JP2008076666A - Driving circuit for organic el element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving circuit for an organic EL element capable of suppressing the variation of ground potential caused by ground wiring resistance, thereby preventing image quality from degrading. <P>SOLUTION: A common ground line 90 is laid out in two adjacent output stages respectively. Then two adjacent lines of the laid-out ground line are connected respectively by another ground line 91. A similar operation is repeated to connect ground parts of respective output stages finally up to ground terminals 41 and 42. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a drive circuit for an organic EL (electroluminescence = electroluminescence) element. More specifically, the present invention relates to a ground wiring layout in a drive circuit of a display device which is a current output type drive circuit, for example, a display device composed of organic EL elements arranged in a matrix.

FIG. 1 shows the overall circuit configuration of the prior art.
An organic EL panel 10 in which organic EL elements are arranged in a matrix is driven by a data line driving circuit (column driver) 11 and a scanning line driving circuit (low driver) 12. The scanning line driving circuit 12 sequentially scans a series of element groups arranged in the row direction in the column direction, and is scanned by the data line driving circuit 11 by the scanning line driving circuit 12 to drive the element groups in the selected row. A current is selectively supplied to selectively drive the organic EL element to emit light. The data line driving circuit 11 is composed of a constant current source equal to or more than the data line, and each constant current source is composed of a current mirror circuit. In accordance with a control signal from the control circuit 13, modulation such as current modulation and output pulse width modulation is performed, and gradation display of the organic EL panel 10 is performed.

FIG. 2 is a block diagram of a conventional data line driving circuit.
The data line driving circuit 11 includes a control signal generation unit 20 that generates various control signals, a reference current generation unit 21 that generates a reference current for each RGB, an n-bit shift register 22, and an n-channel output stage 23. Yes.

FIG. 3 shows a partial circuit configuration of the output stage.
Actually, the reference current generation circuit 21 is arranged for each color of RGB, but is omitted in FIG. 3 and only one color is shown. The reference current generated by the reference current generator 21 for each RGB color is folded back to an n-channel output stage 23 by a current mirror circuit composed of a transistor M0 and transistors M1 to Mn, and further from a current mirror circuit composed of an output PMOS transistor. Output.

FIG. 4 shows a conventional layout example in which the circuit configuration shown in FIG. 3 is arranged on a chip.
As shown in FIG. 4, the ground line 40 of the output stage 23 including the reference current generating circuit 21 is common to all output channels. The ground pads 41 and 42, which are ground terminals, are arranged on the left and right sides of the chip in order to eliminate unevenness of the output pad pitch.

  Therefore, as shown in FIG. 5, the currents Iref1, Iref2,..., Iref (N) flowing through the output stage 23 are grounded to the left ground pad 41 in the left block and to the right ground pad 42 in the right block. To flow.

  In addition, in organic EL panels with large screens, the organic EL driver has a large number of output terminals per chip, and the trend toward narrower pitches and multiple outputs will increase as the screen size increases in the future. Therefore, it is predicted that the wiring resistance of the ground line cannot be ignored.

  When the wiring resistance of the ground line cannot be ignored, as shown in FIG. 5, the influence of the voltage drop Vdrop of each wiring resistance indicated by the reference symbol R becomes large. As can be seen from FIG. 5, since the current Iref is concentrated closer to the ground terminal, the voltage drop due to the wiring resistance becomes larger closer to the ground terminal.

  Accordingly, the distribution of the ground potential in the chip becomes a parabola that protrudes upward as shown in FIG. 6 (a line indicated by a solid line in the figure). In the prior art, the reference current Iref is returned to each output stage 23 by a current mirror circuit (Node A in FIG. 5). Specifically, Vgs (= reference voltage at NodeA) of the transistor M0 determined by flowing the reference current Iref to the diode-connected NMOS transistor M0 is input to the gates of the NMOS transistors M1 to Mn and is equivalent to the reference current Iref. Output currents (Iref1 to Iref (N)) are returned to the output stages 23.

  Here, if the GND potential in the chip has a distribution as shown in FIG. 6, the Vgs (Vref−Vgnd) of the NMOS transistors M <b> 1 to Mn in each output stage 23 becomes the NMOS transistor in the reference current generator 21. Since the Vgs are different due to the different ground potentials of the NMOS transistors M1 to Mn in each output stage 23, unlike the Vgs of M0, the reference current Iref generated by the reference current generator 21 is accurately supplied to each output stage 23. It wo n’t be wrapped.

  Therefore, the actual distribution of the output current has a shape as shown in FIG. 7, and this significantly reduces the image quality.

  An object of the present invention is to provide a drive circuit for an organic EL element that solves such a problem by providing a ground wiring layout in which the ground potential at the output stage is constant.

