in a place where the anode and the cathode are in contact, and the leakage current can be suppressed by breaking or bending the cathode of the defective portion. Thereby, the light emission failure as the whole display panel can be prevented. The first reverse bias voltage may be a sufficiently large voltage necessary for suppressing the leakage current.

  On the other hand, during the light emission period, the second reverse bias voltage is applied to the non-light-emitting light-emitting elements, and therefore the second reverse bias voltage and the drive power source (current source) are applied to the light-emitting elements connected to the non-selected scan electrodes. Alternatively, a reverse bias voltage equal to the voltage difference from the output terminal voltage of the voltage source is applied.

  In this means, the second reverse bias voltage is changed to a voltage different from the first reverse bias voltage, for example, an appropriate voltage for suppressing the occurrence of a transient phenomenon immediately after the connection state of the scan electrode or the signal electrode is switched. Since it can be set, it is possible to avoid the occurrence of an excessive or too small voltage application state for the light emitting element immediately after switching, and to obtain a target light emission luminance immediately after switching.

  In addition, the second reverse bias voltage can be set smaller than the first reverse bias voltage, and the number of times the first reverse bias voltage is applied can be suppressed to once per frame. It is possible to suppress the short circuit phenomenon between the anode and the cathode. As a result, it is possible to accurately control the light emission luminance while preventing defective light emission, and to suppress the short-circuit phenomenon between the anode and the cathode in the insulating portion.

  According to the means described in claims 2, 3, 21, and 22, the first reverse bias voltage is applied to the scan electrode during the light emission stop period, the signal electrode is connected to the ground, and the selection is performed during the light emission period. The scan electrode thus connected is connected to the ground, the second reverse bias voltage is applied to the non-selected scan electrode, the signal electrode of the light emitting element that emits light is connected to the drive power supply, and the signal electrode of the non-light emitting light emitting element is connected to the ground. Drive control to connect to

  According to the means described in claims 4, 5, 23, and 24, the light emission stop period is provided for each frame, and during that period, the leakage current of the defective portion in the display panel is suppressed with respect to the scan electrode. Since the first reverse bias voltage having a sufficient magnitude required for the above can be applied, it is possible to reliably prevent the light emission failure. In this case, the light emission stop period may be provided after the end of the frame and before the next frame starts.

  According to the means described in claims 6 and 25, since the constant current source is used to cause the light emitting element to emit light, the light emitting element can be driven with a constant current, and the light emitting element is caused by fluctuations in power supply voltage or changes with time. Stable luminance can be obtained regardless of the increase in resistance. In particular, according to this means, since the occurrence of a transient phenomenon immediately after switching is suppressed, constant current driving can be performed immediately after switching, and it is difficult to be affected by the increase in resistance of the light emitting element, and the display device having the conventional configuration In contrast, the luminance half-life can be extended.

  According to the means described in claims 7 and 26, the second reverse bias voltage is substantially equal to the voltage that the light-emitting element steadily bears when a drive current is supplied from the current source to the light-emitting element. Is set. With this setting, for example, when a reset period in which all the scan electrodes and signal electrodes are connected to the ground is provided for each horizontal scan period, when the reset period is switched to the scan period of the next scan electrode, It is possible to suppress the occurrence of a transient phenomenon that occurs between parasitic capacitances.

  That is, paying attention to each signal electrode, there is no charge accumulation in the parasitic capacitance of the light emitting element in the reset period, only the selected scan electrode is connected to the ground by switching to the next scan period, and other non-selected Since all of the scan electrodes are connected to the second reverse bias voltage side, the voltage of the transient signal electrode immediately after the switching becomes substantially equal to the second reverse bias voltage. Therefore, if the second reverse bias voltage is set to be approximately equal to the voltage that the light emitting element normally bears, a steady voltage is applied to the light emitting element that emits light immediately after switching. A constant current drive becomes possible, and the planned luminance can be obtained.

