A Pseudo-Differential Measuring Approach for Implementing Microcontroller-Based Capacitive Touch Sensing in Low-Power Quality Situation

Noise or unstable power supply can influence the sensing results of classic charge-transfer-based capacitive touch sensing methods. If such sensing methods are implemented in devices that share power supply with other heavily changing loads, the sensing methods are inclined to fail because of brownout. This paper proposes an inverse charge-transfer sensing method that can be applied in low-power quality situation. The proposed method includes a reference channel. The sensing capacitors in sensing channels and reference channel can be precharged to the same terminal voltage. Therefore, the inconsistencies in the sensing results induced by low-power quality can be compensated using a reference channel. The experimental result indicates that the proposed method exhibits excellent touch signal-to-noise ratio improvement: from 21.96 to 29.22 dB in the switching noise case and from 18.31 to 31.34 dB in the brownout case, and able to distinguish touched and untouched state under the brownout case.