JP3039506B2 - Liquid crystal display device, driving device for driving the device, and driving method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for driving a liquid crystal display device capable of high-speed and wide-field display, a driving method thereof, and a liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, a display device using a liquid crystal has been regarded as important because of its advantages of being thin, lightweight and low power consumption.
In these liquid crystal display devices, a nematic liquid crystal having a twisted molecular arrangement is generally used. Due to the magnitude of the twist angle, STN (Super Twisted Nematic) type or TN (Twisted Nematic) type liquid crystal display device is used. being classified.

[0003] The STN type liquid crystal display device has a steep electro-optical characteristic, so that it can be driven by electrodes in a simple matrix form, and an inexpensive display device can be manufactured. However, there is a problem that viewing angle dependence is large and operation speed is slow, such as inversion of display depending on an observation angle. On the other hand, the TN type liquid crystal display device has a high contrast ratio and is used for applications requiring high display performance. However, as described above, the TN type liquid crystal display device has a large viewing angle dependence and a low operation speed.

Therefore, a high-speed / wide-viewing-angle liquid crystal display device in which the viewing angle dependency of the liquid crystal display device is improved and the responsiveness is also improved has been researched and developed. As a first conventional example for high-speed and wide-field display, there is an active matrix type liquid crystal display device using a liquid crystal having polarization. Here, the polarization is a value of the electric dipole moment per unit volume. A substance that causes polarization only when an external electric field is applied is called a paraelectric substance. In particular, a substance in which electric dipole moments are aligned in one direction and polarization (spontaneous polarization) occurs even in the absence of an external electric field is ferroelectric. Call body.

In the first conventional example, a ferroelectric liquid crystal having a chiral smectic C phase or an antiferroelectric liquid crystal having a chiral smectic Ca phase is used as a liquid crystal having a response time shorter than the frame period and having polarization. That is being considered. A typical example is a surface stabilized ferroelectric liquid crystal (SSFLC: Surface Stabilized Ferroelectr).
ic Liquid Cristal), Applied Physics Lets, Vol. 36, p. 899 (Applied physics Let
ters 36, p.899). Note that the frame period is a time required to write display data to one entire screen of the liquid crystal display.

The surface-stabilized ferroelectric liquid crystal has a response speed two orders of magnitude or more faster than a TN liquid crystal, has a wide viewing angle, and has a spontaneous polarization stabilized only in two directions perpendicular to the substrate. Has a memory effect, and simple matrix driving is possible. However, halftone display is difficult due to the memory effect, and in practice, halftone display using active devices is being studied. This is the case, for example, in Ferroelectrics, Vol.
Page (Ferroelectrics, 122, p. 1).

[0007] Further, as a liquid crystal having polarization, thresholdless antiferroelectric liquid crystal, strain spiral ferroelectric liquid crystal, twisted ferroelectric liquid crystal, monostable ferroelectric liquid crystal, and the like have attracted attention. The thresholdless antiferroelectric liquid crystal has a feature of high speed and a wide viewing angle, and a feature of enabling gray scale display by using an active matrix type driving by a conventional active device. This is, for example, AM Elcidi 9
7. Digest of Technical Papers 1
Page 13 (AM-LCD97, DIGEST OF TECHNICAL PAPERS, p.133)
Or in Japan Journal of Applied Physics, Volume 36, page 720 (Japan Journal of Applied Physics)
al of Applied Physics, Vol. 36, p. 720).

[0008] The above-mentioned strained spiral ferroelectric liquid crystal can display gray scale by using an active matrix type driving by a conventional active device, and can display at high speed and in a wide field of view. This is, for example, the 720 of the Japan Journal of Applied Physics Volume 36
Page (Japan Journal of Applied Physics Volume36, p.72
0).

The above-mentioned twisted ferroelectric liquid crystal and monostable ferroelectric liquid crystal can also perform gradation display by using an active matrix type driving by a conventional active device, and can perform high-speed and wide-field display. . Regarding the twisted ferroelectric liquid crystal, for example, Applied Physics Letters, Vol.
60, p.280). The monostable ferroelectric liquid crystal is described in, for example, JP-A-8-152598.

On the other hand, as a second conventional example, there is an active matrix type liquid crystal display device using a nematic liquid crystal having a response time shorter than a frame period. As this conventional example, L-66 of IDR C97
OCB (Optically compensated) using bend alignment of nematic liquid crystal described on page (IDRC97, p.L-66)
Birefringence) mode liquid crystal display devices. O
In the CB mode liquid crystal display device, not only the speed is higher by one digit or more than that of the conventional TN type liquid crystal display device, but also a wide viewing angle display can be obtained by using a biaxial retardation compensation film together. it can.

[0011]

In the active matrix type liquid crystal display devices shown in the first and second conventional examples,
The following problems occur during driving. That is, in the conventional driving method, the writing voltage is determined only by the video signal of the frame to be displayed this time. Therefore, when the video signal changes, the display is not stable in a short time of about one frame, and the screen speed is high. Switching was difficult.

FIG. 9 is a conceptual diagram showing a write signal, an optical response waveform, and the movement of liquid crystal molecules when a conventional driving method is applied to a liquid crystal having a response time shorter than the frame period and having polarization. The vertical axis in the graph of FIG. 7 indicates the potential applied to the liquid crystal and the amount of light transmitted through the liquid crystal, and the horizontal axis indicates time. In the drawing, a to g indicate continuous frames. From the graph, when the potential of the video signal (write signal 12) changes at a certain frame (for example, d), the display is not stable only in the next one frame (e), and a plurality of frames (for example, f and g) are displayed. It can be seen that the optical response waveform 13 (display gradation) changes over a period of time and settles at a predetermined display gradation.

