A novel noise suppression solution for low cost microcontroller-based touch panel: Using inverse charge transfer capacitive sensing method
The proposed method uses a simultaneous pre-charging schema to sensing capacitance change on the sensing pad. In order to compensating the unstable sensing value due to the changing in power supply, an extra reference capacitor pair is adding to the schema. With simultaneous pre-charging schema, all of the sensing capacitors (Cs) including reference capacitors are charged to same voltage level before transferring charge to sensing pads. Therefore, the charge transfer times of all sensing channels do not interference by unstable power supply because transfer times can be compensated by reference channel. As for the noise injected during touching, the sensing pad discharge and manual leakage control allow using high volume Cs to construct a lower bandwidth passive analog filter front end without being stalling the measuring time significantly, so the stability of input level sensing is guaranteed. By combining the two noise-resisted features, touch sensing design implemented in a single microcontroller does not rely on high quality LDO and even can be feed from bulk converter directly.