JP2008282047A - Driving method and driving device of active type light emitting display panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To compensate the degradation of light emitting efficiency etc., of the EL element accompanying the impression of the inverted bias voltage in the active driving type luminescent display panel capable of impressing the inverted bias voltage to the EL element. <P>SOLUTION: A pixel 10 is constituted of a TFT (Tr1) for control, a TFT (Tr2) for driving, the capacitor C1, and the EL element E1. By alternately switching the switches SW1 and SW2, the normal directional current supply conditions and the inverted bias voltage supply conditions to the EL element E1 can be selected. When transiting the current supply from the inverted bias voltage impressing condition to the normal directional current supply condition, by switching the either switch prior to the other, the potential between the anode and the cathode of the EL element E1 is made the same potential and the charges are discharged. Therefore, the charging by the normal directional current to the parasitic capacitance of the EL element E1 can be performed quickly, thereby the rising of the luminance action of the EL element can be made quickly. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a drive device for a light-emitting display panel, in which a light-emitting element constituting a pixel is actively driven by a TFT (Thin Film Transistor) and a reverse bias voltage can be applied to the light-emitting element, and in particular, a reverse bias voltage. The present invention relates to a driving method and a driving apparatus for an active light emitting display panel that can compensate for a decrease in luminous efficiency of the light emitting element due to the application of light.

  The development of a display using a display panel configured by arranging light emitting elements in a matrix is being widely promoted. As a light-emitting element used for such a display panel, an organic EL (electroluminescence) element using an organic material for a light-emitting layer has attracted attention. This is also due to the fact that the use of an organic compound that can be expected to have good light-emitting characteristics for the light-emitting layer of the EL element has led to an increase in efficiency and longevity that can withstand practical use.

  As a display panel using such organic EL elements, a simple matrix type display panel in which EL elements are simply arranged in a matrix form, and an active matrix type display in which an active element made of TFT is added to each of the EL elements arranged in a matrix form. A panel has been proposed. The latter active matrix type display panel can realize lower power consumption than the former simple matrix type display panel, and has characteristics such as less crosstalk between pixels. Suitable for high definition display.

  FIG. 1 shows an example of the most basic circuit configuration corresponding to one pixel 10 in a conventional active matrix display panel, which is called a conductance control system. In FIG. 1, the gate of the control TFT (Tr 1) composed of N channels is connected to the scan line from the scan driver 1, and its source is connected to the data line from the data driver 2. The drain of the control TFT is connected to the gate of the driving TFT (Tr2) constituted by the P channel and to one terminal of the charge holding capacitor C1.

  The source of the driving TFT (Tr2) is connected to the other terminal of the capacitor C1, and is also connected to an anode power source (VHanod) that supplies a driving current to the EL element E1 as a light emitting element. The drain of the driving TFT (Tr2) is connected to the anode of the EL element E1, and the cathode of the EL element is connected to a cathode side power source (VLcath) via the switch SW1. In the example shown in FIG. 1, a reverse bias voltage power supply (VHbb) can be applied to the cathode of the EL element via the switch SW1, as will be described later.

  In the configuration shown in FIG. 1, when the ON control voltage (Select) is supplied to the gate of the control TFT (Tr1) via the scanning line, the control TFT (Tr1) is supplied with the voltage from the data line supplied to the source. A current corresponding to (Vdata) is passed from the source to the drain. Therefore, the capacitor C1 is charged while the gate of the control TFT (Tr1) is on-voltage, and the voltage is supplied to the gate of the drive TFT (Tr2) as the gate voltage. Therefore, the driving TFT (Tr2) passes a current based on the voltage between the gate and the source (Vgs) to the EL element E1, and drives the EL element to emit light.

  By the way, it is well known that the above-mentioned organic EL element has a light emitting element having a diode characteristic electrically and a capacitance (parasitic capacitance) connected in parallel thereto, It is known that the organic EL element emits light with an intensity substantially proportional to the forward current of the diode characteristic. Furthermore, it is empirically known that the EL element can be extended in life by sequentially applying a reverse voltage (reverse bias voltage) that is not involved in light emission to the EL element.

  Therefore, the configuration shown in FIG. 1 is configured such that a forward or reverse bias voltage can be applied to the EL element E1 using the switch SW1. That is, the potential relationship among the above-described anode-side power supply (VHanod), cathode-side power supply (VLcath), and reverse bias voltage power supply (VHbb) is VHbb> VHanod> VLcath. Therefore, in the state of the switch SW1 shown in FIG. 1, a forward voltage having a value of (VHanod−VLcath) is supplied to the series circuit of the driving TFT (Tr2) and the EL element E1. When the switch SW1 shown in FIG. 1 is switched in the reverse direction, a reverse bias voltage having a value of (VHbb−VHanod) is supplied to the series circuit of the driving TFT (Tr2) and the EL element E1. .

  FIG. 2 also shows a conventional example configured to apply a reverse bias voltage to the EL element in the same manner, and this example also shows a case where the conductance control system is applied. In FIG. 2, portions corresponding to the respective portions described based on FIG. 1 are denoted by the same reference numerals, and therefore individual descriptions are omitted. In the example shown in FIG. 2, first and second change-over switches SW1 and SW2 are provided. By switching the switches SW1 and SW2, the connection relationship between the anode-side power supply (VHanod) and the cathode-side power supply (VLcath). It is comprised so that it may switch.

  That is, when the switches SW1 and SW2 are in the state shown in the drawing, a forward voltage having a value of (VHanod−VLcath) is supplied to the series circuit of the driving TFT (Tr2) and the EL element E1. Accordingly, a forward current can be supplied to the EL element E1, and the EL element E1 can be turned on by the ON operation of the driving TFT (Tr2). Further, when the switches SW1 and SW2 are switched in the direction opposite to the figure, the reverse bias voltage having the same value of (VHanod−VLcath) is supplied to the series circuit of the driving TFT (Tr2) and the EL element E1. Is done. A configuration in which the VLcath is used as a reference potential (ground voltage) is disclosed in Patent Document 1.

