A $145-\mu \mathrm{W}$ Always-on Touch Screen Readout and Always-on Haptic Driver IC for 1.26-Inch Circular Display of Wearable Device

This paper presents a touch screen panel (TSP) read-out and haptic driver IC designed for Always-on-Touch and Always-on-Haptic functionalities with ultra-low power consumption. To maintain always-on functions even when the application processor of the mobile device remains in sleep mode, a TSP analog front-end having a dedicated low power operational mode is proposed. Adapting to a circular display form factor, the mutual capacitances (Cms) sensed by the multi-driving method vary among the TSP receiving electrodes. Each base-capacitance compensator operates independently to compensate varying Cms, leading to an enhanced signal-to-noise ratio (SNR). The proposed system architecture has been realized using a 130-nm process, wherein it achieved an SNR of 51 dB with 400-Hz TSP scan rate under the normal TSP sensing mode. In the low-power TSP sensing mode, it achieved an SNR of 35 dB while consuming $145-\mu\mathrm{w}$ of power. The always-on touch-to-haptic response time was measured to be $790\mu \mathrm{s}$.