DE60300353T2 - Control method for a liquid crystal display for solving the problem of latch-ups due to ESD - Google Patents

Abstract

A method of controlling a liquid crystal display device (8) is described. The liquid crystal display device (8) has a data storage means (32,36) for storing data to be displayed by said device (8), and display means for displaying said data. The method comprises the steps of: (a) generating (130) first data to be displayed by said device (8); (b) applying (132) said first data to said data storage means (32,36); (c) applying (134) said first data in said data storage device (32,36) to said display means for displaying thereby, and (d) at a predetermined time, generating and applying (128) reset command data to said data storage means (32,36). By applying reset command data, the liquid crystal display device (8) becomes unlatched and then continues to function normally, so that the problem of latch up induced by electrostatic discharge is overcome. <IMAGE>

Description

technical area

The The invention relates to a method of controlling a liquid crystal display of the type suitable for use in a vehicle to which Driver of the vehicle to display a warning or other condition signal.

Background of the invention

A liquid-crystal display (LCD) typically comprises two glass plates separated by 5 to 10 μm are spaced apart and confine a cell containing a liquid crystal material is filled. Two polarizers are arranged, one on each side of the cell, their polarization axes being at (an angle of) 90 ° to each other are aligned. The inner surfaces the glass plates can with transparent electrodes, typically of indium tin oxide be formed, coated, the letters to be displayed, symbols or define other patterns. Between the glass plates and the liquid crystal material become alignment or orientation layers of polymer material treated to the adjacent liquid crystal molecules to maintain a defined orientation angle. If the alignment or orientation layers are under a Angle of 90 ° to each other are arranged, the molecules of the liquid crystal material, the inserted between the plates was caused to spiral around 90 °, and the polarized light, which passes through the cell passes through the molecules the 90 ° spiral so led, that the polarization axis is rotated by 90 ° becomes.

By Applying an electric field across the cell, the Polarization properties of the cell can be varied because the liquid crystal molecules to be directed to align with the electric field, and the 90 ° twist in the optical axis is disturbed or distorted. By varying the electric field across the Cell is applied, is the polarization axis of the incident polarized Light is aligned either with that of Auslasspolarisators (an ON state), in which case light is transmitted through the device or its polarization axis is orthogonal to the outlet polarizer (an OFF state), in which case light is not passing through the device is allowed through.

at a multiplexed liquid crystal device are the multiplex drive electrodes in a matrix on the glass plates arranged. A selective addressing of the electrode matrix to be displayed allows a means to change letters, graphic representations or other symbols, there molecules only in selected Segments of the cell are caused to interfere with the created to align the electric field. A drive chip is used to drive signals for displaying the requested image to the electrode matrix to apply.

LCDs for use " Board "of vehicles typically have the form of devices of the type with double super twisted, nematic (DSTN) material with one active Cell to which drive signals are applied during operation display requested image. Such ads are used to the driver information regarding indicate the condition of the vehicle and / or the engine. For example A warning signal may be displayed if one of the doors is open is if the trunk is not closed or if the seat belt of the driver is not created.

Such LCDs are for Electrostatic discharge (ESD) prone, and it was observed that this often causes that the ad is garbled is. This condition, known as a latch-up, can prevent that the displayed information changes correctly. So can an existing Warning signal will continue to be displayed, although the problem is that it has been rectified, or alternatively new Warning signals are prevented from being displayed correctly.

One such latch-up state is of course undesirable, in particular if the liquid crystal display device used to display critical safety alert signals, their ignorance potentially damaging or dangerous consequences may have. Furthermore, such ads are often in Positions that are easily accessible are like on motor vehicle dashboards, and they are therefore very for ESD vulnerable.

It is known, the problem of ESD of liquid crystal displays mechanically to solve. A solution is to provide the LCD with a protective lens. This solution is but expensive, and the lens is often large and so impaired the aesthetics the LCD device disadvantageous.

A another solution is the provision of a conductive Films on the LCD itself. Also, this option is expensive, and the movie has an increased Light attenuation of up to about 65%. Furthermore, the arrangement of the film during the Making the LCD time consuming, and the electrical connection of the Films is difficult.

Another solution is to provide an indium tin oxide layer on the front side of the LCD cell. This in turn is deterringly expensive, difficult to manufacture and has a 30% on the light attenuation increased.

