EP0425210A2
Expired / Lapsed
EP
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Control of liquid crystal display visual properties
Assignee: Teledyne UK Ltd
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Filing: 1990-10-19
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Granted: —
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Expires: 2010-10-19
Abstract
Abstract The contrast or absolute brightness of a multiplexed LCD is maintained at its preselected value using a feedback arrangement which includes an LCD element functioning as a reference element. The reference element is not used to display information but is continually driven ON and OFF. The average transmissivity of the ON and OFF states is determined and compared with a reference value, the result of the comparison being used to control the voltage levels of the drive waveforms applied to the LCD. By selecting appropriate ratios between the ON and OFF times of the reference element, the LCD can be operated to give optimum contrast, or may have its absolute brightness varied. Control may be effected remotely by reprogramming the microprocessor which determines the timing of the drive waveforms.
Inventors
- 👤 Timothy John Eaton
- 👤 Roger John Pittock
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-01 06:53
CPC Classifications
G; G09; G09G; G09G3/00; G09G3/20; G09G3/34; G09G3/36; G09G2320/00; G09G2320/02; G09G2320/029; G09G2320/04; G09G2320/041; G09G2320/043; G09G2360/00; G09G2360/14; G09G2360/145
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
42 words
A liquid crystal display (LCD) comprising a plurality of liquid crystal elements; means for applying voltages across the elements; photodetector means to detect transmissivity of an element; means for adjusting the voltages applied across the elements in dependence on the transmissivity detected.
Claim 2
Dependent Claim
42 words
A liquid crystal display (LCD) comprising a plurality of liquid crystal elements; means for applying voltages across the elements; photodetector means to detect transmissivity of an element; means for adjusting the voltages applied across the elements in dependence on the transmissivity detected.
Claim 3
Dependent Claim
39 words
A liquid crystal display as claimed in Claim 1 in which the elements are arranged such that respective first electrodes of a number of elements are coupled to a single driver stage such that all elements are individually addressable.
Claim 4
Dependent Claim
22 words
A liquid crystal display as claimed in Claim 2 in which the elements are disposed in a matrix of rows and columns.
Claim 5
Dependent Claim
106 words
A liquid crystal display as claimed in Claims 1 to 3 comprising means to repetitively switch the said element between a first state in which it exhibits a first level of transmissivity and a second state in which it exhibits a second level of transmissivity lower than the first level; means coupled to the said photodetector means for obtaining the mean transmissivity of the first and second transmissivities; means for comparing the mean transmissivity with a reference value representative of a desired mean transmissivity; means for producing the reference value; whereby the mean transmissivity of the LCD elements is maintained at the desired mean transmissivity value.
Claim 6
Dependent Claim
92 words
A liquid crystal display as claimed Claim 4 in which the means for producing the reference value comprises first and second reference element means, and further photodetector means, the first reference element means being maintained in the first level of transmissivity, the second reference element means being maintained in the second level of transmissivity, the further photodetector means being coupled to the first and second reference elements so as to produce a signal representing the mean transmissivity of the first and second elements; the signal so produced comprising the said reference value.
Claim 7
Dependent Claim
42 words
A liquid crystal display as claimed in any of claims 1 - 5 in which the said element is illuminated in reflective mode by a light source disposed on the same side of the LCD display panel as the said photodetector means.
Claim 8
Dependent Claim
41 words
A liquid crystal display as claimed in any of claims 1 - 5 in which the said element is illuminated in transmissive mode by a light source disposed on the opposite side of the display panel from the said photodetector means.
Claim 9
Dependent Claim
41 words
A liquid crystal display as claimed in Claim 5 in which the first and second reference elements are illuminated in reflective mode by a light source disposed on the same side of the LCD display panel as the said photodetector means.
Claim 10
Dependent Claim
45 words
A liquid crystal display as claimed in Claim 5 in which the said element and the first and second reference elements are illuminated in transmissive mode by a light source disposed on the opposite side of the LCD display panel as the said photodetector means.
Claim 11
Dependent Claim
28 words
A liquid crystal display as claimed in any preceding claim in which the mean transmissivity of the LCD elements is adjustable in order to obtain desired visual properties.
Claim 12
Dependent Claim
24 words
A liquid crystal display as claimed in Claim 10 in which the mean transmissivity is such as to provide maximum contrast of the display.
Claim 13
Dependent Claim
39 words
A liquid crystal display as claimed in Claim 11 in which the time for which the said element is in the first state and the time for which the said element is in the second state, are independently adjustable.
Claim 14
Dependent Claim
40 words
A liquid crystal display as claimed in Claim 11 in which the time for which the said element is in the first state is substantially the same as the time for which the said element is in the second state.
Claim 15
Dependent Claim
26 words
A liquid crystal display as claimed in Claim 10 in which the mean transmissivity is adjustable so as to adjust the absolute brightness of the display.
Claim 16
Dependent Claim
53 words
A liquid crystal display as claimed in Claim 14 in which the relationship between the time for which the said element is in the first state and the time for which the said element is in the second state is adjustable so as to adjust the absolute level of brightness of the display.
Claim 17
Dependent Claim
53 words
A liquid crystal display as claimed in Claim 15 comprising a microcomputer to produce signals which determine the switching of the elements of the liquid crystal display between first and second states in which the time relationship between the first and second states of the said elements is varied by reprogramming the microcomputer.
References Cited (Backward Citations)
No citation records indexed.
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