RFID Overview

1
RFID Overview

• Agricultural Applications
• ISO Specification
• Requires readers to operate at 134kHz with both
  HDX and FDX tags
• HDX tags widely used - proprietary
• FDX cheaper - but more prone to noise

2
RFID Tag (transponder)

• Tuned circuit
• Power supply, clock divider
• Memory and sequencer
• Transmitter and modulator

Tuned antenna
TX
Sequencer
Memory
Power Supply Clock
3
RFID FDX Tag

• Responds while Reader is transmitting
• Modulates (loads) the transmitter
• Receiver detects change in load

Load
TX
ID data
RX
AM det
4
RFID FDX Tag

• FDX Modulation

5
RFID HDX Tag

• Responds after Reader stops TX
• Uses 125 135kHz FSK transmitter
• Receiver detects FSK transmission

TX
Oscillator
FSK
ID data
FSK Demod
RX
6
RFID HDX Tag

• HDX Modulation

7
RFID Tag Block Diagram
8
RFID Tag Memory Map
9
RFID Tag Styles

• Credit Card
• Rumen bolus
• Ear tag
• Key fob
• Disc
• Watch
• Subcutaneous

10
RFID Reader Transmitter

• Fixed frequency 134.2 kHz
• About 10 Watts (for 1m range)
• ISO defined transmit cycle
• Uses FETs for high efficiency

Matching Network
Antenna Tuning
Micro and 134kHz clock
Push-pull or bridge FETs
11
RFID Reader FDX Receiver

• AM detector recovers modulation
• High gain AC coupled baseband amplifier
• Data slicer for data recovery

Detector
Amplifier
Slicer
12
RFID Reader HDX Receiver

• Bandpass filter
• High gain TRF amplifier
• Limiter
• Frequency discriminator

Frequency Discrim
BP Filter
Amplifier
Limiter
13
RFID Antenna

• Must be resonant
• Component tolerances
• Temperature effects
• Environmental effects
• Q and load impedance important
• Optimum coupling coefficient
• Bigger antenna not necessarily better

14
RFID Coding Techniques

• The data coding system must
• Handle data with either polarity
• Handle data with AC coupling
• Send and recover the data clock
• Be carrier synchronous for speed

Data 1 0
AC coupled
15
RFID Coding Techniques

• Self clocking, polarity insensitive
• Synchronous with carrier (RF/32 etc)
• NRZ not practical due to AC coupling
• Manchester and Biphase popular
• Not sensitive to data polarity

NRZ
PSK
Manchester
Biphase
Data 1 0
Data 1 0
16
RFID Data Error Correction

• Parity bits on data row and column
• Checksum or CRC on message
• Unique header at start of message
• Data not decoded unless CRC matches
• Repeated data not passed on to host
• Memory error correction possible using repeated
  data

17
RFID System Enhancements

• Read/Write tags
• Multi-protocol readers (different tags)
• Addressable tags and data blocks
• Anti-collision technology
• Digital signal processing
• Encryption

18
RFID Equipment

• Short-range Reader

Oxley Typical hand-held readers Allflex