Fast interface electronics for a resistive touch-screen

The paper describes a new interface system for a fast resistive X-Y 4-wire touch screen. The system enables the determination of both: the X-Y position and the touch-point resistance. The interface uses advanced measurement techniques, including three-signal auto-calibration, synchronous detection and two-port measurement. The interface electronics has been designed to interface between the touch-screen sensor and a PC, using the Universal Serial Bus (USB) protocol. The X-Y position interface uses a very linear relaxation oscillator, which converts X-Y position and touch-point resistance signals to a period-modulated signal. A microcontroller is used to read out the modulated signal, to control the switches and to send the information to the USB interface device. The USB interface device is used to communicate between the microcontroller with any device with USB protocol, such as a PC. A phase-locked-loop is included in the USB interface to multiply from 6 MHz to 48 MHz, for the USB communication.