  According to the means described in claims 8 and 27, in the case where the reset period is provided, if the number of scanning electrodes is m and the second reverse bias voltage is Vcc1, the voltage of the transient signal electrode immediately after switching is set. Is (m-1) / m · Vcc1. Therefore, if the voltage that the driven light-emitting element normally bears is VE, the second reverse bias voltage Vcc1 may be set equal to m / (m−1) · VE. When the number of scan electrodes is large, the second reverse bias voltage Vcc1 may be set approximately to VE.

  According to the means described in claims 9 and 28, the threshold voltage of the light emitting element is set to VL, and the second reverse bias voltage Vcc1 is set higher than (VE-VL). A voltage higher than the threshold voltage VL is not applied to the connected light emitting elements, and erroneous light emission can be prevented.

  According to the means described in claims 10, 11, 29, and 30, since the reset period for setting the scan electrode and the signal electrode to the same potential is provided for each horizontal scanning period, before switching to the next scanning period The charge accumulated in the parasitic capacitance of the light emitting element can be discharged, and the rising time from switching to light emission of the light emitting element can be shortened to perform high-speed scanning. In the reset period, the scan electrode and the signal electrode are preferably set to the ground potential.

  According to the means described in claims 12 and 31, since the first reverse bias voltage is larger than the second reverse bias voltage, the light emission luminance is accurately controlled while preventing the light emission failure, and further the insulating portion is used. The short-circuit phenomenon between the anode and the cathode can be suppressed.

  According to the means described in claims 13 and 32, since the first reverse bias voltage is set to be larger than the voltage at which self-repair of the light emitting element occurs, the portion where the thickness of the light emitting layer is thin or the anode and the cathode Leakage current flows in a concentrated manner at the point where the contact is made, and the cathode of the defective portion is bent and bent to suppress the leakage current.

  According to the means described in claims 14 and 33, since the first reverse bias voltage is equal to the power supply voltage constituting the constant current source, it is not necessary to provide a voltage converting means or the like, and the cost can be reduced.

  According to the means described in claims 15, 16, 34, and 35, the first and the second can be switched by switching a scan switch connected to each scan electrode or switching a voltage supplied to the scan switch connected to each scan electrode. The second reverse bias voltage can be switched.

  According to the means described in the seventeenth and thirty-sixth aspects, by changing the time width of the drive current supplied from the drive power source to the light emitting element in each horizontal scanning period, corresponding to the change (for example, proportional to the time width). E) The emission luminance can be controlled.

  According to the means described in claims 18 and 37, the magnitude of the drive current supplied from the drive power source to the light emitting element is changed in each horizontal scanning period, so that the change corresponds to the change (for example, the magnitude of the drive current). The emission brightness can be controlled.

  According to the means described in the nineteenth and thirty-eighth aspects, the emission luminance can be accurately controlled for the organic EL element whose emission luminance changes according to the drive current or the applied voltage. In addition, the luminance half-life can be extended as much as possible for an organic EL element having a characteristic of increasing resistance due to deterioration over time.

(First embodiment)
Hereinafter, a first embodiment in which the present invention is applied to an organic EL element will be described with reference to FIGS. 1 to 4, the same components as those in FIG. 13 are denoted by the same reference numerals, description thereof is omitted, and different portions will be described below.
In FIG. 1, a scanning driver IC 8 (corresponding to a cathode side driving unit) of the display device 7 keeps scanning switches 9 (1) to 9 (m) provided for the scanning lines A (1) to A (m) constant. By switching at the period (horizontal scanning period), the reverse bias voltage Vcc1 (corresponding to the second reverse bias voltage) and the reverse bias voltage Vcc (to the first reverse bias voltage) are applied to the scanning lines A (1) to A (m) Equivalent) or a ground voltage (0 V) is applied.

  The control unit 10 controls the signal driver IC 4 (corresponding to the anode side driving unit) and the scanning driver IC 8 in accordance with image data for displaying an image on the display panel 1, and is configured by a microcomputer, for example. ing. The scanning lines A (1) to A (m) correspond to the scanning electrodes in the present invention, the signal lines B (1) to B (n) correspond to the signal electrodes, and the EL element E (1, 1). ~ E (m, n) corresponds to a light emitting element.