The U.S. Patent No. 6,317,172 (Valeo Electronique) describes a liquid crystal display module which protected against electrostatic discharges. The liquid crystal display module includes a plurality of parallel inputs connected via a plurality of control lines with a plurality of outputs a control module are connected, that of an electrical power supply is supplied. The output of the display module and the electrical Power supply are electrically grounded. The entrance of a branch line is connected to the electrical power supply, and the output This branch line is directly connected to the output of the display module connected. Thus, a protection against a low-impedance shunt Electrostatic discharges provided to the electrostatic Discharges from the sensitive parts of the electrostatic indicator dissipate away.

Solutions of the Problems of LCD latch-up conditions due to ESD based on software or firmware are also known. For example, EP-A-1343136 describes a display driver and a method of controlling a display driver for driving a display panel of a mobile telephone device. The display driver comprises a memory control circuit having a control parameter, the for the display is characteristic stores. The control parameter, the for the display is characteristic, is periodically in a control register entered to prevent the display characteristics by an electrostatic discharge can be influenced.

It would be beneficial an improved solution of Problems of Latch-up of LCD Devices Due to ESD the disadvantages associated with existing solutions are not having. Another object of the invention is to provide a solution on the basis of software necessary for recovery from electrostatic Discharge ensures.

Summary of the invention

Under An aspect of the present invention therefore becomes a method for controlling a liquid crystal display device with a data storage element for storing data stored on the Device to be displayed, and a display device provided for displaying this data, the method being the comprising the steps of: (a) generating first data generated by the device to be displayed; (b) the application of the first data on the data storage element; (c) the application of the in this data storage element located first data on the Display device for the purpose of display by the latter; and (d) the automatically generating and applying reset command data to said data storage element in a fixed reset frequency.

Of the Step of automatically generating and applying the reset command data under the control of an electronic control unit (ECU).

• (c)-(i) Überführen der ersten Daten von der ersten Datenspeichereinrichtung auf die zweite Datenspeichereinrichtung; und
• (c)-(ii) Überführen der ersten Daten von der zweiten Datenspeichereinrichtung auf die Anzeigeeinrichtung, um sie durch diese anzuzeigen.

The data storage element may include a first data storage device and a second data storage device. Accordingly, step (b) may include the following step:
(b) applying the first data to the first data storage device, and
Step (c) may include the following steps:

• (c) - (i) transferring the first data from the first data storage device to the second data storage device; and
• (c) - (ii) transferring the first data from the second data storage device to the display device to display it.

The A liquid crystal display device can be a driver device for taking over the first data from the second data storage device and for applying the first Include data on the display device.

• (c)-(ii)-(I) Überführen der ersten Daten von der zweiten Datenspeichereinrichtung auf die Treibereinrichtung; und
• (c)-(ii)-(II) Überführen der ersten Daten von der Treibereinrichtung auf die Anzeigeeinrichtung zum Zwecke der Anzeige durch diese.

Step (c) - (ii) may therefore comprise the following steps:

• (c) - (ii) - (I) transferring the first data from the second data storage device to the driver device; and
• (c) - (ii) - (II) transferring the first data from the driver device to the display device for display by it.

The method preferably comprises the following step:
(e) performing an image refreshing operation by repeating steps (c) - (i) to (c) - (ii) - (II) at a refresh rate.

In Step (d) becomes the reset command data preferably supplied to the second data storage device. The Panel Reset command data are preferably not supplied to the first data storage device.

The first data storage device may be a random access memory (RAM) or the like. The second data storage device can a buffer, a latch circuit or the like.

By supplying the reset command data to the second data storage device and / or the driver device, the liquid crystal display is "unlatched" and then continues to function normally, overcoming the problem of electrostatic discharge latch-up.

at a further preferred embodiment The method comprises the step of applying the first data on a driver chip, for example, a SED157A chip, thereby the driver chip applies the first data to the display device.

It It can be seen that in the preceding description the order the procedural steps in the order in which they are given, carried out can be; You need to but not.

The Method is particularly suitable for use in devices of the STN or DSTN type, however, it is equally applicable to LCD devices, which contain other materials.

