JP3786200B2 - Display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates Viewing device you PWM control a simple matrix display using a liquid crystal display element and an organic EL display device.
[0002]
[Prior art]
The matrix type display device includes an active matrix type having a non-linear element such as a transistor at each pixel at the intersection of the scanning electrode and the signal electrode, and a simple matrix in which each pixel at the intersection is directly connected to the display element without passing through the non-linear element. Broadly divided into types. As shown in FIG. 7, the simple matrix display 70 has a plurality of signal electrodes X (X1 to X4) and a plurality of scanning electrodes Y (Y1 to Y4) so as to be orthogonal to each other on two opposing substrates. Is provided. The signal electrode and the scanning electrode are usually composed of a large number of electrodes, respectively, but here, four cases will be described as an example.
[0003]
As shown in the timing chart of FIG. 8, the simple matrix display sequentially applies scanning voltages to the scanning electrodes Y1 to Y4 in synchronization with the scanning clock of the scanning side drive circuit 71, that is, the latch pulse LP for signal capture, and simultaneously outputs signals. A signal voltage is applied from the side drive circuit 72 to the signal electrodes X1 to X4. At this time, a crosstalk phenomenon occurs between each scanning electrode and each signal electrode due to capacitive coupling by a display element (for example, a liquid crystal display element or an organic EL display element), and the selected pixel A low voltage is also applied to the other pixels. This crosstalk phenomenon is unavoidable due to the structure of the simple matrix display, but usually the display characteristics are not greatly affected by this phenomenon.
[0004]
By repeating the application of the scanning voltage and the signal voltage for each frame representing image data for one screen, an image is displayed on the display.
[0005]
[Problems to be solved by the invention]
In order to control the display gradation of the simple matrix display, the signal voltage applied to the signal electrodes X1 to X4 is controlled by PWM (Pulse Width Modulation). In this case, a signal voltage having a width controlled according to each pixel is applied to each of the signal electrodes X1 to X4 as shown in (ii) to (v) of FIG. In this example, each signal voltage is applied to the rear part with a predetermined width from a certain position in the middle of the interval period Ti of the scanning clock LP to the end, and shows a case of rearward alignment.
[0006]
In this PWM control, a noise voltage Vnz-x1 is generated at the change point of each signal voltage (in this case, the rising point), as shown with respect to the signal electrode X1 as represented by (vi) in FIG. The noise voltage Vnz-x1 changes the potential of the scan electrodes Y1 to Y4. In addition, noise as indicated by (1) and (2) in the figure also occurs at the end of the interval period Ti of the scanning clock LP. These noise voltages Vnz-x1 also increase the influence of crosstalk. Similarly, the noise voltage Vnz is generated for the other signal electrodes X2 to X4, and the potential of the scanning electrode is changed.
[0007]
These noise voltages Vnz are always generated with the same direction polarity in the same scanning period (for example, Y1) for each frame. Therefore, the display voltage tends to cause shading and display unevenness on the display screen, resulting in deterioration of display quality. It was. Note that the same applies to the case where the PWM control signal voltage is applied to the front part by a predetermined width from the first part of the interval period Ti of the scanning clock LP, only that the noise polarity changes. .
[0008]
Therefore, the present invention provides a display device for PWM control of a simple matrix display that can substantially eliminate the influence of noise voltage generated at the rise and fall of the signal voltage in PWM control on the screen display. For the purpose.
