JP4841812B2 - Organic EL drive circuit - Google Patents

Description

  The present invention relates to an organic EL drive circuit and an organic EL display device, and more specifically, generates a current value corresponding to display data by a D / A conversion circuit using a current mirror circuit, via a terminal pin of an organic EL panel. In the current drive circuit of the column line (anode side drive line, hereinafter the same) for current driving the organic EL panel, the luminance unevenness can be reduced and the influence on the luminance variation of each product can be reduced. It relates to circuit layout.

In an organic EL display panel of an organic EL display device mounted on a mobile phone, a PHS, a DVD player, a PDA (portable terminal device), etc., the number of column pins is 396 (132 × 3) terminal pins and row lines are 162. One having a plurality of terminal pins has been proposed, and column line and row line terminal pins tend to increase further.
The output stage of the current drive circuit of such an organic EL display panel is provided with a drive circuit of a current source, for example, an output circuit using a current mirror circuit, corresponding to a terminal pin, regardless of whether it is an active matrix type or a simple matrix type.

The output circuit by the current mirror circuit is arranged corresponding to the terminal pin, and the drive stage thereof is, for example, a parallel drive current mirror circuit having a large number of output side transistors corresponding to the terminal pin (Japanese Patent Laid-Open No. 2003-255898). A reference current distribution circuit). Then, a reference current is received from the reference current generation circuit in front of the input stage and a mirror current is generated corresponding to the terminal pin, so that the reference current is distributed corresponding to the terminal pin and the output circuit is driven (Patent Document 1). . Further, a D / A conversion circuit (D / A) composed of current mirrors corresponding to the terminal pins is provided in front of the output circuit, and each D / A receives the mirror current as a reference drive current and receives this current. D / A conversion with reference to. In the D / A conversion, the received luminance display data is D / A converted on the basis of the received current to generate an analog conversion current corresponding to the display data corresponding to the terminal pin. The output circuit of the current mirror is driven by the analog conversion current, and a drive current for the organic EL element is generated corresponding to the terminal pin.
By generating a drive current for the organic EL element with such a current mirror configuration, for example, in the case of a passive matrix, a large current of about mA or 1 A is suppressed from a small reference current of about several μA while suppressing power loss. The current can be amplified. As a result, a drive circuit with low power consumption can be realized. In the case of an active matrix, a driving current of 1 nA to 10 μA can be obtained with low power consumption.

In such a current drive circuit of an organic EL display panel, a large number of unit transistors constituting a current mirror are arranged corresponding to pads.
FIG. 4 is an explanatory diagram showing the layout of the unit transistor array block (transistor block) and the transistors formed in the prior art for forming the D / A of the current drive circuit and the output stage current source. Yes.
4A is a transistor block that forms a D / A of the current driving circuit and an output stage current source, FIG. 4B is a plan view of a unit transistor that forms a current mirror, and FIG. 4C is a cross-sectional view thereof. FIG.
In the unit transistor 1, as shown in FIG. 4C, the transistor 1 is isolated in a rectangular region formed by the buried layer (B / L) 11 and the element isolation region 12, and the base region 13b and the emitter are separated. The region 13e and the collector region 13c are formed in a rectangular shape on the surface side of the substrate 16. Reference numerals 14b, 14e, and 14c denote a base contact, an emitter contact, and a collector contact, respectively. The collector contact 14c is connected to the collector region 13c through the collector wall 15 and the buried layer 11.
Reference numeral 17 denotes an NSG interlayer separation film, and reference numeral 18 denotes an upper polysilicon insulating layer (P-SiN).
Then, as shown in FIG. 4A, two such unit transistors 1 are arranged in the arrangement direction (lateral direction in the drawing, row direction) of the pads 2 in the transistor block 3 and are perpendicular to the pad arrangement direction. Many are provided in two rows in the direction (longitudinal direction, column direction). Such transistor blocks 3 arranged in two rows are repeatedly formed in the pad arrangement direction, and the current drive circuit corresponding to the terminal pins of the organic EL display panel is made into an IC.