Next, the operation of this embodiment will be described with reference to FIGS.
FIG. 5 shows voltage waveforms of the scanning lines A (1), A (2), A (m−1), and A (m). The scanning lines A (3) to A (( The same voltage waveform is obtained for m-2). In FIG. 5, periods H3, R3,..., Hm-2, Rm-2 exist between the period R2 and the period Hm-1, but these periods are omitted. In the figure, TF is a frame period, TH is a scanning period, and TR is a reset time.

  1 to 4 show switching states of the scan switch 9 and the drive switch 5 in the period H1, the period R1, the period Hm, and the period HB shown in FIG. 5, respectively. The other periods are not particularly shown, but the switching states of the reset periods R2 to Rm and RB are all the same as the switching state of the period R1, and the switching states of the periods H2 to Hm-1 are the period H1 or the period Hm. It will be the same.

  As already described, the period HB is provided at the end of one frame to prevent the occurrence of light emission failure of the display panel 1. In this period, as shown in FIG. 4, the scanning switches 9 (1) to 9 (m) are all switched to the reverse bias voltage Vcc side, and the driving switches 5 (1) to 5 (n) are all switched to the ground side. The reverse bias voltage Vcc is applied to all the EL elements E (1,1) to E (m, n). The reverse bias voltage Vcc may be a sufficiently large voltage necessary to suppress the leakage current. For example, according to the inventor's experimental data (FIG. 15), the reverse bias voltage Vcc may be 20V.

  Further, reset periods R1 to Rm and RB are provided for the periods H1 to Hm and the period HB, respectively, in order to increase the rising speed from switching to each scanning period until the EL element E emits light. In these periods, the scanning switches 9 (1) to 9 (m) and the drive switches 5 (1) to 5 (n) are all switched to the ground side as shown in FIG. The accumulated charge of the parasitic capacitance of .about.E (m, n) is discharged.

Next, switching from the period RB to the period H1 will be described.
FIG. 6 shows a state before and after switching for the scanning lines A (1) to A (m) and the signal line B (2). The EL elements E (1,2) to E (m, 2) are shown in FIG. The parasitic capacitance C is represented by a capacitor symbol. (A) shows the period RB, and the charges of the parasitic capacitances of the EL elements E (1,2) to E (m, 2) are 0 as described above. When this state is switched to the period H1 shown in (b), only the scanning line A (1) to be scanned is held at the ground potential, and the reverse bias voltage is applied to the other scanning lines A (2) to A (m). Vcc1 is given. The voltage Vc of the signal line B (2) immediately after this switching is expressed by the following equation (1).

Vc = (m−1) / m · Vcc1 (1)
Here, since the number m of scanning lines is set to 64, for example, the above equation (1) can be approximated as the following equation (2).
Vc≈Vcc1 (2)

  A voltage that the EL element E (1,2) steadily bears when a sufficient amount of time has elapsed with the drive current supplied from the current source 6 (2) to the EL element E (1,2). With VE, the transient phenomenon occurring at the time of switching can be most suppressed under the condition that the voltage Vc expressed by the above formula (1) or (2) is equal to VE. The reverse bias voltage Vcc1 satisfying this condition is expressed by the following equation (3) or approximately (4).

Vcc1 = m / (m-1) · VE (3)
Vcc1 ≒ VE (4)
In a normal organic EL element, VE is about 13V. In this case, Vcc1 is about 13V. Since Vcc is 20V, a voltage lower than Vcc is applied to Vcc1.

  7 and 8 show (a) the voltage of the scanning line A (1) when the reverse bias voltage Vcc1 is set according to the equation (3), and (b) the current source 6 (2) to the signal line B (2). The output current and (c) the waveform of the emission luminance of the EL element E (1, 2) are shown. FIG. 7 shows a case where gradation control is executed by controlling the pulse width of the drive current, and FIG. 8 shows a case where gradation control is executed by controlling the magnitude of the drive current. In (b) current waveform and (c) light emission luminance waveform, the solid line indicates the waveform during high luminance light emission, and the broken line indicates the waveform during low luminance light emission.

