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  • Author(s): Du, Li Du;
  • Advisor(s): Chang, Mau-Chung Frank;
  • et al.

Touch sensing has been widely implemented as a main methodology to bridge human and machine interactions. The traditional touch sensing range is two dimensional and therefore limits the user experience. The required physical contact inherent of the technology creates several disadvantages, including unresponsiveness due to wet fingers, and unavoidable fingerprint residue on the screen surface.

To overcome these limitations, we propose a novel 3D contactless touch sensing system called Airtouch System, which improves user experience by remotely detecting single/multi-finger position. A single layer touch panel with triangular electrodes is used to achieve 3D multi-touch detection capability as well as manufacturing cost reduction. A lumped model of the touch panel is proposed to model the touch panel property and define the system specification. The hardware part of the proposed 3D touch sensor uses correlated double sampling (CDS) to achieve a high sensing resolution in Z direction and employs bootstrapping circuitry to reduce the mobile screen’s inter-channel-coupling effects. Additionally, to reduce chip area and assembly, the sensing oscillator is implemented with inverter-based active resonators instead of using either on or off chip inductors. The prototyped 3D touch sensor is fabricated using 65-nm CMOS process technology and consumes an area of 2mm2.

To detect the finger position in space, a new algorithm for finger position estimation is created with grouping filter invented to reduce system background noise. The algorithm is proposed to eliminate the fringing capacitance effect and achieve accurate finger position estimation. EM simulation proved that by taking account of fringing capacitance effect, the proposed algorithm reduced the systematic error by 11dB in the horizontal position detection. Accurate Z direction detection is achieved through using 2nd order polynomial curve to fit the EM model and compensate the non-linear fringing capacitance effect. The proposed system’s hardware circuit consumes 2.3mW and is fully compatible with existing mobile device environments. A prototype is built to demonstrate that the system can successfully detect finger movement in a vertical direction up to 6cm and achieve a horizontal resolution up to 0.6cm at 1cm finger-height. As a new interface for human and machine interactions, this system offers great potential in 3D gesture recognition for small-sized electronics and advanced human interactive games for mobile devices.

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