JP2007094319A - Driving device of organic el display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce power consumption when common electrode wiring of an area for displaying an image is scanned in partial drive. <P>SOLUTION: A segment electrode driver part has a constant current circuit corresponding to each segment electrode wiring and applies constant current from segment electrode wiring in which a pixel to be emitted exists to the selected common electrode wiring. However, since a current value of the constant current in the partial drive is lower than a constant current value in the normal drive, OLED drive voltage (voltage of anode of the organic EL element when the constant current is applied) is also reduced. A power supply circuit which supplies voltage V<SB>CC</SB>for operating the constant current circuit to the segment electrode driver part reduces output voltage V<SB>CC</SB>in the partial drive to prevent increase in difference between the output voltage V<SB>CC</SB>and the OLED drive voltage. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a drive device for an organic EL display device using an organic electroluminescence light emitting element (hereinafter referred to as an organic EL element).

  An organic EL display device (organic EL panel) having a structure in which an organic EL element is disposed in each pixel portion of the matrix electrode is realized. In an organic EL panel, for example, on a substrate such as a glass substrate, a plurality of anode wirings using a transparent conductive film such as ITO that is connected to an anode or forms the anode itself is arranged in a vertical direction, for example, and orthogonal thereto. In this direction, a plurality of cathode wirings using a metal that is connected to the cathode or forms the cathode itself is arranged, for example, in the lateral direction. The intersection of the anode wiring and the cathode wiring becomes a pixel, and an organic thin film (organic EL element) is sandwiched between the wirings. As described above, the pixels constituted by the organic EL elements are arranged on the substrate in a matrix. Since the organic EL element is a current driving element that emits light when a current flows, the luminance depends on the amount of current.

  Organic EL elements have characteristics similar to semiconductor light emitting diodes. That is, when the anode side is set to the high voltage side and a predetermined voltage is applied between both electrodes to supply a current to the organic EL element, light is emitted. Specifically, when the difference between the potential on the anode side and the potential on the cathode side becomes equal to or higher than the emission start voltage, current starts to flow through the organic EL element. Conversely, when the cathode side is set to a high potential, no current flows and no light is emitted.

  The organic EL panel can be driven by a simple matrix driving method. When driving, the anode wiring and cathode wiring of the organic EL panel can be set to either scanning electrode wiring (common electrode wiring) or data electrode wiring (segment electrode wiring). That is, the anode wiring can be a common electrode wiring and the cathode wiring can be a segment electrode wiring, or the anode wiring can be a segment electrode wiring and the cathode wiring can be used as a common electrode wiring. Hereinafter, a case where the cathode wiring is a common electrode wiring and the anode wiring is a segment electrode wiring is taken as an example.

  Each segment electrode wiring is connected to a segment electrode driver having a constant current circuit corresponding to each segment electrode wiring. Each common electrode wiring is connected to a common electrode driver. The segment electrode driver and the common electrode driver drive the organic EL panel according to the control of the controller.

  In an organic EL display device, partial driving may be performed. “Partial drive” is a drive mode in which display is performed only in a partial region using only a part of all lines in the display screen. In normal driving, each common electrode wiring individually corresponding to all lines is sequentially selected to display an image on the entire screen. On the other hand, when performing partial driving, only the common electrode wirings corresponding to some lines are sequentially selected to display in some areas.

  FIG. 10A shows a display example when normal driving (hereinafter referred to as normal driving) is performed, and FIG. 10B shows a display example at the time of partial driving. In the example shown in FIG. 10, the number of lines (number of common electrode wirings) is 64. As shown in FIG. 10B, during partial driving, display is performed on only a part of the screen. Further, the ratio of the selection period of one common electrode wiring to the time (one frame period) from the start of the selection period of a certain common electrode wiring to the next selection start of the common electrode wiring is defined as a duty (or duty ratio). Call. In the case of normal driving illustrated in FIG. 10A, display is performed using all lines (64 lines), so the duty is 1/64. In the case of the partial drive illustrated in FIG. 10B, display is performed using 8 lines out of all lines, so the duty is 1/8.

  Even when the driving mode is switched from the normal driving to the partial driving, one frame period does not change, so that the selection period of each common electrode wiring becomes long. At this time, if the brightness of the organic EL element during normal driving and partial driving is made uniform, the current value of the constant current flowing through the organic EL element during the partial driving decreases, and the organic EL when the constant current is flowing The voltage at the anode of the element decreases. Hereinafter, the voltage of the anode of the organic EL element when a constant current is applied is referred to as an OLED (Organic Light Emitting Diode) drive voltage.

FIG. 11 is an explanatory diagram showing an example of changes in the drive waveform representing the potential of the common electrode wiring and the potential of the segment electrode wiring when switching from normal driving to partial driving. An FLM (first line marker) shown in FIG. 11 is a control signal indicating the start of one frame. LP (latch pulse) is a control signal instructing switching of the common electrode wiring to be selected. COM ₀ and COM _n indicate the potentials of the 0th and nth common electrode lines, respectively. However, it is assumed that the nth common electrode wiring is a common electrode wiring arranged in the display area during partial driving. SEG _n represents an arbitrary potential among the plurality of segment electrode wirings. V _cc is a voltage supplied from the power supply circuit to the segment electrode driver in order to operate the constant current circuit included in the segment electrode driver. Further, V _cc is also a potential set for the unselected common electrode wiring. V _SS is a potential set to the selected common electrode wiring, and is also a potential set to the segment electrode wiring of the column where the pixel to be turned off (non-lighted) exists in the selection line (ie, the selected row). It is.

In FIG. 11, when the potential set for the unselected common electrode wiring and the voltage supplied to the segment electrode driver by the power supply circuit for operating the constant current circuit provided in the segment electrode driver are both V _cc showed that. The potential set for the unselected common electrode wiring may differ from the voltage supplied to the segment electrode driver by the power supply circuit in order to operate the constant current circuit included in the segment electrode driver.

The voltage V _cc supplied from the power supply circuit to the segment electrode driver is determined to be higher than the OLED drive voltage during normal driving by a predetermined value or more in order to operate the constant current circuit.

