Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-06-01
2002-05-14
Saras, Steven (Department: 2775)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S096000, C345S097000
Reexamination Certificate
active
06388650
ABSTRACT:
This invention broadly relates to liquid crystal matrix panels and more particularly it concerns a control method for matrix panels of a direct addressing, ferroelectric liquid crystal (FLC) type with low voltages, so as to enable an apparatus comprising the display panel and the electronic control circuits to be produced at lower costs, without impairing its performances.
As it is known, the panels to which this invention relates are used in devices for displaying images and for optical computation applications, both of the projection and of the direct vision types. In these devices, each picture element (pixel) ideally corresponds to the intersection of an element of a first electrode assembly (for instance arranged as rows) and an element of a second electrode assembly (for instance arranged as columns) and materially it corresponds to an electro-optical cell comprising a ferroelectric liquid crystal in the room existing between two facing electrodes belonging to the above mentioned two electrode assemblies. In usual arrangements, a pair of crossed polarisers operatively completes the cell and makes visible the orientation changes of the director in the liquid crystal that can be of smectic C chiral type.
The panel consisting of FLC cells can be electrically controlled according to various addressing modes (or schemes) or modes for applying voltages and currents to the two electrode assemblies, so as to determine the states of all cells, the number of which is usually much higher than the number of electrodes. This invention relates to the broad case wherein the cells are addressed with voltage signals and the behaviour of the electro-optic cells depends on the differences between the voltages applied to two oppositely arranged electrodes. When we limit ourselves to examining the operation of the panel, it is apparent that voltage assemblies, to which the same voltage differences between the electrodes correspond, are quite equivalent and define the same addressing mode. The addition of a suitable time varying voltage to all voltages of an assembly enables any assembly equivalent thereto to be obtained. If, however, the panel drive circuits are considered, namely the circuits designed to generate the control voltages, only a few choices appear to be valid in implementation economy terms. As a matter of fact, the maximum voltage difference within the concerned integrated circuits is to be as much as possible decreased in fact it noticeably increases their costs and, in the best cases, such as it occurs with the usual choice of the CMOS technology for their implementation, it coincides with the minimum supply voltage difference therewithin. In the best cases, such maximum voltage difference, which we shall indicate hereinbelow as voltage dynamics of the integrated circuit, will be equal to the maximum difference between the voltages applied to the panel electrodes connected to the integrated circuit. According to the fastest addressing modes of the prior art, the maximum voltage differences between the panel electrodes appear between electrodes belonging to the same assembly, rather than between oppositely arranged electrodes. This invention furnishes teachings aimed at defining new addressing modes, having performances equivalent to the performances of any corresponding modes of the prior art, in which the voltage differences of the first type and consequently the voltage dynamics of the integrated circuits can be decreased with equal differences of the second type.
The main object of this invention is to teach new addressing modes with voltage signals having well defined characteristics which enable decreased maximum voltage differences to be established between two electrodes of the panel with respect to the prior art, with equal maximum voltages applied to the cells and broad achievable performances, as it is convenient in view of an inexpensive implementation of the drive circuits.
The device as a whole comprises the assembly of the described panel with the related electronic circuitry to generate the various voltage signals needed for its operation and with the interconnection elements to the panel electrodes. According to the expected application, in addition, polarisers, color filters, light sources and an optical system can be provided therein.
This invention additionally consists in the device comprising the above set forth assembly and operating according to the hereinafter described control method.
A description will follow in respect of the behaviour of the FLC cells as well as of the broad addressing issue of matrix display panels comprising said cells, which is more precisely subject-matter of this invention. This description will set forth suitably accommodated and synthesized knowledges and prior art teachings and it is believed necessary in order to explain the field in which the invention is intended to operate and its scope, as well as to introduce the terms that will be used to describe and to define it.
This invention relates to a matrix panel wherein the ferroelectric liquid crystal cells operate according to a bistable or multistable behaviour in absence of voltage or in presence of a continuously applied, high frequency voltage having a sufficient and suitable r.m.s. amplitude, known as high frequency or alternated current stabilization voltage. As it is known, such a role can be played by the control voltages used.
The ferroelectric liquid crystal can be of smectic C chiral type and the cells can be of the type in which the smectic layers are tilted with respect to a line normal to the cells, possibly broken up into differently tilted portions, with tilting angles smaller than the characteristic angle of the smectic C phase. Multi-stable behaviours can be related to microdomain mixtures of a number of stable states and be utilized for storage of intermediate shades. Reference is made, for instance to P. Maltese, “Advances and problems in the development of ferroelectric liquid crystal displays”, in Molecular Crystals and Liquid Crystals, Gordon and Breach, vol. 215, pages 57 and followings and to the references cited therein.
By means of spaced apart rectangular pulses, of alternately opposite polarities, possibly when a high frequency stabilization voltage Vhf having a predetermined r.m.s. amplitude is present between such pulses, it is possible to obtain, as a result of each pulse, a cyclic transition of a cell from one extreme state to the other. For a given r.m.s. stabilization voltage, this effect occurs when such pulses have a duration which is higher than a sufficient value, that is a function of the voltage of the pulses themselves. Within a large range, the product of such sufficient durations times the corresponding pulse voltages is approximately constant and a bit greater than a minimum pulse area sufficient for the switching function Amin, within the voltage range of interest.
For a more accurate definition of Amin, in a range of high voltages near the maximum practically useable voltage, as well as of other parameters of the cells, not necessary in this specification, reference is made to the description of Italian Patent Application No. RM94A000102. For defining the characteristic voltage of the cells, describing their operation in the addressing stage and particularly explaining a mathematical model of their operation, reference is made to two articles of P. Maltese et al. in “Liquid Crystals”, Vol. 15 (1993) pages 819 and following and in Digest of Technical Papers of 1993 Intl. SID Symposium, pages 642 and following, available by Society for Information Display, 1526 Brookhollow Drive, Suite 82, Santa Ana, Calif. 927055421, as well as in the references cited in said scientific papers.
A uniform cell is mainly characterized by Amin and by the dependence of Amin on Vhf. In view of the operation of the cell in the considered addressing mode, the significant values of Amin shall be determined in correspondence to a r.m.s. amplitude of Vhf equal to the one resulting from the voltages used in the addressing operation. As a matter of fact
Awad Amr
Saras Steven
Smith , Gambrell & Russell, LLP
Universita Degli Studi di Roma la Sapienza
LandOfFree
Low voltage control method for a ferroelectric liquid... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Low voltage control method for a ferroelectric liquid..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Low voltage control method for a ferroelectric liquid... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2816518