Categorization and Characterization of Time Domain CMOS Temperature Sensors

The Design Considerations and Challenges in MOS-Based Temperature Sensors: A Review

This review paper categorizes the state-of-the-art MOS (metal oxide semiconductor)-based temperature sensors according to their thermal sensing principles, including: type I, the logic, saturation and linear MOS-based temperature sensors; type II, the subthreshold MOS-based temperature sensors; and type III, the gate leakage-based temperature sensors. It also discusses in detail the design considerations and challenges of MOS-based temperature sensors, in terms of area, energy efficiency, supply voltage, inaccuracy, noise, as well as process and power supply variations. Based on the aforementioned discussions, the paper concludes that the future MOS-based temperature sensors will mostly likely be based on subthreshold MOS operation, with better trade-offs between area, energy efficiency and accuracy, and with reduced power supply sensitivity and level, as well as a lower-cost, fewer-point calibration method.

High-Precision Low-Temperature Drift LDO Regulator Tailored for Time-Domain Temperature Sensors

This paper proposes a high-precision LDO with low-temperature drift suitable for sensitive time-domain temperature sensors. Its topology is based on multiple feedback loops and a novel approach to frequency compensation, that allows the LDO to maintain a large DC gain while handling capacitive loads that vary over a wide range. The key design constraints are derived by using a simplified, yet intuitive and effective, small-signal analysis devised for LDOs with multiple feedback loops. Simulation and measurement results are presented for implementation in a standard 130 nm CMOS process: the LDO outputs a stable 1 V voltage, when the input voltage varies between 1.25 V to 1.5 V, the load current between 0 and 100 mA, and the load capacitor between zero and 400 pF. It exhibits a DC load regulation of 1 µV/mA, a 288 µV output offset with a standard deviation of 9.5 mV. A key feature for the envisaged application is the very low thermal drift of the output offset: only 14.4 mV across the temperature range of −40 °C to +150 °C. Overall, the LDO output voltage stays within +/−3.5% of the nominal DC value over the entire line voltage, load, and temperature ranges, without trimming. The LDO requires only 1.4µA quiescent current, yet it provides excellent responses to load transients. The output voltage undershoot and overshoot caused by the load current jumping between 0 and 100 mA in 1 µs are: 10%/22% for CL = 0 and 12%/16% for CL = 400 pF, respectively. A comparative analysis against seven LDOs published in the last decade, designed for similar levels of supply voltage and output voltage and current, shows that the LDO presented here is the best option for supplying sensitive time-domain temperature sensors. The smallest thermal drift of the output offset, smaller than +/−15 mV, that is, 6.7 times smaller than its closest competitor, and the best overall performance when PSR up to 1 kHz, was considered.