[0009]
[Means for Solving the Problems]
The display device according to claim 1 is a simple matrix display in which a plurality of signal electrodes and a plurality of scanning electrodes are provided so as to be orthogonal to each other with a capacitively coupled display element interposed therebetween,
A scanning-side driving unit that sequentially scans the plurality of scanning electrodes and supplies a scanning voltage;
A signal-side drive unit that supplies a PWM signal voltage to each of the signal electrodes in synchronization with scanning of the scan-side drive unit;
The drive timing of the scanning side drive unit and the signal side drive unit is controlled, and the PWM signal voltage supplied to each of the signal electrodes can be selected separately from the forward PWM data and the backward PWM data. A control circuit for supplying the signal-side drive unit with a display signal for the pixel, and a control signal including a select signal for selecting either the front-end PWM data or the rear-end PWM data included in the pixel display data And
The signal side driver includes a shift register for holding separately the PWM asked rear and PWM data data submitted prior to individually included in the pixel display data, and the PWM data submitted before held separately to the shift register A data selector that selects any one of the post-alignment PWM data according to the select signal, and the front-end PWM signal corresponding to the pre-alignment PWM data to each of the signal electrodes based on the PWM data output from the data selector And a driver for supplying a post-alignment PWM signal voltage corresponding to the voltage or post-alignment PWM data.
[0010]
The display device according to claim 2 is the display device according to claim 1, wherein the simple matrix display uses an organic EL display element.
[0011]
According to a third aspect of the present invention, in the display device according to the first or second aspect, the PWM signal voltage includes a predetermined PWM signal voltage and a predetermined PWM signal voltage for each scan electrode. It is characterized in that it is controlled so as to be the same number of times within the period.
[0014]
A display device according to a fourth aspect is the display device according to any one of the first to third aspects, wherein the signal-side drive unit predetermines the forward PWM signal voltage and the backward PWM signal voltage. It is characterized by switching every frame period.
[0015]
According to a fifth aspect of the present invention, in the display device according to the first or second aspect , the signal-side drive unit is configured to use the PWM signal voltage for the odd-numbered scan electrodes as the post-shift PWM signal voltage. A post / leading combination that is the forward PWM signal voltage for even-numbered scan electrodes, and the forward PWM signal voltage for odd-numbered scan electrodes and the post-adjusted PWM signal voltage for even-numbered scan electrodes This is characterized in that the front / rearward combination is switched every frame period .
[0016]
The display device according to claim 6 is the display device according to any one of claims 1 to 5 , wherein the signal side drive unit and the scan side drive unit apply the PWM signal voltage and the scan electrode. The scanning voltage to be synchronized is synchronized with the frame period in a predetermined relationship and is converted into an alternating current.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of Viewing device of the present invention will be described with reference to the drawings.
[0018]
FIG. 1 is a diagram showing a schematic configuration of a display device according to an embodiment of the present invention, which includes a simple matrix display 10, a scanning side driving circuit 20, a signal side driving circuit 30, a power supply circuit 40, and a control circuit 50. ing.
[0019]
In FIG. 1, the display 10 is provided with a plurality of signal electrodes X (X1 to X4) and a plurality of scanning electrodes Y (Y1 to Y4) on two opposing substrates so as to be orthogonal to each other. The signal electrode X and the scanning electrode Y are usually composed of a large number of electrodes of about several hundreds, but for ease of understanding, four examples are given here as examples. A liquid crystal display element and an organic EL display element are sandwiched between the signal electrode X and the scanning electrode Y, and their intersections become display pixels. Each of these intersections has a structure coupled by electrostatic capacity, and constitutes a simple matrix display.
[0020]
The power supply circuit 40 generates six types of voltages V0 to V5 necessary for performing AC control on the display device, and supplies them to the scanning side drive circuit 20 and the signal side drive circuit 30, respectively. Each of these voltages is set to a predetermined value so as to increase (or decrease) sequentially from the voltage V0 to the voltage V5. Note that when the AC control is not performed, the number of necessary voltages may be small.
[0021]
The control circuit 50 forms display data, a clock, and various control signals, and supplies them to the scanning side driving circuit 20 and the signal side driving circuit 30, respectively. The display data D is PWM data for signal voltages applied to the signal electrodes X1 to X4 in order to control the display gradation of the display 10.
[0022]
In the present invention, the signal voltage is referred to as “a post-shift PWM signal voltage (hereinafter referred to as a post-shift signal voltage)” that is applied to the rear portion with a predetermined width from a position in the middle of the interval of the scan clock LP to the end. Alternatively, it is possible to arbitrarily select whether to use the “advanced PWM signal voltage (hereinafter referred to as the“ advanced signal voltage ”)” applied to the front part by a predetermined width from the first part of the interval period of the scanning clock. For this reason, the display data D for each pixel includes PWM data (hereinafter referred to as “adjusted data”) D1 for the after-adjusted signal voltage, and PWM data (hereinafter referred to as “adjusted data”) D2 for the approximated signal voltage. Is included. This display data D is supplied to the signal side drive circuit 30.
