A 0.0014 mm² 150 nW CMOS Temperature Sensor with Nonlinearity Characterization and Calibration for the -60 to +40 °C...

Area of Science:

• Integrated Circuit Design
• Sensor Technology
• Low-Temperature Physics

Background:

• Cold chain applications require precise temperature monitoring, especially at sub-zero temperatures.
• Existing complementary metal-oxide-semiconductor (CMOS) temperature sensors often exhibit significant nonlinear errors at low temperatures.
• Accurate temperature sensing is critical for maintaining the integrity of sensitive goods during transport and storage.

Purpose of the Study:

• To develop an ultra-low power CMOS temperature sensor chip capable of operating accurately down to -60 °C for cold chain applications.
• To address and mitigate the nonlinear temperature-dependent errors inherent in proportional-to-absolute-temperature (PTAT) current generation at low temperatures.
• To propose and validate a novel, simplified nonlinear calibration method for enhanced low-temperature sensor accuracy.

Main Methods:

• Design and fabrication of a CMOS temperature sensor chip incorporating a PTAT current generator, current-controlled oscillator, and frequency-to-digital converter.
• Characterization of nonlinear PTAT current errors using foundry-provided device model files.
• Development and simulation of a two-point nonlinear error calibration technique.
• Fabrication in a 0.13 μm CMOS process with a small active die area (0.0014 mm²).

Main Results:

• The fabricated sensor operates at ultra-low power, drawing only 140 nA from a 1.1 V supply.
• Simulations confirmed the superior accuracy of the nonlinear model over the linear model for PTAT current.
• The proposed nonlinear calibration method reduced measurement errors from -1.8 to +5.3 °C (linear calibration) to -0.9 to +1.1 °C over a -60 to +40 °C range.
• Key transistors operate in the deep subthreshold region, contributing to low power consumption.

Conclusions:

• The developed ultra-low power CMOS temperature sensor chip effectively addresses the challenges of low-temperature monitoring in cold chain applications.
• The novel two-point nonlinear calibration method significantly enhances sensor accuracy at temperatures down to -60 °C.
• This technology offers a promising solution for reliable and energy-efficient temperature sensing in demanding cold chain environments.