Abstract: In one embodiment of the present invention, an active matrix liquid crystal device includes an active matrix substrate and a counter electrode substrate separated by a layer of liquid crystal material. A temperature sensing capacitor includes electrodes on the substrates separated by the liquid crystal layer, which thus forms the dielectric of the capacitor. A reference capacitor and a calibration capacitor are also provided and have nominally the same capacitance. These capacitors form part of charge-transfer capacitance measuring branches within a sample/hold circuit. During a calibration cycle, the sample/hold circuit provides a signal dependent on the difference between the capacitances of the calibration capacitor and the reference capacitor and this is supplied to an analog/digital converter, which forms a reference voltage.