  In order to achieve the above object, the present invention provides a plurality of scanning lines for scanning each column of a plurality of organic EL elements arranged in a matrix at a constant cycle, and in a direction crossing the scanning lines. A plurality of data lines arranged and a plurality of drive sources connected to the data lines, respectively, and a drive current from the drive source according to a reference power source is scanned with the organic EL element through the data lines. In an organic EL element driving circuit having a data line driving means for supplying to a column, the ground potential of each output stage of the plurality of driving sources when the driving current flows is constant. A ground wiring layout in which the resistance value of each ground wiring from the output stage to the reference power supply is constant.

  In the above-described circuit according to the present invention, the organic EL element is for monochrome, and in the ground wiring layout, the ground part of the output stage corresponds to a tournament participant part in a tournament table, and the ground part is formed by a plurality of ground wirings. By connecting to the tournament table, the ground wiring is combined into one in the part corresponding to the winning decision, the wiring resistance in the same round part of the plurality of ground wirings is equal, and the part of the next game is divided into two parts. It is connected to the ground wiring, and the portion corresponding to the winning decision and the ground portion of the reference power supply may be connected by another ground wiring.

  In the above-described circuit of the present invention, the organic EL element is for color and is composed of an R element, a G element, and a B element, and the ground wiring layout includes the elements for each color as one group. The ground part of the output stage corresponds to a tournament participant (group) part in the tournament table, and the ground part is connected to the tournament table by a plurality of ground wirings in the part corresponding to the winning decision. Are connected to the ground wiring of the next round in the two divided parts, and the ground resistance of the reference power supply and the part corresponding to the winning decision are combined. The parts may be connected by another ground wiring.

  According to the present invention, since the ground wiring layout in which the resistance value of each ground wiring from the output stage to the reference power supply is made constant, it is possible to suppress the fluctuation of the ground potential due to the ground wiring resistance. As a result, a uniform output current distribution can be obtained, and image quality is not deteriorated.

(Embodiment 1)
FIG. 8 shows a main circuit of Embodiment 1 of the drive circuit for the organic EL element according to the present invention. The organic EL element is for monochrome, and in FIG. 8, transistors M1, M2,..., M (n) form a current mirror circuit with the transistor M0 of the reference current generator 21, and the wiring resistances R, R ′, R ″ represents an equivalent resistance of the ground wiring of the n-channel output stage 23 of the data line driving circuit 11.

  The ground wiring is arranged so that the reference currents Iref1 to Iref2 flowing through the transistors M1 to Mn all flow to the grounds 41 and 42 via the ground wiring equivalent resistance of the same value. As a result, the amount of voltage drop due to the wiring resistance becomes equal in all the channels of the output stage, so that the ground potential of the transistors M1 to Mn when Iref1, Iref2,. Such a non-uniform ground potential distribution is improved, and a uniform distribution is obtained in all channels of the output stage. Accordingly, the Vgs of the transistors M1 to Mn are also uniform, and as a result, the output current distribution can be uniform.

FIG. 9 shows an example of ground wiring actually laid out in the present embodiment.
9, the output stage 1 is an output stage circuit including a transistor M1, the output stage 2 is an output stage circuit including a transistor M2,..., And the output stage n is an output stage circuit including a transistor M (n).

  As shown in FIG. 9, a common ground line 90 is laid out at two adjacent output stages. Next, two adjacent lines in the laid out ground line are connected by another ground line 91. The same operation is repeated, and finally the ground portion of each output stage is connected to the ground terminals 41 and 42.

  As shown in the figure, the ground wiring layout is a tournament table, and the ground part of each output stage corresponds to the tournament participant part in the tournament table. The ground parts of each output stage are connected in a tournament table by a plurality of ground wirings, so that a plurality of ground wirings are grouped together in a part corresponding to the winning decision. The ground resistance 41 of the reference current generator 21 serving as a reference power source is connected to the ground wiring of the next game at the part where the wiring resistance in the same round part of the plurality of ground wirings is equal and divided into two parts. , 42 are connected by a ground wiring 80 different from the above.

(Embodiment 2)
FIG. 10 shows a main circuit of Embodiment 2 of the drive circuit for an organic EL element according to the present invention. The organic EL element is for color and is composed of an R element, a G element, and a B element. In FIG. 10 and the following FIG. 11, reference symbols R, G, and B are assigned to each color element, and the others are marked in the same manner as in the first embodiment.

  When performing color display, the output stage is normally arranged in RGBRGB. In R, G, and B, when the luminous efficiencies are different, the drive currents are different in R, G, and B. Therefore, in the same configuration as in the first embodiment, the current flowing for each pair is unbalanced, resulting in voltage The uniformity of the drop amount is broken, the uniformity of the output current is also deteriorated, and the image quality is deteriorated.

