9.6 A 3.9kHz-frame-rate capacitive touch system with pressure/tilt angle expressions of active stylus using multiple-frequency driving method for 65″ 104×64 touch screen panel

As the demand for interactive displays continues to increase, capacitive touch systems (CTSs) with stylus-based drawing have become indispensable [1-4]. Passive styli are widely used because of their low-cost implementation, but have low SNR and limited drawing expressions [1]. Active styli have gained interest to solve these problems [4]. The pressure of an active stylus can be expressed using a pressure-to-capacitance transducer [3,4], but the tilt angle has not been reported yet. In addition, analog front-end (AFE) ICs with high frame rates are in demand in response to the fast movements of finger and active styli. Conventional AFE ICs adopt a parallel driving method (PDM) to achieve high SNR, but suffer from low frame rates because the number of rows and columns of the driving matrix increases with the number of TX electrodes [3]. In this paper, an AFE IC with high frame rate using a multiple-frequency driving method (MFDM) is proposed for response to fast movements of fingers and active styli, while expressing both the pressure and tilt angle of the active stylus.