As shown in FIG. 11, it is assumed that the normal drive is switched to the partial drive. Then, as already described, the OLED drive voltage decreases. Note that the value of the OLED drive voltage is equal to the potential of the segment electrode wiring in the column where the pixel to be turned on (lighted) is present. As shown in FIG. 11, the OLED drive voltage (on The potential of the segment electrode wiring in the column in which the pixel to be present is present decreases. As a result, at the time of the partial drive, and the OLED driving voltage, the power supply circuit is a difference between the voltage V _cc supplied to the segment electrode driver becomes larger than necessary, the power wasted is increased.

FIG. 12 is an explanatory diagram showing a decrease in the OLED drive voltage. When switching from normal drive to partial drive, the OLED drive voltage decreases. On the other hand, the power supply circuit is a voltage V _cc supplied to the segment electrode driver does not change, the difference between the supply voltage V _cc and the OLED drive voltage by the power supply circuit increases.

  In addition, a driving device for a light-emitting display panel for the purpose of power saving during partial driving has been proposed (for example, see Patent Document 1). The driving device described in Patent Document 1 is applied to an active matrix light-emitting display panel. When performing non-display area scanning during partial driving, low power consumption is realized by stopping the driving of the data driver.

  Further, a signal driving circuit (signal driver) of a liquid crystal panel is described in Patent Document 2, for example. The signal driving circuit described in Patent Document 2 includes a non-display level voltage supply circuit. Then, the signal lines of the block corresponding to the non-display area whose output is set to OFF by the partial display data are driven by the voltage generated by the non-display level voltage supply circuit.

  Further, in an organic EL display device, when a constant voltage is applied to an organic EL element to drive the current, the luminance at a portion far from the common electrode driver decreases, and the luminance changes in the display screen. It has been known. This phenomenon is called luminance gradient. FIG. 13 is an explanatory diagram showing the cause of the luminance gradient. In FIG. 13, the vertical axis represents voltage, and the horizontal axis represents the distance from the common electrode driver in the common electrode wiring. FIG. 13 shows that the voltage at each position on the common electrode wiring increases as the distance from the connection end of the common electrode driver increases. The common electrode wiring itself has a resistance, and the resistance value from the connection end of the common electrode driver to each position on the common electrode wiring increases as the distance from the connection end increases. Further, the current passed through the organic EL element flows from the common electrode wiring to the common electrode driver. The voltage at each position on the common electrode wiring is obtained by the product of the current flowing through the position and the resistance from the connection end of the common electrode driver to the position according to Ohm's law. Therefore, as shown in FIG. 13, the voltage at each position on the common electrode wiring increases as the distance from the connection end of the common electrode driver increases. Then, the difference between the power supply voltage and the voltage at each position on the common electrode wiring decreases as the distance from the connection end of the common electrode driver increases. As a result, at a position away from the common electrode driver, the difference between the power supply voltage and the voltage of the common electrode wiring is reduced, and the voltage applied to the organic EL element is reduced. And when the applied voltage to an organic EL element differs, a difference arises in the electric current which flows and a brightness | luminance inclination arises.

JP 2003-316315 A (paragraphs 0042 and 0043) Japanese Patent Laying-Open No. 2002-351212 (paragraphs 0096-0098, FIG. 10)

As already explained, when switching from normal drive to partial drive, the difference between the OLED drive voltage and the voltage V _cc that the power supply circuit supplies to the segment electrode driver becomes larger than necessary, increasing the wasted power consumption. To do. The drive device described in Patent Document 1 achieves low power consumption. However, the driving device described in Patent Document 1 realizes low power consumption by stopping the driving of the data driver when scanning the non-display area by partial driving. Therefore, wasteful power is consumed when scanning the common electrode wiring in the area where an image is displayed during partial driving.

  Accordingly, an object of the present invention is to provide a drive device for an organic EL display device capable of reducing power consumption when scanning a common electrode wiring in a region for displaying an image during partial drive. .

  Aspect 1 according to the present invention includes an organic EL display device including a plurality of common electrodes and a plurality of segment electrodes arranged so as to intersect with each other, and an organic thin film disposed between the plurality of common electrodes and the plurality of segment electrodes. A segment electrode driver having a constant current circuit for supplying a constant current to the segment electrode for each segment electrode, a common electrode driver for sequentially scanning the common electrode by selecting the common electrode, and a common During normal driving when the electrode driver scans each common electrode, the segment electrode driver supplies a voltage that can output a normal constant current that the constant current circuit should output during normal driving. During partial driving that scans only some of the common electrodes, a voltage lower than the above voltage is applied to the segment electrode driver. To provide a driving device of an organic EL display device characterized by comprising a feeding powering circuit.

  Aspect 2 according to the present invention is an organic EL device according to aspect 1, wherein the power supply circuit supplies, to the segment electrode driver, a voltage capable of outputting a partial time constant current to be output at the time of partial driving. A drive device for a display device is provided.

  Aspect 3 according to the present invention is the control means for lowering the constant current flowing through the constant current circuit during the partial drive from the normal time constant current to the partial time constant current having a current value smaller than the normal time constant current. And a constant current circuit of the segment electrode driver that reduces the constant current flowing through the segment electrode from the normal time constant current to the partial time constant current according to the control means during partial driving. .

  According to Aspect 4 of the present invention, in the Aspect 1, the segment electrode driver applies a voltage supplied from the power supply circuit to the segment electrode without using a constant current circuit at the time of partial driving. Provided is a drive device for an organic EL display device in which a current is passed through an organic thin film between a common electrode selected by an electrode driver.

  Aspect 5 according to the present invention provides the driving apparatus for an organic EL display device according to aspect 4, wherein the number of common electrodes to be scanned during partial driving is 16 or less. According to the aspect 5, the luminance gradient at the time of partial driving can be made inconspicuous.

  According to the present invention, when the common electrode driver scans only a part of the common electrodes, the power consumption when scanning the part of the common electrodes can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Also in the following description, the case where the cathode wiring is the common electrode wiring and the anode wiring is the segment electrode wiring is taken as an example.

