Design Of CMOS Temperature Sensors Integrated With RFID Tag Chip

Transcription

1 Design Of CMOS Temperature Sensors Integrated With RFID Tag Chip Hua Peng ChongQing College of Electronic Engineering ChongQing College, China Abstract To study the application of temperature sensor in RFID chip. To make innovative design based on the existing related technologies. The article introduced the development and the important role of RFID technology, described the theory of temperature sensor and RFID technology, established the design model of RFID tag chip with integrated CMOS temperature sensor, and described the design principle of the CMOS temperature sensor. This paper studied the overall performance of COMS temperature sensor, analyzed the simulation data, and concluded that the integrated chip model could realize the capture of temperature. The RFID tag chip integrated with temperature sensor can achieve the design goal of this paper. Keywords - temperature sensor; RFID chip; CMOS; design principle I. INTRODUCTION With the rapid development of modern society, people's collection and processing of information is becoming more and more important, all kinds of sensors have been developed very quickly. In recent years, the combination of RFID and sensing technology has become a trend, it also becomes a hot research and application, in particular, the rise of cold chain logistics is to provide a broad application space for the integration of temperature sensor RFID tags. RFID technology is a kind of technology that relies on the radio frequency signal to carry on the information transmission, which is able to achieve the recognition target without contact information and the electronic tag is one of the core components. Its development is the result of a number of technological developments, including antenna technology, integrated circuit technology, electromagnetic field propagation technology, encoding decoding technology and data information exchange, etc. (Dakin, 1985). RFID technology first appeared in the second war period, but in recent years, it has been greatly developed, many countries have focused on supporting and developing RFID technology, today, some large international companies have joined the ranks of RFID technology, such as NXP, TI, Microchips, Motorola and other companies have introduced the corresponding products, and each has its own characteristics from the system. The application of RFID is becoming more and more extensive, at present, many companies in some industries are seeking to use RFID technology to simplify the operation, meet regulatory requirements and prevent the introduction of counterfeit products into the supply chain, both protecting the safety of consumers and the company's profitability. Some industry experts believe that RFID technology has no competitive advantage, but as a supplement to the bar code technology, in many cases, such as tracking tray and cardboard boxes in a warehouse, using RFID technology has overcome some of the limitations found in some bar code applications. ecause it is not an optical technology like bar code, so there is no inherent line of sight between the reader and the reader. In addition, RFID is a wireless transmission data, but also a read / write technology, so it can be updated or changed in the tag data content (akker, 1996). Figure 1 is a part of the application of the RFID technology. (a) Application of RFID in Antenna (b) Application of RFID In Shopping Fig. 1. Part of The Applications of RFID Technology DOI /IJSSST.a.16.4A ISSN: x online, print

2 II. OVERVIEW OF CMOS TEMPERATURE SENSOR Temperature sensor is a kind of sensor that can be output to the corresponding signal through the temperature of the sensor and the bad environment, it is widely used in the fields of industry, agriculture, science and life, is also the most basic and most of the sensor. It has mainly experienced three stages of development: (1) the traditional split vertical, which is caused by temperature changes by the sensing element, generates a relative current, voltage, resistance, etc.. (2) integrated temperature sensor and temperature switch controller for analog output, the main output is a type of sensor that is proportional to the temperature of the analog signal or the control switch. (3) intelligent temperature sensor, digital signal output of integrated temperature sensor, can be integrated with advanced digital signal processing system (ao, 1995). Integrated temperature sensor is one of the most widely used today, compared with the traditional temperature sensor, it has small size, low power consumption, good output characteristics and many other characteristics. On the same chip, the temperature sensing element and the processing circuit are integrated on the same chip, the traditional sensor technology can be combined with IC technology. Such as reference circuit, linear