Design and implementation of readout circuit on glass substrate with digital correction for touch-panel applications

A readout circuit on glass substrate with digital correction, which contains a transconductance amplifier, counter, and digital correction circuit, has been designed for touch-panel applications for 3-mu m low-temperature polysilicon (LTPS) technology. The voltage difference as a result of a change in capacitance due to a touch event is converted to current by a transconductance amplifier. By charging and discharging the capacitor in the counter, the counter displays different digital-output codes according to touch or non-touch events. Furthermore, not only can the touch or non-touch event be distinguished, but also the influence of LTPS process variation can be compensated by a digital correction circuit in the proposed readout circuit.