A 3.1-μW BJT-Based CMOS Temperature-to-Frequency Converter with Untrimmed Inaccuracy of ±1°C (3σ) from -40°C to 140°C

The temperature compensation for ICs is getting more crucial as the process nodes and circuit performances are advanced. A temperature-sensing core needs to be small enough to locate beside the critical nodes in an IC closely for proper compensation. Also, a highly energy-efficient core with low power consumption is desired to monitor temperature being changed slowly and continuously. The temperature sensors based on RC oscillators have emerged for these area- and energy-efficient solutions thanks to their simple architectures compatible with digital systems [1–4]. They measure the duty ratio of an oscillator clock period which relies on the ratio of the PTAT and CTAT properties of the BJT core, and convert it to temperature in the digital domain. In this paper, we present an ultralow-power small-size BJT-based CMOS temperature sensor with an RC oscillator. The proposed sensor creates a temperature-dependent clock frequency that is easily converted back to temperature without any analog trimming. The comparator offset in the RC oscillator is automatically suppressed by a cap-flipping technique, achieving inaccuracy of $\pm 1^{\circ}\mathrm{C} (3 \sigma)$ from $- 40^{\circ}\mathrm{C}$ to $140^{\circ}\mathrm{C}$ with 0.025-mm
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area occupation and $3.1- \mu \mathrm{W}$ power consumption in CMOS 110-nm process.