JP2006126601A - Drive circuit of organic electroluminescence display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the possibility of the occurrence of spike noise, in a power supply voltage which is supplied to a segment driver. <P>SOLUTION: The segment driver 12 starts driving of a second segment electrode line (corresponding to SEG<SB>2</SB>), after predetermined time, later from when starting of driving a first segment electrode line (corresponding to SEG<SB>1</SB>); and then after still a predetermined time later, starts driving of a third segment electrode line (corresponding to SEG<SB>3</SB>). In this way, drive starting time is delayed sequentially. As a result, a current I<SB>vin</SB>, which is supplied to the segment driver 12, is changed smoothly and the fluctuation of the power supply voltage V<SB>in</SB>becomes small. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  An organic EL display device using an organic EL panel having a structure in which an organic EL element is arranged in each pixel portion of a 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 formed of the organic EL elements are arranged on the substrate in a matrix form (see, for example, Patent Document 1).

  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.

  In an organic EL display device using an organic EL panel, a common driver is mounted in order to apply a drive voltage (generally a ground potential) as a selection voltage to each common electrode wiring line-sequentially. In addition, a segment driver that includes a constant current circuit connected to each segment electrode wiring and drives the constant current circuit according to display data is mounted. The common driver and the segment driver are each realized by a one-chip IC.

  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. In the passive organic EL panel, when line-sequential driving is performed, a current flows through the organic EL element of each pixel only during one selection period (when lighting) in one frame. Therefore, in order to ensure high luminance as the whole organic EL panel, it is necessary to flow a large amount of current through each organic EL element at a time.

  Also, a driving method of providing a period in which the common electrode wiring and the segment electrode wiring are set to, for example, the ground potential at the end of the selection period for the purpose of shortening the time from when voltage is applied to the pixel to when light is emitted Is often used. In such a period, no current flows through the pixel. That is, the constant current circuit does not pass current. Therefore, even when all the pixels in the display area are lit, the period for supplying current and the period for not supplying current appear alternately for the segment driver including the constant current circuit.

Japanese Patent Application Laid-Open No. 9-232074

  Then, particularly in the fully lit state, the period during which a large current is supplied to the segment driver and the period during which no current is supplied appear alternately, so that spike noise is likely to occur in the output voltage of the power source that supplies current to the segment driver. Become. When a large spike noise occurs, an overvoltage is applied to the transistor circuit constituting the segment driver, which may cause the transistor circuit to fail. In general, a stabilizing capacitor is inserted between the power supply line (a line for supplying current to the segment driver) and the ground level. The capacitor expands and contracts. When large spike noise occurs, the degree of expansion / contraction increases and may cause abnormal noise. Hereinafter, the reason why spike noise occurs will be described.

FIG. 3 is a schematic diagram showing one common electrode wiring 81, the switching unit 11a in the common driver 11, and the constant current circuits 12a, 12b, 12c, and 12n in the segment driver 12 together with diodes that schematically represent pixels. The voltage of the power supply for the segment driver 12 _{V in,} the current through the power line and _{I vin.} SEG _i (i = 1 to n) represents the i-th segment electrode, and COM _x represents the x-th common electrode.

FIG. 4 is a timing diagram for explaining the operations of the common driver 11 and the segment driver 12. In FIG. 4, V _ss indicates a ground potential, and V _COMH indicates a non-selection voltage applied to the common electrode wiring. FIG. 4 shows the state in the fully lit state.

In a selection period in which the common driver 11 applies a selection voltage to one common electrode wiring, a selection voltage (ground potential in this example) is applied to the common electrode by the common driver 11, and a segment corresponding to a pixel to be lit A predetermined voltage is applied to the electrode. In FIG. 4, the broken line waveforms in the segment electrodes SEG _{1 to} SEG ₃ indicate that a constant current flows through the segment electrode wiring. In the example shown in FIG. 4, a period in which the common electrode and the segment electrode are set to the ground potential is provided at the start of the selection period.