JP 2002-169510 A

  Incidentally, since the organic EL element is a current light emitting element, the driving TFT is generally driven by a constant current. As described above, the EL element has a predetermined parasitic capacitance, and when the EL element becomes equal to or higher than a predetermined light emission threshold voltage, the EL element is brought into a light emitting state. For this reason, even if a drive voltage is applied in the forward direction to the EL element, a predetermined time is required to charge the parasitic capacitance and reach the light emission threshold voltage. In addition, since the constant current drive is performed as described above, the impedance is substantially high, and it takes much more time to rise to the light emission threshold voltage of the EL element.

In addition to this, when a means for applying a reverse bias voltage to the EL element is employed as shown in Patent Document 1 , charges are accumulated in a reverse bias state with respect to the parasitic capacitance of the EL element. For this reason, a time from when the forward voltage is applied until the EL element reaches the light emitting state is further required. For this reason, the lighting time rate of the EL element is lowered, and the luminous efficiency is substantially lowered. In addition, each EL element has problems such as deterioration of gradation control linearity under the influence of variations in time until the light emission state is reached.

That is, the invention disclosed in Patent Document 1 merely discloses that a forward voltage is simply applied from a reverse bias applied state to an EL element, and the above-described problems remain. It has been done.

The present invention has been made paying attention to the technical problems described above, and in particular, in an active light-emitting display panel driving device employing means for applying a reverse bias voltage to an EL element , the EL element is Discharging means for discharging the charge accumulated in the parasitic capacitance of the EL element that operates between the period for performing the operation of applying the reverse bias voltage and the period for performing the lighting operation, or the forward direction with respect to the parasitic capacitance of the EL element By providing a charging means for performing a charging operation for charging, a driving method of a light-emitting display panel that can solve the above-described problems such as a decrease in luminous efficiency or a deterioration in gradation linearity as described above It is another object of the present invention to provide a driving device.

The basic aspect of the driving method of the active light emitting display panel according to the present invention, which has been made to solve the above-described problems, is a light emitting element, a driving TFT for driving and driving the light emitting element, and And a driving method of an active light emitting display panel, comprising: a power supply circuit that supplies a forward current to the light emitting element during the lighting operation of the light emitting element; and a circuit that applies a reverse bias voltage to the light emitting element. A discharge operation for discharging the charge accumulated in the parasitic capacitance of the light emitting element, which is different from the lighting operation, between the period during which the light emitting element performs the application operation of the reverse bias voltage and the period during which the lighting operation is performed. having a characteristic feature in which a period for performing a charging operation for charging in a forward direction with respect to the parasitic capacitance of different light emitting element and the period to perform or the lighting operation, .

The driving method of the active type light emitting display panel according to the first aspect of the present invention is the discharge operation for discharging the charge accumulated in the parasitic capacitance of the light emitting element different from the lighting operation. In the period of executing the above, the discharge operation for discharging the charge accumulated in the parasitic capacitance of the light emitting element is performed by setting the anode and the cathode of the light emitting element to the same potential.

According to a second aspect of the present invention, there is provided a driving method for an active light emitting display panel according to claim 3, wherein charging is performed in a forward direction with respect to a parasitic capacitance of the light emitting element different from the lighting operation. The charging operation of performing a switching operation of a selection switch that gives a potential difference that can be turned on to the light emitting element in a period of performing the operation, and charging the parasitic capacitance of the light emitting element in the forward direction via the selection switch To be executed.

According to a third aspect of the present invention, there is provided a driving method for an active light emitting display panel according to claim 4, wherein charging is performed in a forward direction with respect to a parasitic capacitance of the light emitting element different from the lighting operation. In the period of performing the operation, the current from the charging power source is caused to flow in the forward direction from the connection point between the light emitting element and the driving TFT to the parasitic capacity of the light emitting element, thereby reducing the parasitic capacity of the light emitting element. On the other hand, the charging operation for charging in the forward direction is performed.

According to a fifth aspect of the present invention, there is provided a driving method for an active type light emitting display panel as claimed in claim 5, wherein the parasitic capacitance of the light emitting element different from the lighting operation is charged in the forward direction. By performing bypass control on the driving TFTs connected in series to the light emitting element during the period of performing the operation, the charging operation for charging the parasitic capacitance of the light emitting element in the forward direction is performed. .

On the other hand, the basic form of the drive device for the active light emitting display panel according to the present invention, which has been made to solve the above-mentioned problems, is a light emitting element and a driving device for driving the light emitting element to be lit as described in claim 6 . A drive device for an active light emitting display panel, comprising: a TFT; a power supply circuit that supplies a forward current to the light emitting element during the lighting operation of the light emitting element; and a circuit that applies a reverse bias voltage to the light emitting element The light emitting element operates between a period during which the reverse bias voltage application operation is performed and a period during which the lighting operation is performed, and charges accumulated in the parasitic capacitance of the light emitting element different from the lighting operation. It is the configuration provided with the charging means for performing a charging operation in a forward direction with respect to the parasitic capacitance of different light emitting element and the discharging means to discharge operation for discharging or the lighting operation, .

The drive device for an active light-emitting display panel according to the first aspect of the present invention is characterized in that, as described in claim 7, the light-emitting element performs the reverse bias voltage applying operation and the lighting operation. Discharge means for performing a discharge operation for discharging charges accumulated in the parasitic capacitance of the light emitting element different from the lighting operation by setting the anode and the cathode of the light emitting element to the same potential. It is configured to have.

According to a second aspect of the present invention, there is provided a driving device for an active light emitting display panel, wherein the light emitting element performs the reverse bias voltage application operation and the lighting operation period. Charging means for performing a charging operation in a forward direction with respect to the parasitic capacitance of the light emitting element different from the lighting operation based on a switching action of a selection switch that operates between the light emitting elements and provides a potential difference that can be lit to the light emitting elements. It is configured to have.