Short description the drawings

The The present invention will now be described by way of example only to the attached drawings described in which show:

1 a schematic side view of a double STN (DSTN) liquid crystal display;

2 a perspective view of in 1 shown double STN (DSTN) liquid crystal display;

3 a schematic block diagram of a liquid crystal display driver chip, which is suitable for use with the inventive method;

4 a flow chart to the process steps of a main control circuit for displaying an image on the liquid crystal display of 1 and 2 to illustrate; and

5 a flow diagram to the method steps of a modified control circuit according to the invention for displaying an image on the liquid crystal display of 1 and 2 to illustrate.

detailed Description of the Preferred Embodiments

With reference to the 1 and 2 is a liquid crystal display device 8th of the type exhibiting a first, active cell 10 and a second, passive cell 12 includes. The active cell 10 has a front and a rear glass plate (only the rear 19 is in 2 shown) between which a liquid crystal material is provided, such as a super twisted nematic material. The passive cell 12 is of similar design, and the two cells 10 . 12 are connected to each other by means of a connecting layer 13 conventionally connected to form a dual cell array, commonly referred to as a double super twisted nematic (DSTN) device.

A heating element 14 formed of a layer of indium tin oxide (ITO) extends through the passive cell 12 through in contact with the liquid crystal material. Front and back device polarizers 18 . 20 are on the front surface of the active cell 10 or the back surface of the passive cell 12 are arranged and aligned so that their polarization axes are orthogonal to each other. A temperature sensor (not shown) may be provided on the device to measure the temperature of the liquid crystal material within the active cell 10 continuously monitor.

In the 1 and 2 The illustrated DSTN device is of the type suitable for use with a vehicle to indicate to the driver information regarding the condition of the vehicle and / or the engine. Typically, the ad can 8th be used to provide a warning signal if one of the doors is open, if the trunk is not closed or if the driver's seat belt is not closed. Further, the display may be used to provide an indication of engine speed, engine temperature, fuel economy, or a warning that engine oil level is low, or may be used to display Global Positioning System (GPS) information ,

A suitable matrix of electrodes (not shown) is on the active cell 10 provided to the in operation from an associated voltage source (not shown) by means of first and second driver chips 22 . 24 on the glass plate 19 are appropriate, suitable drive voltage signals are applied. Typically, the driver chips 22 . 24 Standard chips such as SED157A. The cell 12 remains passive and is intended to improve the contrast of the display.

An electronic interface unit of the display 8th is operated under the control of an electronic control unit (ECU). Suitable drive voltage signals for the electrode matrix of the active cell are applied in response to "build-on-demand" signals received from the electronic control unit, wherein the construction of the display request signals by means of respective connector wires 26 . 27 in the driver chips 22 . 24 be entered. When used in the aforementioned automotive application, the display is 8th typically a high density display, for example, 386x64 pixels, and may be powered to display the requested image using a multiplex addressing technique in a manner that should be familiar to one skilled in the art.

In operation, the heating element 14 the DSTN device via an H-bridge circuit (not shown) by means of a first terminal 16 (as in 2 shown) and a second terminal via the second connector 26 Supplied with electricity. The use of an H-bridge circuit ensures that there is a minimum DC offset to the heating element 14 which could otherwise degrade the performance of the liquid crystal device. The heating element 14 is turned on and off by applying a sawtooth-shaped PWM drive voltage through the H-bridge circuit. The sawtooth rise of the PWM drive voltage for the heating element 14 has the advantage that no high currents are quickly removed from the voltage source (eg, the vehicle battery), which could otherwise affect the DSTN drive voltage derived from the same voltage source. Typically, the increase in power takes "on" from zero to the maximum current for the heating element 14 1.6 seconds, and the power-down "OFF" takes 3.2 seconds.

The 3 Figure 5 shows in the form of a schematic diagram a SED157A LCD driver chip as discussed above, hereinafter referred to as "IC 22 This type of chip is well known in the art together with others of a similar type and is available in the form of standard packages 22 is therefore well understood by those familiar with this field of technology. Only those parts of the IC 22 which are important to the understanding (and not necessarily the operation) of the invention will be described in detail.

The IC 22 comprises a first data storage device in the form of a RAM 32 which is arranged to store data to be displayed by the LCD device. The RAM 32 has a capacity of 16,640 bits divided into 65 rows and 256 columns, each bit effectively corresponding to a respective pixel in the associated display (in 3 not shown). For each pixel in the display, a bit value of 1 in the RAM causes 32 In general, the pixel will be lit, while a bit value of 0 will cause the pixel to not glow. Desired bits can be specified by specifying row and column addresses in the RAM 32 be accessed.

