A Readout IC for Capacitive Touch Screen Panels With 33.9 dB Charge-Overflow Reduction Using Amplitude-Modulated Multi-Frequency Excitation

摘要

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-inline-formula tex-math notation="LaTeX"$mu text{m}$ /tex-math/inline-formula standard CMOS process and was measured with a 32-in 104 inline-formula tex-math notation="LaTeX"$times $ /tex-math/inline-formula 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.