FIG. 10 is a conceptual diagram showing a write signal, an optical response waveform, and the movement of liquid crystal molecules when a conventional driving method is applied to a nematic liquid crystal having a response time equal to or shorter than a frame period. The vertical and horizontal axes in the graph of FIG.
This is the same as in FIG. From the graph, when the potential of the video signal changes at a certain frame (for example, d),
It can be seen that the display is not stable only in the next one frame (e) and the optical response waveform 13 changes over a plurality of frames (for example, f and g) and settles at a predetermined display gradation.

In view of the above, the present invention makes it possible to stabilize the display state in a short time of about one frame even when using a liquid crystal whose response time is shorter than the frame period, and to enable high-speed screen switching. It is an object to provide a driving device for driving a liquid crystal display device, a driving method thereof, and a liquid crystal display device.

[0015]

In order to achieve the above object, a liquid crystal display device according to the present invention provides a write signal voltage corresponding to display data to each of pixels sequentially designated, so that each display frame has a write signal voltage. In the liquid crystal display device for displaying an image, the video signal voltage of the m-th pixel in the previous display frame n-1 is V _S (m, n-1), and the m-th video signal in the next frame n to be displayed. When the voltage is V _S (m, n), the write signal voltage V _ex (m, n) of the m-th pixel in frame n is equal to the video signal voltage V _S (m, n).
Linear sum of _{S (m, n-1)} : V ex (m, n) = AV S (m, n) + BV S (m, n-1) ( where, A, B are constants) to a value that satisfies the A display control means for setting is provided.

In the liquid crystal display device of the present invention, an appropriate write signal voltage V _ex (m, n) is obtained from the video signal voltage V _S (m, n-1) and the video signal voltage V _S (m, n). Can be. Therefore, even when a liquid crystal whose response time is shorter than the frame period is used, the display state can be stabilized in a short time of about one frame, and the screen can be switched at high speed.

Here, the display control means controls the video signal voltage V
A memory for storing _{S (m, n-1)} , the video signal voltage V _S (m,
n) and an arithmetic unit for calculating the write signal voltage V _ex (m, n) from the video signal voltage V _S (m, n-1). In this case, the video signal voltage V _S (m, n-1) in the previous display frame n-1 is temporarily stored in the memory, and the video signal voltage V _S (m, n-1) is temporarily stored in the next frame n. The video signal voltage V _S (m, n) is input to the arithmetic unit, and the write signal voltage V _ex (m, n) can be calculated.

More preferably, the liquid crystal is a ferroelectric liquid crystal,
It is composed of antiferroelectric liquid crystal, thresholdless antiferroelectric liquid crystal, strain spiral ferroelectric liquid crystal, twisted ferroelectric liquid crystal, monostable ferroelectric liquid crystal, or nematic liquid crystal. This enables high-speed screen switching in a state in which a liquid crystal whose response time is shorter than the frame period is used.

A driving device for driving the liquid crystal display device, wherein the first device latches a video signal voltage V _S (m, n).
A latch circuit, and a second latch circuit that latches the video signal voltage V _S (m, n−1), wherein the computing unit converts the video signal voltage V _S (m, n) from the first latch circuit into: A video signal voltage V _s (m, n-1) is input from the second latch circuit to calculate a write signal voltage V _ex (m, n).

According to the above-described driving device, the video signal voltage required for the operation can be smoothly input to the arithmetic unit via the first and second latch circuits.

According to a driving method of the present invention, in a driving method for driving a liquid crystal display device for displaying an image of each display frame by applying a write signal voltage corresponding to display data to each of pixels sequentially designated, display frame n-1 a video signal voltage of the m-th pixel in V _S (m, n-
1) When the m-th video signal voltage in the next frame n to be displayed is V _S (m, n), the m-th video signal voltage in the frame n
The write signal voltage V _ex (m, n) of the pixel No. is a linear sum of the video signal voltages V _S (m, n) and V _S (m, n−1): V _ex (m, n) = AV _S (m, n) + BV _S (m, n-1) (where A and B are constants).

According to the driving method of the present invention, an appropriate write signal voltage V _ex (m, n) is obtained from the video signal voltage V _S (m, n-1) and the video signal voltage V _S (m, n). Therefore, even when a liquid crystal having a response time shorter than the frame period is used, the display state can be stabilized in a short time of about one frame.

Here, the pixel voltage for displaying a specific gray scale in frame n-1 is V _prev , and the specific gray scale is frame n-1.
Let V _{next be} the pixel voltage for displaying the image and V ₁ be the write signal voltage for displaying the gray scale at the time of transition from frame n-1 to frame n. = (V ₁ -V _prev ) / (V _next -V _prev ) It is preferable that B = (V ₁ -V _next ) / (V _next -V _prev ). in this case,
By measuring the voltage at the time of gradation change corresponding to a specific situation, it can be applied to a general situation.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing an embodiment of the present invention in detail, the principle of the present invention will be described. That is,
In a liquid crystal display device using a liquid crystal having a response time equal to or less than a frame period and having polarization, when a video signal changes, the display gray scale changes over a plurality of frames and the display gray scale is settled to a predetermined display gray scale. The factors will be described.

