Optimize Design Of 8-Bit SAR A/D Converter

In the front and the end of the advanced electronics systems, analog to digital converters (A/D converters) are applied to improve the performance of the digital processing technique. Of all kinds of A/D converters, successive approximation (SAR)A/D converters are frequently the architecture of choice for medium-to-high-resolution applications with sample rates under 5 mega samples per second (Msps). Because of providing low power consumption as well as a small scale factor, SAR A/D converters have a wide variety of applications.A 8-bit medium speed, low power A/D designed in this paper, is composed of digital-analog (D/A) converters, comparators ,bandgap and so on. By optimizing the performances of every module, it can operate well from from a signal 4.5V to 5.5V power supply.In D/A coverter module, in order to extend the resolution of D/A converter, the combination of differently scaled DACs is designed. A charge scaling D/A converter with capacitor voltage divider and resistance divider is designed, which extends the resolution of a parallel D/A converter as well as improve speed rate greatly. The comparator has the character of high gain with the structure of three-stage coupled capacitance, which reduces power consumption as well as satisfies the requirement of high speed comparator. Bandgap voltage circuits is an important module for A/D converter, which affects the accuracy of A/D converter. The bandgap designed in this paper has the capability of anti-fluctuation of power supply and temperature. It can work from a signal 4.5V to 5.5V power supply and from -50℃ to 100℃ temperature and always get 1.246V output voltage.By using the CSMC 0.6 μm CMOS Nwell technology, the circuits are verified in circumstances of Cadence spectre with Unix operating system. The simulation shows that the high speed comparator, the D/A converter and the bandgap meet the requirements of the 8-bit A/D converter, and the SAR A/D converter can work well.