[First Embodiment] FIG. 1 is a block diagram showing an example of a driving device for an organic EL display device according to a first embodiment of the present invention. The organic EL display device (organic EL panel) 4 includes a plurality of common electrode wirings (not shown) and a plurality of segment electrode wirings (not shown). The common electrode wiring (common electrode) and the segment electrode wiring (segment electrode) are arranged so as to be orthogonal to each other with the organic thin film (organic EL element) interposed therebetween. Each intersection of the common electrode wiring and the segment electrode wiring becomes a pixel. In each pixel, when an electric current flows from the segment electrode wiring side to the common electrode wiring side, the organic thin film of the pixel emits light.

  A driving device for driving the organic EL panel 4 includes a controller (hereinafter simply referred to as a controller) 1 having a memory unit, a common electrode driver unit (common electrode driver) 2, and a segment electrode driver unit (segment electrode driver) 3. And a power supply circuit (switching regulator) 5. An external MPU 6 may be included in the drive device that drives the organic EL panel 4. A memory unit (not shown) included in the controller 1 stores image data of an image to be displayed. The controller (control means) 1 displays an image on the organic EL panel 4 by controlling the common electrode driver unit 2, the segment electrode driver unit 3, and the power supply circuit 5.

  Further, an external MPU (Micro Processing Unit) 6 is connected to the controller 1. The external MPU 6 transmits to the controller 1 a signal for instructing register settings in the controller 1 and image data to be stored in the memory unit. The signal transmitted from the external MPU 6 to the controller 1 includes a signal instructing switching to partial driving or normal driving. The external MPU 6 transmits image data to the controller 1 and rewrites the image data stored in the memory unit inside the controller 1. In FIG. 1, signals and data transmitted from the external MPU 6 to the controller 1 are collectively expressed as I / F signals.

The common electrode driver unit 2 selects individual common electrode wirings one by one in accordance with the controller 1 and sets the potentials of the common electrode wirings in the selected row and the non-selected row, respectively. Then, the common electrode driver unit 2 scans the common electrode wiring while sequentially selecting each common electrode wiring. A voltage for setting the potential of each common electrode wiring is supplied from the power supply circuit 5. The common electrode driver unit 2 sets the common electrode wiring in the selected row to a selection potential (V _SS ). Here, the case where V _SS is the ground potential (0 V) will be described as an example, but V _SS may not be the ground potential. In addition, the common electrode driver unit 2 sets the other common electrode wiring to a non-selection potential ( _VCH ) during selection of a certain common electrode wiring.

  In accordance with the controller 1 and display data of the selected row, the segment electrode driver unit 3 supplies a constant current to the common electrode wiring of the selected row from the segment electrode wiring of the column where the pixel to be lit is present during the selection period. That is, the segment electrode driver unit 3 supplies a constant current to the organic thin film on the selected common electrode wiring from the segment electrode wiring in the column where the pixels to be lit exist.

  However, the segment electrode driver unit 3 switches the constant current value according to the controller 1. When switching from normal driving to partial driving, the controller 1 sequentially selects only some of the common electrode wirings that the organic EL panel 4 has (for example, only eight wirings from the 0th row to the 7th row). Scan. At this time, the controller 1 makes the selection period longer in the partial driving than in the normal driving so that one frame period does not change. Further, the controller 1 increases the selection period so that the constant current value during the partial drive is lower than that during the normal drive so that the luminance of the pixel during the partial drive does not increase. Switch values.

  FIG. 2 is an explanatory diagram illustrating a configuration example of the segment electrode driver unit according to the first embodiment. In the present embodiment, the segment electrode driver unit 3 includes a constant current circuit 12 and an analog switch 11 for each segment electrode wiring. However, FIG. 2 shows only one set of constant current circuit 12 and analog switch 11 corresponding to one segment electrode wiring.

The controller 1 outputs a switch control signal (hereinafter referred to as SW control signal) to each analog switch 11, and the anode side of the organic EL element (organic thin film) 13 is connected to the constant current circuit 12 or the voltage _VSS. Connect to one of the wires that supply Specifically, for the analog switch 11 corresponding to the segment electrode wiring of the column where the pixel to be lit is present, the controller 1 connects the segment electrode wiring and the constant current circuit 12 (terminal A shown in FIG. 4). The analog switch 11 is set so as to be connected. Then, a constant current flows from the anode side to the cathode side of the organic EL element 13, and the organic EL element 13 emits light. The controller 1 is, with respect to the analog switch 11 corresponding to the column of the segment electrode wiring to emit light pixels is not present, and the segment electrode wiring, and a wiring for supplying a voltage V _SS (terminal shown in FIG. 4 B) The analog switch 11 is set so as to be connected. In this case, the anode side of the potential V _SS becomes an organic EL element, since the potential and equipotential of the selected common electrode wiring, the current from the anode side to the cathode side does not flow, the organic EL element 13 does not emit light.

  In addition, the controller 1 controls the constant current circuit 12 so that the constant current circuit 12 causes a constant current smaller than that during normal operation to flow during partial driving. The constant current that the constant current circuit 12 should flow during normal driving is referred to as normal time constant current. A constant current that the constant current circuit 12 should flow during partial driving is referred to as a partial constant current. The current value of the partial time constant current is smaller than that of the normal time constant current. For example, the controller 1 includes a register that stores information indicating whether normal driving or partial driving is performed, and allows a partial time constant current to flow from the constant current circuit 12 according to the information stored in the register. It may be controlled whether a constant current is normally applied. Alternatively, after switching to the partial drive according to the instruction from the external MPU 6, the constant current circuit 12 is controlled so that the partial current is supplied from the constant current circuit 12, and the normal drive is performed according to the instruction from the external MPU 6. After switching, the constant current circuit 12 may be controlled so that the constant current circuit 12 supplies a constant current at normal time.

  Even during partial driving, the organic EL element 13 is caused to emit light by passing a constant current (partial constant current) from the constant current circuit 12 to the organic EL element 13. Therefore, in the present embodiment, constant current driving is performed on the organic EL element 13 regardless of whether it is partial driving or normal driving.

