Design Of Resistive Touch Screen Controller

With the development of technology, the touch-screen technology is widely used in military, industrial control and civil handling devices. Therefore, touch-screen controller has become the research focus.The four-wire resistive touching-screen is popular in the touching-screen system because of its low cost and convenient operation. Glass substrate is covered with two layers of transparent and uniform conductive films, which are used as X-Plate and Y-Plate respectively. The two layers will contact when something touches the screen. The output voltage is proportional to the distance between touch point and the edge. In addition, the touching pressure can be perceived by four-wire resistance touch-screen. The voltage representing the location and pressure is quantified and transferred to the embedded program by the resistance touch-screen controller. Just in this way the tactual localization is achieved.In this paper, the analysis of the four-wire resistive touching-screen controller TSC2046E provided by Texas Instrument is done by the method of reverse design using the Charted 0.35um Mix-Signal process. The core of the controller chip is a 12 bit successive approximation analog to digital converter (ADC) based on charge redistribution theory. The 2.5V inner bandgap reference designed can be used as the reference voltage of ADC in the mode of battery monitor and temperature sensing. The digital interface of the chip uses SPI interface and is also compatible with the Microwire interface of National Semiconductor. The performance optimization for each block of TSC2046E is done in this paper by forward engineering. The model block simulation and whole circuit checking is done as well. And the results show that the performance of the extraction circuit meets the design requirements.Then SYGD1001 is redesigned with TSC2046E's SAR ADC and the bandgap reference part. After the optimization of interface circuit and control circuit's timing sequence, the chip is tapeouted through MPW Center in Peking University. The test result after package shows that the chip working sequence is correct and the conversion precision is up to 12 bit as well as the 11bit no missing codes. The analysis of testing result shows good linearity of AD. When the clock frequence is 10.87 KHz, the power dissipation of SYGD1001 is only 0.4422mW.