FIG. 5 is an equivalent circuit diagram of the pixel section for explaining the above factors. The pixel equivalent circuit can be treated as a circuit in which a resistor 31 and a capacitor 32 are connected in series and a high-frequency pixel capacitor 33 that does not change due to polarization rotation is connected in parallel. If the pixel has an auxiliary capacitance,
It is assumed that this auxiliary capacitance is included in the high-frequency pixel capacitance 33. R _sp resistor 31, C _sp capacity 32 and,, C _pix high frequency pixel capacitor 33 respectively, the liquid crystal, is a constant determined by an alignment film and the active element. The time constant of the resistor 31 and the capacitance 32 corresponds to the time constant of the liquid crystal. The equivalent circuit of this figure, when the time T _on, charge Q _pix accumulated when the active element is turned on during the time T _on may be represented by the following formula (1).

(Equation 1) (However, τ _sp = R _sp C _sp … (2))

Here, the last time t ₁ -dt of the frame n-1
, The pixel voltage V _pix (n-1) and the polarization voltage V _sp (n-1)
Is equal to V _pix (t ₁ -dt ₁ ) = V _pix (n-1) = V _sp (t ₁ -dt ₁ ) = V _sp (n-1) …… (3)

At the instant t ₁ when the writing of the frame n is performed, the pixel voltage V _pix (t ₁ ) is equal to the writing signal voltage V _ex (n), since the polarization has not yet rotated. V _pix (t ₁ ) = V _ex (n) …… (4) V _sp (t ₁ ) = V _sp (n−1) …… (5)

At the time of transition during writing (t _{1 to} t ₂ ), the pixel voltage V _pix (t ₂ ) is calculated by using the equation (2) as follows: V _pix (t ₂ ) = V _ex (n )… (6) V _sp (t ₂ ) = V _sp (t ₁ ) + [V _pix (t ₁ ) -V _sp (t ₁ )] (1-L _sp ) = (1-L _sp ) V _ex ( n) + L _sp V _sp (n-1) …… (7) (However, K _sp = C _sp / C _pix … (8),

(Equation 2) Can be represented by

Then, at the instant t ₃ after the active element is turned off and the polarization is rotated and the charge is redistributed,
The pixel voltage V _pix (t ₃ ) is given by

(Equation 3) Can be represented by

By using equations (3) to (10), the pixel voltage V _pix (n) in frame n and the polarization voltage V _sp (n) in frame n are

(Equation 4) Can be represented by

Here, a case where a certain gray scale is displayed over a continuous frame using Expression (11) will be described. For example, in the case where a display gradation in which the pixel voltage is ± V _prev is continuously displayed over a plurality of frames, the pixel voltage V _pix (n−1) = − V _prev of frame n−1 to the frame n of frame n−1 The write signal voltage V _ex (n) when shifting to the pixel voltage V _pix (n) = V _prev is given by the following equation:

(Equation 5) Can be represented by The frame n-1 of the pixel voltage _{V pix (n-1) =} V pixel voltage V _pix frame n from _prev (n)
= −V _prev , the write signal voltage V _ex (n) is
Next formula

(Equation 6) Can be represented by

Next, the pixel voltage in frame n-1 is ±
It is _assumed that the pixel voltage in the frame n shifts from the display gradation of V _prev to the display gradation of ± V _next .
Specifically, it is assumed that the pixel voltage is −V _prev in frame n−1 and the pixel voltage is + V _next in frame n.

As described above, in the display gradation where the pixel voltage is ± V _next , the pixel voltage V
_pix (n-1) =-V pixel voltage V of frame n from _next
pix (n) = write signal voltage V _ex (n) when shifting to V _next
Has the following formula

(Equation 7) Is supplied.

In the conventional driving method, even when the display gradation changes, the write signal voltage V
_ex (n) was applied. In this case, the pixel voltages of the frame n V _{pi x} (n) is

(Equation 8) And not V _next . This is the reason that the display changed once cannot be stabilized in one frame by the conventional driving method.

Therefore, in the driving method of the present invention, 1
To obtain a predetermined display in the frame, the write signal voltage V
_ex (n)

(Equation 9) Is given. This makes it possible to pixel voltage V _pix frame n (n) to V _{ne xt.} V _pix (n) = V _next (17) That is, a display gradation in which the pixel voltage is ± V _next is obtained by writing one frame.

When actually driving the liquid crystal display device, the video signal and the pixel voltage can be made to correspond to one to two. What is not one-to-one is to prevent image sticking,
This is because there are two types of pixel voltages for one video signal.
It is used as a kind of pixel voltage. Therefore, a video signal can be used in place of the pixel voltage, and the write signal voltage V _ex (m, n) of the m-th pixel in the n-th frame becomes the m-th pixel in the previously displayed frame n-1. V _ex (m, n) of the video signal voltage V _S (m, n−1) of the pixel of the pixel No. and the m-th video signal voltage V _S (m, n) in the next frame n to be displayed: = AV _S (m, n) + BV _S (m, n-1) (18) (where A and B are constants).

FIG. 6 is a conceptual diagram showing a write signal, an optical response waveform, and the movement of liquid crystal molecules when the driving method of this embodiment is applied to a liquid crystal having a response time shorter than the frame period and having polarization. The vertical axis in the figure shows the potential applied to the liquid crystal from the outside, and the amount of light transmitted through the liquid crystal,
The horizontal axis indicates time. In the drawing, a to g indicate continuous frames. From the graph, even if the potential of the video signal (writing signal 12) changes at a certain frame (d), the display is stabilized in the next one frame (e) and a plurality of frames (e to g) are displayed.
It can be seen that the optical response waveform 13 (display gradation) settles at a predetermined display gradation over a period of time.

