Patent ID: 8378954

Claim:
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.