Patent ID: 8354991

Claim:
An active matrix liquid crystal device comprising: an active matrix first substrate; a second substrate carrying a common electrode for the active matrix; a layer of liquid crystal material between the first and second substrates; a first capacitance to voltage converting circuit including a temperature sensing first capacitor comprising first and second electrodes on the first and second substrates, respectively, separated by the liquid crystal layer, which forms the first capacitor dielectric; a second capacitance to voltage converting circuit including a reference second capacitor; a third capacitance to voltage converting circuit including a calibration third capacitor of substantially the same capacitance as the second capacitor; a differential sample/hold circuit configured to, supply a first signal dependent on the difference between the capacitances of the second and third capacitors during a calibration cycle of a measurement cycle, and supply a second signal dependent on the difference between the capacitances of the first and second capacitors during a sampling cycle of the measurement cycle; and an analog/digital converter arranged to convert the first signal to a reference voltage and convert the second signal to a measure of the capacitance of the first capacitor, during a conversion cycle of the measurement cycle, wherein each of the first, second and third capacitance to voltage converting circuits includes, a first electronic switch for connecting the respective one of the first to third capacitors to a voltage for charging thereof, a transfer capacitor, a second electronic switch between the respective capacitor and the transfer capacitor for sharing charge therebetween, a third electronic switch for connecting the transfer capacitor to an output of the converting circuit, and a fourth electronic switch for discharging the transfer capacitor.