A fully integrated touch screen controller based on 12b 825kS/s SAR ADC

This paper describes a low-power 12 bits 825kS/s successive approximation register analog to digital converter (SAR ADC) for personal digital assistants, portable instruments, and touch-screen monitor applications. The proposed SAR ADC is based on 3-stage 4-4-4 C-DAC architecture and a high-speed 3-stages comparator. It features 8 general-purpose input channels and 8 dedicated channels supporting 4, 5, 7, and 8-wire resistive touch-screen panels. It has a full-scale input range, power-down mode for low current consumption, and a novel pen-touch detection control with fast response able to support any touch-screen panel. The ADC performs plusmn1.3 LSB DNL and plusmn5 LSB INL when tested up to 125C at supply voltages ranging from 2.7V to 3.6V. Fabricated in a 0.13um CMOS with fringe capacitors, it occupies an area of 0.17 mm² and has a total dissipation of 200uA at full speed. The circuit has been integrated on Freescale MCF5227x micro-controller unit (MCU) family of devices with a 166 MHz ColdFire(R) core processor and an LCD controller.