A Passive UHF RFID Tag IC

1
A Passive UHF RFID Tag IC
CLASS REPRESENTATION Represented by Khalil
Monfaredi Advanced VLSI Course Seminar
2
Outline

• Introduction to RFID (Radio Frequency
  Identification) Tag LSI (30)
• Current Mode Rectifier (30)
• Current Mode Demodulator (20)
• FeRAM (10)
• Summary (10)

3
Block diagram of the UHF RFID tag LSI with 2Kb
FeRAM.
1
4
RFID Ubiquitous Sensing Networks
Security
Health care

Thermometer
Infrared
Acceleration
Danger

• The present
• Person-to-person networking

• The future
• Thing-to-thing networking

• Thing-to-thing networking will begin
• Sensing tags will play an important role

5
Requirements

• Communication distance ? Long distance (10 m)
• Incorporation of sensor device ? Transmit not
  only ID but also sensing data
• Necessity of battery ? Battery life as long as
  possible
• Low cost

6
Comparison of Tags
Active tag Semi-passive tag Passive tag
Communication distance Good Fair Poor
Incorporation of sensor Easy Possible Difficult
Necessity of Battery Need Need No need
Cost High Fair Low

• Limited battery life Solves by wireless
  power transmission

7
Required conversion efficiency
Base station
CW
CW
Tag
Standby
Recharge
Downlink
Uplink
Time1s
Time3ms
Supply energy 40?Ws
Consume energy0.3?Ws
Conversion efficiency gt 0.75
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Issues concerning rectifier
CMOS rectifier
DCcurrent
RFin40?W
Threshold voltage Vth
Vin0.2V
Vin
Vth
0
Zin
Zin700?Vin0.2V
Region that cannot be rectified
2

• Cannot be rectified below threshold voltage Vth.
• Vth0V There is a possibility that off-leak
  will occur.

9
Proposed rectifier

• Apply a bias voltage Vbth ? Vth - Generating
  voltage of Vbth in the same IC chip

DC 0.3V _at_RFin0.2V
Vbth-Vth?0
(S)
M1
(G)
0.2V
RFin
Vbth
RFin
Vbth
Vth
(D)
0
M2
Vbth
Region that cannot be rectified
2
10
Stacked configuration

• Stack 6 units of rectifiers to obtain over 1.5V
  DC

DC
Output DC voltage
Vbth
RFin
Stack 6 units
gt1.5V
Vbth
0.3V
DC-
2

• How will 12 Vbth voltage sources be realized?

11
Realization of proposed rectifier
INV1
INV2
High
Low
Vbth distributor
PLS
DC
Vbth
Cb1
VDD
Cb2
6 units stacked
VbthVth
Cb3
RFin
Vbth generator
Cb4
Vbth distributor
2
DC-
12
Realization of proposed rectifier
INV1
INV2
Low
High
Vbth distributor
PLS
DC
Vbth
Cb1
Cb2
6 units stacked
Vbth
Cb3
RFin
Cb4
Vbth
Vbth distributor
2
DC-
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Conventional NMOS Half-wave Rectifier
Parasitic capacitance CP Large Vth drop
External cancellation
CP2
Vbth External
DC
Vbth
IN
Mn2
CP3
CP
Vbth
Mn1
2
DC -
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Proposed CMOS Half-wave Rectifier
Parasitic capacitance CP Small Vth drop
Internal cancellation
DC
PMOS
CINF
Cb
IN
CP
Mp1
Mn1
Cb
1
DC -
IVC
(Internal Vth cancellation)
15
Proposed CMOS Full-wave Rectifier Circuit
Good configuration for high efficiency
IN
D1
CINF
VDD
Over current
IVC
IVC
IN -
Over-current protection
(AC GND)
CP
IVC
IVC
VSS
D2
1
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Why Current Mode Demodulator?
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Voltage Detection for Demodulator
Near
VIN
VIN
Device breakdown (4V)
Small
Far
IIN
Tag input
Large
Operating region
Detection result
Incoming Power Prec
Time
1
Far
Near
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Current Detection for Demodulator
Near
IIN
IIN
Device breakdown (4V)
I IN
VIN,
Large
Tag IC
VIN
IIN
Far
Prec
Tag input
Large
Operating region
Detection result
Modulation index (15)
Incoming Power Prec
Time
1
Far
Near
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Current-mode Demodulator Block Diagram
ISIG (IPK IASK)
IREF IPK x n
IPK
IASK
Modulated current
(baseband)
ISIG
IASK
LPF
Subtraction

VASK
Reference Current Generator
IREF
IPK
Current comparator
1
Current Peak Hold
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3
21
3
3
22
3
3
23
3
3
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FeRAM
Adopted from ISSCC 2006 and also
Stefano Bonetti, Johan Dahlbäck, Hanna Henricsson
and Jutta Müntjes
26th of October 2005
2B1750 Smart Electonic Materials, KTH
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FeRAM - Theory
Example PZT (lead zirconate-titanate)
4

• Spontaneous polarization above the
  Curie-temperature TC is the structure cubic,
  below a dipole moment occurs (displacement)
• A different charge ?Q can be observed whether the
  material is switching or non-switching

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WL
4
WL
WL
PL
PL
PL
BL
BL
BL
Vref
Sense AMP
Sense AMP
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4
28
4
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FeRAM - Requirements

• Small size
• High speed
• High lifetime
• Destructive reading (after every reading
  operation is a writing operation required)
• Low coercive field
• Low power memory devices
• Large hysteresis
• High remanent polarization

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FeRAM Characteristics
EEPROM FeRAM FeRAM
Cell structure Cell structure
Programming principle Programming principle Charge injection Polarization change Polarization change
Read Speed 25µs 25µs 25µs
Read Power 12.5µW 12.5µW 12.5µW
Write Speed 3ms 3ms 25µs
Write Voltage 16V 16V 3V
Write Power 35.0µW 35.0µW 15.7µW
High speed Low power
1
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Advantages of the Tag with FeRAM
Condition Read/Write operations
Operating time
Throughput
Read 3.6ms
Write 19.4ms
44tags/s
EEPROM
2.9 times higher
66 reduction
Read 3.6ms
Write 4.2ms
FeRAM
129tags/s
1
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Tag IC Performance Summary
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Summary
Passive UHF Read/Write Tag IC with FeRAM
4.3m Read/Write communication distance CMOS only
rectifier which has 36.6 efficiency, 2.1 times
higher than the conventional Low-voltage
current-mode demodulator which has 27dB dynamic
range for the incoming power Fabricated in
0.35-µm CMOS/FeRAM technology
Tag throughput with FeRAM
2.9 times higher than tags with EEPROM for both
read and write operations
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References

• 1 H. Nakamoto et al., A Passive UHF RFID Tag
  LSI with 36.6 Efficiency CMOS-Only Rectifier and
  Current-Mode Demodulator in 0.35µm FeRAM
  Technology, ISSCC Dig. Tech. Papers, session 17,
  2006.
• 2 T. Umeda et al., A 950MHz Rectifier Circuit
  for Sensor Networks with 10m-Distance, ISSCC
  Dig. Tech. Papers, pp. 256-257, Feb., 2005.
• 3 A. Djemouai And M. Sawan., New Cmos
  Current-mode Amplitude Shift Keying Demodulator
  (Askd) Dedicated For Implantable Electronic
  Devices, IEEE (ISCAS), pp. 441-444, 2004.
• 4 S. Bonetti et al., FeRAM, MRAM, RRAM ,
  online resource Oct., 2005.