The Design of Normalized Caplicitance in Capacitance Array of SAR ADC

Abstract

In SAR ADC, the capacitance array is a very important unit, it will determine the conversion performance in whole ADC. In 12-bit SAR ADC, the matching precision of the capacitor array must should be larger than 12-bit. But in normal semiconductor foundry, the high matching precision capacitor array almost should be constituted by unit capacitors. This paper introduces a new design, for getting a smaller layout area, the main body frame of capacitor array uses the M+N bit sectional type, but in traditional design schematic, the bridging capacitor will be not equal to the unit capacitor. In this improved design, for solving this problem, this paper improves the least N bit sectional capacitor array, letting the bridging capacitor also constituted by unit capacitors. So in this paper, the whole capacitor array all uses the unit capacitors to get the high matching precision performance.