Reference-less SAR ADC for on-chip thermal monitoring in CMOS

This brief presents a SAR ADC based design for on-chip temperature sensing which does not require an explicit voltage reference. Instead, the reference is implemented digitally using only the inputs from the sensor. We demonstrate two novel approaches to implicitly implement the reference: polarity-based and ratio-metric based approaches. Simulation results in 65nm CMOS for a 12-bit ADC demonstrate the feasiblity of these new ideas, and illustrate that after applying a room temperature trim, the reference-less SAR results in roughly ×2 times lower errer due to mismatch and process spread compared to a traditional SAR based sensor design and hence can achieve better temperature accuracy.