[0023]
The data shift clock CK is a clock for shifting the display data D and is supplied to the signal side drive circuit 30. The scanning clock LP is supplied to the scanning side drive circuit 20 to be a scanning signal for scanning the scanning electrode Y, and is supplied to the signal side driving circuit 30 to be a latch signal for latching the display data D for one line. The AC signal FR is an inverted signal for AC driving, and is not necessary when AC is not performed.
[0024]
The select signal SL is a signal for selecting whether to use the trailing data D1 or the leading data D2 of the supplied display data D, and is supplied to the signal side drive circuit 30.
[0025]
The start signal ST is a signal for starting scanning, and is supplied to the scanning side drive circuit 20.
[0026]
The scanning side drive circuit 20 receives the start signal ST, the scanning clock LP, and the AC signal FR, and sequentially scans the scanning electrodes Y1 to Y4 at a scanning clock interval while generating a predetermined scanning voltage.
[0027]
The internal structure of the signal side drive circuit 30 is shown in FIG. The shift register 31 sequentially takes and shifts display data D (D1, D2) by the shift clock CK. Data latch circuit when the display data D for one line (D1, D2) is stored in the shift register 31, the latch the display data D (D1, D2) by the scan clock LP.
[0028]
As shown in FIG. 3, the data selector 33 is composed of AND circuits AND1 and AND2, a NOT circuit NOT, and an OR circuit OR, and the display data D from the data latch circuit 32 is preceded by the trailing data D1. The shift data D2 is selected and output according to the select signal SL. This selection is performed so that the forward and backward movements of the scanning electrodes Y1 to Y4 are approximately equal times within an arbitrary period, such as for each pixel data, for each frame, for each of a plurality of frames.
[0029]
The level shifter 34 converts the level of the display data D1 or D2 selected from the data selector 33 and supplies it to the driver 35. The driver 35 generates a trailing signal voltage or a leading signal voltage based on the voltages V0, V2, V3, and V5 from the power supply circuit 40 in accordance with the level-shifted display data D1 or D2, respectively. Supply to X4.
[0030]
FIG. 4 is a timing chart for explaining the operation of the display device according to the first embodiment of the present invention.
[0031]
In FIG. 4, the scanning clock LP is output at every scanning interval Ti as shown in (i), and the scanning electrode Y is sequentially applied to the scanning electrodes Y1 to Y4 every frame in synchronization with the scanning clock LP as shown in (vii). Select repeatedly.
[0032]
On the other hand, the signal electrodes X1 to X4 are supplied with the trailing signal voltage in the first frame, and therefore the trailing signal voltage rises in the middle of each scanning interval Ti and continues to the end. The rise timings differ for each scanning interval and for each signal electrode X1 to X4 according to display data.
[0033]
At the rising edge of this signal voltage, a positive noise voltage Vnz-x1 is generated in the first frame as shown with respect to the signal electrode X1 as shown in FIG. 4 (vi), and this noise voltage Vnz-x1 is generated by the scanning electrodes Y1 to Y1. The potential of Y4 (mainly selected scan electrode, eg, Y1) is varied.
[0034]
In the subsequent second frame, the signal electrodes X1 to X4 are supplied with the leading signal voltage, and therefore the leading signal voltage falls in the middle of each scanning interval Ti. The timing of their fall differs for each scanning interval and for each signal electrode X1 to X4 according to display data.
[0035]
At the rise of the signal voltage, a negative noise voltage Vnz-x1 is generated in the second frame as shown with respect to the signal electrode X1 as shown in FIG. 4 (vi), and the noise voltage Vnz-x1 is generated by the scanning electrodes Y1 to Y1. The potential of Y4 is changed in the opposite direction to the first frame. Further, the influence of crosstalk is increased by the noise voltage Vnz-x1.
