A MOS-Based Temperature Sensor With Inherent Inaccuracy Reduction Enabled by Time-Domain Operation
Elisabetta Moisello, Calogero Marco Ippolito, Giuseppe Bruno, P. Malcovati, Edoardo Bonizzoni
Abstract
This article presents a MOS-based ON-chip temperature sensor system addressing both high-resolution and low-inaccuracy requirement, red while requiring a single temperature calibration point. Hence, the proposed temperature sensor system proves to be a low-cost solution, well addressing the requirements of the spreading market of system-on-chips (SoCs), mobile and wearable devices, and consumer electronics in general. The temperature sensor features a two-phase time-domain architecture, which employs as a sensing element a single NMOS transistor, biased alternatively with different currents, thus allowing achieving an inherent inaccuracy reduction. The proposed sensory system, fabricated in a standard 130-nm CMOS process, comprises, along the sensor core, a switched-capacitor analog interface circuit and a 1-bit second-order sigma-delta ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Sigma \Delta $ </tex-math></inline-formula> ) analog-to-digital converter (ADC). The proposed temperature-to-digital converter (TDC), experimentally characterized considering a batch of 16 samples, achieves 40-mK resolution at 20-kHz switching frequency and +0.75/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 0.92\,\,^{\circ} \text{C}$ </tex-math></inline-formula> inaccuracy across the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 40\,\,^{\circ} \text{C}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$90 ^{\circ} \text{C}$ </tex-math></inline-formula> temperature range after one-point calibration at room temperature, consuming <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$25.4 \mu \text{W}$ </tex-math></inline-formula> , including the analog buffer added for testing purposes.