The Design of High Resolution Capacitance Array in SAR ADC

Abstract

In SAR ADC, the capacitance array is a very important unit, it will determine the conversion performance in whole ADC. In L-bit SAR ADC, the resolution of the capacitance array must should be larger than L-bit. For getting a smaller layout area, the main body frame of capacitance array uses the M+N bit sectional type, but in traditional design schematic, the least N bit sectional capacitance array’ parasitic capacitance will directly reduce the conversion precision. At the same time, the bridging capacitor will be not equal to the unit capacitor. In this improved design, for solving those problems, this paper improves the least N bit sectional capacitor array, letting the bridging capacitor also constituted by unit capacitors, and this capacitance array also can ignore the parasitic capacitors at anywhere. So in this paper, the whole capacitor array all uses the unit capacitors to get the high matching precision performance, at the same time, in this improved design, the parasitic capacitors at the anywhere all could not reduce the conversion resolution of the capacitance array.