| In portable electronic products,due to its advantages of convenience, flexibility and occupying less space,the touch-screen has gradually replaced keyboard, and becomes the input devices of embedded computer systems.A/D converter is the core circuit of touch-screen controller and needs to be higher accuracy and lower power consumption with less speed requirement.Of all kinds of A/D converters,successive approximation(SAR)A/D converters are the best choice for medium-to-high-resolution applications with sample rate less than 5 mega samples per second(Msps)due to their low power consumption and small volume.A 12-bit low power SAR A/D converter with medium speed is designed,which can work under a 3.3 V to 5.5 V power supply.Its typical throughput rate is up to125kbit/s. This paper mainly focuses on three analog parts:D/A converters,reference voltage sources and comparators.A charge scaling D/A converter with capacitor voltage divider is presented,which extends the resolution of a parallel D/A converter as well as reduces the chip area.A fine-tuning circuit is included to ensure D/A converter's higher precision.For the design of the comparator,the architecture of low-gain and high-bandwidth preamplifiers followed by a latch is employed,which satisfies the requirement of high speed and reduces the power consumption.The built-in 2.5V self-biasing reference voltage source improves the accuracy of the reference voltage,and also reduces power consumption.The SAR A/D converter is designed in CSMC 2P3M-0.5um-MIX-CMOS process. The post simulation is completed.Under 3.5V power supply,the power consumption is 2.1582mW including the internal reference voltage source and 0.58W excluding the internal reference voltage source respectively;The INL and DNL of the presented A/D converter are within 1LSB.The simulation result shows that the high speed comparator and the D/A converter meet the requirements of the 12-bit A/D converter,and the SAR A/D converter can work well. |
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