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_EXTs to multiple TX electrodes in order to increase frame rate, the readout circuit suffers from charge overflow because of the superposition of V_EXTs. 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.

In this paper, we propose a sensing mode reconfigurable analog front-end (AFE) IC for a capacitive touch sensor (CTS) and amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT)-based active-matrix capacitive fingerprint sensor (CFS). The CTS consists of the transmit and receive electrodes for enabling the mutual-capacitance (C_M) sensing mode, which can detect the multi-touch. The CFS has the array of a-IGZO TFT and a sensing electrode for enabling the self-capacitance (C_S) sensing mode to achieve the high sensitivity. In addition, it can reduce the number of sensing lines by adopting the active-matrix type structure to achieve the low-manufacturing cost. To sense the CTS and CFS, the proposed AFE IC is reconfigured to operate the C_M and C_S sensing modes, respectively. The proposed AFE IC was fabricated using a 0.13μm CMOS process technology with 20 V high-voltage devices, and demonstrated with a 128× 72 32 -inch CTS and a 96× 96 0.27 -inch CFS, which represents a pixel resolution of 500 pixel-per-inch. The proposed AFE IC achieves the signal-to-noise ratios of 47.8 dB and 25.0 dB for the CTS and CFS, respectively.