FIG. 7 is a block diagram for conceptually explaining the present invention. In the present invention, in order to perform the operation of Expression (18), the drive circuit 3 including the memory 21 and the operation unit 22
0 is required. The memory 21 stores the video signal voltage V _S (m, n−) of the m-th pixel in the previously displayed frame n−1.
1) is stored as the previous display video signal 11a. The arithmetic unit 22 calculates the next display video signal 11b as the video signal voltage V _S (m, n-1) of the m-th pixel in the frame n to be displayed next, and the previous display video signal 11a stored in the memory 21. Then, the calculation shown in Expression (18) is performed to set the write signal 12 and output it to the liquid crystal display (LCD) 14.

On the other hand, the factors that settle to a predetermined display gradation when a nematic liquid crystal is used are basically the same as those of the liquid crystal having the above-mentioned polarization. In the case of a nematic liquid crystal, it is not necessary to consider the influence because it has no polarization, but it is necessary to consider an apparent change in the dielectric constant.

Specifically, a constant C _diel represented by the following equation is used instead of the constant C _sp in the equations (1) to (18).

(Equation 10) (Where q is the rotation angle of the liquid crystal molecules from the direction perpendicular to the substrate, e
_para is the permittivity in the direction parallel to the long axis of the liquid crystal molecules, e _vert is the permittivity in the vertical direction, e ⁰ is the permittivity in a vacuum state, S is the area of the pixel electrode, and d is the thickness of the liquid crystal layer.

The expression (2) is replaced by the following expression τ _diel = R _diel C _diel ... (20), and the expression (8) is replaced by the following expression K _diel = C _diel / C _pix. )) And replace equation (9) with the following equation

[Equation 11] Can be considered as follows.

That is, when the display is changed from the display gradation in which the pixel voltage is ± V _prev to the display gradation in which the pixel voltage is ± V _next in the frame n, the pixel voltage V _pix of the frame n-1 is changed. As a write signal voltage for changing (n-1) =-V _prev to pixel voltage V _pix (n-1) = V _next of frame n, the following equation is used.

(Equation 12) In supplying a write signal voltage V _ex (n) represented. Accordingly, the pixel voltage V _pix (n) of the frame n becomes V _next .

In this case, as in the case where the liquid crystal having polarization is used, the memory for storing the pixel voltage V _pix (n−1) = − V _prev in the previous display frame n−1 as the previous display video signal. 21 and an arithmetic unit 22 for setting the write signal 12 from the previous display video signal and the next display video signal. In this case, the arithmetic unit 22 calculates the write signal voltage V _ex from the previous display video signal and the next display video signal using Expression (23).
(m, n) is calculated.

When actually driving the liquid crystal display device, the
For the same reason as when a liquid crystal having a pole is used, the expression (1
8), the video signal power of the m-th pixel in frame n-1 is used.
Pressure V _S(m, n-1) and the m-th video signal voltage of frame n
V_SAs the linear sum with (m, n), the m-th picture of n frame
Elementary write signal voltage V_ex(m, n) is obtained.

FIG. 8 is a conceptual diagram showing a write signal, an optical response waveform and the movement of liquid crystal molecules when the driving method of this embodiment is applied to a nematic liquid crystal having a response time equal to or shorter than a frame period. The vertical and horizontal axes in the graph of FIG. 9 are the same as those in FIG. From the graph, even if the potential of the video signal (writing signal 12) changes at a certain frame (d), the display is stabilized in the next one frame (e), and the display is stable over a plurality of frames (e to g). It can be seen that the optical response waveform 13 (display gradation) is settled at a predetermined display gradation.

As described above, in the liquid crystal display device using the liquid crystal having polarization and the liquid crystal display device using the nematic liquid crystal, since the memory 21 is provided, the next display video signal and the previous display video signal are separated. The proper write signal voltage V _ex (m, n), that is, the write signal 12, can be obtained by performing the operation of Expression (18). Therefore, when a liquid crystal whose response time is shorter than the frame period is used, the display state is stabilized in a short time of one frame, and the screen can be switched at a high speed.

Here, the present invention will be described in more detail. FIG. 1 is a block diagram showing an example of a driving device for driving an active matrix type liquid crystal display device according to a first embodiment of the present invention. This liquid crystal display device displays an image of each display frame by giving a write signal voltage corresponding to display data to each pixel sequentially specified. A driving device 30 for driving the liquid crystal display 14 is connected between the signal source 15 and the liquid crystal display 14. At least the liquid crystal display 14 and the driving device 30
Are arranged on the same substrate.

The driving device 30 includes an analog / digital converter circuit (hereinafter abbreviated as an ADC circuit) 16 connected to the signal source 15, a first latch circuit 19 connected to the ADC circuit 16, and a connection to the ADC circuit 16. Output control buffer 18. The driving device 30 further includes a memory 21 connected to the output control buffer 18, a second latch circuit 20 connected to the memory 21 via a node connecting the output control buffer 18 and the memory 21, and a first latch circuit. An arithmetic unit 22 connected to the circuit 19 and the second latch circuit 20 and a timing control circuit 17 are provided.

The ADC circuit 16 has a clock ADCLK which will be described later.
, The analog signal from the signal source 15 is converted into a digital signal. The output control buffer 18 has an output control function, and receives an after-mentioned control signal OE to set an output terminal to a high impedance (hereinafter, referred to as Hi-Z) state. Here, it is assumed that when the control signal OE is at a high level, the input data is output, and when the control signal OE is at a low level, the output becomes Hi-Z.

