JPH0750390B2 - Display device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device such as a liquid crystal display device to which a matrix driving method is simply applied.

2. Description of the Related Art FIG. 2 is a block diagram showing the configuration of a conventional simple matrix drive type liquid crystal display device. The display panel 1 of this liquid crystal display device has 16 data-side electrodes X (hereinafter referred to as segment electrodes) and 10 scanning-side electrodes Y (hereinafter referred to as common electrodes) vertically and horizontally via a liquid crystal layer. It is configured by arranging pixels of 16 × 10 dots in a matrix by crossing three-dimensionally. Further, each segment electrode X is connected to the data side drive circuit 2, and each common electrode Y is connected to the scanning side drive circuit 3.

In the data side circuit 2, an analog switch 4 is connected to each segment electrode X, and a voltage generating source (not shown) 4 is connected via the switches 5 and 6 and the analog switch 4.
The modulation voltages V ₀ , V ₂ , V ₃ and V ₅ of various kinds are selectively applied to each segment electrode X. The analog switch 4 is connected to a level converter 7, and the level converter 7 is connected to a shift register 9 via a latch circuit 8. The shift register 9 is a circuit for performing a shift operation in synchronization with a clock signal CP2 input from its clock input terminal to transfer the display data D corresponding to each segment electrode X, and the display transferred by the shift register 9 is displayed. The data D is held in the latch circuit 8 in synchronization with the clock signal CP1 and sent to the level converter 7. In the level converter 7,
The level of the modulation voltage according to the sent display data D is determined, and the modulation voltage of that level is applied to the corresponding segment electrode X.

On the other hand, also in the scanning side drive circuit 3, an analog switch 10 is connected to each common electrode Y, and four types of write voltages V ₀ , V ₁ are supplied from a voltage source (not shown) via the switches 11, 12 and the analog switch 10. , V ₄ and V ₅ are selectively applied to each common electrode Y. The analog switch 10 is connected to the level converter 13, and the level converter 13 has a latch circuit 14
Is connected to the shift register 15 via. The shift register 15 is a circuit for performing a shift operation in synchronization with a clock signal CP1 input from the clock input terminal thereof and transferring scan data S for line-sequentially designating the common electrode Y. Transferred scan data S
Is held by the latch circuit 14 in synchronization with the clock signal CP1 and sent to the level converter 13. In the level converter 13, the level of the write voltage is determined according to the presence or absence of the scan data S, and the write voltage of that level is applied to the corresponding common electrode Y.

FIG. 3 is a waveform diagram showing the relationship between the write voltage V _C applied to any common electrode Y of the display panel 1 in the liquid crystal display device and other timing signals, and FIG. 5 is a waveform diagram showing the relationship between the modulation voltage V _S applied to any segment electrode Y of FIG.

In FIGS. 3 and 4, FIGS. 3 (1) and 4
FIG. 1A shows the waveform of the AC inversion signal M that serves as a guide for inverting the polarity of the voltage applied to the pixel for each field, and FIGS. 3B and 4B show the common electrode. The waveform of the clock signal CP1 that gives the timing for switching and selecting Y, that is, the timing for holding the display data D corresponding to all the pixels on one common electrode Y every time the scanning line is switched is shown. In the clock signal CP1, ten pulses corresponding to ten common electrodes Y are output during one field period.

As shown in FIG. 3 (3), in the first field, the voltage V ₀ is applied to the common electrode Y as the write voltage V _C for selecting the common electrode Y, and when it is not selected, the write voltage V _C is the voltage V _{C. 4} is applied to the common electrode Y. In contrast, in the second field voltage V ₅ is applied as a write voltage V _C at the time of selection, voltages V ₁ as the write voltage V _C at the time of non-selection
Is applied.

As shown in FIG. 4 (3), the modulation voltage V _S for turning on the pixel is set to the voltage V _S in the first field.
₅ , the voltage V ₀ is applied to the segment electrode X in the second field, and the voltage V ₃ is used in the first field and the voltage V ₂ is used in the second field as the modulation voltage V _S for turning off the pixel. It is applied to the segment electrode X.

FIG. 5 shows an applied voltage based on the segment electrode X in the pixel which is driven on in the first field (FIG. 5 (1)) and an applied voltage in the pixel which is driven off (the fifth voltage).
Each waveform in FIG. 2B is shown.

