28.1 A Capacitive Touch Chipset with 33.9dB Charge-Overflow Reduction Using Amplitude-Modulated Multi-Frequency Excitation and Wireless Power and Data Transfer to an Active Stylus

As the demand for high frame rate and SNR increases in capacitive touch systems (CTSs), several driving methods have been reported [1], [5]. However, when excitation circuits simultaneously send excitation signals V EXT s to multiple TX electrodes in order to increase frame rate, the readout circuit suffers from charge overflow because of the superposition of V EXT s. To prevent this, driving methods such as time-division [1], [5] and reduced-amplitude excitation [3], and signal omitting and linear interpolation in the digital domain [4] have been adopted in AFE ICs, but they degrade the frame rate, and SNR, and increase the computational load of the CTS, respectively. In this paper, amplitude-modulated multiple-frequency excitation (AM-MFE) is used to prevent charge overflow without degrading the frame rate, SNR, and computational load. In addition, an electric pencil case (EPC) is proposed for wireless power and data transfer to an active stylus, so as to avoid the need to replace the battery of the stylus or charge it via an adapter.