The memory 21 has a capacity of one frame or more, and is controlled by an address signal ADR and a control signal R / W. Here, the memory 21 performs a read operation when R / W is at a high level, and performs a write operation when R / W is at a low level. First and second latch circuits 19,
Reference numerals 20 denote circuits for receiving and holding input data while receiving the clock LACLK. Here, data is fetched at the rising edge of the clock and held until the next rising edge.

The first latch circuit 19 outputs the video signal voltage V
_S (m, n) is latched, and the second latch circuit 20 latches the video signal voltage V _S (m, n-1). The arithmetic unit 22 calculates the video signal voltage V _S (m, n−1) of the m-th pixel of the previous display frame n−1 and the video signal voltage V _S (m, n−1) of the next display frame n-1 by using the above equation (18). From the linear sum with the m-th video signal voltage V _S (m, n), the write signal voltage V _{ex for} the m-th pixel in frame n
(m, n) is set. The timing control circuit 17 controls the timing of each signal. The memory 21 and the computing unit 22 constitute a display control unit.

FIG. 2 is an enlarged exploded perspective view showing a part (for one pixel) of the liquid crystal display in the embodiment. The liquid crystal display 14 includes a liquid crystal layer (liquid crystal molecules 1).
0) transparent substrates 23 and 24 which are closely opposed to each other across
A plurality of signal electrode lines 26 and a plurality of scanning electrode lines 27 extending at right angles to each other are provided. The transparent substrate 2 of the transparent substrate 24
On the third side, a pixel electrode 28 is provided.
Are arranged corresponding to the intersections of each signal electrode line 26 and each scanning electrode line 27. On the transparent substrate 24 side of the transparent substrate 23, a common electrode 29 is formed.

The active element 25 has a function of writing a write signal applied to the signal electrode line 26 in a state selected by a signal applied to the scan electrode line 27. The liquid crystal sandwiched between the transparent substrates 23 and 24 includes a ferroelectric liquid crystal, an antiferroelectric liquid crystal, a thresholdless antiferroelectric liquid crystal, a strain spiral ferroelectric liquid crystal, a twisted ferroelectric liquid crystal, and a monostable ferroelectric. Liquid crystal,
Alternatively, a nematic liquid crystal can be used.

FIG. 3 is a timing chart showing signals when the active matrix type liquid crystal display device is driven. ADCLK is an address clock having a period T synchronized with the video signal when data of one pixel of the video signal from the signal source 15 is transferred in the period T. ADR is an address signal for sequentially outputting address values for selecting M or more data cells (active elements 25), which is the number of pixels of the liquid crystal display 14, within one frame period in synchronization with the clock ADCLK. is there.

R / W is a control signal that goes high (read operation) in the first half of the period T and goes low (write operation) in the second half. OE is a control signal that goes to a low level (Hi-Z) when the control signal R / W is at a high level, and goes to a high level (output possible) when the control signal R / W is at a low level. LACLK rises a pulse between the time from when the control signal R / W changes to the high level to when the output of the memory 21 is stabilized and the time when the control signal R / W changes to the low level. This clock is synchronized with the address clock ADCLK.

Here, the period Tm, n is considered. During this period Tm, n, the m-th video signal in the n-th frame is A
This is a period during which the signal is output from the DC circuit 16. The value of the output ADC _ O of the ADC circuit 16 at this time V _S (m,
n), during this period, at the moment when the clock LACLK changes to the high level, the data V _S is stored in the first latch circuit 19.
(M, n) is captured and held. The value of the address signal ADR also changes in synchronization with the address clock ADCLK, and when the control signal R / W is at a high level, the memory 2
The m-th data V _S (m, m,
n-1) is output, and is captured and held by the second latch circuit 20 at the moment when the clock LACLK changes to the high level.

Next, when the control signal R / W changes to a low level and the control signal OE changes to a high level, the ADC
Output data V _S (m, n) of the circuit 16 is transferred to the memory 21 as a BUF _ O via the output control buffer _{18, V S (m, n} -1) is in the memory 21 which has been stored until then Is stored in a memory cell (not shown).

On the other hand, the computing unit 22 inputs V _S (m, n) as the next display video signal via the first latch circuit 19 from the moment when the pulse of the clock LACLK rises.
V _S (m, n−1) as a previous display video signal, which is a video signal one frame before, is input via the second latch circuit 20. The arithmetic unit 22 uses the two video signals of the next display video signal V _S (m, n) and the previous display video signal V _S (m, n−1), and calculates the m-th frame n of the frame n from Expression (18). , The write signal voltage V _ex (m, n) of the pixel is calculated. By this operation,
The next write signal voltage V _ex (m,
n) is obtained.

As described above, the operation of driving the LCD 14 by the write signal voltage V _ex (m, n) calculated from the next display video signal and the previous display video signal, and updating the contents of the memory 21 sequentially by 1 The operation of holding the data as data for a frame is repeated.

If the response time is equal to or less than the frame period, use the equation (16) and then use the equation (18) between the case where the polarized liquid crystal is used and the case where the nematic liquid crystal is used. There is only the difference between using equation (23) and then using equation (18). Therefore, in the present embodiment, Expression (16)
And a K _sp and K _diel together K in (23), also,
Both L _sp and L _diel can be treated as L. K and L are values determined by the configuration of the liquid crystal display element, and can be calculated from the components and determined.