According to a third aspect of the present invention, there is provided a driving apparatus for an active light-emitting display panel according to claim 9, wherein the light-emitting element performs a reverse bias voltage application operation and a lighting operation period. A charging power source that performs a charging operation in a forward direction with respect to the parasitic capacitance of the light emitting element from a connection point between the light emitting element and the driving TFT, and uses the charging power source. Different from the lighting operation, a charging unit that performs a charging operation in a forward direction with respect to the parasitic capacitance of the light emitting element is provided.

According to a fifth aspect of the present invention, there is provided a drive device for an active light-emitting display panel according to claim 10, wherein the light-emitting element performs a reverse bias voltage application operation and a lighting operation period. And a bypass control means that bypasses the driving TFT connected in series with the light emitting element, and performs a charging operation in a forward direction with respect to the parasitic capacitance of the light emitting element different from the lighting operation. The charging means is provided.

  In the following, characteristic features of the drive device for the light emitting display panel according to the present invention will be described separately from the first to fifth embodiments. First, according to the first embodiment of the driving device of the present invention, the anode and the cathode of the light emitting element are set to the same potential at the timing when the light emitting element shifts to the lighting operation, thereby being accumulated in the parasitic capacitance of the light emitting element. It is characterized in that a discharge operation for discharging the charged electric charge is executed.

  In the first embodiment of the drive device according to the first aspect of the present invention, as shown in FIG. 2, the first and second change-over switches SW1 and SW2 are provided, and the switches SW1 and SW2 are switched. The present invention is applied to an example in which the connection relationship between the anode side power source (VHanod) and the cathode side power source (VLcath) is switched. In the drawings shown below, parts corresponding to the parts already described are denoted by the same reference numerals, and therefore descriptions of individual functions and operations will be omitted as appropriate.

  Note that the first embodiment of the drive device according to the present invention is not only applied to the drive unit using the conductance control system as shown in FIG. 2, but also the digital gradation shown in FIG. A light-emitting display panel including the 3-TFT pixel 10 to be realized can also be suitably used. Further, the first embodiment of the first mode of the driving apparatus according to the present invention is similarly applied to a light emitting display panel having pixels by a voltage programming method, a threshold voltage correction method, and a current mirror method, which will be described later. Can do.

  Note that the configuration including the 3TFT pixel 10 illustrated in FIG. 3 includes an erasing TFT (Tr3) as compared to the configuration illustrated in FIG. 2, and during the lighting period of the EL element E1, By turning on the erasing TFT (Tr3), the charge of the capacitor C1 can be discharged. Thus, the lighting period of the EL element E1 can be controlled, and gradation expression can be performed digitally.

  The switching operation timing of the first and second switches SW1 and SW2 in FIGS. 2 and 3 is shown in FIG. In the lighting state before reaching t1 shown in FIG. 4, the second switch SW2 is connected to the anode side power source (VHanod). This is indicated by the symbol “H” in FIG. In the same lighting state before reaching t1, the first switch SW1 is connected to the cathode side power supply (VLcath). This is indicated by the symbol “L” in FIG.

  Therefore, when the potential difference of the series circuit including the driving TFT (Tr2) and the EL element E1 is referred to as a pixel portion voltage, the pixel portion voltage at this time is a value of (VHanod−VLcath) as shown in FIG. The forward voltage is applied, and the EL element E1 can be turned on depending on the driving TFT. In FIG. 4, this state is simply indicated as “lighting”.

  On the other hand, when t1 shown in FIG. 4 is reached, the second switch SW2 is connected to the cathode side power source (VLcath), and the first switch SW1 is connected to the anode side power source (VHanod). As a result, as shown in FIG. 4, a reverse voltage having a value of (VHanod−VLcath) is applied to the pixel portion voltage, and the EL element E1 is reversed via the driving TFT (Tr2). A bias voltage is applied. In FIG. 4, this state is simply indicated as “reverse buy”. By applying the reverse bias voltage, charges due to the reverse bias voltage are accumulated in the parasitic capacitance of the EL element E1.

  Subsequently, when t2 shown in FIG. 4 is reached, only the second switch SW2 is switched and connected to the anode power source (VHanod). As a result, the first and second switches are both connected to the anode-side power source (VHanod), and the pixel section voltage becomes zero voltage, that is, the same potential as shown in FIG. Therefore, the electric charge due to the reverse bias voltage accumulated in the parasitic capacitance of the EL element E1 is discharged through the driving TFT (Tr2). In FIG. 4, this state is simply indicated as “discharge”. In other words, the combination of the first and second switches SW1 and SW2 with the anode side power source (VHanod) and the cathode side power source (VLcath) discharges the charge due to the reverse bias voltage accumulated in the parasitic capacitance of the EL element. Discharging means is configured.

  At t3 after the above-described discharge operation, only the first switch SW1 is switched and connected to the cathode side power supply (VLcath). As a result, the pixel portion voltage is set to a forward voltage having a value of (VHanod−VLcath) as shown in FIG. 4, and the EL element E1 is again turned on depending on the driving TFT (Tr2). .

  According to the operation described above, by setting the anode and the cathode of the EL element to the same potential via the driving TFT at the timing of shifting from the reverse bias voltage application state to the EL element to the forward current supply state, Electric charges due to the reverse bias voltage accumulated in the parasitic capacitance of the EL element can be discharged. Therefore, when a forward bias is applied to the EL element, charge accumulation based on the forward bias can be immediately started with respect to the parasitic capacitance.

  That is, as compared with the case where the forward bias is applied while the charge of the reverse bias state is accumulated in the parasitic capacitance of the EL element, the start-up of light emission of the EL element can be made much faster. Therefore, it is possible to avoid problems such as a decrease in light emission efficiency as the lighting time rate of the EL element decreases. In addition, since each EL element can be less affected by variations in time until the light emission state is reached, problems such as deterioration of linearity of gradation control can be improved.