  When the period RB is switched to the period H1, the voltage applied to the EL element E (1,2) becomes a steady settling voltage VE immediately after the switching, so that the output current of the current source 6 (2) (as an example, 150 μA) Flows to the EL element E (1,2) as it is, and the EL element E (1,2) is driven at a constant current from the beginning of switching. As a result, as shown in FIG. 7, the light emission luminance of the EL element E (1,2) matches the target luminance from the beginning of switching from the period RB to the period H1, and the pulse width of the output current of the current source 6 (2). The light emission luminance can be increased or decreased in proportion to.

  Further, when the emission luminance is increased or decreased by controlling the magnitude of the drive current as shown in FIG. 8, the current source 6 (2) outputs a current having a magnitude corresponding to the emission luminance, and the EL is accordingly generated. The voltage VE that the element E (1,2) steadily bears also increases or decreases. For this reason, the reverse bias voltage Vcc1 needs to be increased or decreased in accordance with the above equation (3). By controlling the current of the current source 6 (2) and the reverse bias voltage Vcc1 in this way, the emission luminance of the EL element E (1,2) can be matched with the target luminance from the beginning of switching from the period RB to the period H1. Thus, the emission luminance can be increased or decreased in proportion to the magnitude of the output current of the current source 6 (2).

  The above operation is not limited to the switching from the period RB to the period H1, but also the switching from the period R2 to the period H2, ..., the switching from the period Rm-1 to the period Hm, and the like. Further, when the number m of scanning lines is large to some extent (for example, 64 lines), the same is true even when the reverse bias voltage Vcc1 is set approximately according to the equation (4). Even if the reverse bias voltage Vcc1 slightly deviates from the equation (3) or (4), the above action does not immediately disappear.

However, if the reverse bias voltage Vcc1 is lowered too much, the applied voltage of the EL element E connected to the non-selected scanning line A becomes equal to or higher than the light emission threshold value VL of the EL element E, so that the reverse bias voltage is emitted. The lower limit value Vcc1 (min) that can be set as Vcc1 is expressed by the following equation (5).
Vcc1 (min) = VE-VL (5)

  Thus, for each frame, a sufficiently large reverse bias voltage Vcc is applied to the EL element E in the period HB, and lower than the voltage Vcc to the non-light-emitting EL element E in the other periods H1 to Hm. When the reverse bias voltage Vcc1 is applied, the reverse bias voltage Vcc is applied only once per frame, so that the damage to the insulating portion of the EL element E is reduced, and the occurrence of a short circuit between the cathode and the anode in the insulating portion. Can be prevented. According to the experimental results, the ratio of the pixel in which the short circuit between the cathode and the anode in the insulating portion occurs is Vcc = 20V in the conventional method, and Vcc1 = 13V and Vcc = 20V in the method of the present invention. It was confirmed that the ratio decreased from 75% to 0%.

Furthermore, according to the driving method of the present embodiment, even if the EL element E increases in resistance due to aging, it is possible to suppress a decrease in luminance due to the influence, and to extend the luminance half-life as compared with a display device having a conventional configuration. it can. FIG. 9 shows the experimental results showing the temporal change in the light emission luminance. In the figure, the solid line indicates the case of the present embodiment, and the broken line indicates the case of the conventional configuration. In this experiment, Vcc = 20V, Vcc1 = 13V, m = 64, and n = 128, using an organic EL panel and a constant current driver, a frame frequency of 120 Hz, TR = 10 μsec, TH = 1/120 / The luminance was measured in an 85 ° C. atmosphere at an initial luminance of 200 Cd / m ² at 64 sec. As compared with the conventional method, a luminance half life of about 1.6 times was obtained.

  As described above, the display device 7 according to the present embodiment provides the period HB in which the light emission of all the EL elements E is stopped for each frame, and the reverse bias voltage Vcc is applied to all the scanning lines A during the period HB. In addition, since all the signal lines B are connected to the ground and the reverse bias voltage Vcc is applied to all the EL elements E, the cathode of the defective portion of the display panel 1 is bent and bent to suppress leakage current. it can.