In this two-row arrangement of transistor blocks 3, each terminal pin of the organic EL display panel is arranged by repeating G, R, and B, and accordingly, the arrangement is assigned corresponding to G, R, and B. A pad (output terminal) 2 connected to each terminal pin is also arranged in correspondence with the terminal pin arrangement.
For example, when the pad pitch is 50 μm, the element formation width is 44 μm, the horizontal interval is 6 μm, two transistors are formed in the element formation width of 44 μm at an interval of 50 μm, and each terminal pin is driven. A large number of transistors necessary for the circuit to be formed are formed in the vertical direction.
As a result, the unit transistors 1 in the two-row arrangement coincide with the positions of the pads 2 corresponding to the respective output terminal pins, and are, for example, about several tens to one hundred in the vertical direction (the length is 1.0 mm to The transistor 1 is arranged with a length of about 3.0 mm. Most of these transistors 1 are current mirror connected in the upper wiring layer.
At this time, the current mirror output circuit (output stage current source) and the current switching D / A of the current mirror configuration are selected from the two transistors in the positions where the pair characteristics are aligned as much as possible.

The current switching D / A in this specification and claims refers to D / A conversion by switching ON / OFF the current of the current source according to bit data for the currents of a plurality of current sources. This is a circuit for obtaining a current value.
FIG. 4A shows two rows, but in order to improve the integration rate, three terminal pins of G, R, and B are one unit (corresponding to a pixel pitch in the column direction of G, R, and B). In some cases, transistor blocks in which unit transistors 1 are arranged in six rows are repeatedly arranged in the row direction. At this time, the width in the terminal pin direction (low direction) is 150 μm. In this case, a drive circuit for current-driving each terminal pin corresponding to each pad 2 in units of two rows of G, R, and B, respectively. Is assigned in the vertical direction.
By the way, a drive circuit for an organic EL element is known in which an organic EL element arranged in a matrix is driven by current and the anode and cathode of the organic EL element are dropped to the ground (Patent Document 2). Also, a technique for driving an organic EL element with low power consumption using a DC-DC converter is known (Patent Document 3).
JP 2003-255898 A Japanese Patent Application Laid-Open No. 9-232074 JP 2001-143867 A

In the organic EL drive circuit that generates a drive current using the D / A having the current mirror circuit configuration described above, when a large current of about mA or 1 A is generated from a very small reference current of about several μA, the D / A A variation in the conversion accuracy of A causes a variation in the output current of the output stage current source, which causes luminance unevenness.
In particular, in the current mirror D / A having a current mirror configuration, by switching the current from the current source, the current amplified by weighting the reference current by 2 times, 4 times, 8 times, 16 times,. Since it is obtained as a mirror-connected output side transistor, the number of transistors to be current-mirror connected is about several tens to 100. Therefore, it is important to ensure the pair characteristics of the transistors in the current mirror configuration with respect to the input side transistors. This pair characteristic is affected by the distance between transistors that are integrated into an IC and the position where the transistors are selected.

In addition, the D / A conversion circuit composed of a current mirror is required to have high conversion accuracy in order to generate a drive current corresponding to display data indicating the light emission luminance of the organic EL element. When the vertically long transistor blocks 3 as described above are arranged in correspondence with the pads, the transistors of the transistor block 3 located at both ends of the formation area of the transistor block 3 are deteriorated in pairing.
The reason is that the transistor block 3 located inside has the same transistor block 3 at both ends (both sides), whereas the transistor block 3 is only on one side at both ends. As a result, the transistors formed in the transistor blocks 3 at both ends have characteristics that are not uniform in terms of physical properties as compared to the transistors formed in the inner transistor block 3 and are biased in physical stress. The difference comes out. As a result, the bare characteristics of the transistor as the current mirror circuit deteriorate.
As a result, the difference in the output current value between the terminal pins becomes large, which appears as uneven brightness. In particular, when a plurality of drive ICs are used, uneven brightness at the boundary between the ICs becomes conspicuous.
In the above-mentioned Japanese Patent Application Laid-Open No. 2003-255898 (Patent Document 1), in order to prevent luminance unevenness at the boundary between ICs, in the current mirror circuit that distributes the reference current, the input-side transistor has several tens of outputs. It is arranged at the center of the side transistor.

