462-nW 2-axis gesture sensor interface based on capacitively controlled ring oscillators

This paper presents a 2-axis gesture sensor interface that consumes 462 nW powered by a 0.8 V supply. The system consists of two proximity sensor (PS) interfaces that provide digital data outputs. A single PS interface consists of a capacitively controlled ring oscillator (CCRO) whose frequency is sensitive to the capacitance between two copper plates in a coplanar deployment and additional capacitive load introduced by the presence of a hand. The CCRO in each interface is followed by a modified cascaded integrator comb (CIC) filter that performs the frequency-to-digital conversion, filtering and downsampling. When a total of three sensor plates are arranged in parallel, the middle one acting as a shared ground plate, the location of a user's hand can be obtained in two dimensions. Measurement results show that hand sweep gestures at 6-cm distance from the sensing plates can be detected by a lightweight algorithm.

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