A Miniaturized 0.003 mm2 PNP-Based Thermal Sensor for Dense CPU Thermal Monitoring

Compact integrated thermal sensors are utilized to measure hot / cold spots in CPU cores in multiple locations and are important for the power/performance of the chip. Bipolar junction transistors (BJT) are the industry standard for temperature sensing elements because of their predictable physics. This paper reports on one of the smallest PNP BJT bandgap based thermal sensors to date. Miniaturization was achieved by using switched capacitor circuits with very small capacitors as opposed to the standard resistor-based bandgaps. Digitally controlled trims enable either a higher resolution or a nearly linear response to temperature. This ultra-miniature 0.003 mm2, PNP thermal- based sensor is fabricated in TSMC 65nm. It achieves a measured total +/- 3 sigma error of +/- 1.35 degrees C with a resolution of 65mK and a 4.1ms conversion time. The sensor is optimized for dense CPU thermal mapping.