  Next, FIG. 5 explains a second embodiment of the first form of the driving apparatus according to the present invention. In FIG. 5, a basic configuration including a driving TFT (Tr2), an EL element E1, and a capacitor C1 is shown, and the others are omitted. In the configuration shown in FIG. 5 as well, the above-described conductance control method or a 3TFT pixel configuration for realizing digital gradation can be adopted, and further, a voltage programming method, a threshold voltage correction method, a current method, which will be described later, are employed. The present invention can be similarly applied to a light-emitting display panel provided with a mirror type pixel.

  In the second embodiment of the first form shown in FIG. 5, the switch SW1 arranged on the cathode side of the EL element E1 constitutes a three-input select switch. A switch SW3 is connected between the anode and cathode of the EL element E1. That is, by turning on the switch SW3, the anode and the cathode of the EL element E1 can be in the same potential state. Note that the switch SW3 shown in FIG. 5 is preferably formed of a TFT.

  In the state shown in FIG. 5, the switch SW1 selects VLcath, and therefore a forward voltage is supplied to the pixel portion. At this time, the switch SW3 is controlled to be turned off. Subsequently, when the switch SW1 selects VHbb, a reverse bias voltage is supplied to the pixel portion. Also at this time, the switch SW3 is controlled to be turned off. By applying the reverse bias voltage, charges based on the reverse bias voltage are accumulated in the parasitic capacitance of the EL element E1 as described above.

  Subsequently, the switch SW1 selects an empty terminal, that is, a high impedance, and at this time, the switch SW3 is controlled to be turned on. Accordingly, at this time, the charge based on the reverse bias voltage accumulated in the parasitic capacitance of the EL element E1 is discharged via the switch SW3. Then, after the discharge operation is finished, the switch SW3 is turned off, and the switch SW1 is brought into a state of selecting VLcath shown in FIG. Therefore, the forward voltage is applied again to the pixel portion, and the EL element E1 is brought into a lightable state depending on the driving TFT (Tr2).

  The switch SW3 interlocked with the switching operation of the select switch SW1 shown in FIG. 5 constitutes a discharging means for discharging charges due to the reverse bias voltage accumulated in the parasitic capacitance of the EL element. Therefore, even in the configuration shown in FIG. 5, it is possible to obtain the same effect as that of the first embodiment of the first mode described with reference to FIGS. In the configuration shown in FIG. 5, the three-input select switch SW1 is provided on the cathode side of the EL element E1, but the cathode side of the EL element E1 is a fixed power source, and the anode side of the EL element E1, ie, the drive Even if a three-input select switch is arranged at the source of the driving TFT via the driving TFT (Tr2), the same effect can be obtained.

  Next, FIG. 6 explains a second embodiment of the driving apparatus according to the present invention. According to a second aspect of the drive device of the present invention, at the timing when the light emitting element shifts to the lighting operation, a switching operation of a selection switch that gives a potential difference that can be turned on to the light emitting element is executed, and the light emitting element is passed through the selection switch. It is characterized in that a charging operation is performed with respect to the parasitic capacitance.

  Also in the second embodiment shown in FIG. 6, a basic configuration including a driving TFT (Tr2), an EL element E1 as a light emitting element, and a capacitor C1 is shown, and the others are omitted. In the configuration shown in FIG. 6 as well, the above-described conductance control method or a 3TFT pixel configuration for realizing digital gradation can be adopted, and further, a voltage programming method and a threshold voltage correction method, which will be described later, are used. The present invention can be similarly applied to a light-emitting display panel provided with pixels by a current mirror method.

  Also in the second embodiment shown in FIG. 6, the switch SW1 arranged on the cathode side of the EL element E1 constitutes a three-input select (selection) switch so that three different potential levels can be selected. It is configured. That is, the switch SW1 is configured so that the potential levels of V4, V1, and V3 can be alternatively selected as shown in FIG. On the other hand, a potential level indicated as V2 is applied to the source side of the driving TFT (Tr2). Each potential level shown in FIG. 6 has a relationship of V1> V2 ≧ V3> V4.

  That is, the potential level shown as V2 here corresponds to the anode side power supply (VHanod) shown in FIG. The potential level shown as V4 corresponds to the cathode side power supply (VLcath), and the potential level shown as V1 corresponds to the reverse bias voltage power supply (VHbb). In the state shown in FIG. 6, the switch SW1 selects the potential level indicated as V4. According to this state, the forward voltage is applied to the pixel portion, and the EL element E1 depends on the driving TFT (Tr2). And is ready to light.

  From the state shown in FIG. 6, the switch SW1 selects the potential level indicated as V1. Thereby, a reverse bias voltage is applied to the pixel portion, and charges due to the reverse bias voltage are accumulated in the parasitic capacitance of the EL element E1. Subsequently, the switch SW1 selects a potential level indicated as V3. Here, when V2 = V3, the pixel portion voltage is zero voltage, that is, the same potential. Therefore, the electric charge due to the reverse bias voltage accumulated in the parasitic capacitance of the EL element E1 is discharged through the driving TFT (Tr2).

  When V2> V3, the charge due to the reverse bias voltage accumulated in the parasitic capacitance of the EL element E1 is discharged, and at the same time, precharged slightly in the forward direction. Subsequently, the switch SW1 is switched to the state shown in FIG. As a result, the pixel portion voltage is set to the forward voltage, and the EL element E <b> 1 is again turned on depending on the driving TFT (Tr2).

  According to the configuration shown in FIG. 6, the discharge means for discharging the charge due to the reverse bias voltage accumulated in the parasitic capacitance of the EL element, or the EL element in particular, depending on the selection order of the power supply and the switch SW1 that have a relationship of V2 ≧ V3. Precharge means for slightly charging the forward voltage with respect to the parasitic capacitance is configured. Therefore, also in the configuration shown in FIG. 6, the same effect as that of the first embodiment described above can be obtained.

  In the embodiment shown in FIG. 6, a three-input select switch SW1 is provided on the cathode side of the EL element E1, but the cathode side of the EL element E1 is used as a fixed power source, and the anode side of the EL element E1, that is, driving Even if a three-input select switch is arranged at the source of the driving TFT via the driving TFT (Tr2), the same effect can be obtained.

