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Digital Temperature Sensing in a Variable Supply Environment

This project explores digital temperature sensing, focusing on overcoming challenges in variable supply environments. It compares digital and analog temperature sensors, highlighting the importance of supply-insensitive biasing and digital correction methods for accurate temperature measurement. The research emphasizes the limitations of traditional analog sensors and presents innovative solutions to optimize sensor performance despite supply variations. By creating decoupled delays from supply shifts, the project aims to enhance the reliability and accuracy of temperature sensing in real-world applications.

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Digital Temperature Sensing in a Variable Supply Environment

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  1. Digital Temperature Sensing in a Variable Supply Environment EE241 Term Project Matthew Spencer Steven Callender Spring 2009

  2. Accurately Measures BJT Current • Big, Power-Hungry, Analog Circuit Classic Temperature Measurement is Analog [1] M. Pertijs, K. A. Makinwa, J. H. Huijsing. A CMOS Smart Temperature Sensor With a 3σ Inaccuracy of +/-0.1°C From -55°C to 125°C. IEEE JSSC, December 2005

  3. Measure Delay Pretty Well • Ignore Supply and Process Digital Replacements Ignore Real Effects [2] Poki Chen et al. An Accurate CMOS Time-to-Digital-Converter-Based Smart Temperature Sensor. JSSC 2005 [3] K. Woo, D. Ham et al. Dual-DLL-Based CMOS All-Digital Temperature Sensor for Microprocessor Thermal Monitoring. ISSCC 2009.

  4. Motivation • Current sensors: What makes them good? • Comparing digital sensors and Simulation • Digitally Assisted Supply Correction • Supply Insensitive Biasing Outline

  5. Vdd to delay constants mismatched • Optimal Resolution, not supply rejection A Worrisome Graph from a Paper …

  6. “Linear With Supply” Costs a Lot of Area

  7. Use Digital Algorithm to Help Measurement • Use Several f(C) to Guess Vdd and T Can the We Correct for Supply with Math?

  8. Good Vdd Guess, but Bad T Guess • Exponentially sensitive to Vdd Digital Correction Can’t Handle Vdd Errors

  9. Strong coupling between Vdd and temperature in delay variations • Very hard to isolate each effect for a given delay variation (How much is due to Vdd and how much is due to temperature?) • Solution: Supply insensitive biasing • Idea: “remove” any Vdd shifts from the point of view of the delay cells Accounting for Vdd shifts: A Better Approach

  10. Once delay variations are decoupled from supply shifts, problem becomes trivial • Supply insensitive biasing is the most viable approach, but there are still issues: • Device Sizes • Topology: New approaches may need to be explored Accounting for Vdd shifts: A Better Approach

  11. Literature ignores real environments • Correcting for supply hasn’t worked yet • Delay is a BAD temperature metric • … But finding something else is hard Conclusion

  12. Thank You • Questions?

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