Project Overview

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Design Considerations and Trade-offs for Passive
RFID tags
Faisal Hussien, Didem Turker, Rangakrishnan
Srinivasan, Mohamed Mobarak, Fernando P. Cortes
Edgar Sánchez-Sinencio
Analog Mixed-Signal Center
Texas AM University
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Outline

• RFID System Architecture.

• Potential Applications.

• System Design Methodology.

• Passive Tag Building Blocks.

• Design Example A 13.56 MHz Passive RFID tag.

• Future Trends.

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Passive RFID System Architecture
Master/Slave operation.
The Reader detects any tag within its zone of
operation.
Typical Frequencies of operation associated with
their range of operations
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Passive RFID Link
The Reader provides the tag with the power, clock
and data, while the tag responds with its stored
data.
Tags can be passive or active, R/O or R/W.
Inductive coupling is used at Low Frequencies,
while Propagating coupling is used at High
Frequencies.
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Outline

• RFID System Architecture.

• Potential Applications.

• System Design Methodology.

• Passive Tag Building Blocks.

• Design Example A 13.56 MHz Passive RFID tag.

• Future Trends.

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RFID Technology Application Areas

• Access Control Security
• Electronic Article Surveillance
• Employee Entry / ID Badges

• Sensors / Data Acquisition
• Biomedical Monitoring
• Oil Drilling Pipe Monitoring
• Civil Engineering Stress

• Logistics / Tracking
• Animal Tracking / Vaccination History
• Supply Chain Management
• Airline Baggaging

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RFID Technology - Application Specific Features

• Transmission Frequency
• Power Generation
• (Passive/Active)
• Read / Write Capability
• Authorization Control
• Transmission Range
• Data Capacity
• Anti-collision Procedures
• Encryption Algorithms

K. Finkenzeller, RFID Handbook, 2ND ed.,
Wiley,West Sussex, England 2003
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Outline

• RFID System Architecture.

• Potential Applications.

• System Design Methodology.

• Passive Tag Building Blocks.

• Design Example A 13.56 MHz Passive RFID tag.

• Future Trends.

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Typical Passive RFID Tag Structure
Possible Uplink modulation schemes ASK, PWM or
FSK modulation.
Possible Downlink modulation scheme
BackScatter modulation.
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System Design Steps
Step 1 Extraction of the design specifications
for the target application
The frequency of operation (range of operation,
complexity, and penetrating capability)
The antenna directivity (expected direction of
the communication link) The data rate (amount of
data exchanged, and the required on-time of the
tag)
Step2 Calculation of the power budget
Step3 Selection of the uplink modulation scheme
(Reader to tag)
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Step4 Decision on the downlink (tag to reader)
modulation scheme
Step5 Decision on the implementation of the
power generation circuit
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Outline

• RFID System Architecture.

• Potential Applications.

• System Design Methodology.

• Passive Tag Building Blocks.

• Design Example A 13.56 MHz Passive RFID tag.

• Future Trends.

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Antenna
Loop antennas are used at low frequencies to
provide inductive coupling.
Electric dipole, folded dipole, printed dipole,
printed patch, or log-spiral antennas can be used
at higher frequencies to provide propagation
coupling.

• Low frequency means simple and cheap tag and
  large antenna size
  
• High frequency means complex and expensive tags
  and smaller antenna

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Uplink Data Modulation
Random data transmitted should not affect the
power received by the tag.
Clock recovery scheme should be included.
ASK, PWM or FSK can be used.
Theoretical comparison of BER vs. SNR for
modulation schemes
PWM scheme provides signal power for transmission
of both 0 and 1 and clock is recovered
internally. On/Off Keying lacks signal power for
certain data bits and requires a coding scheme
for clock recovery and to maintain tag power.
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Downlink Data Modulation
A modulation scheme with a low-power
implementation is required.
Changing the input impedance of the tag antenna
changes the amplitude, or phase of the back
scattered signal introducing Backscatter
Modulation.
Trade-off remarks power losses of the modulator
circuit versus the type of modulation
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Power Generating Circuit
It makes use of RF-DC conversion and subsequent
voltage regulation to obtain the desired stable
power supply.
Performance is affected by the choice of the
downlink and uplink modulation schemes
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Outline

• RFID System Architecture.

• Potential Applications.

• System Design Methodology.

• Passive Tag Building Blocks.

• Design Example A 13.56 MHz Passive RFID tag.

• Future Trends.

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Tag Specifications
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A 13.56 MHz RFID Passive Tag (Design Example)
For a stream of 010101010
(a) Charge pump output.
(b) Regulator, Voltage reference output
(c) Output Data stream of demodulator
(a) (b) (c)
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Chip Micrograph
Backscatter modulator
Charge pump capacitor load
PWM Demodulator
rectifier
Charge pump
Voltagereference
Regulator
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Test Setup
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Outline

• RFID System Architecture.

• Potential Applications.

• System Design Methodology.

• Passive Tag Building Blocks.

• Design Example A 13.56 MHz Passive RFID tag.

• Future Trends.

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Future Trend
RFID systems can be used in many applications
other than identification process.
Low-cost, low power systems like RFID can be
integrated with other long range,
powerful systems to obtain a suitable infrastruc
ture for different applications.
Combining RFID standard with the existing
standards such as
Bluetooth, Wi-Fi, and Zigbee
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More details, please see
http//amsc.tamu.edu/
May 2005
Analog and Mixed-Signal Center, TAMU Department
of Electrical Engineering