JPS63231421A - Method for driving liquid crystal light valve - Google Patents

Abstract

PURPOSE:To obtain liquid crystal light value driving at a high contrast ratio with the decreased light leakage by correction pulses by driving the liquid crystal light valve by the writing and correction pulses of the pulse width shorter than the response time of a liquid crystal. CONSTITUTION:One frame of a driving waveform is divided to a period (LZ period) t11 when a switching element is held at a low impedance and a period (HZ period) t12 when the switching element is held at a high impedance. The voltage pulses (writing pulses) to determine the light transmission state of the liquid crystal light valve and the voltage pulses (correction pulses) to correct the DC component of the voltage to be impressed to the ferroelectric liquid crystal are impressed in the LZ period t11. An electric field VLC is generated across the liquid crystal by the capacity of the liquid crystal and the electric charge charged in a capacitor in the LZ period t11. The effect of the electric field VLC continues even after the start of the HZ period t12 and the perfect optical response is eventually attained. The driving with the decreased light leakage and at the high contrast ratio is thereby permitted.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for driving a liquid crystal light valve.

More specifically, the present invention relates to a method for driving a liquid crystal light valve in which a ferroelectric liquid crystal is used and a switching element is formed on a liquid crystal element substrate.

[Prior Art] When a ferroelectric liquid crystal is used in a liquid crystal light valve for forming a latent @ on a photoreceptor in a printer using an electrophotographic method, for example, the method disclosed in Japanese Patent Application Laid-Open No. 187324/1980 In order to avoid deterioration of the quality of the liquid crystal or deterioration of the alignment state due to DC driving, a driving method was used in which a DC component correction pulse was applied to make the average direct voltage of the driving voltage zero.

[Problem that the invention seeks to solve]

However, in the conventional driving method, the liquid crystal responds to the DC component correction pulse, causing light leakage and lowering the contrast ratio. Alternatively, there is a problem in that it is necessary to take measures such as changing the intensity of the strong light emission in order to avoid a decrease in contrast ratio due to the DC component correction pulse.

The present invention is intended to solve this serious problem, and its purpose is to develop an optical system that has not been previously reported in a liquid crystal light valve that uses ferroelectric liquid crystal and connects a switching element to each display dot. The objective is to obtain a high-performance liquid crystal light valve using a new driving method that utilizes response characteristics.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides a first display device including a plurality of display dots formed of transparent electrodes and a plurality of switching elements disposed on the same substrate as the display dots and connected to each of the display dots. In a method for driving a liquid crystal light valve, the liquid crystal light valve has a structure including a substrate and a second substrate provided with a counter electrode facing the display dots, and a ferroelectric a liquid crystal is sandwiched between the first substrate and the second substrate. , one frame of the drive waveform is a period in which the switching element is made to have a low impedance (
tll (hereinafter abbreviated as LZ period) and a period in which the switching element is made to have a high impedance (hereinafter referred to as a period).

Hz period) divided into tu, the LZ period! ! To the 凰,
J: A voltage pulse that determines the light transmission state of the liquid crystal light valve (hereinafter referred to as a write pulse) and a voltage pulse that corrects the DC component of the voltage applied to the ferroelectric liquid crystal (hereinafter referred to as a write pulse).
It is characterized in that a correction pulse (abbreviated as a correction pulse) is applied.

The present invention will be described in detail below with reference to examples.

[Actual N examples]

First, the electro-optical characteristics that are applied to the liquid crystal element when a switching element is provided in each of the plurality of display dots used in the present invention will be explained.

A shift register circuit using Po1y-84 on a quartz substrate, a data latch circuit, a drive circuit including a transformer 5 transmission gate, a 100 μm square display dot connected to the transmission gate, and a capacitance of 0.5 pF connected in parallel with the display dot. A TPT substrate with a capacitor 〇8 of And so. This liquid crystal element was heated to a second temperature at 45°C.
The response time τ at which the transmittance changes to (A) by applying a square wave of ±107 as shown in 201 in the figure was measured.
8 and 91. As shown in Figure 3-), the LZ period t
Voltage pulses of ±10 V shown in the waveform 301 are alternately applied to the liquid crystal at u, and the other periods are the H2 period 11
The optical response τ was measured using the total change in pulse width ('=tt□).Then, the pulse width Ij W
The liquid crystal element responded even at 1c2oμs.