At the time of full lighting, there is a period in which a constant current flows in all the segment electrode wirings, and a period in which the segment electrode is set to the ground potential in the selection period, that is, a period in which no current flows, is provided. A period in which I _vin increases and a period in which no current flows alternately occur. Since such a large current change occurs, spike noise occurs _in the power supply voltage Vin as shown in the lowermost stage of FIG. As described above, when spike noise occurs, problems such as failure of the transistor circuit and generation of abnormal noise occur.

  Therefore, an object of the present invention is to provide a drive circuit for an organic EL display device that can reduce the possibility of occurrence of spike noise in a power supply voltage supplied to a segment driver.

  The drive circuit of the organic EL display device according to the present invention includes drive start time discrete means for shifting the time of starting application of the power supply voltage to each constant current circuit in the plurality of constant current circuits during the selection period. To do.

  All segment electrode wirings are grouped into a group consisting of a predetermined number of segment electrode wirings, and the driving start time discrete means starts applying the power supply voltage to the constant current circuits corresponding to the segment electrode wirings in each group. You may be comprised so that a time may be shifted.

  In the group, the discrete means for driving start time is the start of applying the power supply voltage to the constant current circuit corresponding to the segment electrode wiring to be driven first in the group, and the constant current corresponding to the segment electrode wiring to be driven last. It is preferable to shift the time point at which the application of the power supply voltage to the constant current circuit is started so that the time difference from the time at which the application of the power supply voltage to the circuit starts is within the invalid period.

  The drive start time discrete means is used to start applying the power supply voltage to the constant current circuit corresponding to one segment electrode wiring in the group and to the constant current circuit corresponding to the segment electrode wiring to be driven next. The time point at which the application of the power supply voltage is started to the constant current circuit is shifted so that the difference from the time at which the application of the power supply voltage is started is the same for all the segment electrode wirings in the group.

  According to the present invention, it is possible to reduce the possibility that spike noise occurs in the power supply voltage supplied to the segment driver, and to reduce the possibility that the segment driver breaks down or abnormal noise occurs in the drive circuit.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of a drive circuit together with an MPU (Micro Processing Unit) 40 and an organic EL panel 10 existing outside the drive circuit. The MPU 40 outputs display data to the drive circuit. The display data is stored in a memory built in the controller 13.

  FIG. 1 also clearly shows a stabilization capacitor 15 inserted in the power supply line to the common driver 11 and a stabilization capacitor 16 inserted in the power supply line to the segment driver 12.

  Similar to the configuration shown in FIG. 3, the segment driver 12 includes a constant current circuit corresponding to each segment electrode wiring on a one-to-one basis.

  The controller 13 outputs data (Data) corresponding to the display data in the memory to the segment driver 12 at a predetermined timing. Further, the controller 13 outputs a clock pulse (CP) and LP as timing signals to the segment driver 12. The segment driver 12 latches the input Data for one row using LP.

  Further, the controller 13 outputs, as timing signals, the FLM (first line marker) indicating the start of one frame and the LP (latch pulse) indicating switching of the driving common electrode wiring (selected row) to the common driver 11. .

The segment driver 12, in response to input of the LP, already applied a power supply voltage (input voltage) V _in order to drive the constant current circuit in response to Data being latched. That is, by applying a power supply voltage V _in the constant current circuit corresponds to the segment electrode wirings corresponding to Data on the lighting, the input side of the constant current circuit corresponds to the segment electrode wirings corresponding to Data showing the off Is set to the ground potential V _ss .

Here, the segment driver 12 does not start driving the constant current circuits at the same time, but shifts the driving start time. Specifically, all the segment electrode wirings are grouped, and after the predetermined time has elapsed since the first segment electrode wiring in each group starts to be driven, the second segment electrode wiring in each group starts to be driven, When a predetermined time further elapses, the drive start time is sequentially shifted so as to start driving the third segment electrode wiring in each group. Drive start and is specifically by making the start of application of power supply voltage V _in to the corresponding constant-current circuit flows a constant current (lit).

The operation of the segment driver 12 will be described in detail with reference to the timing chart of FIG. As shown in FIG. 2, the controller 13 outputs FLM to the common driver 11 at the start of one frame. When the FLM is input, the common driver 11 applies a selection voltage to each row, that is, each common electrode wiring in order from the first row (here, corresponding to COM ₁ ) in the selection period. The selection period corresponds to a period from when one LP is output until the next LP is output.