  Next, FIG. 7 explains a third embodiment of the driving apparatus according to the present invention. According to a third aspect of the drive device of the present invention, at the timing when the light-emitting element shifts to the lighting operation, the parasitic power source is connected to the parasitic capacitance of the light-emitting element from the connection point between the light-emitting element and the driving TFT. It is characterized in that a charging operation in which a current flows in the forward direction is executed.

  Also in FIG. 7, a basic configuration including a driving TFT (Tr2), an EL element E1, and a capacitor C1 is shown, and others are omitted. In the configuration shown in FIG. 7 as well, the above-described conductance control method or a 3-TFT pixel configuration that realizes digital gradation can be adopted, and further, a voltage programming method and a threshold voltage correction method described later. The present invention can be similarly applied to a light-emitting display panel provided with pixels by a current mirror method.

  In the driving device of the third embodiment shown in FIG. 7, a charging operation is executed in the forward direction with respect to the parasitic capacitance of the EL element from the connection point between the EL element E1 as the light emitting element and the driving TFT (Tr2). A power supply V5 that can be charged is prepared. In this case, the charging power source V5 is configured as a constant voltage power source, and acts to perform a charging operation in the forward direction with respect to the parasitic capacitance of the EL element E1 via the switch SW4.

  That is, in the state shown in FIG. 7, the switch SW1 selects VLcath, and therefore, a forward voltage is supplied to the pixel portion. At this time, the switch SW4 is controlled to be turned off. Subsequently, when the switch SW1 selects VHbb, a reverse bias voltage is supplied to the pixel portion. Also at this time, the switch SW4 is controlled to be turned off. By applying the reverse bias voltage, charges based on the reverse bias voltage are accumulated in the parasitic capacitance of the EL element E1 as described above.

  Subsequently, the switch SW1 returns to the original state shown in FIG. 7, that is, the forward bias state. At the same time, the switch SW4 is controlled to be on. Therefore, at this time, although the charge based on the reverse bias voltage is accumulated in the parasitic capacitance of the EL element E1, the voltage of the charging power supply V5 supplied via the switch SW4 is in the forward direction with respect to the parasitic capacitance. Therefore, the forward voltage from the charging power source V5 is immediately charged in the parasitic capacitance of the EL element E1. As described above, since the charging power source V5 is configured as a constant voltage power source, the above-described forward charging operation is performed instantaneously.

  Then, after a predetermined time (time until the charging operation is completed), the switch SW4 is turned off. Therefore, the forward voltage is applied again to the pixel portion, and the EL element E1 is brought into a lightable state depending on the driving TFT (Tr2).

  According to the third embodiment of the driving apparatus of the present invention shown in FIG. 7, the connection between the EL element and the driving TFT is performed at the timing of transition from the reverse bias voltage application state to the EL element to the forward current supply state. From this point, since the charging operation is performed in which the current flows from the charging power source to the parasitic capacitance of the EL element in the forward direction, the charge due to the reverse bias voltage accumulated in the parasitic capacitance of the EL element is immediately discharged. At the same time, the charge based on the forward bias can be instantaneously accumulated with respect to the parasitic capacitance of the EL element.

  As a result, the start-up of the light emission of the EL element can be accelerated, and problems such as a decrease in light emission efficiency can be avoided as the lighting time rate of the EL element decreases. In addition, since each EL element can be less affected by variations in time until the light emission state is reached, problems such as deterioration of linearity of gradation control can be improved.

  In the embodiment shown in FIG. 7, it is also effective to connect, for example, a diode in the direction shown in the drawing instead of the switch SW4. That is, as shown in FIG. 7, the forward voltage is applied to the pixel, and the anode voltage level when the forward voltage is charged to the parasitic capacitance of the EL element is approximately equal to the voltage level of the charging power supply V5. By setting to, the diode can be automatically controlled to be turned off by the threshold voltage. In such a configuration, it is not necessary to provide a control logic and a control line for controlling on / off of the switch SW4.

  Next, FIGS. 8 to 16 illustrate a fourth embodiment of the drive device according to the present invention. According to a fourth embodiment of the driving device of the present invention, the gate voltage of the driving TFT is controlled at the timing when the light emitting element shifts to the lighting operation, so that the current of the light emitting element can be increased with a larger current than that during the lighting operation of the light emitting element. It is characterized in that the charging operation is executed in the forward direction with respect to the parasitic capacitance.

  First, FIG. 8 shows a basic configuration of a fourth embodiment of the drive device according to the present invention, and FIG. 9 is a timing chart for explaining the basic operation. In FIG. 8, a basic configuration including a driving TFT (Tr2), an EL element E1 as a light emitting element, and a capacitor C1 is shown, and the others are omitted. As shown in FIG. 9, in the lighting state before reaching t1, the switch SW1 shown in FIG. 8 is in the state shown in the figure, and the pixel portion voltage is in the forward direction. When t1 is reached, the switch SW1 is switched to the VHbb side, whereby the pixel portion voltage is set to a reverse voltage, that is, a reverse bias state.

  At this time, in the embodiment shown in FIG. 8, a voltage of the same level as VHanod is applied to the gate of the driving TFT (Tr2). That is, when the voltage across the capacitor C1 is VCgat, an operation for setting VCgat to a zero voltage state (the same potential) is performed. On the other hand, in this state, the charge due to the reverse bias voltage is accumulated in the parasitic capacitance of the EL element E1.

  When t2 is reached, the switch SW1 returns to the state shown in FIG. 8, and the pixel portion voltage is set to the forward voltage state. At this time, a bias voltage sufficient to turn on the driving TFT is supplied to the gate of the driving TFT (Tr2). That is, as shown in FIG. 9, VCgat is set to a value of “zero charge voltage”. As a result, during the instantaneous period (charging period shown in FIG. 9), a forward current larger than that in the lighting state flows through the driving TFT (Tr2) to the EL element E1, thereby increasing the parasitic capacitance of the EL element. The electric charge due to the forward current is accumulated instantaneously. When t3 is reached, the voltage applied to the gate of the driving TFT (Tr2) is set to a preset lighting voltage for causing a predetermined constant current to flow through the EL element E1.

