A 2.3-mW 11-cm Range Bootstrapped and Correlated-Double-Sampling Three-Dimensional Touch Sensing Circuit for Mobile Devices

This brief discusses an oscillator-based capacitive 3-D touch-sensing circuit for mobile devices. The proposed 3-D touch sensor uses correlated double sampling to achieve a high sensing resolution in the Z-direction and employs bootstrapping circuitry to reduce the mobile screen's interchannel-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 3-D touch sensor is fabricated using 65-nm CMOS process technology and consumes an area of 2 mm
²
, with a 2.3-mW power consumption from a 1-V power supply. Measured together with a 3.4" HTC standard mobile screen, the sensor achieves an 11-cm Z-direction sensing range with a 1-cm resolution, demonstrating the potential implementation of 3-D finger position sensing in a mobile device.