The power supply circuit 5 supplies the voltages V _SS and V _CH to the common electrode driver unit 2. The power supply circuit 5 also supplies the voltage _VSS to the segment electrode driver unit 3. Furthermore, the power supply circuit 5 supplies the segment electrode driver unit 3 with a voltage V _cc for operating a constant current circuit included in the segment electrode driver unit 3 (that is, a voltage at which the constant current circuit can output a constant current). Supply. In the present embodiment, the voltage V _CH that the power supply circuit 5 supplies to the common electrode driver unit 2 and the voltage V _cc that the power supply circuit 5 supplies to the segment electrode driver unit 3 are the same, and the same voltage output terminal The case of outputting will be described as an example.

Power supply circuit 5, at the time of the partial driving, the voltage value of the voltage V _cc, thereby lower than the normal driving. As an aspect for instructing the power supply circuit 5 to perform the partial drive or the normal drive, for example, there is an aspect in which the external MPU 6 instructs the power supply circuit 5 to perform the partial drive or the normal drive. Alternatively, the controller 1 may instruct the power supply circuit 5 as to whether the partial drive or the normal drive is received when the controller 1 receives a signal indicating the partial drive or the normal drive from the external MPU 6. FIG. 1 shows a case where the controller 1 instructs the power supply circuit 5 to perform partial driving or normal driving.

FIG. 3 is an explanatory diagram illustrating an example of a component related to the output of the voltage V _cc (= V _CH ) in the power supply circuit 5. An input voltage _VIN from another power source (not shown) is input to the power circuit 5. The power supply circuit 5 includes a capacitor 21 for stabilizing the input power supply. One electrode of the capacitor 21 is connected to an input terminal of the input voltage V _IN, and the other electrode is connected to the input end of the voltage V _SS. The capacitor 21 has a capacitance C ₁ that can sufficiently stabilize the input voltage. An inductor 22 and a switching regulator control circuit (hereinafter simply referred to as a control circuit) 23 are provided at the subsequent stage of the capacitor 21.

In the example shown in FIG. 3, the control circuit 23 has five terminals, VIN, / SHDN, GND, SW, and FB. VIN is an input terminal of the input voltage _{V IN.} / SHDN is a terminal to which a shutdown control signal is input. The shutdown function not used, the input terminal of the input voltage V _IN is connected to the terminal VIN. When the control circuit 23 does not have a shutdown function, / SHDN may not be provided. GND _is a terminal connected to an input terminal of the _{V SS.} SW is a terminal that functions as a drain of an internal FET switch (not shown). FB is connected to an external resistor voltage dividing circuit and serves as an input terminal for feedback input. The inductor 22 has one end connected to the terminal VIN and the other end connected to the terminal SW.

Further, a Schottky diode 24 is provided after the connection point between the terminal SW and the inductor 22. The anode of the Schottky diode 24 is connected to the connection point between the terminal SW and the inductor 22. The cathode of the Schottky diode 24 is connected to the output terminal of the output voltage (here, V _cc (= V _CH )).

A first resistor 25 and a feedforward capacitor 28 are connected in parallel between a connection point between the output terminal of the output voltage and the cathode of the Schottky diode 24 and the terminal FB. The first resistor 25 is a resistor circuit whose resistance value can be switched by a SW control signal from the outside of the power supply circuit 5. Feedforward capacitor 28 is a capacitor for operation stabilization (specifically, prevent oscillation) and has a sufficient capacity C _f to prevent oscillation.

The power supply circuit 5 includes a second resistor 26 connected in series with the first resistor 25. One end of the second resistor 26 is connected to the first resistor 25 via a connection point between the first resistor 25 and the feedforward capacitor 28 and the terminal FB. The other end of the second resistor 26 via the connection point between the input end of the terminal GND and capacitor 21 and the voltage _{V SS,} is connected to the input end of the voltage _{V SS.}

The power supply circuit 5 includes a capacitor 27 for stabilizing the output voltage. One electrode of the capacitor 27 is connected to the electrode of the feedforward capacitor 28 (the electrode not connected to the terminal FB). The other electrode of the capacitor 27 is connected to the end of the second resistor 26 (the end not connected to the terminal FB). Capacitor 27 has a sufficiently stabilized capacity sufficient C ₂ output voltage.

The control circuit 23 senses (detects) the voltage at the terminal FB, and when the voltage at the terminal FB falls below the internal reference voltage, the terminal SW operates and raises _Vcc . As a result, the voltage at the terminal FB increases and the operation of the terminal SW is stopped. By repeating this, _Vcc is kept within a certain range. The output voltage _Vcc is determined by the resistance values of the first resistor 25 and the second resistor 26 and the above-described reference voltage. Specifically, the resistance value of the first resistor 25 is R ₁ , the resistance value of the second resistor 26 is R ₂ (both are in kΩ), and the above reference voltage is F _BB (the unit is V). )), The output voltage V _cc is determined as V _cc = {(R ₁ + R ₂ ) / R ₂ } · F _BB . Therefore, when the resistance value of the first resistor 25 is switched to a small resistance value, the output voltage _Vcc decreases, and when the resistance value of the first resistor 25 is switched to a large resistance value, the output voltage _Vcc increases. To do.

  FIG. 4 is an explanatory diagram illustrating a configuration example of the first resistor 25. As shown in FIG. 4, the first resistor includes two types of resistors 251 and 252 having different resistance values. Here, it is assumed that the resistance value of the resistor 251 is larger than the resistance value of the resistor 252. Further, the first resistor 25 includes an analog switch 253. For example, the analog switch 253 is connected to the second resistor 26, and one end of each of the two types of resistors 251 and 252 is connected to the output end of the output voltage. The analog switch 253 connects one of the resistors 251 and 252 to the second resistor 26 in accordance with an SW control signal input from the outside (for example, the external MPU 6 or the controller 1). As a result, the resistance value of the first resistor 25 changes according to the SW control signal input from the outside.