That is, in the first field, the voltage applied to the pixel which is turned on and is turned on, for example, is the write voltage V _C (=) applied to the common electrode Y as shown in FIG.
V ₀ ) and the modulation voltage V _S (= V ₅ ) corresponding to the ON drive applied to the segment electrode X becomes a difference V ₀ −V ₅ , which is applied to a pixel which is driven OFF and becomes a non-lighting display state, for example. As shown in FIG. 5 (2), the voltage is the difference V ₀ −V ₃ between the write voltage V _C (= V ₀ ) and the modulation voltage V _S (= V ₃ ) corresponding to the off driving. In the second field, the polarities of these applied voltages are reversed, whereby alternating current inversion drive is performed.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the above-described liquid crystal display device, among the pixels arranged on the common electrode Y, the difference between the number of pixels that are driven on and the number of pixels that are driven off, that is, the display pattern for each scanning line There is a problem that the load capacitance applied to the common electrode Y differs depending on the difference between the two, and therefore even if there is a pixel that is driven on or a pixel that is driven off, there is a difference in brightness between scanning lines.

That is, when the pattern shown in FIG. 6 is displayed on the display panel 1, for example, in the upper half screen having the horizontally long white strip portion in the black background portion, the a portion and the b portion have the same black display. In fact, the part b is actually darker than the part a. This phenomenon is the same between the parts c and d on the opposite side.

The reason is that there are no pixels that are turned on on a scan line that does not include a white band, whereas a large number of pixels corresponding to the white band are driven on in a scan line that includes a white band. Therefore, the transient current flowing through the common electrode Y corresponding to this scanning line is large, and the rounding of the waveform of the write voltage V _C applied to the common electrode Y shown in FIG. That is, the write voltage
If the rounding of the waveform of V _C is large, the effective value of the drive signal of the off drive applied to the pixel shown in FIG.
As a result, the portion b becomes darker than the portion a.

Further, in the lower half screen having a horizontally elongated black strip portion in the white background portion of the pattern shown in FIG. 6, even though the e portion and the f portion have the same white display, the f portion is actually larger than the e portion. The part becomes brighter. A similar phenomenon occurs between the g portion and the h portion on the opposite side.

In this case, the phenomenon is that all the pixels are turned on on the scanning line that does not include the black band portion, whereas the number of pixels that are on-driven corresponding to white display is on the scanning line that includes the black band portion. Therefore, the transient current flowing through the common electrode Y corresponding to this scanning line is reduced accordingly, and the rounding of the waveform of the write voltage V _C applied to the common electrode Y shown in FIG. 3 (3) is accordingly reduced. Arises to become. That is, if the waveform rounding of the write voltage V _C is small, the effective value of the drive signal for ON drive applied to the pixel shown in FIG. 5 (1) becomes high, and as a result, the part b is more effective than the part e. Becomes brighter.

Therefore, an object of the present invention is to provide a display device capable of eliminating a difference in contrast due to a difference in display pattern between scan lines.

Means for Solving the Problems The present invention has a display panel in which a dielectric layer is interposed between a plurality of scanning side electrodes and a plurality of data side electrodes arranged in a direction intersecting with each other, and the scanning side electrode and the data side are provided. Each pixel constituted by the dielectric layer at the intersection of the electrodes is turned on / off by sequentially applying the write voltage to the scan electrodes while the modulation voltage according to the display data is applied to the data side electrodes. In the display device described above, an extension of each scanning-side electrode formed to extend beyond the substantial display area of the display panel, and a plurality of correction data-side electrodes arranged in a direction intersecting with the extension. A correction area of a display panel formed by interposing a second dielectric layer having a larger dielectric constant than the dielectric layer and a pixel on the scanning side electrode to which a writing voltage is applied, which is turned on. of A correction area that selects the number of electrodes on the correction data side that are complementary to each other and applies a modulation voltage that is equivalent to driving the electrodes on to correct the load capacitance at each electrode on the scanning side to a substantially constant value. A display device comprising: a driving unit.

According to the present invention, in the practical display area of the display panel, the number of correction data that is complementary to the number of data side electrodes to which the modulation voltage corresponding to ON driving is applied. Since the correction voltage corresponding to the ON drive is applied to the side electrodes by the correction drive means, the load capacitances applied to the respective scan side electrodes become substantially equal. Therefore, the rounding of the write voltage waveform applied to each scanning-side electrode is almost equal without being affected by the difference in the display pattern in each scanning line, and the brightness of the pixels to be driven on or off is the same. Differences between them are improved.

Embodiment FIG. 1 is a block diagram showing the configuration of a simple matrix drive type liquid crystal display device which is an embodiment of the present invention.

