| 摘要 |
A sensor is arranged to determine the presence of an object from a change in a capacitance of a sensing element. The sensor comprises a capacitance measurement circuit operable to perform measurement cycles to measure a capacitance of the sensing element, and a controller circuit. The control circuit is operable to detect a periodic noise signal induced on-the sensing element, to determine a first part, of a repeating pattern of the periodic noise signal, which causes a change in an amount of charge present on the sensing element, which affects the measurement of the capacitance of the sensing element by the capacitance measurement circuit, to determine.a second part of the repeating pattern of the periodic noise signal, which does not cause a change in the amount of charge present on the sensing element, and to control the measurement cycles of the capacitance measurement circuit to perform the measurement cycles during the second part of the periodic noise signal and not to perform the measurement cycles during the first part of the periodic noise signal. The sensor is therefore arranged to detect a synchronous pattern of the noise signal induced. on the key, during a noise sensing phase, and to synchronise the generation of a plurality of measurement cycles within the bursts to reduce the effeets of the noise signal on the measurement of the change in the capacitance of the sensing element. The sensor can be used, for example, to form a two dimensional touch sensor, which can be overlaid on a liquid crystal display (LCD) screen. As such, the effects of noise on the detection of an object, caused by a noise source such as common voltage signal of the LCD screen can be reduced. |
