Based On The High Precision Of The Touch Screen Controller Chip Low-power Adc Design

In portable electronic products,due to its advantages of convenience,occupying less space and flexibility,touch-screen has gradually replaced keyboard,and become the input devices of embedded computer systems.Portable or battery-powered electronic devices require low voltage and low power consumption.Analog-to-digital converter(ADC) is the core of the touch screen controller,so the design of high performance ADC appears to be the hot spot.The core of this design is to design a high-resolution and low-power ADC under the premise of small chip area. Successive approximation(SAR) ADC has the following characteristics:8-16bits resolution,low power consumption and a small area.SAR ADC which is the best choice of this design is commonly used for medium-to-high-resolution applications sample rates under 5 Mega samples per second(Msps).A 12-bit 125k sample/s CMOS successive approximation ADC based on the touch screen controller is presented,which is in SMIC 2P2M 0.35um CMOS technology.In order to reduce power consumption.ADC that can work in the Power-Down mode and Power-Up mode is designed.When the screen is touched,ADC instantly powers up to full power.There is no need for additional delays to ensure full operation.Otherwise it powers down.At the mean while between conversions the reference is off and ADC is off.A charge scaling D/A converter with capacitor voltage divider is designed,which reduces the chip area effectively.The value of the coupling capacitor is optimized based on the parasitic capacitors.That can improve the resolution of the ADC.The circuit can operation from 2.5V to 5.3V voltage range and can work from -40℃to 85℃temperature range.It has been proved that in this situation the power of the ADC is less than 1mW and the resolution is 12-bit.The main advantages of the circuit are that it is high in resolution,low in power and small in area.This is valuable to guiding the touch screen controller design.