Design and Implementation of Readout Circuit on Glass Substrate for Touch Panel Applications

A readout circuit on glass substrate for touch panel application has been designed and fabricated in a 3-mu m low temperature poly-silicon (LTPS) technology. In this work, the switch-capacitor (SC) technique is applied to amplify the small voltage difference from capacitance change due to the touch event on panel. In addition, the corrected double-sampling (CDS) technique is also employed to reduce the offset originated from LTPS process variation. The minimum detectable voltage difference of the proposed circuit is 40 mV. To further identify the different touch area during touch events, a 4-bit analog-to-digital converter is used to converter the output of readout circuit into 4-bit digital codes.