During partial driving, the controller 1 (which may be the external MPU 6) inputs an SW control signal that instructs connection between the resistor 252 having the smaller resistance value and the second resistor 26 to the analog switch 253. When the SW control signal is input from the outside, the analog switch 253 connects the resistor 252 having the smaller resistance value and the second resistor 26, and sets the resistance value of the first resistor 25 to be small. As a result, the voltage value of the output voltage decreases. That is, the power supply circuit 5 reduces the output voltage V _cc (= V _CH ).

Further, during normal driving, the controller 1 (which may be the external MPU 6) inputs an SW control signal that instructs connection between the resistor 251 having the larger resistance value and the second resistor 26 to the analog switch 253. When the SW control signal is input from the outside, the analog switch 253 connects the resistor 251 having the larger resistance value and the second resistor 26, and sets the resistance value of the first resistor 25 to be large. Then, the voltage value of the output voltage increases. That is, the power supply circuit 5 increases the output voltage V _cc (= V _CH ).

Thus, the power supply circuit 5 increases the output voltage V _cc (= V _CH ) during normal driving and decreases the output voltage V _cc (= V _CH ) during partial driving.

However, the voltage V _cc output during normal driving is determined as a voltage that allows the constant current circuit to output a normal constant current at least during normal driving, and the voltage V _cc output during partial driving is also at least partial. It is determined as a voltage that allows the constant current circuit to output a partial constant current during driving.

FIG. 5 is an explanatory diagram showing changes in the voltage _Vcc and the OLED drive voltage when the normal drive is switched to the partial drive in the present embodiment. As already described, the current value of the partial constant current that the constant current circuit 12 passes during the partial drive is larger than the current value of the normal constant current that the constant current circuit 12 (see FIG. 2) passes during the normal drive. small. Accordingly, as shown in FIG. 5, the OLED drive voltage decreases when switching to the partial drive. Further, when switching from the normal drive to the partial drive, the resistance value of the first resistor 25 (see FIG. 3) is decreased, so that the voltage _Vcc is also decreased.

FIG. 6 is an explanatory diagram illustrating an example of a change in drive waveform representing the potential of the common electrode wiring and the potential of the segment electrode wiring when switching from normal driving to partial driving in the present embodiment. In this example, it is assumed that all the common electrode wirings (64 wires) are sequentially scanned during normal driving. Then, eight common electrode wirings are arranged in the display area during partial driving, and the eight common electrode wirings are sequentially scanned during partial driving. In the example shown in FIG. 6, driving is assumed to start with normal driving. Therefore, it is assumed that the voltage V _CH output from the power supply circuit 5 to the common electrode driver unit 2 and the voltage V _cc output from the power supply circuit 5 to the segment electrode driver unit 3 have not yet decreased. In addition, it is assumed that the constant current circuit corresponding to the segment electrode wiring in the column in which the pixel to emit light flows normally passes a constant current, and the OLED drive voltage has not decreased yet.

Further, in FIG. 6, while the LP is at high level, the common electrode driver section 2 sets the potential of each common electrode wiring V _SS, also the segment electrode driver section 3 the potential of each segment electrode wirings V _SS The case of setting to is shown as an example. Such driving is called reset driving. Thus, by setting each common electrode wiring and each segment electrode wiring to the same potential between the selection periods, the charge accumulated in the reverse bias in the organic EL element can be discharged, and at the start of light emission The amount of charge to be charged can be reduced.

In FIG. 6, COM ₀ and COM _n indicate the potentials of the 0th and nth common electrode wirings, respectively. However, it is assumed that the nth common electrode wiring is a common electrode wiring arranged in the display area during partial driving. SEG _n represents an arbitrary potential among the plurality of segment electrode wirings.

  The controller 1 outputs FLM indicating the start of one frame and LP instructing switching of the common electrode wiring to be selected to the common electrode driver unit 2. When the FLM becomes high level, the common electrode driver unit 2 sequentially selects each common electrode wiring from the first row according to LP. The controller 1 also outputs LP to the segment electrode driver unit 2 when outputting LP.

COM ₀ indicates the potential of the 0th common electrode wiring. After the first LP is output, the common electrode driver section 2 sets the potential of 0-th common electrode wiring V _SS, it sets the potential of the other of the common electrode wiring V _CH. At this time, the segment electrode driver unit 3 supplies a normal time constant current from the constant current circuit corresponding to the segment electrode wiring in the column where the pixel to be lit is present. Specifically, the analog switch 11 (see FIG. 2) connects the segment electrode wiring of the column where the pixel to emit light exists and the constant current circuit 12 (see FIG. 2), and the constant current circuit 12 is organic. A normal time constant current is supplied to the selected common electrode wiring through the EL element 13. As a result, the potential of the segment electrodes (OLED driving voltage) is higher than the potential V _SS of the selected row. Note that the analog switch 11 (see FIG. 12) corresponding to the segment electrode wiring of the column where there is no pixel to emit light connects the segment electrode wiring to the wiring that supplies the voltage _VSS , and does not cause the organic EL element to emit light. Like that.

  The operation when the controller 1 outputs the next LP and the next common selection wiring is selected is the same.

Then, it is assumed that the external MPU 6 outputs a signal instructing the controller 1 to switch to partial driving. At this time, the controller 1 (or the external MPU 6) inputs an SW control signal that instructs connection between the resistor 252 and the second resistor 26 to the analog switch 253 (see FIG. 4). As a result, the power supply circuit 5 decreases the output voltage V _cc (= V _CH ). In addition, the controller 1 increases the output interval of LP (that is, increases the selection period of one common electrode wiring), and normally supplies the constant current output from the constant current circuit to the segment electrode driver unit 3. Control to switch from time constant current to partial time constant current.

When switching to partial driving is instructed from the external MPU 6, the controller 1 controls the common electrode driver unit 2 to scan the common electrode wiring arranged in the display area during partial driving. And the common electrode driver part 2 switches the common electrode wiring arrange | positioned at the display area at the time of partial drive, whenever LP is input. The common electrode driver section 2 sets the potential of the common electrode wirings selected V _SS, sets the potential of the other of the common electrode wiring V _CH. However, _VCH is lower than that during normal driving.

