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This letter 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 (600 $\text{k}\Omega $ ) 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 second-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 180-nm CMOS technology, the sensor occupies 0.12 mm2. After a 1-point trim, it achieves +0.2 °C/−0.1 °C ( $3{\sigma }$ ) inaccuracy in a ±10 °C range around body temperature (37.5 °C). It consumes 6.6 ${\mu }\text{W}$ from a 1.6-V supply, and achieves 200- ${\mu }\text{K}$ resolution in a 40-ms conversion time, which corresponds to a state-of-the-art resolution FoM of 11 fJ $\cdot \text{K}^{2}$ . Duty cycling the sensor results in even lower average power: 700 nW at 10 conversions/s.

This paper describes a compact, energy efficient, resistor-based temperature sensor that can operate over a wide temperature range (−55 °C–125 °C). The sensor is based on a Wheatstone bridge (WhB) made from silicided poly-silicon and non-silicided poly-silicon resistors. To achieve both area and energy efficiencies, the current output of the WhB is digitized by a continuous-time zoom analog-to-digital converter (ADC). Implemented in a standard 180-nm CMOS technology, the sensor consumes 52 $\mu \text{A}$ from a 1.8-V supply and achieves a resolution of 280 $\mu \text{K}_{\mathbf {rms}}$ in a 5-ms conversion time. This corresponds to a state-of-the-art resolution figure-of-merit (FoM) of 40 fJ $\cdot ~\text{K}^{2}$ . After a first-order fit, the sensor achieves an inaccuracy of ±0.12 °C (3 $\sigma $ ) from −55 °C to 125 °C.

This paper presents a 7-MHz CMOS RC frequency reference. It consists of a frequency-locked loop in which the output frequency of a digitally controlled oscillator (DCO) is locked to the combined phase shifts of two independent RC (Wien bridge) filters, each employing resistors with complementary temperature coefficients. The filters are driven by the DCO’s output frequency and the resulting phase shifts are digitized by high-resolution phase-to-digital converters. Their outputs are then combined in the digital domain to realize a temperature-independent frequency error signal. This digitally assisted temperature compensation scheme achieves an inaccuracy of ±200 ppm from –45 °C to 85 °C after a two-point trim. The frequency reference draws 430 $\mu \text{A}$ from a 1.8-V supply, while achieving a supply sensitivity of 0.18%/V and a 330-ppb Allan deviation floor in 3 s of measurement time.

Resistor-based temperature sensors can achieve higher resolution and energy-efficiency than traditional BJT-based sensors. To reach similar accuracy, however, they typically require 2-point (2-pt) calibration, compared to the low-cost 1-pt calibration required by BJT-based sensors. This paper presents a hybrid temperature sensor that uses an inherently accurate, but power-hungry, thermal-diffusivity (TD) sensor [1] to self-calibrate an inaccurate, but efficient, resistor-based sensor [2]. The use of an on-chip reference obviates the need for accurate temperature stabilized ovens or oil baths, drastically reducing calibration time and costs. Furthermore, by sharing most of the readout circuitry, the associated area overhead can be reduced. After self-calibration at room temperature (RT, $\sim 25^{\circ}\mathrm{C})$ and at an elevated temperature $(\sim 85^{\circ}\mathrm{C})$, the proposed hybrid temperature sensor achieves an inaccuracy of $0.25^{\circ}\mathrm{C} (3^{\sigma})$ from $-55^{\circ}\mathrm{C}$ to $125^{\circ}\mathrm{C}$.

Energy efficiency and accuracy are important specifications of CMOS temperature sensors. BJT -based sensors achieve state-of-the-art accuracy [1], while Wheatstone-bridge (WhB) sensors achieve lower accuracy but state-of-the-art energy efficiency [2], [3]. This paper presents a WhB sensor that is read out by an energy-efficient continuous-time delta-sigma modulator (CTDSM). Compared to [2], [3], the modulator achieves better energy efficiency with the help of a return-to-CM (RCM) DAC and an OTA with a tail-resistor linearization scheme. Moreover, better accuracy is achieved by embedding the DAC in the bridge and by using more sensitive silicided-diffusion resistors instead of silicided-poly resistors. Compared to the state-of-the-art [3], the proposed sensor achieves a 2× improvement in resolution FoM (10fJ.K2), and a 2× improvement in inaccuracy (0.4° C(3σ) from −55° C to 125°C after a 1-point trim).

Systems-on-chip traditionally rely on bulky quartz crystals to comply with wired communication standards like CAN or USB 2.0. Integrated frequency references with better than 500ppm inaccuracy could meet this need, resulting in higher integration and lower cost. Candidate architectures have employed RC-, LC- or TD (thermal diffusivity)-based time constants, all of which can be realized in standard CMOS. Compared to LC $(\sim 20\mathrm{mW}, \sim 100\mathrm{ppm})$ [1] or TD $(\sim 2\mathrm{mW},\sim 1000\mathrm{ppm})$ [2] references, RC references offer the lowest power consumption and competitive accuracy $( [3]. However, due to the nonlinear temperature dependence of on-chip resistors, such references require complex temperature-compensation schemes based on higher-order correction polynomials and extensive calibration [3], [4], or complicated analog compensation networks [5].

