Synaptics Incorporated
Calibrating a continuous-time receiver for capacitive sensing

Abstract:

Embodiments herein describe input devices that include receivers for sampling capacitive sensing signals. In one embodiment, the receivers perform continuous demodulation where the sampling of the capacitive sensing signal is not synchronized with the modulated signal applied to the sensor. To calibrate, the receiver generates first and second measurements of the capacitive sensing signal when driving a modulated signal onto one or more sensor electrodes during two respective time periods. However, the phase of at least one signal is controlled during the time periods so that the first and second measurements have a phase difference of ninety degrees. Using the first and second measurements, the receiver can determine a phase offset between the capacitive sensing signal and the modulated signal which can be used to alter future measurements so that at least some of these measurements are captured when the capacitive sensing signal is at a peak amplitude.