A 6.6-μW Wheatstone-Bridge Temperature Sensor for Biomedical Applications

Abstract

This paper presents a compact, energy-efficient and low-power Wheatstone bridge temperature sensor for biomedical applications. To maximize sensitivity and reduce power dissipation, the sensor employs a high-resistance (600k) bridge that consists of resistors with positive (silicided-poly) and negative (n-poly) temperature coefficients. Resistor spread is then mitigated by trimming the n-poly arms with a 12-bit DAC, which consists of a 5-bit series DAC whose LSB is trimmed by a 7-bit PWM generator. The bridge is readout by a 2 nd -order delta-sigma modulator, which dynamically balances the bridge by tuning the resistance of the silicided-poly arms via a 1-bit series DAC. As a result, the modulator's bitstream average is an accurate and near-linear function of temperature, which does not require further correction in the digital domain. Fabricated in a 180nm CMOS technology, the sensor occupies 0.12mm 2 . After a 1-point trim, it achieves +0.2°C/−0.1°C (3σ) inaccuracy in a ±10°C range around body temperature (37.5°C). It consumes 6.6μW from a 1.6V supply, and achieves 200μK resolution in a 40ms conversion time, which corresponds to a state-of-the-art resolution FoM of 11fJ•K 2 . Duty-cycling the sensor results in even lower average power: 700nW at 10 conversions/s.

Experimental Demonstration of STT-MRAM-based Nonvolatile Instantly On/Off System for IoT Applications: Case Studies

“…Power Management [25,66] Protocol Framework [64] Digital Signal Processor Analysis of Energy Harvesting Model [45] memory technology in IoT applications. The on-chip 2MB STT-MRAM (replaces lash) is currently utilized as irmware for the startup program in the Ambiq Apollo4 microprocessor [1].…”

“…The energy harvesting technology can dramatically extend the lifetime of the system and has attracted much attention for IoT devices. For example, the implantable medical application can work for up to 10 years by collecting human-body energy into electricity through biomedical sensors [45]. Since the harvested energy is usually unstable and diicult to utilize efectively, the system with the energy harvesting technology may sufer unpredictable frequent energy failures and intermittently luctuating energy conditions.…”

A MOS-Based Temperature Sensor With Inherent Inaccuracy Reduction Enabled by Time-Domain Operation

“…Indeed, ON-chip temperature sensors constitute a fundamental block in a wide range of applications [1] as they can be used for realizing precise relative measurements, which require high resolution, or for implementing reliable absolute measurements, which necessitate low inaccuracy. Precise relative temperature measurements are needed in micro-electro-mechanical systems (MEMS) to compensate for the thermal drift of their parameters, which would otherwise determine a degradation in their performance [2], [3], [4], [5], while reliable absolute temperature measurements are required in biomedical applications [6], [7], [8], e.g., for implementing the reference detectors in contactless temperature sensors for the human body [9], and in thermal monitoring of the food and healthcare products cold chain maintenance [10], [11], [12]. Moreover, ON-chip temperature sensors are a fundamental block in microprocessors thermal management, as they enable responsive temperature tracking in order to allow dynamic voltage and frequency scaling (DVFS) and the cooling fans speed regulation [13], [14], [15], as well as in bandgap reference generation [16], [17].…”