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This paper describes a compact resistor-based temperature sensor intended for the thermal monitoring of microprocessors and DRAMs. It consists of an RC poly-phase filter (PPF) that is read out by a frequency-locked loop (FLL) based on a dual zero-crossing (ZC) detection scheme. The sensor, fabricated in 65 nm CMOS, occupies 5800 μm 2 and achieves moderate accuracy (±1.2 °C (3σ) inaccuracy) over a wide temperature range (−50 to 105 °C) after a one-point trim. This is 2 better than previous compact resistor-based sensors. Operating from 0.85 to 1.3 V supplies, it consumes 32.5 μA and achieves 2.8 mK resolution in a 1-ms conversion time, which corresponds to a resolution FoM of 0.26 pJ·K 2 . Index Terms-CMOS temperature sensor, resistor-based temperature sensor, RC poly phase filter, frequency-locked loop (FLL), dual zero-crossing (ZC) detection, one-point trim.

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This article presents an energy-efficient dual-RC frequency reference intended for wireless sensor nodes. It consists of a digital frequency-locked loop (FLL) in which the frequency of a digitally controlled oscillator (DCO) is locked to a temperature-independent phase shift derived from two different RC poly-phase filters (PPFs). Phase shifts with complementary temperature coefficients (TCs) are generated by using PPFs made from different resistor types (p-poly and silicided p-poly). The phase shift of each filter is determined by a zero-crossing (ZC) detector and then digitized by a digital phase-domain modulator (-M). The results are then combined in the digital domain via fixed polynomials to produce a temperature-independent phase shift. This highly digital architecture enables the use of a sub-1-V supply voltage and enhances energy and area efficiency. The 28-MHz frequency reference occupies 0.06 mm 2 in a 65-nm CMOS process. It achieves a period jitter of 7 ps (1σ ) and draws 142 μW from a 0.9-V supply, which corresponds to an energy consumption of 5 pJ/cycle. Furthermore, it achieves ±200 ppm inaccuracy from −40 • C to 85 • C after a two-point trim.

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