At this time, the segment electrode driver section 3 passes a partial time constant current from a constant current circuit corresponding to the segment electrode wiring in the column where the pixel to be lit is present. Specifically, the analog switch 11 (see FIG. 2) connects the segment electrode wiring in the column where the pixel to be lit is connected to the constant current circuit 12 (see FIG. 2), and the constant current circuit 12 A partial time constant current is passed through the selected common electrode wiring through the organic EL element 13. As a result, the potential of the segment electrode wirings (OLED driving voltage) is higher than the potential V _SS of the selected row. However, since the current value of the partial time constant current is lower than the normal time constant current, the OLED drive voltage also decreases. Incidentally, the segment electrode driver unit 3, for the segment electrode wirings of the columns of pixels to emit light is not present, is connected to the wiring for supplying the voltage V _SS (terminal shown in FIG. 2 B), the pixel (organic EL element) So that no current flows in

Therefore, when switching from the normal drive to the partial drive, both the voltage V _cc (voltage for operating the constant current circuit) output from the power supply circuit 5 and the OLED drive voltage decrease. That is, the voltage _Vcc is lowered so that the difference between the voltage _Vcc and the OLED drive voltage does not widen. Therefore, it is possible to reduce the power consumption when scanning the common electrode wiring in the region where an image is displayed during partial driving.

In the above example, as shown in FIG. 3, the same output terminal of voltage _{V cc} and the voltage _{V CH,} it shows the case where the _V cc ₌ V _CH. In the power supply circuit 5, the output terminal of the voltage V _cc, may be different from the output terminal of the voltage V _CH. Further, the voltage V _cc and the voltage V _CH may not be equal.

[Embodiment 2] Next, a second embodiment of the present invention will be described. The drive device of the second embodiment is shown in the same block diagram (see FIG. 1) as the drive device of the first embodiment, and will be described with reference to FIG.

In the second embodiment, the configuration and operation of the power supply circuit 5 are the same as those in the first embodiment. By SW control signal supply circuit 5 from the outside (external MPU6 or controller 1), a first resistor 25 (see FIGS. 3 and 4) for the point of changing the output voltage _{V cc} by switching the resistance value also, the This is the same as the first embodiment. However, the voltage V _cc in the present embodiment is the voltage for operating the constant current circuit included in the segment electrode driver unit 3 or the voltage for applying to the segment electrode. 3 represents a voltage to be supplied. Specifically, the output voltage V _cc of the power supply circuit 5 at the time of normal driving, a voltage capable of normally outputting the normal constant current in the constant current circuit during driving. Further, the output voltage V _cc of the power supply circuit 5 when the partial drive is used as the voltage applied to the segment electrodes.

  The operation of the common electrode driver unit 2 according to the controller 1 is the same as that in the first embodiment.

In the second embodiment, the segment electrode driver unit 3 operates in the same manner as in the first embodiment during normal driving. That is, at the time of normal driving, the segment electrode driver unit 3 performs a constant current from the segment electrode wiring of the column where the pixel to be lit exists in the selection period to the common electrode wiring of the selected row according to the controller 1 and the display data of the selected row Shed. Also, the segment electrode wirings of the columns of pixels to emit light is not present, connected to a wiring for supplying a voltage V _SS, so as not the constant current flows to the organic EL element.

However, at the time of partial drive, the segment electrode driver unit 3 operates as follows. The segment electrode driver unit 3 is a wiring for supplying the voltage _Vcc to the segment electrode wiring of the column where the pixel to be lit is present during the selection period without passing through the constant current circuit according to the display data of the controller 1 and the selected row. Connect to. Then, the constant voltage of V _cc -V _SS is applied to the segment electrode wiring and the organic EL element between the common electrode wiring of the selected row, a current flows from the anode side to the cathode side. Note that, during partial driving, the voltage _Vcc is lower than during normal driving, so that the current flowing through the organic EL element during partial driving is less than the constant current flowing during normal driving. Also, the segment electrode wirings of the columns of pixels to emit light is not present, connected to a wiring for supplying a voltage V _SS, so as not the constant current flows to the organic EL element. This is the same as during normal driving.

  FIG. 7 is an explanatory diagram illustrating a configuration example of the segment electrode driver unit according to the second embodiment. Components similar to those in the first embodiment will be described with the same reference numerals as in FIG. In the present embodiment, the segment electrode driver unit 3 includes a constant current circuit 12 and an analog switch 17 for each segment electrode wiring. However, FIG. 7 shows only one set of constant current circuit 12 and analog switch 17 corresponding to one segment electrode wiring.

The controller 1 outputs a SW control signal (switch control signal) to each analog switch 17, and supplies the constant current circuit 12, wiring for supplying the voltage V _cc , or voltage V _SS to the anode side of the organic EL element 13. Connect to one of the supplied wires.

Hereinafter, first, the operation during normal driving will be specifically described. During normal driving, the controller 1 connects the segment electrode wiring and the constant current circuit 12 (terminal A shown in FIG. 7) for the analog switch 17 corresponding to the segment electrode wiring in the column where the pixel to be lit exists. The analog switch 17 is set so that Then, a constant current flows from the anode side to the cathode side of the organic EL element, and the organic EL element 13 emits light. The controller 1 is, with respect to the analog switch 17 corresponding to the column of the segment electrode wiring pixel to emit light is not present, and the segment electrode wiring, and a wiring for supplying a voltage V _SS (terminal shown in FIG. 7 B) The analog switch 17 is set so as to be connected. Then, the anode side of the organic EL element becomes equipotential with the potential of the selected common electrode wiring, and the organic EL element 13 does not emit light.

  Thus, during normal driving, the driving device performs constant current driving on the organic EL element.