  Unlike the reverse bias voltage Vcc1 applied in the periods H1 to Hm, the reverse bias voltage Vcc in this case can be set to a voltage large enough to suppress the leakage current. For this reason, the light emission failure of the display panel 1 can be prevented reliably. The reverse bias voltage Vcc is applied only once per frame period, but it is known from the inventors' knowledge that one time is sufficient to suppress the leakage current. Moreover, since the reset periods R1 to Rm and RB are provided for the periods H1 to Hm and the period HB, respectively, the light emission rising speed of the EL element E can be increased.

  On the other hand, in the periods H1 to Hm, the reverse bias voltage Vcc1 applied to the non-selected scanning line A is set to a voltage lower than the reverse bias voltage Vcc, that is, the voltage shown in the expression (3) or (4). Therefore, a transient phenomenon immediately after switching from the reset period R to the scanning period H can be suppressed, and the EL element E can be driven with a constant current from the beginning of switching. As a result, it is possible to accurately control the light emission luminance in a wide range from low luminance to high luminance by controlling the pulse width or magnitude of the driving current. In addition, even when the EL element E has a high resistance due to changes over time, a decrease in luminance due to the influence can be suppressed, and the luminance half-life can be extended as compared with a display device having a conventional structure. Furthermore, in this driving method, since the large reverse bias voltage Vcc is applied only once per frame, damage to the insulating portion of the EL element E is reduced, and the occurrence of a short circuit between the cathode and the anode in the insulating portion is prevented. can do.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIGS.
FIG. 10 shows the electrical configuration of the display device. The same components as those in FIG. The display device 11 shown in FIG. 10 differs from the display device 7 shown in FIG. 1 in the configuration of the scan driver IC.

  That is, the scan driver IC 12 has scan switches 13 (1) to 13 (m) for the scan lines A (1) to A (m), and these scan switches 13 (1) to 13 (m). The scanning lines A (1) to A (m) are connected to the power supply line 15 side or the ground side, respectively. Further, a power supply selection switch 16 for connecting the power supply line 15 to the reverse bias voltage Vcc1 side or the Vcc side is provided outside the scan driver IC 12. These scanning switches 13 (1) to 13 (m) and the power source selection switch 16 correspond to the cathode side drive unit referred to in the present invention, and are switched and controlled by a switching signal from the control unit 10. The reverse bias voltages Vcc1 and Vcc are the voltages as described in the first embodiment. Furthermore, in this embodiment, Vcc is also supplied to the signal driver IC4.

  FIG. 11 shows an electrical configuration of the power source selection switch 16. Between the power supply line 17 and the power supply line 15 having the reverse bias voltage Vcc, a series circuit of a diode 18 and a MOSFET 19 and a series circuit of a MOSFET 20 and a resistor 21 are connected. Among these, the switching signal Sa is given to the gate of the MOSFET 19 from the control unit 10 via the resistor 22. Resistors 23 and 24 are connected in series between the power supply line 17 and the ground, and the common connection point is connected to the gate of the MOSFET 20 and to the ground via the capacitor 25.

  In this configuration, when the switching signal Sa is at the H level (Vcc), the MOSFET 19 is turned off, and the power supply line 15 is lower than the reverse bias voltage Vcc by the voltage drop due to the source-drain voltage of the MOSFET 20 and the resistor 21. A reverse bias voltage Vcc1 is output. In this case, the source-drain voltage of the MOSFET 20 is determined by the element constant. On the other hand, when the switching signal Sa is at the L level (0 V), the MOSFET 19 is turned on, and a voltage substantially equal to the reverse bias voltage Vcc is output to the power supply line 15 through the diode 18 and the MOSFET 19.

