This article presents a readout integrated circuit (ROIC) for capacitive touch-screen panels (TSPs) employing an amplitude-modulated multiple-frequency excitation (AM-MFE) technique. To prevent charge overflow, which occurs periodically at the beat frequency of the excitation frequencies, the ROIC modulates the amplitude of the excitation voltages at a mixing frequency derived from the excitation frequencies. Thus, the ROIC can sense the charge signal without charge overflow and maximize the signal-to-noise ratio (SNR) by increasing the amplitude of the excitation voltages up to the sensing range of the readout circuit. The proposed ROIC was fabricated in a 0.13- $\mu \text{m}$ standard CMOS process and was measured with a 32-in 104 $\times $ 64 touch-screen panel using 1 and 10 mm metal pillars. It reduces charge overflow up to 33.9 dB compared to operation without AM-MFE. In addition, the ROIC achieves a frame rate of 2.93 kHz, and SNRs of 41.7 and 61.6 dB with 1 and 10 mm metal pillars, respectively.

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.