The optical response T of the liquid crystal element at this time is only about 20% saturated during the 'Lz period t11, as shown in Figure 3 (6), and is saturated 80 μs after the Hz period tn. Ta. This is the liquid crystal capacitance CLC during LZ period t11.
i and capacitor C8 are charged with charge Q.

During the Hz period t1, this electric charge Q generates an electric field VLO at both ends of the liquid crystal.

The effect of this electric field VLO is the same as when a sufficiently long pulse is applied to the liquid crystal molecules, and the operation continues even after the Hz period t12, resulting in a complete optical response.

A novel driving method using the above electro-optic effect will be described below.

Implementation u2 Using the same liquid crystal element as used in implementation row 1, the drive waveform and optical response in the case where the correction pulse corrects the DC component of the frame following the correction pulse are shown in FIG. 1, LZ period t 11 A correction pulse with a polarity that moves the liquid crystal molecules in the opposite direction to the direction in which writing is desired in the subsequent frame is applied to the first half t III of the L2 period 11, and the second half t 14 of the L2 period 11 is applied.
In this step, a write pulse with a polarity that operates the liquid crystal molecules is applied to the side where the iF is to be written. When driving in this way, one frame is a period of (to to t1s) from the perspective of the drive waveform, but from the perspective of the operating state of the liquid crystal light valve, one frame is a period of (t14 to t23). It can be considered as At this time, the status of the %LCD light valve is that the previous frame is in a light-blocking state (hereinafter abbreviated as OFF) and the next frame is in a light-transmitting state.g! (hereinafter abbreviated as ON)
The ON frame such that the integral i of the total transmitted light amount as ON is
Integral diagonal of the total amount of transmitted light when the OFF frame is OFF such that the next frame is OFF at N. 1j OF
F is the largest, frame period f: t1268 ms
, the minimum contrast ratio c Rmin (=801/BOFF B
It became 13.5.

Implementation row 3 Using the same liquid crystal element as used in implementation row 1, the driving waveform and optical response when the correction pulse corrects the DC component of the frame before the correction pulse LZ period t shown in FIG.
In the first half of t11, liquid J! is written in the opposite direction to the writing state of the previous frame! A correction pulse with a polarity that operates I is applied, and in the latter half t14 of the LZ period ill, a write pulse with a polarity that operates liquid crystal molecules on the side to be written is applied. In this case as well, from the operating state of the liquid crystal light valve, one frame can be regarded as (t14~jss), for example, and as in the case of implementation row 2, the center when changing from CJFF → RoN → RoN The integral direct SON of the total amount of transmitted light when the ON period is ON is the smallest, and from ON to OF
F-+OIF The central OFF period when it changes to F is O.
Integral of total transmitted light amount as FF 1i80! tF is the largest, pulse width PWi3Qμs, frame period t t
When driven at 1268 ms, the minimum contrast ratio CRmin was 2t126.

Implementation row 4 As shown in FIG.
A liquid crystal element with a reduced number of terminals was made by grouping the terminals from the gate electrodes No. 2 into multiple groups and pulling them out of the substrate, and enclosing the liquid crystal composition CB-1018 manufactured by Chisso Co., Ltd., as shown in Figure 6. -Each TFTi50f, 502 summarized
When multiplex driving was performed by sequentially selecting the waveforms of .
The min was 13.6.

Implementation column 5 As shown in FIG.
Nonlinear element (MIM element) 72 with 1os-Cf structure
T-connection was made and the drive was performed using a drive waveform as shown in 701 in FIG.

The liquid crystal composition used was the aforementioned CS-XOIS, and when the pulse width was set to FW=3Qμs, the obtained minimum contrast ratio CRmin was 12.2.

In the above example, the switching elements were formed using TPT made of poly-34 or α-8iH, or M elements. However, this is not limited to this example, and bidirectional diodes, etc. can be used if arranged. It is. Also the pulse width! It is clear that driving conditions such as pressure vary depending on the configuration of the liquid crystal element or the liquid crystal composition used.

