A Fully-Dynamic Capacitive Touch Sensor With Tri-level Energy Recycling and Compressive Sensing Technique

Abstract

Capacitive touch screens have become the dominant user interface over the past decade. Achieving high framerates with low power consumption remains a critical design goal for touch systems. The conventional charge-recycling technique reduces driving power by 64%, but it relies on off-chip capacitors. To address this issue, we propose a tri-level energy recycling scheme, in which energy released during the 2-to-1 transition is recycled to power the 0-to-1 transition on the complementary channel. This approach achieves a 25% power reduction using on-chip transmission gates. Additionally, a compressive sensing method is introduced to selectively process touched RX channels while bypassing the others, reducing the number of fine ADCs by a factor of four compared to conventional two-step sensing. The proposed techniques are implemented in a 65 nm CMOS process and integrated into a 32×20 channel prototype occupying 2.4 mm². Measurement results show that the chip consumes only 2.6 mW at a framerate of 1513 Hz. The signal-to-noise ratio (SNR) reaches 49.7 dB for finger touch and 28.7 dB for a 1 mm Φ stylus, resulting in an energy efficiency of 10.66 pJ/step.