A long-range UHF RF identification (RFID) sensor has been designed using a 0.35- ?m CMOS standard process. The power-optimized tag, combined with the ultralow-power temperature sensor, allows an ID and a temperature reading range of 2 m from a 2-W effective radiated power output power reader. The temperature sensor is based on a ring oscillator, where the temperature dependence of the oscillation frequency is used for thermal sensing. The temperature sensor exhibits a resolution of 0.035°C and an inaccuracy value lower than 0.1°C in the range from 35°C to 45°C after two-point calibration. The average power consumption of the temperature sensor is only 110 nW at ten conversions per second while keeping a high resolution and accuracy. These properties allow the use of the RFID as a batteryless sensor in a wireless human body temperature monitoring system.

Full Passive UHF Tag With a Temperature Sensor Suitable for Human Body Temperature Monitoring

Microprocessor design has recently encountered many constraints such as power, energy, reliability, and temperature. Among these challenging issues, temperature-related issues have become especially important within the past several years. We summarize recent thermal management techniques for microprocessors, focusing on those that affect or rely on the microarchitecture. We categorize thermal management techniques into six main categories: temperature monitoring, microarchitectural techniques, floorplanning, OS/compiler techniques, liquid cooling techniques, and thermal reliability/security. Temperature monitoring, a requirement for Dynamic Thermal Management (DTM), includes temperature estimation and sensor placement techniques for accurate temperature measurement or estimation. Microarchitectural techniques include both static and dynamic thermal management techniques that control hardware structures. Floorplanning covers a range of thermal-aware floorplanning techniques for 2D and 3D microprocessors. OS/compiler techniques include thermal-aware task scheduling and instruction scheduling techniques. Liquid cooling techniques are higher-capacity alternatives to conventional air cooling techniques. Thermal reliability/security issues cover temperature-dependent reliability modeling, Dynamic Reliability Management (DRM), and malicious codes that specifically cause overheating. Temperature-related issues will only become more challenging as process technology continues to evolve and transistor densities scale up faster than power per transistor scales down. The overall objective of this survey is to give microprocessor designers a broad perspective on various aspects of designing thermal-aware microprocessors and to guide future thermal management studies.

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Recent thermal management techniques for microprocessors

An ultra-low power embedded CMOS temperature sensor based on serially connected subthreshold MOS operation is implemented in a 0.18 μm CMOS process for passive RFID food monitoring applications. Employing serially connected subthreshold MOS as sensing element enables reduced minimum supply voltage for further power reduction, which is of utmost importance in passive RFID applications. Both proportional-to-absolute-temperature (PTAT) and complimentary-to-absolute-temperature (CTAT) signals can be obtained through proper transistor sizing. With the sensor core working under 0.5 V and digital interfacing under 1 V, the sensor dissipates a measured total power of 119 nW at 333 samples/s and achieves an inaccuracy of + 1/-0.8°C from - 10°C to 30°C after calibration. The sensor is embedded inside the fabricated passive UHF RFID tag. Measurement of the sensor performance at the system level is also carried out, illustrating proper sensing operation for passive RFID applications.

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A Sub- $\mu$ W Embedded CMOS Temperature Sensor for RFID Food Monitoring Application

We propose a fully-integrated temperature sensor for battery-operated, ultra-low power microsystems. Sensor operation is based on temperature independent/dependent current sources that are used with oscillators and counters to generate a digital temperature code. A conventional approach to generate these currents is to drop a temperature sensitive voltage across a resistor. Since a large resistance is required to achieve nWs of power consumption with typical voltage levels (100 s of mV to 1 V), we introduce a new sensing element that outputs only 75 mV to save both power and area. The sensor is implemented in 0.18 μm CMOS and occupies 0.09 mm 2
 while consuming 71 nW. After 2-point calibration, an inaccuracy of + 1.5°C/-1.4°C is achieved across 0 °C to 100 °C. With a conversion time of 30 ms, 0.3 °C (rms) resolution is achieved. The sensor does not require any external references and consumes 2.2 nJ per conversion. The sensor is integrated into a wireless sensor node to demonstrate its operation at a system level.

A Fully-Integrated 71 nW CMOS Temperature Sensor for Low Power Wireless Sensor Nodes

This work presents a low power temperature sensor that is suitable for passive wireless systems. The test chip is fabricated with a 0.18 mum CMOS technology and the total area is 0.05 mm2. With temperature inaccuracy of -1.6degC/+3degC from 0degC to 100degC, the temperature sensor consumes only 220 nW at 1V under room temperature. The data conversion rate is 100 sample/s with an output resolution of 0.3degC, which is sufficient for most sensor applications.

An ultra low power 1V, 220nW temperature sensor for passive wireless applications

A time-to-digital-converter-based CMOS smart temperature sensor without a voltage/current analog-to-digital converter (ADC) or bandgap reference is proposed for high-accuracy portable applications. Conventional smart temperature sensors rely on voltage/current ADCs for digital output code conversion. For the purpose of cost reduction and power savings, the proposed smart temperature sensor first generates a pulse with a width proportional to the measured temperature. Then, a cyclic time-to-digital converter is utilized to convert the pulse into a corresponding digital code. The test chips have an extremely small area of 0.175 mm/sup 2/ and were fabricated in the TSMC CMOS 0.35-/spl mu/m 2P4M process. Due to the excellent linearity of the digital output, the achieved measurement error is merely -0.7/spl sim/+0.9/spl deg/C after two point calibration, but without any curvature correction or dynamic offset cancellation. The effective resolution is better than 0.16/spl deg/C, and the power consumption is under 10 /spl mu/W at a sample rate of 2 samples/s.

A time-to-digital-converter-based CMOS smart temperature sensor

A time-to-digital-converter-based CMOS smart temperature sensor is proposed for high-accuracy portable applications. Conventional smart temperature sensors rely on an analog-to-digital converter, which consumes much chip area and operating power, for digital output code conversion. For the purpose of cost reduction and power saving, the proposed smart temperature sensor first generates a pulse with a width proportional to the measured temperature. Then, a cyclic time-to-digital converter (TDC) is utilized to convert the pulse into the corresponding digital code. The test chips, with extremely small area of 0.175 mm/sup 2/, were fabricated by the TSMC CMOS 0.35 /spl mu/m 2P4M process. Due to the excellent linearity of the digital output, the achieved measurement error is merely -0.6/spl deg/C to +0.8/spl deg/C without any curvature correction or dynamic offset-cancellation. The effective resolution is better than 0.15/spl deg/C, and the power consumption is 10 /spl mu/W.

A temperature sensing system is provided. The temperature sensing system is used for converting a temperature into a corresponding digital signal. The temperature sensing system includes a temperature sensor for generating a time signal varying with the temperature, and a time-to-digital conversion circuit electrically connected with the temperature sensor for converting the time signal into the corresponding digital signal.

Chin-Chung Tsai

Papers

A time-to-digital-converter-based CMOS smart temperature sensor

A time-to-digital-converter-based CMOS smart temperature sensor

Digital temperature sensing system