FIG. 5 shows an output current characteristic with respect to a terminal pin in the circuit disclosed in Japanese Patent Laid-Open No. 2003-255898. The inter-terminal characteristics of the output current of the current drive circuit are shown with the number of terminal pins of G, R, and B being 45 pins each. The line connecting the points is the actual measured value, and the solid line between these lines is the regression curve. The vertical axis represents the current change rate, and the unit is [%]. The horizontal axis is the terminal pin number (terminal position).
As seen from this characteristic, the output current decreases as the terminal pins at both ends are approached. The terminal pins at both ends correspond to the transistor blocks 3 at both ends of the formation area of the transistor block 3 on the substrate.
Even if the input side transistor is arranged at the center of a large number of output side transistors and the reference current is distributed as disclosed in JP-A-2003-255898, the luminance unevenness of the display screen of the organic EL panel cannot be sufficiently suppressed. The drop in the output current of the terminal pins at both ends has a great influence on the luminance variation for each product.
SUMMARY OF THE INVENTION An object of the present invention is to solve such problems of the prior art, and can reduce luminance unevenness and reduce the influence on luminance variation for each product, and an organic EL display device Is to provide.

The organic EL drive circuit or the organic EL display device according to the first aspect of the invention for achieving such an object is characterized in that an integrated organic EL drive for driving an organic EL element through current through a terminal pin of an organic EL panel is provided. In the circuit, a plurality of pads provided corresponding to the terminal pins and display data for luminance display by the organic EL elements respectively provided corresponding to the plurality of pads are received and an analog current corresponding thereto is generated. to have a D / a current mirror configuration, n times the array direction of the pad pitch of the pad (n is a positive integer) at least with respect to substantially the width has a width of the corresponding pad array direction There is provided a transistor array block having a plurality of at least two rows of rectangular transistor blocks having a plurality of transistors formed with two transistors. An organic EL element in which the transistors constituting the D / A conversion circuit are selected in the area inside the transistor arrangement block, and the D / A conversion circuits of the transistor blocks located in the areas at both ends of the transistor arrangement block are arranged in a matrix form It is a dummy circuit that is not used for driving.
In addition, the D / A conversion circuit is a current switching D / A, and further includes a plurality of current sources provided corresponding to pads for current driving the organic EL element, and the plurality of current sources are respectively connected to the pads. The transistors that are driven by the output currents from the corresponding D / A conversion circuits and that constitute the current source are selected in the transistor block, and the current source in the transistor block in which the dummy circuit is located in both end areas is selected. The current source of this dummy circuit is connected to the terminal pin of the organic EL panel for icon display .

In the second invention, the D / A conversion circuit and the current source are provided corresponding to the display colors of R, G, and B, the transistor block corresponds to R, G, and B, and R , G, B transistor blocks are sequentially repeated, a plurality of dummy circuit transistor blocks are provided, and the current source is an output stage current source having a current mirror circuit. A plurality of current sources corresponding to display colors of R, G, and B are connected in parallel to terminal pins of an organic EL panel for icon display .

As described above, in the first and second inventions, the basic configuration is a dummy circuit in which the transistor blocks located at both ends in the drive circuit formation region of the IC chip are not targeted for operation. The D / A or D / A formed in the transistor block located inside the circuit and the current source of the output stage reduce the bias of physical stress of the transistors forming these circuits, and the D / A The current mirror circuit can be composed of a highly paired transistor.
Thereby, since the drop of the output current of the terminal pins at both ends is reduced, the luminance unevenness can be reduced, and the influence on the luminance variation for each product can be suppressed.

FIG. 1 is an explanatory diagram of a layout of unit transistors constituting a D / A of a current driving circuit and a current mirror of an output stage current source of an embodiment to which an organic EL driving circuit of the present invention is applied.
FIG. 2 is an explanatory diagram of the output current characteristics between terminals.
FIG. 3 is a detailed explanatory diagram when R, G, and B are assigned to one transistor block.
FIG. 4 is a diagram illustrating a layout of a transistor block in the prior art for forming a D / A of a current driving circuit and an output stage current source, and an explanatory diagram of a transistor formed thereon, and
FIG. 5 is an explanatory diagram of the inter-terminal characteristics of the output current in FIG.
1 to 3, the same components as those in FIGS. 4 and 5 are denoted by the same reference numerals.