amplifier, temperature compensation and other signal processing circuit can be very good use of IC technology to achieve, so the linear design of the integrated temperature sensor is not required, and the design of temperature compensation is realized. Integrated temperature sensor is mainly composed of temperature sensing circuit, reference circuit and related control unit circuit, etc., a smart temperature sensor is usually connected to a digital converter and a storage device. ipolar technology is the first technology used to design commercial integrated circuits, many types of integrated temperature sensors are designed using bipolar technology, such as LM135, ADR590, etc.. ut with the rapid development of integrated circuit technology, it drives the product to become smaller and smaller and meet the requirements of high performance. CMOS process due to its easy realization of mixed signal processing circuit, and also the size of miniature, the chip area is small, so it is widely used, gradually in the integrated circuit design in the dominant position. CMOS process compatible bipolar devices (parasitic longitudinal substrate PNP transistor), very suitable for design of temperature sensor. With the rapid development of CMOS integrated circuit design technology, today's CMOS temperature sensor has been able to meet many aspects of the application, and the direction of the intelligent temperature sensor is also developed. ut, due to the deviation of the process and the physical characteristics of the parasitic bipolar transistor in CMOS process, the CMOS temperature sensor is the problem of the low temperature measurement accuracy, its application in many fields (Chen, 2005). III. INTEGRATED TEMPERATURE SENSOR OF THE RFID TAGS AT HOME AND AROAD RESEARCH STATUS So far, there are many reports on the integration of RFID tag chip with temperature sensor, and the research on this aspect is more obvious than that in China. In 2007 Pardo D. and so on in the RFID IEEE international conference to do a report, a passive UHF RFID temperature sensor for human body temperature monitoring is described, it discusses the problem that the temperature sensor is integrated on RFID, at the same time, the optimization criteria of the modules are given. In 2006, Opasjumruskit K. et al. In a theoretical study of a passive RFID temperature sensor, it is expected that its operating frequency is 100 khz khz-150. They have carried on the detailed division and the analysis to the RFID tag chip module, the theoretical simulation shows that the error of the measurement error of the temperature at 0 degrees -100 is less than 2.5, and the error can be less than 1. In the domestic research of RFID temperature sensor, Shen Hongwei et al. et al., in 2008, has studied the ultra high frequency RFID temperature sensor. They proposed the design idea of RFID passive tag chip with temperature sensing function, class EPC 0 protocol for 900MHz, they use multi-voltage design idea to put forward the electronic tag structure and reference circuit (ao, 1993). Using Chartered 0.35 m CMOS Technology Library for circuit simulation, the simulation results show that the proposed circuit is in the range of temperature measurement at the -10 of -120, error less than 2. RFID tag chip fabrication in integrated temperature sensor, March 2006 German KSW company released a new RFID smart tag Vario Sens asic integrated temperature sensor. Vario Sens temperature tags follow the ISO air interface protocol, it works in the HF-3.56-MHz frequency band, with a total of 8 K bit of the read write EEPROM storage space. Vario Sens temperature tag using 1.5 V battery, the use of about 1.5 years, its main application areas are chemical industry chemical monitoring, medical industry, drug transport and perishable food tracking, etc.. Gentag is a company based in Washington, D. C., Columbia, for the RFID intellectual property development company, in July 2006, the company announced that it has been designed, patented and successfully tested an ultra linear, low power, single calibration temperature sensor circuit, this circuit can be directly applied to any one of the two generation high frequency or MHz global RFID market. Gentag claims that the sensor can only increase the cost of very small tags. May 2008 IDS Microchip AG company launched the IDS SL13A smart active tag chip, IDS-SL13A compatible ISO15693 standard, is a passive / semi passive tag chip, it is specially designed for the single cell with sensor function to optimize the smart tags for the power supply. It can assign a unique identification code to any product that is labeled. An environmentally friendly battery (1.5 V or 3 V) can be used to support the integration of real-time clock and EPROM memory, to record data from the internal temperature sensor or other external sensor (Varghese, 2004). DOI /IJSSST.a.16.4A ISSN: x online, print