The display panel 21 of this liquid crystal display device is substantially composed of a display area 21a for displaying an image and a correction area 21b for correcting the contrast in the display area. Of these, the display area 21a includes 16 segment electrodes X1 to X16.
(Hereinafter, any segment electrode is indicated by a symbol X), and 10
The common electrodes YA to YJ (hereinafter, an arbitrary common electrode is denoted by a symbol Y) are crossed vertically and horizontally through the liquid crystal layer, and the segment, the electrode X, and the common electrode Y are formed.
Arranged in a matrix by the liquid crystal layer at the intersection of
16 x 10 dot pixels are given. Also, the correction area
Reference numeral 21b denotes a display area of eight correction segment electrodes X17 to X24 (hereinafter, any correction segment electrode is indicated by reference numeral Xa), which is half the number of the segment electrodes X, and the common electrode Y.
The extension formed over 21a is vertically and horizontally crossed via a dielectric layer having a dielectric constant ε2 (2 × ε1) which is twice the dielectric constant ε1 of the liquid crystal layer. Further, each segment electrode X and the correction segment electrode Xa are connected to the data side drive circuit 22, and each common electrode Y is connected to the scanning side drive circuit 23.

In the data side drive circuit 22, an analog switch 24 is provided for each segment electrode X and correction segment electrode Xa.
Connected, switches 25 and 26 and analog switch 24
Four types of modulation voltage from a voltage source not shown via
V ₀ , V ₂ , V ₃ and V ₅ are selectively applied to each segment electrode X and correction segment electrode Xa. The analog switch 24 is connected to a level converter 27, and the level converter 27 is connected to a shift register 29 via a latch circuit 28. The shift register 29 performs a shift operation in synchronization with a clock signal CP2 input from its clock input terminal, and each segment electrode X and correction segment electrode Xa.
Is a circuit for transferring the display data D and the correction data Da corresponding to, and the display data D and the correction data Da transferred by the shift register 29 are held by the latch circuit 28 in synchronization with the clock signal CP1 and the level converter 27 Sent to. The level converter 27 determines the level of the modulation voltage according to the sent display data D and correction data Da, and applies the modulation voltage of that level to the corresponding segment electrode X and correction segment electrode Xa. The display data D and the correction data Da are given from the display control circuit 37 to the shift register 29.

On the other hand, the configuration of the scanning side drive circuit 23 is the same as that of the conventional liquid crystal display device, and the analog switch 30 is connected to each common electrode Y, and is not shown via the switches 31 and 32 and the analog switch 30. Four types of write voltages V ₀ , V ₁ , V ₄ , and V ₅ are selectively applied to each common electrode Y from a voltage generation source. The analog switch 30 is connected to the level converter 33, and the level converter 33 is connected to the shift register 35 via the latch circuit 34. The shift register 35 is a circuit for performing a shift operation in synchronization with a clock signal CP1 input from its clock input terminal and transferring scan data S for line-sequentially designating the common electrode Y.
The scan data S transferred by the shift register 35 is sent to the level converter 33 held by the latch circuit 34 in synchronization with the clock signal CP1. In the level converter 33, the level of the write voltage is determined according to the presence or absence of the scan data S, and the write voltage of that level is applied to the corresponding common electrode Y.

The substantial display area 21 in the panel 21 of this liquid crystal display device
The drive at a is performed in the same manner as in the case of the conventional liquid crystal display device described above. That is, a modulation voltage corresponding to ON drive or OFF drive corresponding to the display data D is applied to each segment electrode Y, while a write voltage is applied line-sequentially and a write voltage is applied to the common electrode Y. Among the pixels of the common electrode Y, the pixel corresponding to the segment electrode X to which the modulation voltage corresponding to ON driving is applied is, for example, in a lighting state, and the pixel corresponding to the segment electrode X to which the modulation voltage corresponding to OFF driving is applied. Is in a non-lighting state.

On the other hand, of the display data D and the correction data Da given to the shift register 29 from the display control circuit 37, the correction data
Da indicates that the display data D is α in the display area 21a (α = 0, 1, 2,
, 16) when specifying that the modulation voltage corresponding to the ON drive should be applied to the segment electrode Y, β of the correction segment electrodes Xa in the correction area 21b, that is, β = int {(16−α) / 2} (1) (where int {x} is a function that finds the integer part of x) is specified so that a modulation voltage equivalent to ON drive should be applied to the correction segment electrodes Xa. Is set.