[0036]
Thus, although the noise voltage Vnz-x1 is generated at the change point of the rise or fall of the signal voltage, the polarity of the noise voltage is reversed every frame. Therefore, in the scanning period in which the scanning electrode Y1 is selected, the influence of the noise voltage Vnz-x1 is canceled out as shown by the arrow line in FIG. Similarly, the noise voltage is extinguished in the scanning period in which the scanning electrodes Y2 to Y4 are selected. The same applies to the third and subsequent frames. Furthermore, noise as indicated by (1) and (2) in the figure is generated at each end point of the interval period Ti of the scanning clock LP, but noise indicated by (1) and (2) in these figures is also generated. Each frame has a reverse polarity.
[0037]
In addition, as for the signal electrodes X2 to X4, the influence of the noise voltages Vnz-x2 to x4 is eliminated, as described for the signal electrode X1.
[0038]
As a result, it is possible to substantially eliminate the shading and unevenness of the display that have conventionally occurred due to the noise voltage Vnz.
[0039]
Further, the switching between the front alignment and the back alignment may be performed every predetermined frame period (for example, every 2 periods, every 4 periods, etc.) instead of being performed every frame. By making the PWM signal voltage applied to each of the signal electrodes X1 to X4 so that the forward and backward movements of the respective scanning electrodes (for example, Y1) are approximately equal in an arbitrary period, The influence of the noise voltage Vnz generated at the rise or fall of the signal voltage in the PWM control on the screen display is eliminated. This arbitrary period may be within a range that causes no problem in viewing the display image.
[0040]
Further, in FIG. 4, the signal electrodes X3 and X4 are different from those shown in the figure, and the signal electrodes X1 and X4 are used as the forward signal voltage in the first and third frames and as the backward signal voltage in the second and fourth frames. The signal voltage of X2 may be reversed. In this way, the influence of the noise voltage Vnz can be eliminated even between the signal electrodes X1 to X4. The combination of the signal electrodes may be alternate (that is, X1, X3 and X2, X4) as long as all signal electrodes X are divided into two. This concept can be similarly applied to other embodiments of the present invention.
[0041]
FIG. 5 is a timing chart for explaining the operation of the display device according to the second embodiment of the present invention.
[0042]
In FIG. 5, the PWM signal voltage to the signal electrodes X1 to X4 is shifted toward the scanning period in which the scanning electrodes Y1, Y3, that is, the odd-numbered scanning electrodes are selected in the first frame and the third frame. The scanning electrodes Y2 and Y4, that is, the signal voltage of the rear / front-adjusted combination (hereinafter referred to as the rear / front-adjusted signal voltage) that is forward-adjusted with respect to the scanning period in which the even-numbered scan electrodes are selected. Further, in the second frame and the fourth frame, the scanning electrodes Y1, Y3, that is, the odd-numbered scanning electrodes are shifted toward the scanning period, and the scanning electrodes Y2, Y4, that is, the even-numbered scanning electrodes are selected. A signal voltage (hereinafter referred to as a forward / backward signal voltage) of a forward / backward combination that is rearward with respect to the scanning period being generated is generated.
[0043]
The noise voltage Vnz in this case is a positive-negative-positive-negative noise voltage Vnz-x1 generated in the first frame, as shown for the signal electrode X1 as representative of FIG. Then, a negative-positive-negative-positive noise voltage Vnz-x1 is generated.
[0044]
Thus, although the noise voltage Vnz-x1 is generated at the change point of the rise or fall of the signal voltage, the polarity of the noise voltage Vnz-x1 is reversed corresponding to the scan electrodes Y1 to Y4 for each frame. Therefore, the influence of the noise voltage Vnz-x1 is eliminated in the scanning period in which each of the scanning electrodes Y1 to Y4 is selected, as indicated by the arrow line in FIG. The same applies to the third and subsequent frames.