Next, the operation during partial driving will be specifically described. At the time of partial driving, for the analog switch 17 corresponding to the segment electrode wiring of the column in which the pixel to emit light exists, the controller 1 and the segment electrode wiring and the wiring for supplying the voltage _Vcc (terminal C shown in FIG. 7) Set the analog switch to connect. Then, a constant voltage (V _cc −V _SS ) is applied to the organic EL element, a current flows, and the organic EL element emits light. At this time, since a constant current is not sent from the constant current circuit to the organic EL element, constant voltage driving is performed instead of constant current driving. The controller 1 is, with respect to the analog switch 17 corresponding to the column of the segment electrode wiring pixel to emit light is not present, and the segment electrode wiring, and a wiring for supplying a voltage V _SS (terminal shown in FIG. 7 B) The analog switch 17 is set so as to be connected. This operation is the same as in normal driving. Thus, the constant current circuit 12 is not used during partial driving.

FIG. 8 is an explanatory diagram showing changes in the voltage _Vcc when the normal drive is switched to the partial drive in the present embodiment. The output voltage V _cc and the OLED drive voltage of the power supply circuit 5 during normal driving is the same as that shown in FIG. When the normal driving is switched to the partial driving, the first resistor 25 (see FIG. 3) of the power supply circuit 5 is switched so that the resistance value is reduced by an external SW control signal. As a result, the output voltage V _cc Will decline. In addition, when switched to the partial drive, among the analog switches (see FIG. 7) included in the segment electrode driver unit 3, the analog switch corresponding to the segment electrode wiring of the column where the pixel to emit light is present is the segment electrode. The wiring and the wiring for supplying the voltage _Vcc (terminal C shown in FIG. 7) are connected. Therefore, the potential of the segment electrode wiring in the column where the pixel to be lit is present is _Vcc . That is, the value of the output voltage _Vcc of the power supply circuit is equal to the potential of the segment electrode wiring.

FIG. 9 is an explanatory diagram showing an example of changes in drive waveforms representing the potential of the common electrode wiring and the potential of the segment electrode wiring when switching from normal startup to partial driving in the present embodiment. In this example, as in the case shown in FIG. 6, 64 common electrode wirings are sequentially scanned during normal driving, and 8 common electrode wirings are sequentially scanned during partial driving. Similarly to the case shown in FIG. 6, the driving is started by the normal driving. Therefore, it is assumed that the voltage V _CH output from the power supply circuit 5 to the common electrode driver unit 2 and the voltage V _cc output from the power supply circuit 5 to the segment electrode driver unit 3 have not yet decreased. In addition, it is assumed that the constant current circuit corresponding to the segment electrode wiring in the column where the pixel to emit light is present outputs a constant current. Furthermore, it is assumed that reset driving is performed as in the case shown in FIG.

In FIG. 9, COM ₀ and COM _n indicate the potentials of the 0th and nth common electrode wirings, respectively. However, it is assumed that the nth common electrode wiring is a common electrode wiring arranged in the display area during partial driving. SEG _n represents an arbitrary potential among the plurality of segment electrode wirings.

  The driving waveform during normal driving is the same as that shown in FIG.

It is assumed that the external MPU 6 outputs a signal instructing the controller 1 to switch to partial driving during normal driving. At this time, the controller 1 (or the external MPU 6) inputs an SW control signal that instructs connection between the resistor 252 and the second resistor 26 to the analog switch 253 (see FIG. 4). As a result, the power supply circuit 5 decreases the output voltage V _cc (= V _CH ). Further, the controller 1 lengthens the output interval of LP (that is, lengthens the selection period of one common electrode wiring).

When switching to partial driving is instructed from the external MPU 6, the controller 1 controls the common electrode driver unit 2 to scan the common electrode wiring arranged in the display area during partial driving. And the common electrode driver part 2 switches the common electrode wiring arrange | positioned at the display area at the time of partial drive, whenever LP is input. The common electrode driver section 2 sets the potential of the common electrode wirings selected V _SS, sets the potential of the other of the common electrode wiring V _CH. However, _VCH is lower than that during normal driving.

At this time, the segment electrode driver unit 3 sets the potential of the segment electrode in the column where the pixel to be lit is present to _Vcc . Specifically, the analog switch 17 (see FIG. 7) connects the segment electrode wiring in the column where the pixel to be lit is present and the wiring for supplying the voltage _Vcc (terminal C shown in FIG. 7). Then, a constant voltage is applied to the organic EL element 13 (see FIG. 7) between the segment electrode wiring and the selected common electrode wiring, and a current flows through the organic EL element 13. Incidentally, the segment electrode driver unit 3, for the segment electrode wirings of the columns of pixels to emit light is not present, is connected to the wiring for supplying the voltage V _SS (terminal shown in FIG. 7 B), the pixel (organic EL element) So that no current flows in

Therefore, in this embodiment, at the time of partial driving, the output voltage V _cc of the power supply circuit is lowered, and the wiring for supplying the voltage V _cc is connected to the segment electrode wiring of the column where the pixel to emit light is present. Therefore, the phenomenon (see FIG. 12) that has occurred in the past that the difference between the voltage _Vcc and the OLED drive voltage is widened during partial drive does not occur. As a result, it is possible to reduce power consumption when scanning the common electrode wiring in a region where an image is displayed during partial driving.

  Further, in the partial drive in the present embodiment, a constant current is applied to the organic EL element that emits light instead of flowing a constant current from the constant current circuit to the organic EL element that emits light. As described above, when a constant voltage is applied to the organic EL element to flow a current, a luminance gradient is generated as described with reference to FIG. However, the luminance gradient is not noticeable when the number of common electrode lines to be scanned is small (for example, when the number of common electrode lines to be scanned is 16 or less). Therefore, the number of common electrode wirings to be scanned during partial driving is preferably 16 or less. Further, in the normal driving in the present embodiment, since a constant current is supplied from the constant current circuit to the organic EL element that emits light, the problem of luminance gradient does not occur.

Also in this embodiment, as described in the first embodiment, the output terminal of the voltage V _cc, may be different from the output terminal of the voltage V _CH. Further, the voltage V _cc and the voltage V _CH may not be equal.

An organic EL panel having 128 segment electrode wirings and 64 common electrode wirings and having a dot size of 0.3 mm × 0.3 mm was driven by the driving apparatus of the first embodiment. The luminance of the organic EL element at the time of lighting was set to 100 cd / m ² . Further, the voltage _Vcc output from the power supply circuit 5 to the segment electrode driver unit 3 during normal driving is set to 16V. Then, the common electrode wiring was sequentially selected by normal driving (duty ratio 1/64), and all 128 × 64 pixels were turned on (lighted). At this time, the power supply current was 18 mA. The OLED drive voltage was 13V.

