An efficient tool for the assisted design of SAR ADCs capacitive DACs

The optimal design of SAR ADCs requires the accurate estimate of nonlinearity and parasitic capacitance effects in the feedback charge redistribution DAC. Since both contributions depend on the specific array topology, complex calculations, custom modeling and heavy simulations in common circuit design environments are often required. This paper presents a MATLAB-based numerical environment to assist the design of the charge redistribution DACs adopted in SAR ADCs. The tool performs both parametric and statistical simulations taking into account capacitive mismatch and parasitic capacitances computing both differential and integral nonlinearity (DNL, INL). An excellent agreement is obtained with the results of circuit simulators (e.g. Cadence Spectre) featuring up to 10^4 shorter simulation time, allowing statistical simulations that would be otherwise impracticable. The switching energy and SNDR degradation due to static nonlinear effects are also estimated. Simulations and measurements on three designed and two fabricated prototypes confirm that the proposed tool can be used as a valid instrument to assist the design of a charge redistribution SAR ADC and to predict its static and dynamic metrics