  According to the configuration of FIG. 8 and the control mode shown in FIG. 9, the gate voltage of the driving TFT is controlled by controlling the gate voltage of the driving TFT at the timing of transition from the reverse bias voltage application state to the EL element to the forward current supply state. The charging operation is performed in the forward direction with respect to the parasitic capacitance of the EL element with a larger current than that during the lighting operation of the element. Therefore, the start-up of light emission of the EL element can be accelerated, and problems such as a decrease in light emission efficiency can be avoided as the lighting time rate of the EL element decreases. In addition, since each EL element can be less affected by variations in time until the light emission state is reached, problems such as deterioration of linearity of gradation control can be improved.

  FIG. 10 shows a first embodiment of the fourth mode of the driving apparatus according to the present invention, the basic mode of which has been described with reference to FIGS. 8 and 9, and FIG. 11 illustrates the more detailed operation in this case. It is a timing chart. In FIG. 10, the switch SW5 is equivalent to the control TFT (Tr1) in the configuration shown in FIG. 1, and in this case, FIG. 10 has a pixel configuration by a conductance control system. Can be said.

  In the configuration shown in FIG. 10, the Vdata supplied from the data driver is the first timing of each head of the reverse bias voltage application period, forward current charging period, and subsequent lighting period as shown in FIG. In FIG. 4, a reverse bias data voltage, a charging data voltage, and a lighting data voltage are provided, respectively. When these data voltages arrive, the switch SW5 is turned on, and a write operation is performed based on the data voltages. The VCgat and pixel unit voltage setting operation pattern shown in FIG. 11 is the same as the pattern shown in FIG. 9 already described.

  Instead of the pixel configuration based on the conductance control method shown in FIG. 10, the 3TFT method that realizes the digital gradation drive shown in FIG. 3 can be adopted. Also in this case, the driving operation shown in FIG. 11 can be suitably employed, and problems such as a decrease in the light emission efficiency of the EL element can be avoided. In addition, problems such as deterioration of gradation control linearity can be improved.

  FIG. 12 shows a second embodiment of the fourth mode according to the present invention. The pixel configuration shown in FIG. 12 is called a voltage programming system. In this voltage programming method, a switch SW7 is connected in series between the drain of the driving TFT (Tr2) and the anode of the EL element E1. The charge holding capacitor C1 is connected between the gate and source of the driving TFT (Tr2), and the switch SW6 is connected between the gate and drain of the driving TFT (Tr2). In addition, this voltage programming method is configured such that a data signal is supplied from the data line to the gate of the driving TFT (Tr2) via the switch SW8 and the capacitor C2.

  In the voltage programming method described above, the switch SW6 and the switch SW7 are turned on, and accordingly, the on state of the driving TFT (Tr2) is secured. When the switch SW7 is turned off at the next moment, the drain current of the driving TFT (Tr2) flows to the gate of the driving TFT (Tr2) via the switch SW6. Thus, the gate-source voltage is pushed up until the gate-source voltage of the driving TFT (Tr2) becomes equal to the threshold voltage of the driving TFT (Tr2), and the switch SW6 is turned off at this point.

  The gate-source voltage at this time is held in the capacitor C1, and the driving current of the EL element E1 is controlled by this capacitor voltage. That is, this voltage programming method acts to compensate for variations in the threshold voltage in the driving TFT (Tr2). Even in the configuration using the driving means based on the voltage programming method shown in FIG. 12, the driving operation shown in FIG. 11 can be suitably employed, and problems such as a decrease in the luminous efficiency of the EL element can be avoided. it can. In addition, problems such as deterioration of gradation control linearity can be improved.

  Further, FIG. 13 shows a third embodiment of the fourth mode according to the present invention, and the configuration shown in FIG. 13 will be referred to herein as a threshold voltage correction method. In the threshold voltage correction method shown in FIG. 13, an EL element E1 is connected in series to the driving TFT (Tr2), and a charge holding capacitor C1 is provided between the gate and source of the driving TFT (Tr2). It is connected. That is, this basic configuration is equivalent to the configuration shown in FIG.

  On the other hand, in the configuration shown in FIG. 13, between the switch SW9 (which is equivalent to the control TFT (Tr1)) connected to the data line and the gate of the driving TFT (Tr2), the TFT (Tr4) and the diode are arranged. A parallel connection with D1 is inserted. The TFT (Tr4) is short-circuited between its gate and drain. Therefore, this functions as an element that gives a threshold characteristic from the switch SW9 to the gate of the driving TFT (Tr2).

  According to this configuration, since the threshold characteristics of the mutual TFTs (Tr2, Tr4) formed in one pixel are made to be very similar characteristics, the threshold characteristics can be effectively canceled. In the configuration using the threshold voltage correction method shown in FIG. 13 as well, the driving operation shown in FIG. 11 can be suitably employed, and problems such as a reduction in the light emission efficiency of the EL element can be avoided. In addition, problems such as deterioration of gradation control linearity can be improved.

  FIG. 14 shows a fourth embodiment of the fourth mode according to the present invention, and the configuration shown in FIG. 14 shows an example of a driving means for an EL element by a so-called current mirror system. This is configured such that data write processing to the charge holding capacitor C1 and lighting operation of the EL element E1 are performed by the current mirror operation.

  That is, a TFT (Tr5) whose gate is commonly connected to the driving TFT (Tr2) is provided symmetrically, and a charge holding capacitor C1 is connected between the gate and source of both TFTs (Tr2, Tr5). ing.

  Further, a switch SW10 is connected between the gate and drain of the TFT (Tr5), and both TFTs (Tr2, Tr5) function as a current mirror by turning on the switch SW10. That is, the switch SW11 is also turned on together with the switch SW10 being turned on, whereby the write current source Icon is connected via the switch SW11.