  The controller 13 outputs LP, CP, and Data to the segment driver 12. The controller 13 outputs data of each pixel to the segment driver 12 for each pixel as Data. The segment driver 12 captures Data by CP and shifts Data internally. When LP is input, the shifted data is latched, and each constant current circuit is driven according to the latched data. When the common driver 11 applies a selection voltage to the i-th row (i is one of 1 to the number of final rows) according to LP, the segment driver 12 captures the data captured in the immediately preceding selection period. Each constant current circuit is driven based on this.

In the example shown in FIG. 2, all segment electrode wirings are grouped as a group of three segment electrode wirings that are provided spatially continuously. FIG. 2 illustrates three segment electrode wirings SEG _{1 to} SEG ₃ , but each group has a (k + 1) th segment electrode wiring, a (k + 2) th segment electrode wiring, and a first segment electrode wiring, respectively. It is composed of the (k + 3) th segment electrode wiring. Here, k is 0 or a multiple of 3 smaller than the total number of segment electrode wirings.

Then, the segment driver 12, the LP is input, to drive the first (k + 1) th segment electrode wiring, the constant current circuit corresponding thereto, and applies the power supply voltage V _in (lit). Here, the segment driver 12 drives the (k + 1) th segment electrode wiring in all the groups. Further, the predetermined time from that point has passed, to drive the first (k + 2) -th segment electrode wiring, the constant current circuit corresponding thereto, and applies the power supply voltage V _in (lit). Here, the segment driver 12 drives the (k + 2) th segment electrode wiring in all the groups. Furthermore, after a predetermined time from that point, in order to drive the first (k + 3) th segment electrode wiring, the constant current circuit corresponding thereto, and applies the power supply voltage V _in (lit). Here, the segment driver 12 drives the (k + 3) th segment electrode wiring in all groups.

  In the example shown in FIG. 2, the period from the start of driving the (k + 1) th segment electrode wiring to the driving of the (k + 2) th segment electrode wiring, and the driving of the (k + 2) th segment electrode wiring The period from the start to driving the (k + 3) th segment electrode wiring is set to 1/3 of the period during which the segment electrode wiring is set to the ground level in one selection period. As described above, when the power supply voltage starts to be applied to the constant current circuit corresponding to one segment electrode wiring in the group, the power supply voltage is applied to the constant current circuit corresponding to the segment electrode wiring to be driven next. It is preferable to shift the time point when the application of the power supply voltage to the constant current circuit is started so that the difference from the time point when the application starts is the same for all the segment electrode wirings in the group.

According to such a driving method, the period during which the maximum current flows in the segment electrode wiring can be shortened. Further, as shown in FIG. 2, the current amount gradually increases (specifically, stepwise) from the time when the current _Ivin does not flow, and the current amount gradually decreases from the time when the maximum current flows. That is, the change in the current _Ivin can be smoothed. As a result, it is possible, as shown in FIG. 2, to reduce the variation in the power supply voltage V _in. In other words, the occurrence of spike noise can be suppressed. Therefore, it is possible to prevent the transistor circuit in the segment driver 12 from being damaged or from generating abnormal noise from the stabilizing capacitor 16.

The amount of current flowing through each segment electrode wiring and the period during which a constant current flows are the same as those shown in FIG. Accordingly, in the present embodiment, by causing the current to the segment driver 12 is temporally dispersed, it is also possible that suppresses the generation of spike noise in the power supply voltage V _in.

  In order to realize the control as described above, the drive circuit is configured as follows, for example.

  The segment driver 12 has a built-in counter for counting the CP. The counter is initialized in response to the input of the LP and starts counting the CP. Then, when the count value corresponding to the period from the start of driving the (k + 1) th segment electrode wiring to the driving of the (k + 2) th segment electrode wiring is reached, the (k + 2) th segment The drive of the electrode wiring is started. When the count value corresponding to the period from the start of driving the (k + 1) th segment electrode wiring to the driving of the (k + 3) th segment electrode wiring is reached, the (k + 3) th segment The drive of the electrode wiring is started. In this case, the drive start point discrete means for shifting the start point of applying the power supply voltage to each constant current circuit in the selection period is realized in the segment driver 12.

