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 mm 2 . After calibration at room temperature (∼25 • C) and at an elevated temperature (∼85 • C), it achieves an inaccuracy of 0.25 • C (3σ ) from −55 • C to 125 • C. The WB sensor dissipates 66 μW from a 1.8-V supply and achieves a resolution of 450 μK rms in a 10-ms conversion time, which corresponds to a resolution figure-of-merit (FoM) of 0.13 pJ•K 2 . 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.

Subranging BJT-Based CMOS Temperature Sensor With a ±0.45 °C Inaccuracy (3σ) From −50 °C to 180 °C and a Resolution-FoM of 7.2 pJ·K² at 150 °C

“…accuracy after one-point trim with polynomial curve fitting [6]. The recent self-calibration approach assisted by a thermal-diffusivity sensor further reduces the calibration cost [7]. However, resistor-based temperature sensors are highly dependent on the temperature dependency of on-chip resistors and may not be favorable in processes with only small TC resistors [8].…”