1. Please check and comment entries here.

Topic review

# Time Domain CMOS Temperature Sensor

View times: 155
Submitted by: Sangjin Byun

## Definition

Temperature sensors is based on the sensory device (CMOS, BJT or resistor) and the measured signal type (voltage, current, frequency, delay time, phase shift or bandwidth), they can be implemented in various ways. By defining the temperature estimation function X(T) as the ratio of two quantities chosen from tREF, t(T), fREF and f(T), a time domain temperature sensor can be implemented based on one among 12 types of operational principles.

## 1. Introduction

Temperature sensors have been increasingly demanded in various applications such as military, aerospace, scientific research, industry, agriculture, medicine, transportation and so on. Based on the sensory device (CMOS, BJT or resistor) and the measured signal type (voltage, current, frequency, delay time, phase shift or bandwidth), they can be implemented in various ways [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. In this paper, we have chosen a time domain CMOS temperature sensor by considering the following factors.

First, measuring something is to represent it by using a ratio of two quantities, i.e., one is to be measured and the other is to be a reference. For example, the height of a person can be represented by a multiple of foot length as shown in Figure 1. So, we need both the person and the reference foot length to measure the height. Even when the height is measured in a metric system, we also need both the person and the reference meter.

Figure 1. Measuring something is to represent it by a ratio of two quantities.

Second, measuring temperature by using a temperature sensor does not mean that we can directly measure temperature itself. What we can really measure by using a temperature sensor are the voltage or current signals or the frequencies or delay times which are one-to-one matched to the temperature.

Third, as CMOS process technology improves, the supply voltage is getting lower and lower and the clock speed is getting higher and higher, which means that the voltage resolution is degraded, whereas the time resolution is improved. This trend has naturally made time domain signal-based circuits more attractive than ever before.

## 2. Discussion

Thus, in this entry we present a new type of time domain CMOS temperature sensor which can estimate temperature by measuring a frequency and a delay time. As summarized in Figure 2, a time domain temperature sensor can be implemented by choosing one among 12 types of operational principles. These operational principles have been categorized as shown in the figure based on the temperature estimation function, X(T), which is, in this paper, defined as the ratio of two quantities chosen from τREF, τ(T), 1/fREF and 1/f(T). Here, T is the temperature and τREF is defined as a temperature-independent reference delay time of a delay cell or a delay line, and τ(T) is defined as a temperature-dependent delay time of a delay cell or a delay line. Similarly, fREF is defined as a temperature-independent reference frequency of an oscillator or a clock signal, and f(T) is defined as a temperature-dependent frequency of an oscillator or a clock signal. If we arbitrarily choose two quantities from these four different kinds of time domain signals and put them into the numerator and denominator of X(T), respectively, overall 16 types of operational principles can theoretically exist, as shown in Figure 2. However, if the two quantities are irrelevant to T at the same time, we cannot use them for temperature estimation.

Figure 2. Twelve types of operational principles based on X(T).

