A Charge Balancing 1450 um²PNP-Based Thermal Sensor for Dense Thermal Monitoring

Thermal sensors are used in CPU's to detect hot spots and determine voltage levels. Since thermal gradients can be instruction dependent, there can be as many as 40 sensors/chip, which requires them to be compact. The industry standard for thermal sensors is the bandgap based PNP BJT sensor, because of its predictable and well-known physics. In this brief, a 1450 $\mu {\mathrm{ m}}^{2}$ charge-sharing BJT-based thermal sensor, with a 50 $\mu {\mathrm{ m}}^{2}$ sensing element, in 65nm is described. After a 1-point trim, the sensor exhibits a peak-to-peak accuracy of -2/+4°C over a 150°C range. After a 2-point trim, this becomes -2.5/+1.5°C over the same range. It also achieves a resolution of 0.22°C in an $821~\mu \text{s}$ conversion time. These specifications, as well as the small area, make the sensor attractive for dense CPU thermal monitoring.