3 IV. ASIC THEORY OF IPOLAR TRANSISTOR IN CMOS PROCESS In forward bias (i.e. the base emitter junction is biased, and the collector base junction is biased), transistor collector current CI presents exponential relationship with the base emitter voltage EV: qv E k IC IS exp 1 (1) Where Ic is the collector current of the bipolar transistor, I s is the saturation current of the bipolar transistor, V E is the bias between the base and emitter forward voltage, k is the Pohl Seidman constant, q is an electronic charge, is the k temperature. If VE 3 the formula (1) can be simplified q as: qv E k IC IS exp (2) The saturation current is about is: 2 2 qnad i E IS (3) Q Among them, A E is the emitter area, n i is the base carrier concentration, D is an effective minority carrier diffusion constant in the base, Q is the number of atoms in the unit area of the intrinsic silicon. Q can be learned through the following formula: N xc Q q N dx (4) xe is the majority carrier concentration, X C and X E are the intrinsic silicon base area and the emission region and the collector region boundary. Under the appropriate temperature, all ionization of doping, the intrinsic carrier concentration is far less than the doping concentration, in this case can be found: xc Q q N dx (5) xe Where N is the base doping concentration. The relationship between I S and was performed in the parameters n i and D, according to the formula: qv g 2 3 k n exp (6) i k D X (7) q You can get together: qv ( E Vg 0 ) IC C exp (8) k Among them, C is a constant, 4-n, and n is a constant process related, V g0 means the band gap voltage of silicon in absolute zero (Nguyen, 2008). V. INTEGRATED TEMPERATURE SENSOR RFID TAG OVERALL STRUCTURE The passive RFID tag chip is in line with the international standard ISO15693, working frequency is MHz. According to the functional division, integrated temperature sensor RFID tag chip can be divided into four modules: RF analog front end, digital controller, memory, temperature sensor. Its structure diagram is shown in Figure 2. Fig. 2. RFID Tag Structure lock Diagram of Integrated Temperature Sensor The RF analog front end includes a rectifier circuit, a voltage regulator circuit, a modulation / demodulation circuit, a reset circuit and a clock extraction circuit, it has four main functions: (1) The energy required to provide work for each part of the RFID tag for the integrated temperature sensor, this is accomplished by the power generation circuit. (2) The clock required for the normal operation of the circuit from the carrier, this is done by the clock extraction circuit. (3) Modulation / demodulation of data on the RFID tag, this is done by a data modulation / demodulation circuit. (4) When the power is reset, the reset circuit is completed. The digital controller is composed of a control module, a modulation and demodulation module, a CRC verification module, mapping module and state machine. The main function of the digital circuit is to deal with the analog circuit and temperature sensor sent over the data, responsible for controlling and communicating with readers, at the same time according to the reader's requirements and EEPROM for communication (erthou, 1990). Memory uses EEPROM as a storage unit, which can save the data for a long time, and according to the needs of the data to update, but it can not DOI /IJSSST.a.16.4A ISSN: x online, print

4 read and write data directly as RAM or ROM, different controls must be carried out for different operations. The main function of the memory in the RFID temperature sensor tag chip is to store the data sent by the digital portion, and send the data to the digital part for processing. Another memory will be provided to the temperature sensor for a stable 1.26 V bias voltage independent of the power supply and temperature. The main function of the temperature sensor is to detect the temperature, and the detection results are transmitted to the digital part by ADC conversion to digital form. Temperature sensor mainly includes PTAT voltage generating module and single slope ADC module. The PTAT voltage generating module is a voltage signal which is proportional to the temperature by the band gap. The output voltage signal is processed by the single slope ADC module, and the output voltage signal is converted to digital output (Tuthill, 1998). The single slope ADC module consists of two parts, a constant current source module and a comparator module, the constant current source module is responsible for generating a constant current which is independent of temperature and power supply voltage, the comparator module compares the PTAT voltage with the charge voltage of the capacitor to obtain a charge time proportional to the temperature. The charging time is sent to the digital module for further processing, the values are stored in the memory. This data is returned by the memory when the