Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2000-05-16
2002-02-12
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169300, C345S076000, C345S208000
Reexamination Certificate
active
06346774
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for driving a simple matrix liquid crystal display device comprising a plurality of liquid crystal elements each being provided in correspondence with each pixel and a plurality of row electrodes and column electrodes for driving the liquid crystal elements by a super-twisted nematic system (hereinbelow, referred to as a STN system) wherein predetermined voltages are applied to the electrodes to control each liquid crystal element so as to produce brightness in response to an effective value of applied voltage whereby a predetermined picture image is displayed on a display area which is comprised of a matrix of the liquid crystal elements. In particular, the present invention relates to a method for driving a simple matrix liquid crystal display device which is capable of reducing voltage for driving the display device.
2. Discussion of the Background
Conventionally, as methods for driving a simple matrix liquid crystal display device provided with electrodes used commonly for a plurality of liquid crystal elements, there are a driving system based mainly on a so-called line successive driving system and a driving system based mainly on a multiple line addressing driving system (or it is called a MLA system).
The line successive driving system is a driving system in which predetermined voltages are successively applied to electrodes of every row, and at the same time, predetermined voltages are applied to a plurality of column electrodes whereby control voltages are applied to the row electrodes. Then, each of the liquid crystal elements is controlled to have a transmittance in response to an average effective voltage applied during a time in which the voltages are once applied to all the row electrodes (hereinbelow, referred to as a frame). A predetermined picture image is displayed for each frame period.
The MLA driving system is a driving system in which all the row electrodes constituting a display picture area are divided into subgroups each comprising a plurality of row electrodes (a simultaneously selected number), and predetermined voltages are applied to row electrodes for each subgroup and at the same time, predetermined voltages are applied to a plurality of column electrodes wherein the above-mentioned operation is repeated at least the same number of times as the simultaneously selected number to all the subgroups. Thus, each of the liquid crystal elements is controlled to have a transmittance in response to an average effective voltage applied during a time in which the above repetitive operations are finished (it is called a frame period), and a displayed picture image is formed in each frame period. Such MLA system is disclosed in Japanese Unexamined Patent Publication JP-A-6-27907, U.S. Pat. No. 5,262,881 and Japanese Unexamined Patent Publication JP-A-8-234164 and so on.
In the MLA driving system, when predetermined voltages are simultaneously applied to a plurality of row electrodes, the voltages applied to the column electrodes are the product of a unit column voltage and values obtained by performing calculation of a plurality of display data at the intersections of column electrodes and row electrodes and column data of orthogonal matrix used for applying the scanning voltages. The maximum value of magnifying power obtained by the matrix calculation suffers restriction by an orthogonal matrix used for the calculation, and it takes at most a value of the number of rows in the matrix.
The liquid crystal display device has been used as a display device for a man-machine interface with the progress of highly intelligent society. In recent years, it is widely used not only for a desktop type personal computer but also for a notebook type personal computer, PDA (a portable information terminal) or a portable telephone, which is suitable for carrying, taking an advantage of thin and light in weight. As a result, the development of the liquid crystal display device tends to increase the surface area of the screen as well as improvements in reduction of the weight and low power consumption.
In such liquid crystal display device, various measures have been taken to lower the power consumption rate. In more detail, there are measures to form a liquid crystal element capable of responding to a low effective voltage or to use a reflection type liquid crystal element without requiring a back light. Further, there is published “General-purpose addressing technology for an effective value response type liquid crystal display device (SID, a record of a meeting of SID international display research society 1988, p. 80-p. 85)” as papers for reporting the relation between a driving method for such liquid crystal display device and electric power consumption. The papers report that when a multiple line driving is performed under conditions that L={square root over (M)} (where M represents the total number of row electrodes for a display area and L represents a simultaneously selected member) and the optimum bias ratio at which a ratio of an effective voltage versus a ratio between an effective voltage in an ON display time and an effective voltage in an OFF display time becomes the maximum is used, a driving voltage for the liquid crystal display device can be reduced in comparison with a case of using the line successive driving system.
The conventional liquid crystal display device uses a lithium ion battery (a button battery) of relatively high voltage (about 3.3 V) and reduced weight. However, the display device requires a driving voltage of 7-9 V even though an improvement of a liquid crystal material has been made, and accordingly, there is a voltage increase of about 3 times. As a result, there caused power loss due to a voltage increase circuit, which was against an attempt to lower consumption power. Thus, it was impossible to achieve the purpose of lowering consumption power to an extent of a sufficient utility. Further, since such voltage increase circuit required a fairly high breakdown strength, a generally utilized 5 V standard logic process device, which has generally been used, could not be used to increase a degree of integration. Accordingly, a logic process for inclusive use had to be developed to increase a degree of integration. As a result, there is resulted an increase of cost for the liquid crystal display device including a driving device and a prolonged term in designing. Further, there were problems of causing an additional cost in changing designing and difficulty in responding a demand of multi-item-small-production.
In forming actually the voltage increase circuit, there is a problem that the effective voltage changes due to the temperature dependence of liquid crystal whereby it is impossible to apply predetermined column voltages and row voltages. Accordingly, it is necessary to determine a voltage increase level in consideration of a temperature for the liquid crystal. However, working voltages to the liquid crystal itself are apt to vary under the above-mentioned condition. Accordingly, it was necessary to determine a voltage increase level with a larger margin so as to assure operating performance in a low temperature region. This created a cause of an increased power consumption rate by the provision of the voltage increase circuit as an addition circuit.
Further, besides the temperature dependence of the driving voltage, the response speed of liquid crystal becomes high in a high temperature region in a liquid crystal display for providing display data of static images, and there causes reduction of the contrast due to the frame response inherent to the passive matrix, whereby a phenomenon which deteriorates visibility takes place. Recently, there is a demand for a small or middle type liquid crystal devices having the performance capable of sequentially displaying cuts of images or scrolling of images of letters regardless of a high temperature region, which inevitably reduces visibility even in a static image with the tendency that liq
Hirai Yoshinori
Kitamura Masakazu
Nagai Makoto
Nakazawa Akira
Tamai Kiyoshi
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Optrex Corporation
Vu David
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