  In the present embodiment, the voltage application timing to the scanning lines A (1) to A (m) and the current supply timing to the signal lines B (1) to B (n) are the same as those in the first embodiment. That is, during the period RB to the period Rm (see FIG. 5), the power source selection switch 16 is switched to the voltage Vcc1 side, and the switches 13 (1), 13 (2) are set in the scanning periods H1, H2,. ,..., 13 (m) are sequentially switched to the ground side, and switches 13 (1) to 13 (m) are all switched to the ground side in the reset periods RB, R1, R2,. On the other hand, in the period HB, the power source selection switch 16 is switched to the voltage Vcc side, and all the switches 13 (1) to 13 (m) are switched to the power source line 15 side.

  Also according to the present embodiment described above, the same operation and effect as the first embodiment can be obtained with respect to the emission luminance. In addition, since the scan driver IC 12 can have the same configuration as the conventional one (see FIG. 13), there is an advantage that the time and cost required for a new design can be reduced. Further, since the power supply on the input side of the scan driver IC 12 can be used as the first reverse bias voltage Vcc, and a voltage stepped down from the first reverse bias voltage Vcc can be used as the second reverse bias Vcc1, Vcc, Vcc1 The cost can be reduced as compared with the case of using a circuit made by boosting two voltages separately. Furthermore, in this embodiment, Vcc is also used as the power source for the signal driver IC4. Therefore, the cost can be reduced as compared with the case where a power supply circuit for the signal driver IC 4 is separately provided.

(Third embodiment)
Next, a third embodiment of the present invention will be described with reference to FIG.
The configuration of this embodiment is the same as that of the first or second embodiment described above, but a method of applying a voltage to the scanning lines A (1) to A (m) is partially different. FIG. 12 shows voltage waveforms of the scanning lines A (1), A (2), A (m−1), and A (m), and a period H3 that exists between the period R2 and the period Hm−1. , R3,..., Hm-2, Rm-2 are omitted.

  As shown in FIG. 12, in this embodiment, the reset period R for each scanning cycle is not provided, and the switching is immediately performed from one scanning cycle to the next scanning cycle. The reset period R is provided for the purpose of discharging the charge accumulated in the parasitic capacitance of the EL element E in the previous scanning cycle and increasing the light emission rising speed in the next scanning cycle. In contrast, in this embodiment, since the reverse bias voltage applied to the EL element E is lowered from Vcc to Vcc1 during the scanning periods H1 to Hm, the light emission rising speed is improved without providing the reset period R. Thereby, it is possible to control using a simpler switching timing without providing the reset period R in particular.

(Other embodiments)
The present invention is not limited to the embodiments described above and shown in the drawings, and can be modified or expanded as follows, for example.
In each embodiment, the first reverse bias voltage Vcc may be set to a voltage large enough to suppress the leakage current. The second reverse bias voltage Vcc1 is applied to the scanning switches 9 (1) to 9 (m) and 13 (1) for the scanning lines A (1) to A (m) or the signal lines B (1) to B (n). ) To 13 (m) or the drive switches 5 (1) to 5 (n) may be set to an appropriate voltage to suppress the occurrence of a transient phenomenon.

A voltage source may be used instead of the current sources 6 (1) to 6 (n) provided in the signal driver IC4. However, a current source is a preferable configuration in order to reduce the effect of increasing the resistance of the light emitting element.
The light emitting element is not limited to the organic EL element E, and can be applied as long as it is a current driven light emitting element.

