Failure Mechanism and Sampling Frequency Dependency on TID Response of SAR ADCs

Abstract

This paper describes the main failure mechanism of charge redistribution Successive Approximation Register (SAR) Analog-to-Digital Converters (ADCs) under radiation. Results of two different radiation experiments (gamma and X-ray) each considering two identical 130nm, 8-bit SAR ADCs, operating with distinct sampling rates, showed that lower sampling frequencies cause the converters to fail at lower accumulated dose, while increasing the sampling frequency increases the converters robustness to radiation. A SPICE model of a SAR ADC is used to simulate radiation induced leakage effects, considering the same technology node and operating conditions of the tested converters. A very good agreement between simulation results and gamma irradiation experimental data allows us to explain the main failure mechanism, which is related to leakage in switches connected to the programmable capacitor array of the internal DAC of the converter.