| 摘要 |
An apparatus for sensing a change in capacitance of a sensing electrode to a system ground, such as that which may be used to form a touch sensor, with the sensing electrode forming touch sensitive surface is arranged to include a sleep mode of operation. The apparatus includes a sample capacitor having a first terminal coupled to the sensing electrode, and a second terminal coupled to a voltage measurement circuit. The voltage measurement circuit is arranged in operation to determine a voltage at the second terminal of the sample capacitor. A voltage biasing arrangement is arranged under the control of a controller to apply a biasing voltage or the system ground to the first terminal or the second terminal of the sample capacitor in accordance with a measurement cycle. The measurement cycle includes an initialisation part, a charging part in which the sensing electrode is charged via the sample capacitor, and a measurement part in which a voltage at the second terminal is measured and it is determined whether there has been a change in capacitance of the sensing electrode in accordance with the measured voltage. Before or after the measurement cycle, the controller is arranged to enter the sleep mode in which the sensing electrode is biased at a voltage which is greater than the system ground, whilst the second terminal of the sample capacitor is floated by not applying the system ground or a biasing voltage, so that the sensing electrode is held at a voltage above the system ground during the sleep mode.
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