  Alternatively, after the controller 13 outputs LP, when it is time to drive the (k + 2) th segment electrode wiring, it outputs a signal to that effect to the segment driver 12, and the (k + 3) th (k + 3) th segment electrode wiring is output. When it is time to drive the segment electrode wiring, a signal to that effect may be output to the segment driver 12. In this case, it is realized in the controller 13.

As described above, in this embodiment, since the segment electrode wiring is started to be shifted, the possibility of spike noise occurring _in the power supply voltage Vin can be reduced.

  In the above embodiment, the case where all the segment electrode wirings are grouped into a group composed of three segment electrode wirings has been described. However, the number of segment electrode wirings constituting the group is two or more. It can be any number.

  However, the sum of the deviation amounts within one group is within a period in which the segment electrode wiring is set to the ground level in one selection period. Here, the shift amount is a difference between the drive start time of the segment electrode wiring that starts driving first and the drive start time of the segment electrode wiring that starts driving last in the group. That is, the drive start time discrete means corresponds to the time point at which the power supply voltage starts to be applied to the constant current circuit corresponding to the segment electrode wiring that is driven first and the segment electrode wiring that is driven last in the group. Under the condition that the time difference from the start of applying the power supply voltage to the constant current circuit is within the invalid period (the period in which the segment electrode wiring is set to the ground level in one selection period), the constant current circuit On the other hand, the start time of applying the power supply voltage is shifted.

  The present invention can be applied to an organic EL display device in order to protect the segment driver and prevent the generation of abnormal noise.

The block diagram which shows the structure of a drive circuit. FIG. 6 is a timing chart for explaining the operation of the drive circuit. The schematic diagram which shows a common driver, a segment driver, a pixel, etc. typically. The timing diagram for demonstrating operation | movement of a general common driver and a segment driver.

Explanation of symbols

10 Organic EL Panel 11 Common Driver 12 Segment Driver 13 Controller 14 Power Supply Circuit 15 Stabilizing Capacitor 16 Stabilizing Capacitor 40 MPU

Claims (4)

The segment in an organic EL display device, comprising: an organic EL panel arranged so that a plurality of common electrode wirings and a plurality of segment electrode wirings intersect; and a common driver that drives the plurality of common electrode wirings in a line-sequential manner. In the drive circuit for driving the electrode wiring, including a plurality of constant current circuits connected to each of the plurality of segment electrode wirings in a one-to-one relationship,
Drive start time discrete means for shifting the start time of applying the power supply voltage to each constant current circuit in a plurality of constant current circuits in a selection period in which the common driver applies a selection voltage to one common electrode wiring; A drive circuit for an organic EL display device. All the segment electrode wires are grouped into a group consisting of a predetermined number of segment electrode wires,
The drive circuit of the organic EL display device according to claim 1, wherein the drive start time discrete means shifts a time when the power supply voltage starts to be applied to the constant current circuit corresponding to the segment electrode wiring in each group. An invalid period during which the constant current circuit is not driven is determined in the selection period,
In the group, the discrete means for driving start time is the start of applying the power supply voltage to the constant current circuit corresponding to the segment electrode wiring to be driven first in the group, and the constant current corresponding to the segment electrode wiring to be driven last. The organic EL display according to claim 2, wherein a time point at which the power supply voltage is started to be applied to the constant current circuit is shifted so that a time difference from a time point at which the power supply voltage is started to be applied to the circuit is within the invalid period. Device drive circuit. The drive start time discrete means is used to start applying the power supply voltage to the constant current circuit corresponding to one segment electrode wiring in the group and to the constant current circuit corresponding to the segment electrode wiring to be driven next. 4. The organic electroluminescent device according to claim 2, wherein a time point at which the power supply voltage is started to be applied to the constant current circuit is shifted so that a difference from a time point at which the power supply voltage starts to be applied is the same for all the segment electrode wirings in the group. A driving circuit for an EL display device.

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