Active Load Modulation

1. Introduction

Inductive coupled RFID systems are being used in a huge number of applications such as payment (credit cards), ticketing (public transport and events), access control (company card) and identity verification (ePass, eID). Inductive coupled RFID systems operated in the 13.56 MHz band and are primarily covered by the ISO/IEC standards 14443, 15693, 18000-3 and 18092. The majority of applications, mentioned above, operate according to ISO/IEC 14443. This standard is designed for high security communication with ID1 sized (smart card) transponders at proximity distances of 10 cm or less. Transponders are field powered and use load modulation to transmit data back to a reader.

Inductive coupled RFID-System

Inductive coupled RFID System with passive transponder

The operating range is limited by the coupling factor between the reader/interrogator antenna and the transponder antenna. If the size of the transponder antenna gets very small, the operating distance drops until there is no more communication possible.
In this aricle, we discuss the possibility to enhance the performance of very small transponder, in the size of a micro SD memory card.