In FIG. 1, 10 is a column driver IC of an organic EL drive circuit, and 10a is an IC of a unit transistor constituting a current mirror of a D / A provided for a terminal pin of an organic EL panel and an output stage current source. It is a layout in a chip.
Reference numeral 3 denotes a transistor block having 2 × 42 transistors in units of 2 columns (2 columns), and is an array block shown in FIG. Reference numeral 6 denotes an arrangement block (dummy circuit) which is the same as the transistor block 3 but is not used for driving the organic EL elements arranged in a matrix.
The transistor block 3 is repeatedly formed in the order of B, G, and R with respect to each pad 2 at a pad pitch in the pad arrangement direction (lateral direction) across a predetermined gap. In the driving circuit formation region of the IC chip, the three transistor blocks 3 at both ends (both sides) are formed as unused transistor blocks 6. The same circuit as the inner arrangement block 3 is formed here, but no connection to the pad 2 is made. Therefore, no drive current is output.

The current drive circuit of the organic EL panel has a reference current generation circuit at the input stage, and a drive stage and an output stage are provided for each terminal pin of the organic EL panel. These are formed in the transistor blocks 3 and 6, respectively. The drive stage is provided with a reference current distribution circuit for distributing a reference current corresponding to each terminal pin and a current switching D / A having a current mirror configuration provided for each terminal pin. This D / A receives the display data and drives an output stage current source provided for each terminal pin.
Reference numeral 4 denotes a block in which the output stage current source in the transistor block 3 is formed, and is composed of 2 × 6 transistors. Reference numeral 5 denotes a block in which a D / A is formed in the transistor block 3, and includes 2 × 36 transistors provided behind the block 4.
An output stage current source circuit and D / A which are not operated as driving organic EL elements adjacent to the array blocks 4 and 5 are formed in the transistor block 3 as dummy blocks 4D and 5D. That is, three transistor blocks 6 are provided on each of the left and right sides of the transistor block formation area 7. The dummy blocks 4D and 5D do not serve as a drive circuit for driving adjacent organic EL elements arranged. Therefore, the dummy blocks 4D and 5D are not connected to the pads 2 or connected to the terminal pins of the dummy blocks 4D and 5D. However, as will be described later, the output stage current of the dummy circuit is used as an icon driving terminal pin of the organic EL panel. A source is connected to drive an organic EL element for icon display.

Here, the current switching D / A of the current mirror configuration is configured by setting the number of transistors of the current mirror circuit of the output stage current source to 10 and the number of transistors of the D / A current mirror circuit to 70, respectively. Alternatively, two dummy transistors are provided to realize the circuit of the embodiment described in Japanese Patent Laid-Open No. 2003-255898. FIG. 2 shows output current characteristics for the terminal pins in that case.
Details of the D / A and output stage current source circuits formed in the transistor blocks 3 and 6 are described in Japanese Patent Application Laid-Open No. 2003-308043 filed by the applicant and published.
As shown in FIG. 2, the number of terminal pins is reduced by two for all of B, G, and R, but the characteristics are flatter than in the case of FIG. 5, and variations in output current between terminal pins are reduced. The vertical axis represents the current change rate, and the unit is [%]. The horizontal axis is the terminal pin number (terminal position).

FIG. 3 is a detailed explanatory diagram of an embodiment in which R / G / B is not an independent transistor block 3 but a single transistor block 3a and a D / A and an output stage current source are allocated therein. . Each transistor block 3a has a configuration in which blocks of B, R, and G output stage current sources are arranged in the horizontal direction corresponding to the pads, and only D / A is arranged in the order of B, R, and G in the vertical direction. It is an arrangement.
The transistor arrangement block 3a is formed by arranging three transistor arrangement blocks 3 in one. The transistor block of the dummy circuit corresponding to the transistor block 6 located at both ends of the transistor block formation area 7 (see FIG. 1) has the same configuration, but is omitted in the drawing. In this case, one dummy circuit transistor block 3a is provided at each end of the IC chip.
3, 4Ri, 4Gi, 4Bi,... Are current sources that constitute an output stage in each transistor block 3a, and are assigned along the arrangement direction of the pads 2. In FIG. 5Ri, 5Gi, 5Bi,... Are D / A in each array block 7. This is assigned in a direction perpendicular to the arrangement direction of the pads 2.
The transistor blocks having the dummy circuits 4D and 5D are also provided at both ends of the transistor block formation area 7 with the same assignment of the output stage current sources 4Ri, 4Gi, and 4Bi and D / A5Ri, 5Gi, and 5Bi.
Similarly to the above, the number of transistors in the transistor block 3a is 84 × 3, and output stage current sources and D / As are provided corresponding to R, G, and B. Therefore, the total number of unit transistors in the transistor block 3a is 84 × 3 = 252.

