King & Spalding L.L.P.
Capacitive touch sensing using an internal capacitor of an analog-to-digital converter (ADC) and a voltage reference
An internal sampling capacitor of an analog-to-digital converter (ADC) in a digital device is charged to a reference voltage, then some of the voltage charge on the internal sampling capacitor is transferred to an external unknown capacitor through a low resistance switch internal to the digital device. After the charge transfer has stabilized, the voltage charge remaining on the internal sampling capacitor is measured. The difference between the known reference voltage and the voltage remaining on the internal sampling capacitor is used to determine the capacitance value of the external capacitor. Alternatively, the external capacitor may be charged to a reference voltage then the external capacitor is coupled to the internal sampling capacitor, e.g., having no charge or a known charge on it, and the resulting voltage charge on the internal sampling capacitor is measured and used for determining the capacitance value of the external capacitor.
Microchip Technology Incorporated
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