Active matrix liquid crystal device
First Claim
1. An active matrix liquid crystal device comprising:
- an active matrix first substrate having an active matrix area;
a second substrate carrying a common electrode for the active matrix;
a layer of liquid crystal material between the first and second substrates;
a temperature sensing first capacitor comprising a first electrode outside the image generating region of the active matrix area on the first substrate separated from the common electrode, which forms a second electrode of the first capacitor, by the liquid crystal layer, which forms the first capacitor dielectric; and
a capacitance measuring circuit arranged, during operation of the active matrix, (i) repeatedly to perform the steps of precharging the first capacitor to a substantially fixed stable known first precharge voltage magnitude and forming a signal representing the capacitance of the first capacitor, (ii) to measure the capacitance of the first capacitor in synchronism with addressing of at least one of a plurality of rows included in a pixel matrix, and (iii) to charge the first capacitor to the same magnitude of voltage during each precharging step.
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Accused Products
Abstract
An active matrix liquid crystal device comprises an active matrix substrate (1) and a counter electrode substrate separated by a layer of liquid crystal material. A temperature sensing capacitor (11) comprises electrodes on the substrates separated by the liquid crystal layer, which thus forms the dielectric of the capacitor. A reference capacitor (CREF) and a calibration capacitor (CCAL) are also provided and have nominally the same capacitance. These capacitors form part of charge-transfer capacitance measuring branches (25, 26, 30) within a sample/hold circuit (12). During a calibration cycle, the sample/hold circuit (12) provides a signal dependent on the difference between the capacitances of the calibration capacitor (CCAL) and the reference capacitor (CREF) and this is supplied to an analog/digital converter (20-22, 31, 32), which forms a reference voltage. During subsequent parts of the measurement cycle, the converter converts the output of the sample/hold circuit using the reference voltage in order to improve the accuracy of measurement of the liquid crystal capacitor (11), and hence the temperature of the liquid crystal material. This temperature measurement may be used, for example, to compensate the AMLCD for the effects of temperature variation in the liquid crystal properties.
14 Citations
33 Claims
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1. An active matrix liquid crystal device comprising:
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an active matrix first substrate having an active matrix area; a second substrate carrying a common electrode for the active matrix; a layer of liquid crystal material between the first and second substrates; a temperature sensing first capacitor comprising a first electrode outside the image generating region of the active matrix area on the first substrate separated from the common electrode, which forms a second electrode of the first capacitor, by the liquid crystal layer, which forms the first capacitor dielectric; and a capacitance measuring circuit arranged, during operation of the active matrix, (i) repeatedly to perform the steps of precharging the first capacitor to a substantially fixed stable known first precharge voltage magnitude and forming a signal representing the capacitance of the first capacitor, (ii) to measure the capacitance of the first capacitor in synchronism with addressing of at least one of a plurality of rows included in a pixel matrix, and (iii) to charge the first capacitor to the same magnitude of voltage during each precharging step. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33)
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Specification