Control of liquid crystal display visual properties to compensate for variation in the characteristics of the liquid crystal
First Claim
1. A liquid crystal display comprising;
- a plurality of liquid crystal elements;
means for applying voltages across the elements;
photodetector means to detect the transmissivity of one of said plurality of elements;
means to repetitively switch said one element at predetermined times 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 a signal corresponding to the mean transmissivity of the first and second transitivities;
means for comparing the obtained signal with a reference signal representative of a desired mean transmissivity;
means for producing the reference signal; and
means for adjusting the voltages applied across the plurality of elements in dependence upon the difference between the obtained and desired reference signals, whereby the mean transmissivity of the liquid crystal elements is maintained at the desired mean transmissivity.
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Accused Products
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.
72 Citations
12 Claims
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1. A liquid crystal display comprising;
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a plurality of liquid crystal elements; means for applying voltages across the elements; photodetector means to detect the transmissivity of one of said plurality of elements; means to repetitively switch said one element at predetermined times 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 a signal corresponding to the mean transmissivity of the first and second transitivities; means for comparing the obtained signal with a reference signal representative of a desired mean transmissivity; means for producing the reference signal; and means for adjusting the voltages applied across the plurality of elements in dependence upon the difference between the obtained and desired reference signals, whereby the mean transmissivity of the liquid crystal elements is maintained at the desired mean transmissivity. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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Specification