Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1999-01-27
2001-11-13
Malinowski, Walter J. (Department: 2164)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S149000
Reexamination Certificate
active
06317172
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the field of liquid crystal display instrument panels, particularly for motor vehicles.
The invention is applicable to liquid crystal display units of the type called passive, in other words those comprising no diodes or transistors in the display unit.
This invention relates more particularly to devices for such instrument panels which comprise a display module comprising a multiplicity of parallel inputs connected via a multiplicity of control lines to a multiplicity of outputs of a control module supplied by an electrical power supply, the output of the display module and the electrical power supply being connected to an electrical ground.
BACKGROUND OF THE INVENTION
The control module consists principally of electronic switches, generally made from semiconductors which cannot withstand electrostatic discharges above approximately 2 kV. Now, it frequently occurs that discharges well in excess of 2 kV, typically 20 or 25 kV, are generated in the liquid crystal display module, as a result, in particular, of the surface stresses to which it may be subjected.
As a result of this, some switches of the control module may be damaged or even destroyed.
To overcome this disadvantage, those skilled in the art have proposed the fitting of a voltage limiting component, such as a Zener diode, to each output of the control module, in such a way that the discharges can be blocked, absorbed, and then dissipated in the form of heat. However, as the number of display segments increases, the number of outputs to be fitted with these components increases, and consequently the cost of the device and its dimensions also become considerable.
SUMMARY OF THE INVENTION
An advantage of certain embodiments of the present invention is therefore to provide a liquid crystal display module device which does not have the aforementioned disadvantage.
For this purpose, the invention proposes a device of the type described in the introduction, and in which at least one branch line is provided and has an input connected to the electrical power supply and an output connected directly to the output of the display module, the branch line having an impedance considerably lower than that of each pair consisting of a control line and the output of the associated control module.
In this way, since the impedance of a branch line with respect to ground is considerably lower than the impedance of each of the control lines added to that of the output of the control module associated with it, the high voltage of a discharge originating from the display module is spontaneously dissipated by the branch line in the direction of ground.
Preferably, the ratio of the impedance of a pair to the impedance of a branch line is at least greater than 10. More preferably, this ratio is at least greater than 100, and even more preferably it is at least greater than 1000.
Additionally, the output of the display module is preferably connected to ground via a coupling resistor.
The invention is particularly applicable to devices designed to form part of an instrument panel of a heating and/or air conditioning installation of a motor vehicle.
REFERENCES:
patent: 4629289 (1986-12-01), Streit
patent: 4954807 (1990-09-01), Fleischer et al.
patent: 5737053 (1998-04-01), Yomogihara et al.
patent: 37 36 761 (1989-05-01), None
patent: 0 717 390 (1996-06-01), None
Patent Abstracts of Japan, vol. 018, No. 532 (P-1810), Oct. 7, 1994 & JP 06 186592 A (Matsushita Electric and Co. Ltd.) Jul. 8, 1994.
Patent Abstracts of Japan, vol. 012, No. 224 (P-721), Jun. 25, 1988 & JP 63 018333 A (Hitachi Ltd; Others:01) Jan. 26, 1994.
Malinowski Walter J.
Morgan & Finnegan , LLP
Valeo Electronique
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