This paper describes a high-resolution energy-efficient CMOS temperature sensor, intended for the temperature compensation of MEMS/quartz frequency references. The sensor is based on silicided poly-silicon thermistors, which are embedded in a Wien-bridge RC filter. When driven at a fixed frequency, the filter exhibits a temperature-dependent phase shift, which is digitized by an energy-efficient continuous-time phase-domain delta-sigma modulator. Implemented in a 0.18-μm CMOS technology, the sensor draws 87 μA from a 1.8 V supply and achieves a resolution of 410 μKrms in a 5-ms conversion time. This translates into a state-of-the-art resolution figure-of-merit of 0.13 pJ·K². When packaged in ceramic, the sensor achieves an inaccuracy of 0.2 °C (3σ) from -40 °C to 85 °C after a single-point calibration and a correction for systematic nonlinearity. This can be reduced to ±0.03 °C (3σ) after a first-order fit. In addition, the sensor exhibits low 1/f noise and packaging shift.

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Temperature sensors are often used for the temperature compensation of frequency references [1-5]. High resolution and energy efficiency are then critical requirements, the former to minimize jitter and the latter to minimize power dissipation in a given conversion time. A MEMS-resonator-based sensor meets both criteria [1], but requires two resonators. In principle, resistor-based sensors also meet these criteria, and are CMOS compatible, but previous designs have been limited by the power dissipation [2-4] or 1/f noise [6] of their readout electronics. This paper describes a CMOS temperature sensor that digitizes the temperature-dependent phase shift of an RC filter. It achieves 410μKrms resolution in a 5ms conversion time, while consuming only 160μW. This corresponds to a resolution FOM of 0.13pJ·K2, a 5× improvement on previous CMOS sensors [6].@en