Therefore, for example, when 12 of the 16 pixels on the common electrode to which the write voltage is applied are driven on and the remaining 4 pixels are driven off, two correction segment electrodes are provided in the correction region 21b. A modulation voltage corresponding to ON drive is applied to Xa. Assuming that the load capacitance applied to the common electrode Y per pixel that is turned on is C1, in this case, the load capacitance of 12 × C1 is applied to the common electrode Y in the display area 21a. On the other hand, the dielectric constant ε2 of the dielectric layer in the correction area 21b
Is twice the dielectric constant ε1 of the liquid crystal layer, the correction area 21b
Then, the load capacitance C2 applied to the common electrode Y per correction segment electrode Xa to which the modulation voltage corresponding to the ON drive is applied is 2 × C1, and the total is 2 × C2 = 2 × 2 (2 × C1) = 4 × C1 (2) The load capacitance of (2) is applied to the common electrode Y. As a result, when the display area 21a and the correction area 21b are combined, a total load capacitance of 16 × C1 is applied to the common electrode Y, and this value is the number of pixels on-driven on the common electrode Y in the display area 21a. No matter how the number of pixels that are driven off, changes to a substantially constant value. Therefore, the rounding of the waveform of the write voltage applied to each common electrode Y is uniform regardless of the display pattern of each scan line, and the brightness of the pixels to be driven on or off is the same as the scan line. There is no difference between them.

In the above embodiment, the dielectric constant ε2 of the dielectric layer in the correction area 21b is set to be twice the dielectric constant ε1 of the liquid crystal layer in the display area 21a, while the number of correction segment electrodes Xa in the correction area 21b is set to the display area 21a. 1/2 of the number of segment electrodes X (16)
Although the case of (8) has been described, the invention is not limited to this. Generally, the dielectric constant ε2 of the dielectric layer is set to several times to several hundred and several tens times the dielectric constant ε1 of the liquid crystal layer, and only the magnification is used for the correction segment. The number of electrodes Xa can be reduced. That is, for example, when using a dielectric layer such that ε2 = Aε1 (A> 0) (3), assuming that the number of segment electrodes X in the display area 21a is V, the correction segment electrodes Xa in the correction area 21b are The number U can be set as U = int (V / A) (4), and the correction area 21b can be reduced accordingly. At this time, the number β of the correction segment electrodes Xa to which the modulation voltage corresponding to the ON drive is applied can be expressed as β = int {(V−α) / A} (5).

EFFECTS OF THE INVENTION As described above, according to the display device of the present invention, the extension portions of the electrodes on the scanning side, which are formed to extend beyond the display area of the display panel, and the extension portions are arranged in a direction intersecting with each other. A correction area is formed by interposing a second dielectric layer having a larger dielectric constant than the dielectric layer in the display area between the plurality of correction data-side electrodes, and a correction voltage is applied to the scan-side electrode. Since the modulation voltage corresponding to the ON driving is applied to the correction data side electrodes of the number which is complementary to the number of ON driven pixels among the pixels, the load capacitance at each scanning side electrode is The value is always a substantially constant value, and the contrast between the scanning lines becomes uniform without being influenced by the difference in the display pattern between the scanning lines, and the display quality can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a liquid crystal display device which is an embodiment of the present invention, FIG. 2 is a block diagram showing a schematic configuration of a conventional liquid crystal display device, and FIG. FIG. 4 is a waveform diagram showing the relationship between the write voltage applied to the electrodes and other timing signals, FIG. 4 is a waveform diagram showing the relationship between the modulation voltage applied to the segment electrodes and other timing signals, and FIG. FIG. 6 is a waveform diagram showing a voltage applied to the pixel, and FIG. 6 is a schematic diagram showing an example of a display pattern in the liquid crystal display device. 21 ... display panel, 21a ... display area, 21b ... correction area, 22 ... data side drive circuit, 23 ... scanning side drive circuit,
37 …… Display control circuit, X …… Segment electrode, Xa …… Correction segment electrode, Y …… Common electrode

Claims (1)

[Claims] 1. A display panel having a dielectric layer between a plurality of scanning side electrodes and a plurality of data side electrodes arranged in directions intersecting with each other, wherein a dielectric at an intersection of the scanning side electrode and the data side electrode. In a display device in which each pixel constituted by layers is driven on / off by sequentially applying a writing voltage to a scanning side electrode in a state where a modulation voltage according to display data is applied to a data side electrode. The extension portion of each scanning-side electrode extending beyond the substantial display area of the display panel and the plurality of correction data-side electrodes arranged in a direction intersecting with the extension portion, With respect to the correction area of the display panel formed by interposing the second dielectric layer having a larger dielectric constant than the dielectric layer, and the number of the ON-driving pixels among the pixels on the scanning side electrodes to which the writing voltage is applied. Complementary function A correction area driving means for selecting the correction data side electrodes by a number corresponding to the above, applying a modulation voltage corresponding to the ON drive to the electrodes, and adjusting the additional capacitance at each scanning side electrode to a substantially constant value. A display device characterized by.