Applied To 12-bit Sar Adc Design, Resistive Touch Screen Control

As the communication bridge between the analog world and digital world, A/D converter has become one of the most important modules in IC.In this thesis, a SAR (Successive Approximation Register) A/D converter is designed for touch panel cotroller in portable electronics equipments.Compared with different kinds of A/D converters, the SAR A/D converter is chosen for tradeoff of in speed, accuracy, power consumption and cost. Meanwhile, the architecture of all charge redistribution is used in the design, because the traditional Track/Hold circuit is unnecessary for its operation mode naturally.Sampled channel is related to the linearity of input voltage and output voltage, so the design of this channel is also involved in this thesis. The capacitor array in D/A converter is used 2-stage D/A converter (4 MSB plus 8 LSB) in order to scale the charge and the area of capacitors can be reduced by this means.Multistage offset cancellation technique which avoids the disadvantage of the traditional IOS (Input Offset Storage) and OOS (Output Offset Storage) is used to calibrate offset error in the comparator. Simulation results show that it can distinguish 200μV at 2MHz under 3V supply voltage controlled by 2MHz clock and can calibrate 10mV input offset effectively, with only 234μW power consumption typically.6 channels sampling is supported in the design, which is controlled by a serial word. This word contains the channel address and the mode control.By optimizing the timing sequence, the A/D converter is operated in a 16 CLK continuous sampling mode, with a throughput rate of 125 kHz and a CLK of 2 MHz.Combining with the tools of hspice and Matlab,the performance of system has been simulated.The results is achieved as+/-2LSB INL (integral nonlinearity), +/-1LSB DNL (differential nonlinearity).The layout design of analog circuit could affect the performance of A/D converter, so an independent chapter is used for the design of capacitor array, omparator, and the I/O.The circuitry was fabricated on the 0.35μm N-well 2P2M(double poly and double metal) mix-signal process of CSMC with a die area of 0.89mm2,and the die was packaged with type TSSOP-16.After testing the chip, an application in a 4-wire touch screen controller with this A/D converter is approved by this design.