An Analysis of Switch Thermal Noise in SAR Converters

This brief presents a comprehensive model of the thermal noise introduced by switches in Successive Approximation Register (SAR) Analog-to-Digital Converters (ADCs). This noise source may become relevant in low-speed SAR designs, where it can be mitigated by properly tuning the comparator bandwidth and sizing the capacitive Digital-to-Analog Converter (CDAC) switches. In Noise-Shaping SARs (NS-SARs), two contributions arise: one is injected during the conversion process, and the second is added during residue generation. The former is suppressed by the noise-shaping loop, while the latter is transferred directly to the output; however, it can be mitigated by properly sizing the amplifier bandwidth. Qualitative insights and design guidelines are provided.