This paper describes a compact resistor-based temperature sensor that has been realized in a 180nm CMOS process. It occupies only 6800µm², thanks to the use of a highlydigital VCO-based phase domain sigma-delta modulator, whose loop filter consists of a compact digital counter. Despite its small size, the sensor achieves ±0.35°C (3σ) inaccuracy from-35°C to 125°C. Furthermore, it achieves 0.12°C (1σ) resolution at 2.8 kSa/s, which is mainly limited by the time-domain quantization imposed by the counter.

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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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