  Therefore, in this embodiment, since the adjacent R output stage, G output stage, and B output stage are handled as one group as shown in FIG. 10, current imbalance between the groups can be eliminated. It becomes possible to ensure the uniformity of the amount. Therefore, it is possible to make the output current distribution uniform even in the drive circuit of the organic EL element for color.

FIG. 11 shows an example of ground wiring actually laid out in the present embodiment.
In FIG. 11, output stage 1 is an output stage circuit including transistor RM1, output stage 2 is an output stage circuit including transistor GM1, output stage 3 is an output stage circuit including transistor BM1, and output stage 4 is an output stage including transistor RM2. Circuit, output stage 5 is an output stage circuit including transistor GM2, output stage 6 is an output stage circuit including transistor BM2,..., Output stage (n-2) is an output stage circuit including transistor RM (n), output stage ( n-1) is an output stage circuit including the transistor GM (n), and the output stage n is an output stage circuit including the transistor BM (n).

  In the present embodiment, as shown in FIG. 11, common ground lines are laid out in three adjacent (R, G, B output stages) output stages. Next, two adjacent lines in the laid out ground line are connected by another ground line 110. The same operation is repeated, and finally the ground portion of each output stage is connected to the ground terminals 41 and 42.

It is a block diagram which shows roughly an example of the whole structure of the conventional organic electroluminescent display panel. It is a block diagram of a data line driving circuit of a conventional organic EL display panel. It is a circuit diagram which shows a part of output stage of the data line drive circuit of the conventional organic EL display panel. It is a figure which shows the example of the conventional layout which arrange | positions the circuit structure shown in FIG. 3 on a chip | tip. It is a figure which shows the output current distribution and voltage drop distribution in the example of a conventional layout. It is a figure which shows the ground potential distribution in the example of a conventional layout. It is a figure which shows the image of the output current distribution in the example of a conventional layout. It is a circuit diagram which shows the principal part of Embodiment 1 of the drive circuit of the organic EL element which concerns on this invention. It is a figure which shows the example of the ground wiring actually laid out in Embodiment 1 of this invention. It is a circuit diagram which shows the principal part of Embodiment 2 of the drive circuit of the organic EL element which concerns on this invention. It is a figure which shows the example of the ground wiring actually laid out in Embodiment 2 of this invention.

Explanation of symbols

10 Organic EL Panel 11 Data Line Drive Circuit (Column Driver)
12 Scanning line drive circuit (low driver)
13 Control circuit 20 Control signal generator 21 Reference current generator 22 n-bit shift register 23 n-channel output stage 41, 42 Ground of reference current generator 90, 91, 110, 111 Ground wiring R, R ′, R ′ '' Equivalent resistance of ground wiring

Claims (3)

A plurality of scanning lines for scanning each column of a plurality of organic EL elements arranged in a matrix at a constant period;
A plurality of data lines arranged in a direction intersecting with the scanning lines;
A data line having a plurality of drive sources each connected to the data line and supplying a drive current from the drive source according to a reference power source to the scanned column of the organic EL element through the data line In an organic EL element drive circuit having a drive means,
A ground wiring layout in which the resistance value of each ground wiring from the output stage to the reference power supply is constant so that the ground potential of each output stage of the plurality of driving sources is constant when the driving current flows A drive circuit for an organic EL element, comprising: The drive circuit according to claim 1,
The organic EL element is for monochrome use,
In the ground wiring layout, the ground part of the output stage corresponds to a tournament participant part in the tournament table, and the ground part is connected to the tournament table by a plurality of ground wirings in the part corresponding to the winning decision. The ground wirings are combined into one, the wiring resistances in the same round part of the plurality of ground wirings are equal and connected to the ground wiring of the next game in the divided part, the part corresponding to the winning decision and the reference power supply The organic EL element drive circuit is characterized in that the ground portions are connected by another ground wiring. The drive circuit according to claim 1,
The organic EL element is for color and is composed of an R element, a G element, and a B element.
In the ground wiring layout, the elements for each color are grouped, and the ground part of the output stage corresponds to a tournament participant (group) part in the tournament table, and the ground part is formed by a plurality of ground wirings. By connecting to the tournament table, the ground wiring is combined into one in the part corresponding to the winning decision, and the wiring resistance in the same round part of the plurality of ground wirings is equal and divided into two parts in the next game. A drive circuit for an organic EL element, which is connected to a ground wiring, wherein a portion corresponding to the winning decision and a ground portion of the reference power source are connected by another ground wiring.

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