A 0.5 V, 0.13 nW, 4-Transistor Over Temperature Protection Circuit for SoCs

A 0.13 nW ultra-low-power over-temperature-protection circuit is proposed for highly integrated System-on-Chips (SoC). The circuit detects a temperature of $120^{\circ} \text{C}$ but can be programmed for other temperature thresholds. The temperature detection is achieved by comparing a reference voltage with a 2-transistor ultra-low-power inverter architecture. The 2transistor inverter is designed to have a proportional-to-absolute-temperature (PTAT) threshold characteristic, and the reference voltage is generated on-chip with a 2-transistor reference. The design is implemented in $0.18 \mu \text{m}$ CMOS technology and occupies an area of $0.0117 \text{mm}^{2}$. The design operates from 0.5 V supply voltage and has a line sensitivity of $0.1^{\circ} \text{C}/\text{V}$ and a hysteresis width of $7.7^{\circ} \text{C}$, as seen from simulations. The trim-free design has a worst-case process variation of 4%.