This article describes a highly energy-efficient Wheatstone bridge temperature sensor. To maximize sensitivity, the bridge is made from resistors with positive (silicided diffusion) and negative (poly) temperature coefficients. The bridge is balanced by a resistive (poly) FIR-DAC, which is part of a 2nd-order continuous-time delta-sigma modulator (CT $\Delta \Sigma \text{M}$ ). Each stage of the modulator is based on an energy-efficient current-reuse OTA. To efficiently suppress quantization noise foldback, the 1st stage OTA employs a tail-resistor linearization scheme. Sensor accuracy is enhanced by realizing the poly arms of the bridge and the DAC from identical unit elements. Fabricated in a 180-nm CMOS technology, the sensor draws 55 $\mu \text{W}$ from a 1.8-V supply and achieves a resolution of 150 $\mu \text{K}_{\mathrm {rms}}$ in an 8-ms conversion time. This translates into a state-of-the-art resolution figure-of-merit (FoM) of 10 fJ $\cdot \text{K}^{2}$ . Furthermore, the sensor achieves an inaccuracy of ±0.4 °C (3 $\sigma$ ) from −55 °C to 125 °C after a ratio-based one-point trim and systematic non-linearity removal, which improves to ±0.1 °C (3 $\sigma$ ) after a 1st-order fit.

An approach based on millisecond pulsed laser is proposed for thermal fatigue property evaluation in this paper. Cyclic thermal stresses and strains within millisecond interval are induced by complex and transient temperature gradients with pulsed laser heating. The influence of laser parameters on surface temperature is studied. The combination of low pulse repetition rate and high pulse energy produces small temperature oscillation, while high pulse repetition rate and low pulse energy introduces large temperature shock. The possibility of application is confirmed by two thermal fatigue tests of compacted graphite iron with different laser controlled modes. The developed approach is able to fulfill the preset temperature cycles and simulate thermal fatigue failure of engine components.

This paper describes a high-resolution energy-efficient CMOS temperature sensor, intended for the temperature compensation of MEMS/quartz frequency references. The sensor is based on silicided poly-silicon thermistors, which are embedded in a Wien-bridge RC filter. When driven at a fixed frequency, the filter exhibits a temperature-dependent phase shift, which is digitized by an energy-efficient continuous-time phase-domain delta-sigma modulator. Implemented in a 0.18- $\mu \text{m}$ CMOS technology, the sensor draws 87 $\mu \text{A}$ from a 1.8 V supply and achieves a resolution of 410 $\mu \text{K}_{\textrm {rms}}$ in a 5-ms conversion time. This translates into a state-of-the-art resolution figure-of-merit of 0.13 pJ $\cdot$ K2. When packaged in ceramic, the sensor achieves an inaccuracy of 0.2 °C (3 $\sigma )$ from −40 °C to 85 °C after a single-point calibration and a correction for systematic nonlinearity. This can be reduced to ±0.03 °C (3 $\sigma )$ after a first-order fit. In addition, the sensor exhibits low 1/ $f$ noise and packaging shift.

Temperature sensors intended for embedded applications should be both energy-and area-efficient. The combination of Wheatstone-bridge (WhB) sensors and continuous-time ADCs has proven to be highly energy efficient [1], [2]. However, their area $(\gt 0.25$ $mm^{2})$ is still larger than that of comparable BJT-based sensors [3], [4]. This paper presents a temperature sensor that uses an FIR-DAC ADC to reduce its area and increase energy-efficiency, both by $2 \times $ compared to the stateof-the-art [5].

This paper presents two high-resolution CMOS temperature sensors intended for the temperature compensation of MEMS/quartz frequency references. One is based on a Wien bridge RC filter, which outputs a temperature-dependent phase shift when driven by a stable frequency; the other is based on a Wheatstone bridge, which outputs a temperature-dependent current. The bridge outputs are digitized by energy-efficient continuous-time delta-sigma modulators. Two prototypes were fabricated in a standard 0.18 μm CMOS technology. Both dissipate less than 200 μW and achieve sub-mK resolution, as well as sub-0.2pJ·K2 resolution FoMs, which corresponds to state-of-the-art energy efficiency.

The thermal diffusivity of silicon D Si has been used to realize fully-CMOS frequency references. However, due to the temperature dependence of Dg, the accuracy of such frequency references is limited to about 1000 ppm (−55 °C to 125 °C, one-point trim) due to the inaccuracy of the on-chip temperature compensation circuitry. As an alternative, we propose a frequency reference based on the thermal diffusivity of silicon dioxide Dox. Since the temperature dependence of Dqx is much less than that of Dg, the resulting frequency reference will be much more stable over temperature. To investigate this idea, a thermal-diffusivity-based frequency-locked loop (FLL) was realized in 0.18-μm CMOS. With ideal temperature compensation, the proposed frequency reference achieves an inaccuracy of 90 ppm (−45 °C to 85 °C, two-point trim). Even with 0.1 °C inaccuracy, which can be achieved by BJT-based temperature sensors, 200 ppm can still be achieved. This demonstrates the feasibility of high-accuracy oxide-based frequency references in standard CMOS.

This paper presents the most energy-efficient CMOS temperature sensor ever reported, with a resolution FoM of 49fJ·K2, 2.7× better than the state-of-the-art. It consists of a Wheatstone bridge made from poly-silicon resistors, which is readout by a 2nd-order Continuous-Time Delta-Sigma modulator (CTDSM). This approach leads to a high resolution (160μK in 10ms) and a low supply-voltage sensitivity (< 20mK/V at room temperature).