In the embodiment of FIG. 3, in each transistor block 3a, a unit transistor 1 that constitutes a current mirror is selected in units of 3 × pad pitch width, and R, G, B output stage current sources and D / A (D / A) is assigned to form each current mirror circuit.
In the embodiment of FIG. 3, the arrangement block of the transistors forming the D / A is a rectangle having a width in the horizontal direction. By doing so, the selection range of the transistors having the pair characteristics constituting the current mirror circuit is expanded in the horizontal direction. In FIG. 4, the transistors having the pair characteristics are selected in the vertical direction, but the probability that the characteristics are uniform is higher than in this case.

By the way, in mobile phones and the like, icons indicating the reception state of radio waves and the remaining battery level are provided at the top of the display screen. Further, many icons are provided on the lower side of the display screen corresponding to specific operations.
Such icons are not the main organic EL elements that are arranged in a matrix and adjacent ones are driven to display the brightness according to the display data at that time, so there is a problem even if there is some variation in display brightness. Absent. Since these icons have large display pixels, a large driving current is required accordingly.
Therefore, the output stage current source of the block 4D of the transistor block 6 of the dummy circuit shown in FIG. 1 is assigned to drive the organic EL elements corresponding to these icons via the pad 2. An output stage current source of a dummy circuit is connected to an icon driving terminal pin of the organic EL panel to drive an organic EL element for icon display. In the case of icon display, the variation in the drive current value does not become a problem, so that the dummy circuit can be used effectively.

Thus, the dummy circuit 6, because the power supply is in a state in which power is supplied, be operated as a icon driven, for variations in the driving current to be sent to the terminal pins corresponding to the main organic EL device It does not affect the action. In short, the present invention does not have to operate as a circuit for driving adjacent organic EL elements in which the dummy circuits are arranged.
When driving this icon organic EL element, the amount of drive current increases, so that a plurality of current sources in the block 4D of the transistor block 6 connected to the pad 2 correspond to the organic EL element of one icon. It is good to drive by the parallel connection of a current source. Thereby, a large drive current can be easily generated.

As described above, in the embodiment, the transistor blocks 3 and 6 are provided with the D / A and the current source. However, in the active matrix organic EL panel, the drive current value is small, so the D / A The output of A itself can be used as the drive current. In this case, D / A is an output stage current source. The layout is such that the block 4 or 4D in which the output stage current source is formed in FIGS. 1 and 3 is eliminated, and the block 5 or 5D in which the D / A is formed comes to the top of the transistor blocks 3 and 6 to the pad 2. Will respond.
Therefore, in the present invention, the circuit provided in the transistor blocks 3 and 6 may be only D / A.

In the embodiment, transistor blocks at both ends (both sides) in the drive circuit formation region of the IC chip are assigned as dummy circuits. Therefore, it goes without saying that a circuit different from the drive circuit of the organic EL element may be formed at both ends of the drive circuit formation region of the IC chip. Such a dummy circuit may have one transistor block or two or more transistor blocks.
Further, the present invention is not limited to a passive type organic EL panel that directly drives an organic EL element directly connected to a column line, but an active matrix type that drives an organic EL element of a pixel circuit via a capacitor of the pixel circuit. It can be applied to an organic EL panel.
By the way, in the embodiment, a bipolar transistor is taken as an example, but it goes without saying that the present invention can be applied even if a MOSFET transistor is used instead of the bipolar transistor.