This entry is adapted from 10.3390/s20072053

## References

1. Yousefzadeh, B.; Heidary, S.; Makinwa, A.A. A BJT-based temperature-to-digital converter with ±60 mK (3σ) inaccuracy from −55 °C to +125 °C in 0.16-μm CMOS. IEEE J. Solid-State Circuits 2017, 52, 1044–1052. [Google Scholar] [CrossRef]
2. Oshita, T.; Shor, J.; Duarte, D.E.; Kornfeld, A.; Zilberman, D. Compact BJT-Based Thermal Sensor for Processor Applications in a 14 nm tri-Gate CMOS Process. IEEE J. Solid-State Circuits 2015, 50, 799–807. [Google Scholar] [CrossRef]
3. Tang, Z.; Tan, N.N.; Shi, Z.; Yu, X.-P. A 1.2V Self-Referenced Temperature Sensor with a Time-Domain Readout and a Two-Step Improvement on Output Dynamic Range. IEEE Sens. J. 2018, 18, 1849–1858. [Google Scholar] [CrossRef]
4. Shor, J.S.; Luria, K. Miniaturized BJT-Based Thermal Sensor for Microprocessors in 32- and 22-nm Technologies. IEEE J. Solid-State Circuits 2013, 48, 2860–2867. [Google Scholar] [CrossRef]
5. Park, H.; Kim, J. A 0.8-V Resistor-Based Temperature Sensor in 65-nm CMOS With Supply Sensitivity of 0.28 °C/V. IEEE J. Solid-State Circuits 2018, 53, 906–912. [Google Scholar] [CrossRef]
6. Pan, S.; Luo, Y.; Shalmany, S.H.; Makinwa, K.A.A. A Resistor-Based Temperature Sensor With a 0.13 pJ K2 Resolution FoM. IEEE J. Solid-State Circuits 2018, 53, 164–173. [Google Scholar] [CrossRef]
7. Deng, F.; He, Y.; Li, B.; Zhang, L.; Wu, X.; Fu, Z.; Zuo, L. Design of an Embedded CMOS Temperature Sensor for Passive RFID Tag Chips. Sensors 2015, 15, 11442–11453. [Google Scholar] [CrossRef]
8. Sonmez, U.; Sebastiano, F.; Makinwa, K.A.A. Compact Thermal-Diffusivity-Based Temperature Sensors in 40-nm CMOS for SoC Thermal Monitoring. IEEE J. Solid-State Circuits 2017, 52, 1–10. [Google Scholar]
9. Ituero, P.; López-Vallejo, M.; Lopez-Barrio, C. A 0.0016 mm2 0.64 nJ Leakage-Based CMOS Temperature Sensor. Sensors 2013, 13, 12648–12662. [Google Scholar] [CrossRef]
10. Xie, S.; Theuwissen, A.J.P. On-Chip Smart Temperature Sensors for Dark Current Compensation in CMOS Image Sensors. IEEE Sens. J. 2019, 19, 7849–7860. [Google Scholar] [CrossRef]
11. Ha, D.; Woo, K.; Meninger, S.; Xanthopoulos, T.; Crain, E.; Ham, N. Time-Domain CMOS Temperature Sensors With Dual Delay-Locked Loops for Microprocessor Thermal Monitoring. IEEE Trans. Very Large Scale Integr. (VLSI) Syst. 2011, 20, 1590–1601. [Google Scholar] [CrossRef]
12. Chen, P.; Chen, C.-C.; Tsai, C.-C.; Lu, W.-F. A time-to-digital-converter-based CMOS smart temperature sensor. IEEE J. Solid-State Circuits 2005, 40, 1642–1648. [Google Scholar] [CrossRef]
13. Chen, P.; Chen, C.-C.; Peng, Y.-H.; Wang, K.-M.; Wang, Y.-S. A time-domain SAR smart temperature sensor with curvature compensation and a 3σ inaccuracy of −0.4 °C ~ +0.6 °C over a 0 °C to 90 °C range. IEEE J. Solid-State Circuits 2010, 45, 600–609. [Google Scholar] [CrossRef]
14. Law, M.-K.; Bermak, A. A 405-nW CMOS Temperature Sensor Based on Linear MOS Operation. IEEE Trans. Circuits Syst. II Express Briefs 2009, 56, 891–895. [Google Scholar] [CrossRef]
15. Lin, Y.-S.; Sylvester, D.; Blaauw, D. An ultra low power 1V, 220nW temperature sensor for passive wireless applications. In Proceedings of the 2008 IEEE Custom Integrated Circuits Conference, San Jose, CA, USA, 21–24 September 2008; pp. 507–510. [Google Scholar]
16. Jeong, S.; Foo, Z.; Lee, Y.; Sim, J.-Y.; Blaauw, D.; Sylvester, D. A Fully-Integrated 71 nW CMOS Temperature Sensor for Low Power Wireless Sensor Nodes. IEEE J. Solid-State Circuits 2014, 49, 1682–1693. [Google Scholar] [CrossRef]
17. Vaz, A.; Ubarretxena, A.; Zalbide, I.; Pardo, D.; Solar, H.; Garcia-Alonso, A.; Berenguer, R. Full Passive UHF Tag With a Temperature Sensor Suitable for Human Body Temperature Monitoring. IEEE Trans. Circuits Syst. II Express Briefs 2010, 57, 95–99. [Google Scholar] [CrossRef]
18. Hwang, S.; Koo, J.; Kim, K.; Lee, H.; Kim, C. A 0.008mm2 500μW 469kS/s frequency-to-digital converter based CMOS temperature sensor with process variation compensation. IEEE Trans. Circuits Syst. 2013, 60, 2241–2248. [Google Scholar] [CrossRef]
19. Anand, T.; Makinwa, K.A.A.; Hanumolu, P.K. A VCO Based Highly Digital Temperature Sensor With 0.034 °C/mV Supply Sensitivity. IEEE J. Solid-State Circuits 2016, 51, 2651–2663. [Google Scholar] [CrossRef]
20. Someya, T.; Islam, A.M.; Sakurai, T.; Takamiya, M. An 11-nW CMOS Temperature-to-Digital Converter Utilizing Sub-Threshold Current at Sub-Thermal Drain Voltage. IEEE J. Solid-State Circuits 2019, 54, 613–622. [Google Scholar] [CrossRef]
21. Tran, T.-H.; Peng, H.-W.; Chao, P.C.-P.; Hsieh, J.-W. A log-ppm digitally controlled crystal oscillator compensated by a new 0.19-mm2 time-domain temperature sensor. IEEE Sens. J. 2017, 17, 51–62. [Google Scholar] [CrossRef]
22. Tang, Z.; Fang, Y.; Shi, Z.; Yu, X.-P.; Tan, N.N.; Pan, W. A 1770-μm2 Leakage-Based Digital Temperature Sensor with Supply Sensitivity Suppression in 55-nm CMOS. IEEE J. Solid-State Circuits 2020, 55, 781–793. [Google Scholar] [CrossRef]
More