[0045]
In the second embodiment, as in the first embodiment, the influence of the noise voltage Vnz can be eliminated. Furthermore, by switching between the back / front signal voltage and the front / back signal voltage, the signal voltage of the signal electrode does not change at each end point of the interval period Ti of the scan clock LP. Decrease. Therefore, noise as indicated by (1) and (2) in FIG. 4 (vi) does not occur and the change point of the PWM signal voltage is reduced, so that the influence on the power supply voltage and the ground voltage can be reduced.
[0046]
FIG. 6 is a timing chart for explaining the operation of the display device according to the third embodiment of the present invention.
[0047]
In FIG. 6, control by an AC signal is added to the second embodiment of FIG.
[0048]
In FIG. 6, as shown in (i), the AC signal FR is switched between positive and negative for each frame to perform AC. For this reason, as shown in (iii) and (iv), during the period in which the AC signal FR is positive, the signal voltage to the signal electrode X is the lighting voltage V0 and the extinguishing voltage V2, and the scanning electrode Y is selected when selected. The voltage V5 is applied when the voltage V5 is not selected. On the other hand, during the period when the AC signal FR is negative, the signal voltage to the signal electrode X is the lighting voltage V5 and the extinguishing voltage V3, and the voltage V0 is applied to the scanning electrode Y when selected and the voltage V4 is applied when not selected. In FIG. 6, the signal electrodes X2 and X3 are not shown.
[0049]
In this example, the period of the AC signal FR is synchronized with the rear / front-end signal voltage or the front / back-end signal voltage. Therefore, the PWM signal voltage to the signal electrodes X1 to X4 is shifted toward the scanning period in which the scanning electrodes Y1 and Y3, that is, the odd-numbered scanning electrodes are selected in the first and second frames. Y2 / Y4, that is, a rear / leading signal voltage that is forwarded is generated for a scanning period in which even-numbered scanning electrodes are selected. In the third and fourth frames, the scanning electrodes Y1 and Y3, that is, the odd-numbered scanning electrodes are moved forward with respect to the scanning period, and the scanning electrodes Y2 and Y4, that is, the even-numbered scanning electrodes are selected. A front / rear signal voltage that is rearward for a scanning period is generated.
[0050]
The noise voltage Vnz in this case is a positive-negative-positive-negative noise voltage Vnz-x1 generated in the first and second frames as shown in FIG. 6 (v) with respect to the signal electrode X1. 3. In the fourth frame, a negative-positive-negative-positive noise voltage Vnz-x1 is generated. Note that, for example, the voltage polarity of the first frame and the second frame is inverted due to alternating current, so the noise voltage Vnz-x1 is in the same direction with respect to the influence on the screen display.
[0051]
Therefore, the polarity of the noise voltage Vnz-x1 is reversed corresponding to the scan electrodes Y1 to Y4 every two frames. FIG. 6 (v) shows the influence of noise on the scan electrode Y, but the scan voltage varies depending on the selection / non-selection as described above in accordance with the AC control, so that the understanding is easy. Is shown as an image diagram.
[0052]
As a result, as indicated by an arrow line in FIG. 6 (v), the noise voltage of the first frame and the noise voltage of the third frame have the influence during the selected scanning period of each of the scanning electrodes Y1 to Y4. The noise voltage of the second frame and the noise voltage of the fourth frame cancel out their influences.
[0053]
Note that the cycle of the AC signal FR and the rear / leading signal voltage or the front / leading signal voltage are not limited to the example of FIG. 6, and appropriate cycles can be selected.
[0054]
In the third embodiment, the same effect as in the second embodiment can be obtained, and also in the AC drive display, the influence of the noise voltage is reduced regardless of the change in the polarity of the drive voltage. can do.
[0055]
【The invention's effect】
According to the present invention, the PWM signal voltage applied to each of the signal electrodes X1 to X4 is controlled so that the forward and backward positions of the scan electrodes (for example, Y1) are substantially equal within an arbitrary period. Therefore, the influence on the screen display of the noise voltage generated at the rise (or fall) of the signal voltage in the PWM control is eliminated. This arbitrary period may be within a range that causes no problem in viewing the display image. As a result, it is possible to substantially eliminate the shading and unevenness of the display that have conventionally occurred due to the noise voltage.
