A Self-Calibrated Hybrid Thermal-Diffusivity/Resistor-Based Temperature Sensor

Abstract

This article describes a hybrid temperature sensor in which an accurate, but energy-inefficient, thermal diffusivity (TD) sensor is used to calibrate an inaccurate, but efficient, resistor-based sensor. The latter is based on silicided polysilicon resistors embedded in a Wien-bridge (WB) filter, while the former is based on an electrothermal filter (ETF) made from a p-diffusion/metal thermopile and an n-diffusion heater. The use of an on-chip sensor for calibration obviates the need for an external temperature reference and a temperature-stabilized environment, thus reducing the cost. To mitigate the area overhead of the TD sensor, it reuses the WB filter's readout circuitry. Realized in a 180-nm CMOS technology, the hybrid sensor occupies 0.2 mm2. After calibration at room temperature (25 °C) and at an elevated temperature (85 °C), it achieves an inaccuracy of 0.25 °C (3 σ) from-55 °C to 125 °C. The WB sensor dissipates 66 μ W from a 1.8-V supply and achieves a resolution of 450 μ K rms in a 10-ms conversion time, which corresponds to a resolution figure-of-merit (FoM) of 0.13 pJ K2. The sensor also achieves a sub-10-mHz 1/f noise corner, which is comparable to that of bipolar junction transistor (BJT)-based temperature sensors.