PTAT voltage generator based on an MOS voltage divider

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Little has been published on the use of charge-based compact models as tools for variable operating temperature design. We analyzed an MOS voltage divider applying the ACM model obtaining an equation relating the voltage at the middle point of the divider (Vx) to the inversion level of the transistors and geometrical parameters. We show that whenever the current through the divider is proportional to the sheet normalization current (easily accomplished with known circuits), then the transistors operate at constant inversion levels regardless of temperature and Vx is proportional to absolute temperature (PTAT). The slope of Vx(T) depends on the current level and the geometrical parameters. The PTAT behaviour of Vx has been known for a long time in the case of weak inversion and this result has been recently extended to strong inversion. In this paper, the ACM model allows us to show that the MOS voltage divider, when properly biased, produces a PTAT output for any inversion level. We support this claim with measurements on a test circuit comprising a bias current generator and an MOS divider. The tested samples displayed the expected behaviour which we compare to values predicted by our theoretical model.

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Journal: TechConnect Briefs
Volume: 3, Technical Proceedings of the 2007 NSTI Nanotechnology Conference and Trade Show, Volume 3
Published: May 20, 2007
Pages: 625 - 628
Industry sector: Sensors, MEMS, Electronics
Topic: Compact Modeling
ISBN: 1-4200-6184-4