The from the LCD device 8th data to be displayed ("display data") are generated by the electronic control unit and in the form of the aforementioned build-up display request signals on the IC 22 applied. The Build-on-Display request signals are transmitted through an MPU (SPI bus) interface unit 34 on the IC 22 upset and from the unit 34 to the RAM 32 transfer. The display data is by means of the RAM 32 in the form of a buffer or latch circuit 36 which is provided to temporarily display the data, applied to the second data storage device.

The display data is passed through the latch circuit 36 a driver in the form of a first driver circuit 38 supplied, wherein the transmission of the display data is achieved on the first driver circuit in a conventional manner.

A Display Timing Generator Circuit (DTGC) 40 generates timing signals based on a clock signal from the associated LCD display and places them on the RAM 32 and the latch circuit 36 on. The DTGC circuit controls the transmission of the display data from the RAM 32 on the latch circuit 36 and from the latch circuit 36 on the driver circuit 38 by synchronizing the clock signal from the display. This control function should be well understood by a person skilled in the art.

4 shows process steps of a main program control circuit L1 for controlling the liquid crystal device. Upon turning on the main program control loop L1, a check is made as to whether a build-up-display-request command signal has been generated by the electronic control unit (step 130 ), ie whether the display buffer must be rebuilt. If there is no build-up request, the main loop is exited and reentered after a predetermined period of time (typically, for example, 160 ms).

If in step 130 When a build-up of the display request has been generated by the electronic control unit (ECU), an image of the required display is generated in the memory of the electronic control unit, and the corresponding display data for that image is given to the RAM 32 via the SPI bus interface 34 fed. The display data will then be under the control of the DTGC 40 in the latch circuit 36 copied (step 132 ). The ad then be in step 134 through the latch circuit 36 on the first driver circuit 38 applied, and the requested drive voltage signals are applied to the electrode array of the active cell 10 created to display the requested image as described above.

In an in 4 not shown, the image is refreshed several times a second (referred to as "image refresh frequency") in a generally conventional manner. A clock signal, typically at 4550 Hz, is sent to the DTGC 40 and with each pulse of the clock signal, the DTGC assigns the RAM 32 on, the display data from one line of the RAM of the latch circuit 36 supply. The display data for all 65 lines of RAM 32 Thus, the latch circuit every 4550/65 seconds, ie at 70 Hz, fed again or "clocked fed".

While the display data is in the RAM 32 are maintained throughout the main control loop L1, the display data is latched 36 Thus, refreshed at a refresh rate of 70 Hz, to ensure that a loss of data or the display does not take place.

5 shows method steps of a modified control loop according to the invention for controlling the liquid crystal display device 8th , The procedure is similar to that described in 4 however, it has an additional sub-loop L2 included within the main control loop L1. During the execution of the main loop L1, the electronic control unit generates a REQUEST_REPORT flag on a regular, timed basis, for example, approximately every 640 ms. The main loop L1 checks for each cycle whether the flag REQUEST_REQUEST was set (step 126 ).

If, when checking, the REQUEST_REPORT flag was not set by the electronic control unit, then the control loop L1 continues the normal check as to whether the set-up-of-display request flag in step 130 was set.

On the other hand, if the REQUEST_REPORT flag is set by the ECU when checking, a reinitialization sequence is performed. In the re-initialization sequence, the electronic control unit generates reset command data and sends it via the interface unit 34 on the latch circuit 36 on (step 128 ). The reset command data gives the display data latch circuit 36 so free that the latch circuit is reset or restarted. The display data in RAM 32 be via the display data latch circuit 36 in the normal way in the display driver 38 copies, which prevents the display from "flashing" under normal operating conditions. If the display is latched by an ESD, there is a visible blink or flicker when the latch is turned on 36 reset and the display is refreshed.

The reset command data becomes the RAM 32 is not supplied, so that the display data stored there remain unaffected by the sequence of the re-initialization. When the sequence of re-initialization is completed, minor loop L2 is exited and the control sequence returns to main loop L1, next checking to see if a build-up display request is made in step 130 took place.

If such a build-up display request has been generated by the electronic control unit, the new display data will be transmitted via the interface 34 the RAM 32 fed and then to the latch circuit 36 applied (step 132 ) as described above. However, if no build-the-display request has been generated, the original display data stored in RAM 32 held as described above, the latch circuit 36 fed. The refresh of the latch circuit is then continued in the manner described above.

