Low voltage temperature sensor design for on-chip thermal management




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As the integration density and power density of modern very-large-scale-integrated (VLSI) circuits keep increasing, on-chip overheating issue is causing performance degrading and even function failures. Thermal management system is therefore integrated on-chip, where a temperature sensor is the most important function block. As the process technologies keep shrinking down and the demands for battery operation increase, low voltage operation has been an important design criterion. Temperature sensors with low and process scalable supply voltages are proposed in this dissertation. Specifically, subthrehsold MOSFET diodes are used as sensing devices. Compared with traditional bipolar junction transistor (BJT) diodes, MOSFETs working in subthreshold region exhibit similar temperature characteristics but need lower and process scalable supply voltage. Other blocks in the sensor such as the error correction amplifier, ADC, etc, have been re-designed to support low voltage operation. Device mismatches in the sensing diodes, the current mirrors, the error correction amplifier, etc, result in large error in the measured temperature, which leads to worse accuracy performance than the BJT-based temperature sensor. Various error correction techniques have been studied and implemented in the dissertation in order to minimize the mismatch induced error and improve the sensing accuracy. Furthermore, scattered temperature sensors with multiple remote sensor nodes distributed across the chip are proposed for modern multi-core digital processer, where multiple hot spots need thermal monitoring simultaneously. Relative inaccuracy has been evaluated and optimized in the scattered temperature sensor which is necessary to improve the performance of the processer through load balancing. Several prototype designs have been taped out in different process technologies and the experimental results demonstrate the low voltage operation as well as the improved sensing accuracy.



Temperature sensor, Low voltage, Subthreshold MOSFET, Relative accuracy, Error correction