reader reads the temperature. VI. TEMPERATURE SENSOR SYSTEM DESIGN A. System Structure Design For the design of CMOS temperature sensor, according to the different temperature principle, people put forward different circuit design: Temperature characteristics of carrier mobility of MOS field effect tube; Temperature properties of V and current gain of the MOS field effect transistor; Frequency temperature correlation principle of ring oscillator; Thermal related properties of internal thermal diffusion constant of silicon crystal. ut these methods have some shortcomings in the performance, design of integrated temperature sensor in standard CMOS process, the sensing temperature element is widely used to work in the sub threshold region of the MOS field effect transistor and substrate PNP transistor fully compatible with CMOS process. ased on the above two kinds of sensing principle of temperature, temperature sensor system design is mainly based on the following two kinds of structure (Choi, 2008): (1) The substrate PNP transistor is fully compatible with the CMOS process, a voltage signal, which is proportional to the absolute temperature, is generated by the JT bandgap circuit, in order to produce a pulse signal, the width of the pulse signal is proportional to the absolute temperature, the pulse signal is converted to digital signal by using a counter; (2) The current characteristics of the MOSFET are used to work in the sub threshold region, a current signal proportional to the absolute temperature, periodic square wave signal is generated by the periodic charge discharge of the integral circuit to generate a frequency proportional to the absolute temperature, finally, the frequency of the pulse can be obtained by using the counter at the specified time. The structure of a temperature sensor integrated in the RFID tag chip is proposed in the paper, the bias circuit and the PTAT current generating circuit, the ADC component (Liu, 2003), the structure is shown in Figure 3. Fig. 3. System Structure of Temperature Sensor. PTAT Application A lot of studies have used the band gap circuit to generate the PTAT current to detect the temperature, the PTAT current can be obtained with a good linearity of the current temperature curve, And its power control is very good. ut considering the band gap circuit, there are JT, its power consumption and area is relatively large, not suitable for passive RFID tag chip. The electric current which is proportional to the temperature is obtained by the relationship between the threshold voltage and the gain factor of the MOS tube, the structure of the circuit is simple and the power supply rejection is better, but the output current of the temperature curve is not an ideal linear relationship, in order to get a higher accuracy of the output results must be calibrated, will lead to an increase in power consumption, also not suitable for passive RFID tag chip (Collins, 1998). In this paper, the PTAT current is generated by the MOS tube operating in the sub threshold region, the structure can obtain a good linearity of the current temperature relationship, at the same time, because most of the tubes work in the sub threshold region, the power consumption of the circuit is also very small, very consistent with the low power requirements of RFID tag chip. However, the structure of the power supply rejection characteristics is relatively poor, the temperature sensitivity is also very small, we can be in the process of circuit design, overcome this difficulty by the optimal design of reference current source, reference voltage source and ADC. So in the design process, we must ensure that the reference current source, reference voltage source stability, improve the resolution of ADC (Hartog, 1983). C. ADC Principle Digital converter, A/D converter, or ADC, is an electronic component that converts analog signals into digital signals, typically a digital converter is an input voltage signal converted to an output digital signal. Analog to digital converter is a system to convert analog signals into digital signals, is a filtering, sampling and maintaining the process of encoding. The analog signal is filtered through the filter DOI /IJSSST.a.16.4A ISSN: x online, print