  Thereby, for example, in the address period, a current path is formed which flows from the VHanod power source to the write current source Icon via the TFT (Tr5) and the switch SW11. Further, due to the action of the current mirror, a current corresponding to the current flowing through the current source Icon is supplied to the EL element E1 via the driving TFT (Tr2). Through the above-described operation, the gate voltage of the TFT (Tr5) corresponding to the value of the current flowing through the write current source Icon is written into the capacitor C1. After the predetermined voltage value is written in the capacitor C1, the switch SW10 is turned off, and the driving TFT (Tr2) supplies a predetermined current to the EL element E1 based on the electric charge accumulated in the capacitor C1. Thus, the EL element E1 is driven to emit light.

  FIG. 15 shows the operation timing performed in the EL element driving means by the current mirror method. The operation timing shown in FIG. 15 is substantially the same as that of FIG. 11 already described. However, the above-mentioned current element type EL element driving means operates as a current writing type. Therefore, the write operation is performed by the data current Idata provided by the current source Icon.

  As shown in FIG. 15, Idata generated from the current source Icon is a reverse bias data current in the first timing of the reverse bias voltage application period, forward current charging period, and subsequent lighting period, respectively. , Charging data current, lighting data current. The switch SW10 is turned on every time when the data currents arrive, and a write operation is performed based on the data currents. By adopting such a driving operation shown in FIG. 15, problems such as lowering the light emission efficiency of the EL element can be avoided, and problems such as deterioration of gradation control linearity can be improved. it can.

  FIG. 16 shows a fifth embodiment of the fourth mode according to the present invention, and FIG. 16 shows an example of an EL element driving means by a current programming method. In this current programming method, a series circuit of a switch SW13, a driving TFT (Tr2), and an EL element E1 is inserted between an anode side power supply (VHanod) and a cathode side power supply (VLcath). A charge holding capacitor C1 is connected between the source and gate of the driving TFT (Tr2), and a switch SW12 is connected between the gate and drain of the driving TFT (Tr2). Further, a write current source Icon is connected to the source of the driving TFT (Tr2) via the switch SW14.

  In the configuration shown in FIG. 16, when the switches SW12 and SW14 are turned on, the driving TFT (Tr2) is also turned on, and the current from the write current source Icon is supplied via the driving TFT (Tr2). Flowing. At this time, a voltage corresponding to the current from the write current source Icon is held in the capacitor C1.

  On the other hand, during the light emitting operation of the EL element, the switches SW12 and SW14 are both turned off and the switch SW13 is turned on. As a result, the anode side power supply (VHanod) is applied to the source side of the driving TFT (Tr2), and the cathode side power supply (VLcath) is applied to the cathode of the EL element E1. The drain current of the driving TFT (Tr2) is determined by the electric charge held in the capacitor C1, and gradation control of the EL element is performed.

  The driving operation shown in FIG. 15 can also be suitably adopted in the configuration using the current programming driving means shown in FIG. 16, and problems such as a reduction in the luminous efficiency of the EL element can be avoided. . In addition, problems such as deterioration of gradation control linearity can be improved.

  According to the driving apparatus according to the fourth embodiment of the present invention shown in FIGS. 8 to 16 described above, the gate of the driving TFT is shifted at the timing of transition from the reverse bias voltage application state to the EL element to the forward current supply state. By controlling the voltage, charging means is provided that performs a charging operation in the forward direction with respect to the parasitic capacitance of the EL element with a larger current than that during the lighting operation of the EL element. Therefore, as described above, it is possible to effectively compensate for the light emission efficiency of the EL element, and to contribute to preventing deterioration of the linearity of gradation control.

  Next, FIG. 17 explains a fifth embodiment of the driving apparatus according to the present invention. According to a fifth aspect of the drive device of the present invention, the drive TFT connected in series with the light emitting element is bypass-controlled at the timing when the light emitting element shifts to the lighting operation, so that the forward direction with respect to the parasitic capacitance of the light emitting element. It is characterized in that the charging operation is executed by the device.

  FIG. 17 also shows a basic configuration including a driving TFT (Tr2), an EL element E1 as a light emitting element, and a capacitor C1, and others are omitted. In the configuration shown in FIG. 17 as well, the above-described conductance control method or the 3-TFT method pixel configuration for realizing digital gradation can be suitably employed. Furthermore, the voltage programming method and threshold voltage correction already described. The present invention can be similarly applied to a light-emitting display panel having pixels using a method or a current mirror method.

  In the driving device of the fifth embodiment shown in FIG. 17, the source / drain of the TFT (Tr6) configured with the N channel is different from the source / drain of the driving TFT (Tr2) configured with the P channel. Each is connected in parallel. Although not particularly illustrated, a predetermined bias voltage (constant voltage) is supplied to the gate of the TFT (Tr6) constituted by the N channel. That is, the TFT (Tr6) constitutes bypass control means for bypassing the driving TFT (Tr2) that operates at a constant current and driving at a constant voltage.

  In the configuration shown in FIG. 17, when the forward current is supplied to the EL element E1 in the state of the switches SW1 and SW2 shown in the figure, and when the switches SW1 and SW2 are switched to the state opposite to the figure, the EL element As described above, the reverse bias voltage is supplied to E1. According to the embodiment shown in FIG. 17, in the state where the reverse bias voltage is applied to the forward current supply state and the charge amount of the forward voltage with respect to the parasitic capacitance of the EL element E1 is small, A charging operation is performed in which the TFT (Tr6) is bypassed and charges are rapidly accumulated in the parasitic capacitance. Therefore, the EL element can be rapidly brought into a light emitting state.

  On the other hand, when a predetermined charging operation is performed in the forward direction with respect to the parasitic capacitance of the EL element, the source potential of the TFT (Tr6) rises, so that the TFT (Tr6) configured by the N channel automatically In this case, the cut-off state is entered, and the above-described bypass operation is stopped.

  In the drive device of the fifth embodiment shown in FIG. 17 as well, the luminous efficiency of the EL element can be effectively compensated, and it can contribute to preventing the deterioration of the linearity of the gradation control.

