Study of the receiving system of a Low Power Tag Detector and its usage in RFID and NFC applications

Author: Jovanka Dimkovska

Mentor: assoc. prof. dr. Matej Rojc
Comentor: assoc. prof. dr. Anton Pleteršek
External comentors: dr. Kosta Kovačič, dr. Tilen Svete
Program: Level 2 study, Electrical Engineering, course Electronics
Date: june, 2022
DKUM: JOVANKA DIMKOVSKA

Abstract

This work presents an observation of the analog and digital architecture of the reception system of a radio-frequency identification (RFID) reader in the high frequency (HF) domain and creation of a near-field communication (NFC) Application, which is developed for Android and iOS users. This thesis includes a description of RFID and NFC technology, as well as a sufficient amount of information about the standards that define those technologies. The reception system of a given interrogator was thoroughly studied, beginning with the analog signal on the interrogator’s antenna and how it is interpreted in the analog domain for determining the presence of an object in its vicinity. The most emphasis in this thesis was given to the reader when it is in a Tag Detector mode. The Tag Detector mode of the reader is the mode in which the interrogator can detect changes on its antenna. Measurements were taken while testing the Tag Detector at various gain settings of the reception system. To improve the accuracy of those detections, the Tag Detector mode was switched to reader mode, allowing the detected tag’s acknowledgment message to be received. The detection range, as well as the reading range of the interrogator, are also discussed. An NFC application was developed that functions as an interrogator for both the iOS and Android operating systems. The goal of this application is to apply the knowledge we have gained from the study about RFID and NFC communications, as well as the comparison between the tag detection and read ranges of the two types of interrogators.

RFID standardization

RFID is employed in situations where a magnetic field is used as the transmission medium for automatic data acquisition. Industrial automation (storage), animal identification, electronic tickets, and other applications are only a few examples. It includes the ISO/IEC 14443, ISO/IEC 15693, FeliCa, and other standards. NFC is a technology designed for high-frequency communications over short distances (up to about 10 cm). It is mostly utilized in mobile phones and similar devices where the device’s role (reader or smart card) can be changed depending on the needs of the user or another device. It covers the ISO/IEC 14443 (NFC-A and NFC-B) and FeliCa communication standards (NFC-F). The system for worldwide standardization is made up of ISO (International Organization for Standardization) and IEC (International Electrotechnical Commission). International standards are developed and issued by ISO, IEC, and other governmental and non-governmental international organizations.

Analysis of the interrogator reception system

The analog and digital architecture of the interrogator, as well as its operation in Low Power Tag Detector mode, are described. The reception principle involves I and Q mixers, analog amplifiers with differential gain, analog band-pass filters, analog-to-digital Converter (ADC), digital band-pass filters and Digital Correlation Systems (DCS). The digital architecture of the interrogator receiving system begins after the analog to digital conversion. We are talking about the digital architecture since the ADC’s output requires additional band-pass filtering. The digital high and low-pass filters were added to provide band-pass filtering and change the sampling rate from 27.12 MHz to 13.56 MHz, respectively. Higher-order harmonics, high-frequency noise, low-frequency noise, and offset induced by the analog amplifiers or the ADC itself are all removed by the band-pass frequency response.

Measurements and digital simulations

A phase shift test was performed to provide information on the stability of the expected phase shift between I and Q clock signals. Measurement and analysis with a DC signal (DC Sweep) were also performed, in which only parameters from the digital-to-analog converter were observed. We proceed to test the responsiveness of the card detector. Two methods were used in this measurement. The obtained results made it possible to compare the two methods. The most important parameters we wanted to compare were the detection range, which indicates at what distance the interrogator detects a change on its antenna, and the reading range, which indicates the distance at which the interrogator successfully receives a confirmation message from the card confirming its presence. Both methods were tested under the same conditions, and the effects of temperature, changes in the environment (influence of nearby objects) and the influence of the degree of amplification of the receiving system are considered. We also provide a description of both applications, which we developed after a thorough survey of RFID and NFC devices, including compliance with standards, and an analysis of the interrogator reception system. The knowledge gained and the sense of approach we have developed in this technological field have been extremely valuable. The goal of developing both applications is to show that users can easily build this kind of tool for personal use to analyze different types of cards and also to write on them. The developed application acts only as an interrogator, which was also the primary goal of the thesis.