The figure which shows the electrical constitution of the display apparatus which shows the 1st Embodiment of this invention (period H1) 1 equivalent diagram (periods R1 to Rm, RB) 1 equivalent diagram (period Hm) 1 equivalent diagram (period HB) The figure which shows the voltage waveform of scanning line A (1), A (2), A (m-1), A (m). The figure which shows the state before and behind switching about scanning line A (1) -A (m) and signal line B (2). (A) Scanning line voltage when driving current pulse width is controlled, (b) Current output from current source to signal line, (c) Light emission luminance waveform of EL element FIG. 7 equivalent diagram when the magnitude of the drive current is controlled Figure showing the change in emission luminance over time FIG. 1 equivalent diagram showing a second embodiment of the present invention The figure which shows the electric constitution of the power supply selection switch FIG. 5 equivalent view showing the third embodiment of the present invention 1 equivalent diagram showing the prior art Figure equivalent to FIG. The figure which shows the relationship between a reverse bias voltage and the generation probability of a poor light emission pixel 7 equivalent diagram Equivalent to FIG. The figure which shows the cross-section of the gap | interval part of two adjacent EL elements (at the time of normal) The figure which shows the cross-section of the gap | interval part of two adjacent EL elements (at the time of a short circuit) The figure which shows the relationship between the frequency | count of application of a reverse bias pulse in one flame | frame, and the occurrence probability of a short circuit The figure which shows the waveform of (a) the voltage of a scanning line before and after a deterioration with time, (b) the current output from a current source to a signal line, and (c) the emission luminance of the EL element. The figure which shows the time change of the light-emitting luminance of EL element

Explanation of symbols

In the drawings, 1 is a display panel, 4 is a signal driver IC (anode drive unit), 6 (1) to 6 (n) are current sources (drive power supplies), 7 and 11 are display devices, and 8 is a scan driver IC ( Cathode side drive unit), A (1) to A (m) are scanning lines (scanning electrodes), B (1) to B (n) are signal lines (signal electrodes), and E (1,1) to E (m , N) are organic EL elements (light emitting elements).

Claims (38)