Further, the number of common electrode wirings to be scanned at the time of partial driving was eight, and partial driving was performed with a duty ratio of 1/8. The luminance of the organic EL element at the time of lighting was set to 100 cd / m ² . Further, the voltage V _cc output from the power supply circuit 5 to the segment electrode driver unit 3 during the partial drive is set to 11V. The power supply current was 2.3 mA when the entire area where the eight common electrode wirings to be scanned were arranged (display area during partial driving) was turned on. The OLED drive voltage was 8.5V.

  The power consumption during partial driving in this embodiment is 11 V × 2.3 mA = 25.3 mW.

The same organic EL panel as that of Example 1 was driven by the driving device of the second embodiment. Normal driving was performed in the same manner as in Example 1. Further, partial driving was performed at a duty ratio of 1/8. The luminance of the organic EL element at the time of lighting was set to 100 cd / m ² . Further, the voltage V _cc output from the power supply circuit 5 to the segment electrode driver unit 3 at the time of partial driving is set to 8.5 V, and a constant voltage is applied to the organic EL element to emit light without using a constant current circuit. Drove. The power supply current was 2.2 mA when the entire area where the eight common electrode wirings to be scanned were arranged (display area during partial driving) was turned on.

  The power consumption during partial driving in this embodiment is 8.5 V × 2.2 mA = 18.7 mW.

[Comparative Example] The same organic EL panel as in Example 1 was driven by a conventional driving method (driving method having a driving waveform illustrated in FIG. 11). Normal driving was performed in the same manner as in Example 1. In addition, the voltage _Vcc output from the power supply circuit 5 was not changed to 16 V even when switched to partial driving. In the partial drive, the partial ratio drive was performed so that the duty ratio was 1/8 and the luminance of the organic EL element during lighting was 100 cd / m ² . At this time, a constant current was supplied from a constant current circuit to the organic EL element to emit light. The power supply current was 2.3 mA when the entire area where the eight common electrode wirings to be scanned were arranged (display area during partial driving) was turned on.

  In this case, the power consumption during partial driving is 16 V × 2.3 mA = 36.8 mW.

  The power consumption in Example 1 using the driving apparatus of the first embodiment is 25.3 mW, which is about 31% lower than the power consumption (35.8 mW) shown in the above comparative example. Has been.

  In addition, the power consumption in Example 2 using the drive device of the second embodiment is 18.7 mW, which is about 49 power consumption compared to the power consumption (35.8 mW) shown in the above comparative example. .2% reduction.

  The present invention can be applied to driving of an organic EL display device, and particularly applicable to driving of an organic EL display device employing partial driving.

1 is a block diagram showing an example of a drive device for an organic EL display device according to a first embodiment of the present invention. Explanatory drawing which shows the structural example of the segment electrode driver part in 1st Embodiment. FIG. 3 is an explanatory diagram illustrating an example of a configuration unit related to output of a voltage V _cc in the power supply circuit 5. Explanatory drawing which shows the structural example of a 1st resistance. Explanatory drawing which shows the change of the voltage _Vcc and OLED drive voltage when switching from normal drive to partial drive in 1st Embodiment. Explanatory drawing which shows the example of the change of the drive waveform showing the electric potential of a common electrode wiring, and the electric potential of a segment electrode wiring. Explanatory drawing which shows the structural example of the segment electrode driver part in 2nd Embodiment. Explanatory drawing which shows the change of the voltage _Vcc when switching from a normal drive to a partial drive in 2nd Embodiment. Explanatory drawing which shows the example of the change of the drive waveform showing the electric potential of a common electrode wiring, and the electric potential of a segment electrode wiring. Explanatory drawing which shows the example of a display at the time of normal drive and partial drive. Explanatory drawing which shows the example of the change of the drive waveform showing the electric potential of a common electrode wiring, and the electric potential of a segment electrode wiring. Explanatory drawing which showed the fall of OLED drive voltage. Explanatory drawing which shows the cause of a brightness | luminance inclination.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Controller 2 Common electrode driver part 3 Segment electrode driver part 4 Organic EL panel 5 Power supply circuit 6 External MPU
25 1st resistance 251 252 Resistance 253 Analog switch

Claims (5)

A drive device for an organic EL display device comprising a plurality of common electrodes and a plurality of segment electrodes arranged so as to cross each other, and an organic thin film disposed between the plurality of common electrodes and the plurality of segment electrodes. And
A segment electrode driver having a constant current circuit for supplying a constant current to the segment electrode for each segment electrode;
A common electrode driver that sequentially scans the common electrode by selecting the common electrode;
During normal driving when the common electrode driver scans each common electrode, the segment electrode driver supplies a voltage that allows the constant current circuit to output a normal constant current that should be output during normal driving. A drive device for an organic EL display device, comprising: a power supply circuit that supplies a voltage lower than the voltage to the segment electrode driver during partial drive in which only a part of the common electrode is scanned . 2. The drive device for an organic EL display device according to claim 1, wherein the power supply circuit supplies, to the segment electrode driver, a voltage capable of outputting a partial time constant current to be output at the time of partial drive. . Control means for reducing the constant current flowing by the constant current circuit during partial driving from a normal constant current to a partial constant current having a current value smaller than the normal constant current,
The drive device for an organic EL display device according to claim 2, wherein the constant current circuit of the segment electrode driver reduces a constant current flowing through the segment electrode from a normal time constant current to a partial time constant current according to the control means during partial drive. . A segment electrode driver applies a voltage supplied from a power supply circuit to a segment electrode without using a constant current circuit during partial driving, so that the segment electrode is connected to the common electrode selected by the common electrode driver. The driving device of the organic EL display device according to claim 1, wherein a current is passed through the organic thin film. The drive device of the organic EL display device according to claim 4, wherein the number of common electrodes to be scanned at the time of partial drive is 16 or less.

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