By Ansoft Corporation

ABSTRACT

This article describes a reference design with circuits and an antenna for an UHF RFID system. A new Class 2 (Gen 2) tag was designed, including the extremely low power integrated circuit integrated with an inexpensive printed antenna. Details on the design of the rectifier power regulator, demodulator, reset circuit, modulator, and antenna are highlighted. The article includes a system-level software verification of the RFID tag system to determine proper voltage regulation and signal demodulation.

INTRODUCTION

Radio Frequency Identification (RFID) is an electronic tagging technology that allows an object, place, or person to be automatically identified at a distance without a direct line-of-sight using a radio wave exchange. Applications include inventory tracking, prescription medication tracking and authentication, secure automobile keys, and access control for secure facilities. RFID is a major trend that provides fundamental shifts along several business vectors and is expected to be a major growth area in wireless electronics. Details of RFID applications and opportunities can be found in many previously published works.

This article details a specific design of a passive backscatter UHF RFID tag circuit that meets the requirements set forth in the EPCglobal Class-1, Generation-2 Protocol. EPCglobal is an organization dedicated to the worldwide adoption and standardization of RFID technology. The design specification sets forth all physical and logical requirements for the tag air interface and digital state machine design.

The first section of this article gives an overview of the RFID system followed by a section that discusses the tag design criteria for predicting range based on the tag integrated circuit power consumption. Issues limiting range, especially the channel electromagnetic effects, are highlighted. Analog circuit design for a 900 MHz tag is the subject of the next section, with specific circuit design and results for the rectifier, regulator, reset circuit, demodulator and modulator circuit. Antenna design and simulation of a simple meander-line dipole tag antenna is performed. The article concludes with a system-level simulation that includes all of the circuit blocks to predict DC power generation and reader-to-tag and tag-to-reader communication.