[0056]
In addition, the switching between the front alignment and the back alignment is performed at predetermined frame periods (for example, every 1 period, every 2 periods, every 4 periods, etc.), so as to be consistent with other display controls. Is easy.
[0057]
Further, the switching point of the PWM signal voltage is reduced by switching between the rear / fronting signal voltage and the front / lasting signal voltage, so that the influence on the power supply voltage and the ground voltage can be reduced. Further, in the AC drive display, the influence of the noise voltage can be similarly reduced regardless of the change in the polarity of the drive voltage.
[Brief description of the drawings]
FIG. 1 shows a structure of a display device according to the present invention.
FIG. 2 is a configuration diagram of a signal side drive circuit in FIG. 1;
FIG. 3 is a diagram showing a configuration example of a data selector in FIG. 2;
FIG. 4 is a timing chart of the display device according to the first embodiment.
FIG. 5 is a timing chart of the display device according to the second embodiment.
FIG. 6 is a timing chart of the display device according to the third embodiment.
FIG. 7 is a diagram showing a basic structure of a conventional simple matrix display.
FIG. 8 is a timing chart of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Simple matrix display 20 Scan side drive circuit 30 Signal side drive circuit 31 Shift register 32 Data latch circuit 33 Data selector 34 Level shifter 35 Driver 40 Power supply circuit 50 Control circuit LP Scan clock (latch pulse)
SL Select signal D (D1, D2) Display data X (X1 to X4) Signal electrode Y (Y1 to Y4) Scan electrode Vnz Noise voltage FR AC signal

Claims (6)

A simple matrix display in which a plurality of signal electrodes and a plurality of scanning electrodes are provided so as to be orthogonal to each other via a capacitively coupled display element;
A scanning-side driving unit that sequentially scans the plurality of scanning electrodes and supplies a scanning voltage;
A signal-side drive unit that supplies a PWM signal voltage to each of the signal electrodes in synchronization with scanning of the scan-side drive unit;
The drive timing of the scanning side drive unit and the signal side drive unit is controlled, and the PWM signal voltage supplied to each of the signal electrodes can be selected separately from the forward PWM data and the backward PWM data. A control circuit for supplying the signal-side drive unit with a display signal for the pixel, and a control signal including a select signal for selecting either the front-end PWM data or the rear-end PWM data included in the pixel display data And
The signal side driver includes a shift register for holding separately the PWM asked rear and PWM data data submitted prior to individually included in the pixel display data, and the PWM data submitted before held separately to the shift register A data selector that selects any one of the post-alignment PWM data according to the select signal, and the front-end PWM signal corresponding to the pre-alignment PWM data to each of the signal electrodes based on the PWM data output from the data selector And a driver for supplying a post-shift PWM signal voltage corresponding to the voltage or the post-push PWM data.   The display device according to claim 1, wherein the simple matrix display uses an organic EL display element.   The PWM signal voltage is controlled such that the forward PWM signal voltage and the backward PWM signal voltage are equal to each scanning electrode within a predetermined period. The display device according to 1 or 2.   4. The display device according to claim 1, wherein the signal-side driving unit switches between the forward PWM signal voltage and the backward PWM signal voltage every predetermined frame period. 5. . The signal-side drive unit is configured such that the PWM signal voltage is the trailing PWM signal voltage with respect to the odd-numbered scanning electrodes and the trailing / leading combination that is the leading PWM signal voltage with respect to the even-numbered scanning electrodes; The forward / rearward combination that is the forward PWM signal voltage for the odd-numbered scan electrodes and the forward-shifted PWM signal voltage for the even-numbered scan electrodes is switched every frame period. Item 3. The display device according to Item 1 or 2 .   2. The signal side driving unit and the scanning side driving unit convert the PWM signal voltage and a scanning voltage applied to the scanning electrode into an alternating current in synchronization with a frame period in a predetermined relationship. 6. The display device according to any one of items 1 to 5.

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