It can be seen that refreshing the data in the latch 36 is performed on a loop which is independent of the main loop L1 or the secondary loop L2 for re-initialization. This is often the case, and therefore the tag is REQUEST_REPLAY in step 126 checked while a refresh operation is being performed. If the REQUEST_REQUEST flag is generated while a refresh operation is being performed, the refresh operation is preferably continued and terminated before the beginning of the reinitialization sequence.

The frequency of the reinitialization sequence may be selected as needed and may take place automatically as described above or at the request of the user. For example, the reinitialization sequence may be at the refresh rate of the LCD device 8th synchronized or set to occur after a preset number of refreshes. Alternatively, the reinitialization sequence may automatically be in step 134 be started in such a way that it always occurs when new data is applied to the display driver the.

It It can be seen that the present invention is a simple and effective method of reducing the effect of unwanted ESD creates an LCD display. The method is software controlled and therefore does not require additional components for the Display. The method eliminates the need for mechanical solutions to the problem the ESD, which costs considerably reduced and the aesthetics and improves the performance of the LCD device.

at a further preferred embodiment can the tax procedure for the LCD is the step of applying a cold start subroutine to increase the response time of the LCD at relatively low temperatures (the reaction time is the time after the application of a drive voltage, that needs the liquid crystal material, to change the state to display the required image). The cold start subroutine is in the co-pending British Patent Application (GB 0121663.9) described by the applicant and includes applying a negative bias across it liquid crystal material for one Period of time depending on the temperature of the material.

After this above particularly preferred embodiments of the present invention It should be clear that the subject in question embodiments are merely exemplary, and that changes and modifications, the professionals with the appropriate knowledge and skills come in, done can be without to abandon the scope of the invention as set forth in the appended claims is.

Claims (12)

Method for controlling a liquid crystal display device ( 8th ) with a data storage element ( 32 . 36 ) for storing data stored on the device ( 8th ) and a display element for displaying said data, the method comprising the steps of: (a) generating ( 130 ) first data on the device ( 8th ), (b) application ( 132 ) of this first data on the data storage element ( 32 . 36 ), (c) application ( 134 ) this in the data storage element ( 32 . 36 ) to the said display device for the purpose of presenting it, the method being characterized by (d) automatically generating and applying ( 128 ) of reset instruction data on said data storage element ( 32 . 36 ) at a fixed reset frequency. A method as claimed in claim 1, wherein the Step of automatically generating and applying command data to reset under the control of a control unit or an ECU (electronic ECU) he follows. A method as claimed in claim 1 or claim 2, wherein the data storage element comprises a first data storage device ( 32 ) and a second data storage device ( 36 ). A method as claimed in claim 3, wherein step (b) comprises the step of: (b) applying said first data to the first data storage device ( 32 ), and wherein step (c) comprises the following steps: (ci) transferring said first data from the first data storage device ( 32 ) to the second data storage device ( 36 ); and (c-ii) transferring said first data from said second data storage device ( 36 ) on the said display element to represent it by this. A method as claimed in claim 3 or claim 4, wherein the liquid crystal display device ( 8th ) a driver or a control program ( 38 ) for accepting said first data from the second data storage device ( 36 ) and applying this first data to the display element. A method as claimed in claim 5, wherein step (c-ii) comprises the steps of: (c-ii-I) transferring said first data from the second data storage device (12) 36 ) into the driver or the control program ( 38 ); and (c-ii-II) transferring said first data from the driver or control program ( 38 ) on the said display element to represent it by this. A method as claimed in any one of the preceding claims, further comprising the following step: (e) perform a Image refresh operation by repeating steps (c-i) to (c-ii-II) with an image refresh operation frequency. A method as claimed in any one of claims 3 to 7, wherein in step (d) the reset command data is applied to the second data storage device (12). 36 ) are applied. A method as claimed in any one of claims 3 to 8, wherein the first data storage device ( 32 ) has a random access memory (RAM) or the like. A method as claimed in any one of claims 3 to 9, wherein the second data storage device ( 36 ) comprises a buffer, a latch circuit or the like. A method as claimed in any one of the preceding claims, wherein the method comprises the step of applying said first data to a driver program chip ( 22 ), said driver program applying the first data to the display element. A method as claimed in any one of the preceding claims, the method comprising the step of applying said command data to reset at a reset frequency, which is synchronized with an image update frequency, or alternatively following a predetermined number of image update operations includes.