Here, a further simple driving method is shown in FIG.
This will be described with reference to FIG. FIG. 4 is a conceptual diagram showing a write signal, an optical response waveform, and the movement of liquid crystal molecules when the present driving method is applied to a liquid crystal having a response time equal to or shorter than a frame period.
The vertical axis in the figure shows the amount of light transmitted through the liquid crystal,
The horizontal axis indicates time. In the figure, a to f indicate successive frames.

[0062] In this driving method, initially over a plurality of frames, alternately applies the write signal voltage + 2V _prev and -2 V _prev for each frame. After several frames after this application, the pixel voltage becomes stable and the optical response waveform 13 becomes constant. The pixel voltage in this case is -V _prev is + 2V after application of _prev + V _prev next, after the application of -2 V _prev. Next, by applying a V ₁ as a write signal voltage after the application of + 2V _prev changing the gradation. Immediately after that, + 2V _next is applied as a write signal voltage. Thereafter, -2V _next is applied, and positive / negative (±) voltages are repeatedly applied. During this gradation change, to be chosen a value of the write signal voltages V ₁ appropriately, the pixel voltage is ± V
_{The next} gradation cannot be stably displayed over a plurality of frames. Therefore, finding the write signal voltages V ₁ capable of stable display.

When a stable display is _achieved , the following equation V ₁ = [(( ₁ ) is obtained from the above equation (16) between the pixel voltage V _prev , the write signal voltage V ₁ , and the next write signal voltage V _next. 1 + K) V _next -KLV _prev ] / (1 + K-KL)... (24) From equations (16) and (24), K,
When L is erased, the pixel voltage of frame n-1 becomes _Vpix (n-
From the display gradation of 1), the pixel voltage of frame n is V
Write signal voltage V that shifts to the display gray scale of _pix (n)
_ex (n) is

(Equation 13) From.

That is, if the voltage at the time of gradation change corresponding to a certain specific situation is measured, it can be applied to a general situation. Also, if Equation (25) is made to correspond to Equation (18), the constants A and B in Equation (18) are expressed by the following equation: A = (V ₁ −V _prev ) / (V _next −V _prev ) (26) ) B = − (V ₁ −V _next ) / (V _next −V _prev ) (27)

Next, a description will be given of an embodiment in which a specific driving is performed by the driving device according to the present embodiment. First, a case in which the polarity of an arbitrary pixel is inverted for each frame will be described.

That is, since the writing voltage in frame 0 is 0 V and the pixel voltage is also 0 V, the relationship expressed by the following equation _Vex (0) = V _pix (0) = 0 (28) is established. . From this state, the next frame 1
Then, a write voltage V _ex (1) for displaying a gradation in which the pixel voltage V _pix (1) = − V _a is applied. This write voltage V
_ex (1) is represented by the following equation: V _ex (1) = − [(V ₁ −V _prev ) / (V _next −V _prev )] × V _a (29) Here, when performing the screen switching from the frame 0 to the frame 1, it is understood that the screen switching is completed in one frame.

In the next frame 2, only the polarity is inverted without changing the gradation of frame 1. That is, the write voltage V _ex (2) at which the pixel voltage becomes V _pix (2) = V _a
Is applied. This write voltage V _ex (2) is given by the following equation:

[Equation 14] Is represented by

In frame 3, only the polarity is inverted without changing the gradation of frame 1. That is, the write voltage V _ex (3) at which the pixel voltage becomes V _pix (3) = − V _a is applied.
This write voltage V _ex (3) is expressed by the following equation:

(Equation 15) Is represented by

[0069] Further, after the pixel voltage is repeated up to eight frames tone is ± V _a, switch the display to the gradation pixel voltage is ± V _b. Since V _pix (8) = V _a , V
_pix (9) = - applying a write voltage to a V _b. Frame 8
When the screen is switched from to the frame 9, the screen switching is completed in one frame. The write voltage V _ex (9) is

(Equation 16) Is represented by

In the next frame 10, it is assumed that only the polarity is inverted without changing the gradation of frame 9. That is, the write voltage V at which the pixel voltage becomes V _pix (10) = V _b
ex (10) is applied. This write voltage V _ex (10) is given by the following equation:

[Equation 17] Is represented by Thus, it can be seen that all display switching is completed in one frame.

Next, an embodiment in which the present invention is applied to a driving method of applying a write voltage of the same polarity to an arbitrary pixel over a plurality of frames and inverting the pixel voltage in a plurality of frames will be described for every four frames. Description will be made with reference to an example in which the polarity of the pixel voltage is inverted.

The pixel voltage V _pix (0) in frame 0 is V
_Let it be a. V _pix (0) = V _a (34) In frame 1, an external voltage is determined and applied so that the pixel voltage remains at V _a . Here, V _ex (1) = V _a (35) can be obtained from the above equation (25). That is, in order to keep the pixel voltage constant, it is necessary to always apply the same write voltage.

Next, until the frame 3, the pixel voltage becomes V _a
An external voltage is applied as follows. V _ex (2) = V _a (36) V _ex (3) = V _a (37) In frame 4, the polarity of the pixel voltage is inverted to −V
_a . In this case, the write voltage is

(Equation 18) Is represented by Thus, from frame 3 to frame 4
When screen switching is performed, screen switching is completed in one frame.

If the pixel voltage in frame 5 remains -V _a , the write voltage may be expressed by the following equation: V _ex (5) =-V _a (39) Next, it is assumed that in the frame 6, the gradation display changes and the pixel voltage is switched to a gradation of ± _Vb . Since it is assumed that the polarity of the four frames is not inverted, the pixel voltage of the frame 6 is V _pix (6) = − V _b , and the writing voltage V _ex (6) for this is expressed by the following equation.