〔Effect of the invention〕

As explained above, in the present invention, in a liquid crystal light valve in which a ferroelectric liquid crystal is suspended, a switching element is connected to each of a plurality of dots, and the response time τ when a step voltage is applied to the liquid crystal is By driving with a write pulse and a correction pulse having a short pulse width Pwt, it is possible to obtain a liquid crystal light valve with a high contrast ratio, which has less deterioration due to evening direct current, and also has less light leakage due to the correction pulse.

[Brief explanation of drawings]

The first frame is a diagram showing the drive waveform and optical response when the correction pulse corrects the DC component of the frame following the correction pulse in the second embodiment of the present invention. FIG. 2 is a diagram showing the drive waveform and optical response when the response time of the liquid crystal composition was measured using a normal rectangular wave in Example 1 of the present invention. FIG. 3 μ) (6) is a diagram showing a drive waveform and optical response when driving is performed using a drive waveform with a high impedance period in a train according to the present invention. FIG. 4 is a diagram showing a drive waveform and an optical response when a correction pulse corrects a DC component of a frame preceding the correction pulse in Example 3 of the present invention. FIG. 5 is a diagram showing the circuit configuration of the liquid crystal element in the fourth embodiment of the present invention. FIG. 6 is a diagram showing drive waveforms in the fourth embodiment of the present invention. FIG. 7 is a diagram showing the circuit configuration of the liquid crystal element in the fifth embodiment of the present invention. FIG. 8 shows the implementation of the present invention f! It is a figure which shows the drive waveform in AJ5. 10t12301, 401, 701- Drive waveform 201 applied to one liquid crystal element...Waveform 51, 71 used for measuring response of liquid crystal
・Display pixel 52, TIFT 53, 73・-〇Charge storage capacitor soi~5
04...'X'FTt-Select gate signal tut(t
+U・Li・period when the switching element has low impedance tu, (tu・li・・period when the switching element has high impedance GUM・・counter electrode and more) Name. 1 b !5ejs - Section 2, Figure 3 (f) Figure 3 (b), Page 4, Figure 5, Figure 5, Figure 7, Figure 8

Claims (5)

[Claims] (1) a first substrate provided with a plurality of display dots formed of transparent electrodes, a plurality of switching elements disposed on the same substrate as the display dots and connected to each of the display dots;
In a method for driving a liquid crystal light valve having a structure in which a second substrate is provided with a counter electrode facing the display dots, and a ferroelectric liquid crystal is sandwiched between the first substrate and the second substrate, the driving waveform is One frame is divided into a period t_1_1 in which the switching element has a low impedance and a period t_1_2 in which the switching element has a high impedance, and a period t_1_1 in which the switching element has a low impedance.
A method for driving a liquid crystal light valve, characterized in that a voltage pulse for determining the light transmission state of the liquid crystal light valve and a voltage pulse for correcting the DC component of the voltage applied to the ferroelectric liquid crystal are applied to the ferroelectric liquid crystal. (2) The pulse width of the voltage pulse that determines the light transmission state of the liquid crystal light valve and the voltage pulse that corrects the DC component of the voltage applied to the ferroelectric liquid crystal is applied during the period t_1_1 when the switching element has low impedance. 2. The method of driving a liquid crystal light valve according to claim 1, wherein the response time is shorter than the response time when a step voltage is applied to the liquid crystal. (3) During the first half period t_1_3 of the period t_1_1 in which the switching element has low impedance, a voltage pulse is applied to correct the DC component of the voltage applied to the ferroelectric liquid crystal, and during the second half period t_1_4, the liquid crystal light valve emits light. 3. The method of driving a liquid crystal light valve according to claim 1, wherein a voltage pulse is applied to determine the transmission state. (4) A voltage pulse that corrects the DC component of the voltage applied to the ferroelectric liquid crystal during the first half t_1_3 of the period t_1_1 in which the switching element has low impedance has a polarity that corrects the DC component of the frame following the voltage pulse. and voltage.
A method for driving a liquid crystal light valve according to at least one of the items. (5) The voltage pulse that corrects the DC component of the voltage applied to the ferroelectric liquid crystal during the first half t_1_3 of the period t_1_1 in which the switching element has low impedance corrects the DC component of the frame preceding the voltage pulse. Claim 1~ characterized in that it is polarity and voltage.
The method for driving a liquid crystal light valve according to at least one of item 3.