Display device including a liquid crystal screen with secured display
View Patent ↗The general field of the invention is that of display devices including a liquid-crystal matrix screen composed of elementary pixels, said screen including at least a first electrode used as voltage reference and called the “backplane,” a second electrode in the form of a matrix electronic network delivering the drive voltages for controlling the pixels and control electronics for said electrodes, said screen being used in the so-called “normally black” mode, that is to say that in the absence of applied voltages, the optical transmission of the pixels is substantially zero. In the device according to the invention, the “backplane” drive voltage is a variable periodic voltage, the amplitude of variation of this voltage being sufficient so that in the absence of voltage on the second electrode, the optical transmission of the pixels is sufficient to be detected by an observer.
1. A display device comprising:
at least one liquid-crystal matrix screen composed of elementary pixels, wherein said at least one liquid-crystal matrix screen comprising:
at least a first electrode used as voltage reference and called the “backplane”;
a second electrode arranged in a form of a matrix electronic network delivering drive voltages for controlling the elementary pixels and control electronics for said first and second electrodes, said at least one liquid-crystal matrix screen being used in a “normally black” mode, that is to say that the maximum amplitude of the drive voltages for controlling the elementary pixels corresponds to a maximum optical transmission,
wherein the drive voltage applied to the “backplane” is a variable periodic voltage having an amplitude variation representing about a third of the maximum amplitude of the drive voltages for controlling the elementary pixels, wherein the amplitude variation being sufficient so that in an absence of voltage on the second electrode, the optical transmission of the elementary pixels is sufficient to be detected by an observer.
2. The display device as claimed in claim 1 , wherein the drive voltages for controlling the elementary pixels is periodic, the amplitude of variation of said drive voltage being centered on the drive voltage applied to the “backplane” in such a way that on average the elementary pixel is subjected to a zero voltage.
3. The display device as claimed in claim 1 , wherein the drive voltage applied to the “backplane” over a period has a first constant value during a first half-period and a second constant value, different from the first value, during a second half-period.
4. The display device as claimed in claim 1 , wherein the drive voltage applied to the “backplane” has a frequency variation that is of same order of magnitude as an image refresh frequency, denoted frame frequency.
5. The display device as claimed in claim 1 , wherein the liquid-crystal matrix screen is of the at least one of a multi-domain vertical alignment (MVA) or an in plane switching (IPS) type.