[Equation 19] Is represented by

Assuming that the pixel voltage of frame 7 is V _pix (7) = − V _b , the write voltage V _ex (7) for this is expressed by the following equation: V _ex (7) = − V _b. 41).

It is assumed that in the frame 8, the inversion of the polarity of the pixel voltage and the change in gradation occur simultaneously. Specifically, the write voltage V _ex (8) at which the pixel voltage becomes V _pix (8) = V _c is expressed by the following equation:

(Equation 20) Is represented by

As described above, the present invention can be applied to the driving method of applying the same polarity write voltage over a plurality of frames and inverting the pixel voltage over a plurality of frames.
Display switching can be performed in one frame.

Next, a second embodiment of the present invention will be described.
I will tell. This embodiment is more suitable for an actual display element.
It concerns the form. In an actual display element,
Quantity C _strAnd gate-source capacitance C_gsTo consider
Is required. However, the storage capacity C_strIs the pixel electrode 28
And the case where it is connected to the scanning electrode line 27.
You. Where V_gonIs an active element in the scanning electrode line 27
The voltage at which 25 turns on is V_goffIs the voltage that turns off,
V_comMeans the voltage of the common electrode 29, respectively.

The operations up to the expression (8) are the same as those in the first embodiment. Thereafter, the voltage in the equivalent circuit is
As shown in FIG. Between t _{2 and} t ₃ , the voltage of the equivalent circuit is as shown in FIG. FIG. 9 is an equivalent circuit diagram showing a pixel portion, (a) shows a state at an instant t ₁ ,
(b) shows the state at the instant t _2. Thus, the t ₃ after polarization after t ₂ has occurred redistribution of the rotating charge,
By applying the law of conservation of charge, the following equation is obtained: C _gs [V _ex (t ₁ ) -V _gon ] + C _str [V _ex (t ₁ ) -V _goff ] + C _pix [V _ex (t ₁ )- V _com ] + C _sp [V _sp (t ₂ ) -V _com ] = C _gs [V _pix (t ₃ ) -V _goff ] + C _str [V _pix (t ₃ ) -V _goff ] + C _pix [V _pix (t ₃ ) -V _com ] + C _sp [V _sp (t ₃ ) -V _com ]... In this driving method, there is a period in which the voltage of the storage capacitor becomes V _gon after the selection period, but since the charge stored in the pixel portion does not change, the above equation can be used.

By rearranging equation (43), the pixel voltage V _pix (n) in the frame n can be _calculated as follows: V _ex (n) = [V _pix (n) -L _W J ₁ V _pix (n-1) + J ₃ ΔV _g ] / (1-L _W J ₁ )... (44) Where J ₁ = C _sp / (C _gs + C _str + C _pix + C _sp ) …… (45) J ₃ = C _gs / (C _gs + C _str + C _pix + C _sp ) …… (46) ΔV _g = V _gon -V _goff (47) Thus, in order not to cause a step response from the gray scale of the pixel voltage V _rep when gradation switching of the pixel voltage V _next as an external _{voltage, V ex (n) = [} V next -L W J 1 V prev + J ₃ ΔV _g ] / (1-L _W J ₁ ) (48) It can be seen that the voltage V _ex (n) should be applied.

Next, a method for obtaining each constant from an externally applied voltage in this embodiment will be described. First,
The write signal voltage V _prev1 is applied over a plurality of frames over a plurality of frames. After several frames after the application, the pixel voltage becomes stable and the optical response waveform becomes constant. The pixel voltage at this time is V _prev1 . Next, the V ₁ is applied as a write signal voltage after V _PREV1 applied, to change the tone. In the frame immediately after that, V _next1 is applied as a write signal voltage. After that, V _{n ext1}
Is applied over a plurality of frames. During this gradation change, unless suitable choice of the values of V _1, the pixel voltage V _next1
Cannot be displayed stably over a plurality of frames. So, to discover the V ₁ capable of stable display. If the display is stable, V _prev1 , V ₁ , and V _next1 are _{calculated according} to the following equation (48) using the following equation: V ₁ = [V _next1 -L _W J ₁ V _prev1 + J ₃ ΔV _g ] / (1 -L _W J ₁ ) The relation of (49) holds. Similarly, when applied to V _prev2 , V ₂ , and V _next2 , the following equation V ₂ = [V _next2 -L _W J ₁ V _prev2 + J ₃ ΔV _g ] / (1-L _W J ₁ ) (50) Holds. Therefore, V _ex (n) = [(V _prev2 -V _prev1 -V ₂ + V ₁ ) V _pix (n)-(V _next2 -V _next1 -V ₂ + V ₁ ) V _pix (n-1)] / (V _prev2 -V _prev1 -V ₂ + V ₁ ) + [(V _prev2 -V ₁ ) (V _next2 -V ₂ )-(V _prev2 -V ₂ ) (V _next1 -V ₁ )] / (V _prev2- V _prev1 -V ₂ + V ₁ )... (51) is established. That is, if a voltage at the time of a gradation change corresponding to a certain specific situation is measured, it can be applied to a general case.

Although the present invention has been described based on the preferred embodiment, the liquid crystal display device of the present invention, the driving device for driving the device, and the driving method thereof are limited to the above embodiment only. Instead, a liquid crystal display device with various modifications and changes from the above embodiment, a driving device for driving the device, and a driving method thereof are also included in the scope of the present invention.

