MDE-3664B TRIND® Start-up, Service, and Parts Manual · June 2013
Page A-7
Wireless Communication and Air Interface
Appendix A - Radio Frequency Identification Defined
Transponders/Tags
The word transponder, derived from TRANSmitter/resPONDER, reveals the function of the
device. The tag responds to a transmitted or communicated request for the data it carries, the
mode of communication between the reader and the tag being by wireless means across the
space or air interface between the two. The term also suggests the essential components that
form an RFID system - tags and a reader or interrogator. Where interrogator is often used as an
alternative to that of reader, a difference is sometime drawn on the basis of a reader together
with a decoder and interface forming the interrogator.
Generally, transponder components are fabricated as low power integrated circuits suitable for
interfacing to external coils, or utilizing “coil-on-chip” technology, for data transfer and power
generation (passive mode).
Basic Features of RFID Transponder
The transponder memory may comprise Read-only Memory (ROM), Random Access
Memory (RAM) and non-volatile programmable memory for data storage depending upon the
type and sophistication of the device. The ROM-based memory is used to accommodate
security data and the transponder operating system instructions which, in conjunction with the
processor or processing logic deals with the internal “house-keeping” functions such as
response delay timing, data flow control and power supply switching. The RAM-based
memory is used to facilitate temporary data storage during transponder interrogation and
response.
The non-volatile programmable memory may take various forms, Electrically Erasable
Programmable Read Only Memory (EEPROM) being typical. It is used to store the
transponder data and needs to be non-volatile to ensure that the data is retained when the
device is in its quiescent or power-saving “sleep” state.
Data buffers are further components of memory, used to temporarily hold incoming data
following demodulation and outgoing data for modulation and interface with the transponder
antenna. The interface circuitry provides the facility to direct and accommodate the
interrogation field energy for powering purposes in passive transponders and triggering of the
transponder response. Where programming is accommodated, facilities must be provided to
accept the data modulated signal and perform the required demodulation and data transfer
processes.
The transponder antenna is the means by which the device senses the interrogating field and,
where appropriate, the programming field and also serves as the means of transmitting the
transponder response to interrogation.
A number of features, in addition to carrier frequency, characterize RFID transponders and
form the basis of device specifications, including:
• Means by which a transponder is powered
• Data carrying options
• Data read rates
• Programming options
• Physical form
• Costs