This article presents an energy-efficient dual- RC frequency reference intended for wireless sensor nodes. It consists of a digital frequency-locked loop (FLL) in which the frequency of a digitally controlled oscillator (DCO) is locked to a temperature-independent phase shift derived from two different RC poly-phase filters (PPFs). Phase shifts with complementary temperature coefficients (TCs) are generated by using PPFs made from different resistor types (p-poly and silicided p-poly). The phase shift of each filter is determined by a zero-crossing (ZC) detector and then digitized by a digital phase-domain ΔΣ modulator ( Φ - ΔΣM ). The results are then combined in the digital domain via fixed polynomials to produce a temperature-independent phase shift. This highly digital architecture enables the use of a sub-1-V supply voltage and enhances energy and area efficiency. The 28-MHz frequency reference occupies 0.06 mm2 in a 65-nm CMOS process. It achieves a period jitter of 7 ps ( 1σ ) and draws 142 μW from a 0.9-V supply, which corresponds to an energy consumption of 5 pJ/cycle. Furthermore, it achieves ±200 ppm inaccuracy from −40∘C to 85 ∘C after a two-point trim.

This letter describes an NPN-based temperature sensor that achieves a 1-point trimmed inaccuracy of ±0.15 °C (3σ) from -15 to 85 °C while dissipating only 210 nW. It uses a dual-mode frontend to roughly halve the power consumption of conventional frontends. First, two NPNs are used to generate a well-defined PTAT bias current, then this current is sampled and applied to the same NPNs to generate well-defined PTAT and CTAT voltages. These voltages are then applied to a low-power tracking ΔΣ modulator-based ADC, which employs a digital filter to efficiently generate a multibit representation of temperature. A prototype fabricated in a 180-nm BCD process achieves 15-mK resolution in a 50 ms conversion time, which translates into a state-of-the-art resolution FoM of 2.3 pJK2.

This paper presents a 210nW BJT-based temperature sensor that achieves an inaccuracy of ±0.15°C (3s) from -15°C to 85°C. A dual-mode front-end (FE), which combines a bias circuit and a BJT core, halves the power needed to generate well-defined CTAT (VBE) and PTAT (?VBE) voltages. The use of a tracking ?S ADC reduces FE signal swing and further reduces system power consumption. In a 180-nm BCD process, the prototype achieves a 15mK resolution in 50ms conversion time, translating into a state-of-the-art FoM of 2.3pJK2.

This article describes a hybrid temperature sensor in which an accurate, but energy-inefficient, thermal diffusivity (TD) sensor is used to calibrate an inaccurate, but efficient, resistor-based sensor. The latter is based on silicided polysilicon resistors embedded in a Wien-bridge (WB) filter, while the former is based on an electrothermal filter (ETF) made from a p-diffusion/metal thermopile and an n-diffusion heater. The use of an on-chip sensor for calibration obviates the need for an external temperature reference and a temperature-stabilized environment, thus reducing the cost. To mitigate the area overhead of the TD sensor, it reuses the WB filter's readout circuitry. Realized in a 180-nm CMOS technology, the hybrid sensor occupies 0.2 mm2. After calibration at room temperature (25 °C) and at an elevated temperature (85 °C), it achieves an inaccuracy of 0.25 °C (3 σ) from-55 °C to 125 °C. The WB sensor dissipates 66 μ W from a 1.8-V supply and achieves a resolution of 450 μ K rms in a 10-ms conversion time, which corresponds to a resolution figure-of-merit (FoM) of 0.13 pJ K2. The sensor also achieves a sub-10-mHz 1/f noise corner, which is comparable to that of bipolar junction transistor (BJT)-based temperature sensors.

Microprocessors and SoCs employ multiple temperature sensors to prevent overheating and ensure reliable operation. Such sensors should be small (<10,000μm2) to monitor local hot-spots in dense layouts. They should also be moderately accurate (1°C) up to high temperatures (≥125°C), so that the system throttling temperature can be set as close as possible to the maximum allowable die temperature. Furthermore, they should be fast (1kS/s) and consume low power (tens of μW).

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}.

This paper describes a compact resistor-based temperature sensor that has been realized in a 180-nm CMOS process. It occupies only 6800 μ m², thanks to the use of a highly digital voltage-controlled oscillator (VCO)-based phase-domain sigma-delta modulator, whose loop filter consists of a compact digital counter. Despite its small size, the sensor achieves ±0.35 °C (3 σ) inaccuracy from-35 °C to 125 °C. Furthermore, it achieves 0.12 °C (1 σ) resolution at 2.8 kSa/s, which is mainly limited by the time-domain quantization imposed by the counter.

A resistor-based temperature sensor has been realized in 180 nm CMOS for SoC thermal management applications. Occupying only 6800 μm², it is the smallest resistor-based temperature sensor ever reported. This is achieved by employing a compact highly-digital VCO-based ADC. After a 2-point trim, the sensor achieves an inaccuracy of ±0.35 °C (3σ) in a temperature range from-35 °C to 125 °C. By achieving a resolution of 0.12 °C (rms) at 2.8kSa/s, it can track the fast thermal-transients in SoCs.