FIG. 1 is an explanatory diagram of a layout of unit transistors constituting a D / A of a current drive circuit and a current mirror of an output stage current source of an embodiment to which an organic EL drive circuit of the present invention is applied. FIG. 2 is an explanatory diagram of the inter-terminal characteristics of the output current. FIG. 3 is a detailed explanatory diagram when R, G, and B are assigned to one transistor block. FIG. 4 is an explanatory diagram of the layout of the transistor block in the prior art for forming the D / A of the current driving circuit and the output stage current source, and the transistors formed thereon. FIG. 5 is an explanatory diagram of the inter-terminal characteristics of the output current in FIG.

Explanation of symbols

1 ... unit transistor, 2 ... pad,
3, 3a ... transistor block,
6 ... Dummy circuit transistor block,
4Bi, 4Ri, 4Gi ... current drive circuit,
5Bi, 5Ri, 5Gi ... D / A,
7 ... A transistor block formation area,
10: Column driver IC.

Claims (3)

In an organic EL drive circuit that is made into an IC that drives an organic EL element through a terminal pin of an organic EL panel,
A plurality of pads provided corresponding to the terminal pins;
A plurality of D / A conversion circuits having a current mirror configuration that is provided corresponding to the plurality of pads and receives display data for luminance display by the organic EL element and generates an analog current corresponding to the display data;
A plurality of transistors having a width in the pad arrangement direction substantially corresponding to n times the pad pitch in the arrangement direction of the pads (n is a positive integer) and at least two transistors formed with respect to this width. A transistor array block having a plurality of at least two rows of rectangular transistor blocks,
Transistors constituting the D / A conversion circuit are selected in an area inside the transistor arrangement block, and the D / A conversion circuits of the transistor blocks located in both end areas of the transistor arrangement block are arranged in a matrix. It is a dummy circuit that is not used to drive the organic EL element ,
The D / A conversion circuit is a current switching D / A,
The D / A conversion circuit further includes a plurality of current sources provided corresponding to the pads for current-driving the organic EL element, and the plurality of current sources are provided corresponding to the pads, respectively. The transistors constituting each of the current sources are driven in the transistor block, and the dummy circuit includes the current sources in the transistor blocks located in the areas at both ends. The current source of the dummy circuit is an organic EL driving circuit connected to a terminal pin of an organic EL panel for icon display. 2. The organic EL drive circuit according to claim 1 , wherein the dummy circuit includes a plurality of transistor blocks, and the plurality of current sources of the dummy circuit are connected in parallel to terminal pins of the organic EL panel for displaying the icon. In an organic EL drive circuit that is made into an IC that drives an organic EL element through a terminal pin of an organic EL panel,
A plurality of pads provided corresponding to the terminal pins;
A plurality of D / A conversion circuits having a current mirror configuration that is provided corresponding to the plurality of pads and receives display data for luminance display by the organic EL element and generates an analog current corresponding to the display data;
A plurality of transistors having a width in the pad arrangement direction substantially corresponding to n times the pad pitch in the arrangement direction of the pads (n is a positive integer) and at least two transistors formed with respect to this width. A transistor array block having a plurality of at least two rows of rectangular transistor blocks,
Transistors constituting the D / A conversion circuit are selected in an area inside the transistor arrangement block, and the D / A conversion circuits of the transistor blocks located in both end areas of the transistor arrangement block are arranged in a matrix. It is a dummy circuit that is not used to drive the organic EL element,
The D / A conversion circuit is a current switching D / A,
The D / A conversion circuit further includes a plurality of current sources provided corresponding to the pads for current-driving the organic EL element, and the plurality of current sources are provided corresponding to the pads, respectively. The transistors constituting each of the current sources are driven in the transistor block, and the dummy circuit includes the current sources in the transistor blocks located in the areas at both ends.
The D / A conversion circuit and the current source are provided corresponding to display colors of R, G, B, the transistor block corresponds to R, G, B, and R, G, B The transistor blocks of the dummy circuit are provided in sequence and arranged, a plurality of the transistor blocks of the dummy circuit are provided, and the current source is an output stage current source having a current mirror circuit,
An organic EL driving circuit in which a plurality of current sources corresponding to display colors of R, G, and B of the dummy circuit are connected in parallel to terminal pins of an organic EL panel for icon display.

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