5 circuit, the sample and hold circuit is changed into a step shape signal, and then, by means of the encoder, the level of the step signal is converted into binary code. The integral type and the voltage frequency conversion type are the input analog quantity to convert to the time (pulse width signal) or the frequency (periodic pulse signal), and then through the subsequent counter to realize the analog to digital conversion. In this paper, the input signal of IPTAT is ADC, integral ADC can be used, the traditional single rate integral type ADC as shown in Figure 4, the ADC is characterized by simple circuit structure, low power consumption. sensor is sensitive to the change of the power supply voltage, need further improvement. Fig. 5. Output Data Curve Under Different Power Supply Voltage Fig. 4. Principle Diagram of Single Slope Integral Type ADC The single slope integral ADC is divided into three parts, which are the integral circuit, voltage comparator circuit and counter. When the switch A is closed, PTAT current charges the capacitor Cp, the comparator output high, counter start count. When the charging voltage is equal to the reference voltage Vref, the comparator output is changed to a low level, and the counter is stopped when the comparator is reversed. At this time, A disconnect switch, the voltage on the capacitor Cp is charged by discharge switch, end of a measurement cycle. The traditional single rate integral type ADC does not apply to the analog of the PTAT current. So we use a ADC containing the CCO structure of the current control oscillator, the ADC consists of a current controlled oscillator and a counter. CCO design for converting current into a periodic pulse signal, IPTAT is proportional to the temperature of the current CCO to get a frequency and temperature dependent pulse signal. This signal is used as a counter clock signal, after a counter is obtained by a digital signal that is proportional to the temperature, the temperature is sensed. VII. SIMULATION RESULTS OF THE WHOLE CIRCUIT When the supply voltage varies between 1.6V-2.0V, temperature sensor output is also a certain change, Figure 5 shows the output of the temperature sensor 1.6V, 1.8V, 2.0V, the power supply voltage of the data curve. The output pulse frequency can be decreased with the increase of the power supply voltage, which leads to a small reading of the temperature, this phenomenon has a great influence on the measurement accuracy, it also shows that the temperature We simulate the whole circuit of the temperature sensor, when the temperature was changed at , the output frequency of the temperature sensor is linear with temperature, and increases with temperature [17]. VIII. CONCLUSION The main work of this paper is to study the design and research of CMOS temperature sensor integrated with RFID tag chip. Design and Simulation of the analog part of the temperature sensor circuit was completed. Through simulation analysis, the design of the sensor could complete the temperature reading, but in some detail the need to adjust the improvement and the overall design was successful. ACKNOWLEDGEMENTS This work is supported by 2015 Science and Technology Research Project of Chongqing Academic Affairs, Intelligent Electronic Guiding System sased on NFC and RFID Technologies. Project Number: KJ REFERENCES [1] Dakin J P, Pratt D J, ibby G W, Distributed optical fibre Raman temperature sensor using a semiconductor light source and detector. Electronics Letters, vol.21, No.13, pp , [2] akker A, Huijsing J H, Micropower CMOS temperature sensor with digital output. Solid-State Circuits, IEEE Journal of, vol.31,no.7, pp , [3] ao X, Dhliwayo J, Heron N., Experimental and theoretical studies on a distributed temperature sensor based on rillouin scattering. Journal of Lightwave Technology, vol.13,no.7, pp , 1995 [4] Chen P, Chen C C, Tsai C C., A time-to-digital-converter-based CMOS smart temperature sensor. Solid-State Circuits, IEEE Journal of,vol. 40,No.8, pp , [5] ao X, Webb D J, Jackson D A., 32-km distributed temperature sensor based on rillouin loss in an optical fiber. Optics Letters, vol.18,no.18, pp , DOI /IJSSST.a.16.4A ISSN: x online, print

6 [6] Varghese O K, Mor G K, Grimes C A., A titania nanotube-array room-temperature sensor for selective detection of hydrogen at low concentrations. Journal of nanoscience and nanotechnology, vol.4, No.7, pp , [7] Nguyen L V, Hwang D, Moon S., High temperature fiber sensor with high sensitivity based on core diameter mismatch. Optics express, 16(15): pp , [8] erthou H, Jörgensen C K., Optical-fiber temperature sensor based on upconversion-excited fluorescence. Optics letters, vol.15no.19, pp , [9] Tuthill M., A switched-current, switched-capacitor temperature sensor in 0.6-μm CMOS. Solid-State Circuits, IEEE Journal of, vol.33no.7, pp , [10] Choi H Y, Park K S, Park S J, Miniature fiber-optic high temperature sensor based on a hybrid structured Fabry-Perot interferometer. Optics letters, vol.33no.21, pp , [11] Liu H, Liu H Y, Peng G D, Strain and temperature sensor using a combination of polymer and silica fibre ragg gratings. Optics Communications, vol.219, No.1, pp , [12] Collins S F, axter G W, Wade S A., Comparison of fluorescencebased temperature sensor schemes: Theoretical analysis and experimental validation. Journal of applied physics, vol. 84,No. 9, pp , [13] Hartog A H, A distributed temperature sensor based on liquid-core optical fibers. Lightwave Technology, Journal of, vol.1,no.3, pp , DOI /IJSSST.a.16.4A ISSN: x online, print