FIG. 5 is a connection diagram illustrating an example of a pixel configuration in an active matrix display panel that can apply a reverse bias voltage to a light emitting element. FIG. 6 is a connection diagram illustrating another configuration example in which a reverse bias voltage can be applied to the light emitting element. It is the connection diagram which showed the pixel configuration example of 3TFT system which implement | achieves digital gradation. It is a timing chart explaining 1st Example of the 1st form in the drive device concerning this invention. It is a connection diagram similarly showing the 2nd example of the 1st form. It is a connection diagram which similarly shows the Example of a 2nd form. It is a connection diagram similarly showing the Example of a 3rd form. It is a connection diagram which similarly shows the example of a basic composition of a 4th form. It is a timing chart explaining the operation | movement in the basic structural example shown in FIG. It is a connection diagram which shows 1st Example of the 4th form in the drive device concerning this invention. It is a timing chart explaining the operation | movement in the structural example shown in FIG. It is a connection diagram which shows 2nd Example of the 4th form in the drive device concerning this invention. It is a connection diagram similarly showing the 3rd example of the 4th form. It is a connection diagram similarly showing the 4th example of the 4th form. It is a timing chart explaining the operation | movement in the structural example shown in FIG. It is a connection diagram which shows 5th Example of the 4th form in the drive device concerning this invention. It is a connection diagram similarly showing the Example of a 5th form.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Scan driver 2 Data driver 10 Pixel C1 Capacitor D1 Diode E1 Light emitting element (organic EL element)
Icon write current source SW1 to SW14 switch Tr1 control TFT
Tr2 driving TFT
Tr3-Tr6 TFT

Claims (10)

A light emitting element, a driving TFT for driving the light emitting element to light, a power supply circuit for supplying a forward current to the light emitting element during the lighting operation of the light emitting element, and applying a reverse bias voltage to the light emitting element A driving method of an active light emitting display panel comprising a circuit,
A discharge operation for discharging the charge accumulated in the parasitic capacitance of the light emitting element, which is different from the lighting operation, is performed between a period in which the light emitting element performs the application operation of the reverse bias voltage and a period in which the lighting operation is performed. A method for driving an active light-emitting display panel, characterized in that a period for performing a charging operation for performing forward charging on a parasitic capacitance of the light-emitting element different from the lighting operation is provided . In a period of performing a discharge operation for discharging the charge accumulated in the parasitic capacitance of the light emitting element different from the lighting operation,
2. The active operation according to claim 1, wherein the discharge operation for discharging the charge accumulated in the parasitic capacitance of the light emitting element is performed by setting the anode and the cathode of the light emitting element to the same potential. Type light emitting display panel driving method. In a period of performing a charging operation for charging the parasitic capacitance of the light emitting element different from the lighting operation in a forward direction,
And characterized by performing the charging operation to perform the switching operation of the selection switch to provide a possible lighting potential difference to the light emitting element, to charge the forward direction with respect to the parasitic capacitance of the light emitting element via the select switch A method for driving an active light-emitting display panel according to claim 1. In a period of performing a charging operation for charging the parasitic capacitance of the light emitting element different from the lighting operation in a forward direction,
From the connection point between the light emitting element and the driving TFT, the current from the charging power source flows in the forward direction with respect to the parasitic capacitance of the light emitting element, thereby charging the parasitic capacitance of the light emitting element in the forward direction. The method of driving an active light emitting display panel according to claim 1, wherein the charging operation is performed. In a period of performing a charging operation for charging the parasitic capacitance of the light emitting element different from the lighting operation in a forward direction,
The series-connected the driving TFT to the light emitting element by bypass control, as described in claim 1, characterized by performing the charging operation for charging in a forward direction with respect to the parasitic capacitance of the light emitting element Driving method of active type light emitting display panel. A light emitting element, a driving TFT for driving the light emitting element to light, a power supply circuit for supplying a forward current to the light emitting element during the lighting operation of the light emitting element, and applying a reverse bias voltage to the light emitting element A drive device for an active light emitting display panel comprising a circuit,
A discharge operation in which the light emitting element operates between a period in which the application operation of the reverse bias voltage is performed and a period in which the lighting operation is performed, and discharges charges accumulated in the parasitic capacitance of the light emitting element different from the lighting operation. discharging means performs or the drive device for an active type light emitting display panel, characterized by comprising a charging means for charging operation in a forward direction with respect to the parasitic capacitance of different light emitting element and the lighting operation. The light emitting element operates between a period for performing the application operation of the reverse bias voltage and a period for performing the lighting operation,
Discharging means for performing a discharging operation for discharging charges accumulated in a parasitic capacitance of the light emitting element different from the lighting operation by setting the anode and the cathode of the light emitting element to the same potential, The drive device for an active light-emitting display panel according to claim 6. The light emitting element operates between a period for performing the application operation of the reverse bias voltage and a period for performing the lighting operation,
Based on the switching action of a selection switch that gives a potential difference that can be lit to the light emitting element, the charging device includes a charging unit that performs a forward charging operation on a parasitic capacitance of the light emitting element different from the lighting operation. The drive device for an active light-emitting display panel according to claim 6. The light emitting element operates between a period for performing the application operation of the reverse bias voltage and a period for performing the lighting operation,
A charging power source that performs a charging operation in a forward direction with respect to the parasitic capacitance of the light emitting element from a connection point between the light emitting element and the driving TFT is provided, and is different from the lighting operation using the charging power source. The driving device of the active type light emitting display panel according to claim 6, further comprising a charging unit that performs a charging operation in a forward direction with respect to the parasitic capacitance of the light emitting element . The light emitting element operates between a period for performing the application operation of the reverse bias voltage and a period for performing the lighting operation,
By providing bypass control means for bypassing the driving TFT connected in series with the light emitting element, charging means for performing a charging operation in a forward direction with respect to the parasitic capacitance of the light emitting element different from the lighting operation is provided. and active type light emitting display panel driving device according to claim 6, wherein.

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