A display panel in which light emitting elements are arranged in a matrix at each intersection of a plurality of scanning electrodes and signal electrodes;
A light emission stop period for stopping the light emission of the light emitting element is provided, and a first reverse bias voltage is applied to the light emitting element during the light emission stop period, while a second reverse bias is applied to the non-light emitting light emitting element during the light emission period. An anode side drive unit configured to apply a bias voltage and a cathode side drive unit,
The display device, wherein the second reverse bias voltage is set to a voltage different from the first reverse bias voltage.   2. The anode-side drive unit and the cathode-side drive unit apply a first reverse bias voltage to the scan electrode and connect the signal electrode to the ground during the light emission stop period. Display device.   The anode side drive unit and the cathode side drive unit connect a selected scan electrode to the ground in the light emission period, apply a second reverse bias voltage to the non-selected scan electrode, and emit light signals of the light emitting elements 3. The display device according to claim 1, wherein the electrode is connected to a driving power source, and the signal electrode of the non-light emitting element is connected to the ground.   The display device according to claim 1, wherein the anode side drive unit and the cathode side drive unit provide the light emission stop period for each frame.   The display device according to claim 1, wherein the light emission stop period is provided after the end of a frame and before the start of the next frame.   6. The display device according to claim 1, wherein the driving power source connected to the signal electrode is a constant current source.   The second reverse bias voltage is set to be approximately equal to a voltage that is regularly borne by the light emitting element when a driving current is supplied from the constant current source to the light emitting element. The display device according to claim 6.   The second reverse bias voltage Vcc1 is set to be equal to m / (m-1) · VE, where VE is the voltage that the driven light emitting element constantly bears and m is the number of scan electrodes. The display device according to claim 7, wherein the display device is provided.   The second reverse bias voltage Vcc1 is more than (VE-VL), where VE is the voltage that the driven light emitting element is constantly burdened with, and VL is the light emission threshold voltage of the light emitting element. 9. The display device according to claim 1, wherein the display device is set high.   10. The display device according to claim 1, wherein the anode side drive unit and the cathode side drive unit are provided with a reset period in which the scan electrode and the signal electrode are set to the same potential for each horizontal scanning period. .   The display device according to claim 10, wherein the anode side drive unit and the cathode side drive unit set the scanning electrode and the signal electrode to a ground potential in the reset period.   The display device according to claim 1, wherein the first reverse bias voltage is larger than the second reverse bias voltage.   13. The display device according to claim 1, wherein the first reverse bias voltage is set larger than a voltage at which self-repair of the light emitting element occurs.   The display device according to claim 6, wherein the first reverse bias voltage is equal to a power supply voltage constituting the constant current source.   15. The anode-side drive unit and the cathode-side drive unit switch the first and second reverse bias voltages by switching a scan switch connected to each scan electrode. The display apparatus in any one.   The anode-side driving unit and the cathode-side driving unit switch the first and second reverse bias voltages by switching a voltage supplied to a scanning switch connected to each scanning electrode. Item 15. The display device according to any one of Items 1 to 14.   The anode side drive unit and the cathode side drive unit are configured to perform gradation control by controlling a time width of a drive current supplied to the light emitting element in each horizontal scanning period. The display device according to claim 1.   The anode side drive unit and the cathode side drive unit are configured to execute gradation control by controlling the magnitude of a drive current supplied to the light emitting element in each horizontal scanning period. The display device according to claim 1.   The display device according to claim 1, wherein the light emitting element is an organic EL element. In a method for driving a display panel in which light emitting elements are arranged in a matrix at each intersection of a plurality of scanning electrodes and signal electrodes,
A first reverse bias voltage is applied to the light emitting element during a light emission stop period in which light emission of the light emitting element is stopped, and a non-light emitting element is different from the first reverse bias voltage in a subsequent light emission period. A display panel driving method comprising applying a second reverse bias voltage.   21. The display panel driving method according to claim 20, wherein a first reverse bias voltage is applied to the scan electrode and the signal electrode is connected to the ground during the light emission stop period.   In the light emission period, the selected scan electrode is connected to the ground, the second reverse bias voltage is applied to the non-selected scan electrode, and the signal electrode of the light emitting element that emits light is connected to the driving power source, so that non-light emission 22. The display panel driving method according to claim 20, wherein the signal electrode of the element is connected to the ground.   23. The display panel driving method according to claim 20, wherein the light emission stop period is provided for each frame.   24. The method of driving a display panel according to claim 20, wherein the light emission stop period is provided after the end of the frame and before the start of the next frame.   25. The display panel driving method according to claim 20, wherein the driving power source connected to the signal electrode is a constant current source.   The second reverse bias voltage is set to be approximately equal to a voltage that is regularly borne by the light emitting element when a driving current is supplied from the constant current source to the light emitting element. 26. A method of driving a display panel according to claim 25.   The second reverse bias voltage Vcc1 is set to be equal to m / (m-1) · VE, where VE is the voltage that the driven light emitting element constantly bears and m is the number of scan electrodes. 27. The method of driving a display panel according to claim 26, wherein:   The second reverse bias voltage Vcc1 is more than (VE-VL), where VE is the voltage that the driven light emitting element is constantly burdened with, and VL is the light emission threshold voltage of the light emitting element. 28. The method for driving a display panel according to claim 20, wherein the display panel is set high.   29. The display panel driving method according to claim 20, further comprising a reset period in which the scanning electrode and the signal electrode are set to the same potential every horizontal scanning period.   30. The display panel driving method according to claim 29, wherein the scanning electrode and the signal electrode are set to a ground potential in the reset period.   31. The method of driving a display panel according to claim 20, wherein the first reverse bias voltage is larger than the second reverse bias voltage.   32. The display panel driving method according to claim 20, wherein the first reverse bias voltage is set to be larger than a voltage at which self-repair of the light emitting element occurs.   26. The method of driving a display panel according to claim 25, wherein the first reverse bias voltage is equal to a power supply voltage constituting the constant current source.   34. The display panel driving method according to claim 20, wherein the first and second reverse bias voltages are switched by switching a scanning switch connected to each scanning electrode.   34. The display panel according to claim 20, wherein the first and second reverse bias voltages are switched by switching a voltage supplied to a scanning switch connected to each scanning electrode. Driving method.   36. The display according to claim 20, wherein gradation control is performed by controlling a time width of a driving current supplied to the light emitting element in each horizontal scanning period. Panel drive method.   36. The display according to claim 20, wherein gradation control is performed by controlling the magnitude of a driving current supplied to the light emitting element in each horizontal scanning period. Panel drive method. 38. The display panel driving method according to claim 20, wherein the light emitting element is an organic EL element.

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