[0083]

As described above, according to the liquid crystal display device of the present invention, the driving device for driving the device, and the driving method thereof, even if a liquid crystal having a response time shorter than the frame period is used, one frame can be obtained. The display state can be stabilized in a short time, and the screen can be switched at high speed.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of a driving device for driving an active matrix liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view showing a liquid crystal display in the embodiment.

FIG. 3 is a timing chart showing signals when driving the liquid crystal display device according to the embodiment.

FIG. 4 is a conceptual diagram showing a write signal, an optical response waveform, and a movement of liquid crystal molecules when the driving method of the present invention is applied to a liquid crystal whose response time is equal to or shorter than a frame period.

FIG. 5 is an equivalent circuit diagram illustrating a pixel portion.

FIG. 6 is a conceptual diagram showing a write signal, an optical response waveform, and movement of liquid crystal molecules when the driving method of the present invention is applied to a liquid crystal having polarization.

FIG. 7 is a block diagram for conceptually explaining the present invention.

FIG. 8 is a conceptual diagram showing a write signal, an optical response waveform, and movement of liquid crystal molecules when the driving method of the present invention is applied to a nematic liquid crystal.

FIG. 9 is an equivalent circuit diagram showing a pixel unit according to a second embodiment of the present invention, where (a) shows a state at an instant t ₁ ,
(b) shows the state at the instant t _2.

FIG. 10 is a conceptual diagram showing a write signal, an optical response waveform, and the movement of liquid crystal molecules when a conventional driving method is applied to a liquid crystal having polarization.

FIG. 11 is a conceptual diagram showing a write signal, an optical response waveform, and movement of liquid crystal molecules when a conventional driving method is applied to a nematic liquid crystal.

[Explanation of symbols]

 Reference Signs List 10 liquid crystal molecule (liquid crystal) 11 video signal 12 write signal 13 optical response waveform 14 liquid crystal display 15 signal source 16 analog-to-digital converter circuit 17 timing control circuit 18 output control buffer 19 first latch circuit 20 second latch circuit 21 memory 22 arithmetic unit Reference Signs List 23 transparent substrate 24 transparent substrate 25 active element 26 signal electrode line 27 scanning electrode line 28 pixel electrode 29 common electrode

Continuation of the front page (72) Inventor Hiroyuki Sekine 5-7-1 Shiba, Minato-ku, Tokyo Within NEC Corporation (58) Field surveyed (Int. Cl. ⁷ , DB name) G02F 1/133 505 G09G 3 / 36

Claims (6)

(57) [Claims] 1. A liquid crystal display device that displays an image of each display frame by sequentially applying a write signal voltage corresponding to display data to each of pixels that are designated in sequence, the liquid crystal display device comprising: a video signal voltage of the pixel _{V S (m, n-1} ), when a next video signal voltage of the m-th in the frame n to be displayed and V _S (m, n), of the m-th in the frame n Pixel write signal voltage V _ex (m,
n) is a linear sum of the video signal voltage V _S (m, n) and V _S (m, n−1): V _ex (m, n) = AV _S (m, n) + BV _S (m, n) -1) A liquid crystal display device comprising a display control means for setting a value satisfying (where A and B are constants). 2. The display control means according to claim 1, wherein
A memory for storing _{S (m, n-1)} , the video signal voltage V _S (m,
2. The liquid crystal display device according to claim 1, further comprising: an arithmetic unit for calculating a write signal voltage V _ex (m, n) from n) and the video signal voltage V _S (m, n-1). 3. The liquid crystal is ferroelectric liquid crystal, antiferroelectric liquid crystal, thresholdless antiferroelectric liquid crystal, strain spiral ferroelectric liquid crystal, twisted ferroelectric liquid crystal, monostable ferroelectric liquid crystal, or nematic. 3. The liquid crystal display device according to claim 1, comprising a liquid crystal. 4. A driving device for driving the liquid crystal display device according to claim 2, wherein the first latch circuit latches a video signal voltage V _S (m, n); and a video signal voltage V _S ( m, n-1) and a second latch circuit for latching the video signal voltage V from the first latch circuit.
_S (m, n) is converted from the second latch circuit to the video signal voltage V
_S (m, n-1) are input respectively, and the write signal voltage V _ex (m, n)
A driving device for calculating 5. A driving method for driving a liquid crystal display device that displays an image of each display frame by applying a write signal voltage corresponding to display data to each pixel sequentially specified, the method comprising: When the video signal voltage of the m-th pixel in 1 is V _S (m, n−1) and the m-th video signal voltage in the next frame n to be displayed is V _S (m, n), the frame n , The write signal voltage V _ex (m,
n) is a linear sum of the video signal voltage V _S (m, n) and V _S (m, n−1): V _ex (m, n) = AV _S (m, n) + BV _S (m, n) -1) A driving method for driving a liquid crystal display device, which is set to a value that satisfies (where A and B are constants). 6. A pixel voltage for displaying a specific gray scale in frame n-1 is V _{pr ev} , a pixel voltage for displaying a specific gray scale in frame n is V _next , and a frame from frame n-1 to frame n-1 When the write signal voltage for displaying the gradation at the time of transition to n is V ₁ , the constants A and B are calculated by the following equation: A = (V ₁ −V _prev ) / (V _next −V _prev ) B The driving method for driving a liquid crystal display device according to claim 5, wherein each of the values is set to a value that satisfies = (V ₁ -V _next ) / (V _next -V _prev ).