Dynamic range enhanced readout circuit for a capacitive touch screen panel with current subtraction technique

Abstract

A dynamic range enhanced readout circuit using current subtraction technique is presented for a capacitive touch screen panels. A low-voltage, analog front-end circuit using a high-voltage input signal is implemented. A high voltage (> 10 V) parallel pulse signal is used as the transmitter signal. The receiver system was designed with low voltage (<; 5 V). A current-subtraction circuit (CSC) with a current mirror and switches is proposed to improve the signal-to-noise ratio (SNR). SNR is improved by removing excessive current from the touch screen panel. High-voltage parallel signaling method is used to further enhance the dynamic range. Dynamic range was increased by a factor of four and reduced the feedback capacitance from 20 to 5 pF. The proposed IC was implemented in a TSMC 0.18-μm high-voltage CMOS process. The power consumption of the chip is 11.2 mW and the chip size is 2.5 mm × 2.5 mm.