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<strong>RFID</strong> <strong>Radio</strong> <strong>Circuit</strong> <strong>Design</strong> <strong>in</strong> <strong>CMOS</strong><br />
M<strong>in</strong>hong Mi, Ansoft Corp.<br />
1
Outl<strong>in</strong>e<br />
• Overview of <strong>RFID</strong> <strong>Radio</strong>s at System Level<br />
• Power Generation/Management <strong>Circuit</strong><br />
• Recitifier, Charge-pump, Low-Drop Out (LDO) Voltage Regulator, Reset <strong>Circuit</strong><br />
• Demodulator <strong>Circuit</strong><br />
• Envelope Detector, R<strong>in</strong>g Oscillator, Comparator<br />
• Modulator <strong>Circuit</strong><br />
• Bias Generator, Phase Modulator<br />
• Overall <strong>Radio</strong> Simulation and Verification<br />
• Input Impedance Simulation (under large signal condition)<br />
• System/Nexxim Co-sim (with deep-modulated ASK <strong>in</strong>put)<br />
• Antenna <strong>Design</strong><br />
2
Overview of<br />
<strong>RFID</strong> <strong>Radio</strong> <strong>Circuit</strong>s<br />
at System Level<br />
3
Overview for <strong>RFID</strong> <strong>Radio</strong><br />
⎛ 4πfd<br />
⎞<br />
Loss[ dB]<br />
= 20 log⎜<br />
⎟ −10<br />
log Gt −10<br />
log<br />
⎝ c ⎠<br />
Antenna ga<strong>in</strong> Gt=3dB Antenna ga<strong>in</strong> Gr=1.64 dB<br />
Base<br />
station<br />
EIRP = 4W<br />
f=950MHz<br />
Distance<br />
d= 10m<br />
Loss ~ 47 dB<br />
Tx Antenna Ga<strong>in</strong> 3 dB<br />
Rx Antenna Ga<strong>in</strong> 1.64 dB<br />
Frequency 950 MHz<br />
Distance 10 meter<br />
Speed of Light 3.00E+08 m/s<br />
Loss 47.36 dB<br />
Tx Power 46.43 dBm<br />
Rx Power -0.92 dBm<br />
Tag<br />
Gr<br />
Receiv<strong>in</strong>g power<br />
~ -1dBm<br />
4
CW >= 8*RTcal<br />
ASK<br />
<strong>in</strong>put<br />
Overview for <strong>RFID</strong> <strong>Radio</strong> (2)<br />
Envelope<br />
Detector<br />
1⋅Tari<br />
=<br />
⎧ 6.<br />
25µ<br />
s<br />
⎪<br />
⎨12.<br />
5µ<br />
s<br />
⎪<br />
⎩ 25µ<br />
s<br />
pivot =<br />
RTcal<br />
2<br />
RTcal = 0 length + 1 length<br />
Waveform<br />
shaper<br />
(A/D)<br />
Data Rate<br />
Register<br />
Counter<br />
Digital<br />
Comparator<br />
Osc<br />
process, environment variations<br />
To get TRCal to calibrate for l<strong>in</strong>k<br />
frequency (LF) when backscatter<strong>in</strong>g<br />
Tag1: f osc1<br />
LF =<br />
DR<br />
TRcal<br />
DR: Divide Ratio = 64/3 or 8<br />
T pri<br />
=<br />
LF<br />
1<br />
Tag1: f osc2 …<br />
5<br />
Sent from reader !!<br />
TRcal<br />
= = L<strong>in</strong>k Period<br />
DR<br />
Tag1: f osc3
Overall Block Diagram for <strong>RFID</strong> <strong>Radio</strong><br />
To demodulator<br />
Rectifier<br />
Charge_pump<br />
Bandgap ref<br />
Modulator<br />
Env_detector<br />
Bias Gen<br />
LDO<br />
Regulator<br />
Reset<br />
Comparator<br />
R<strong>in</strong>g Oscillator<br />
6
Power<br />
Generation & Management<br />
<strong>Circuit</strong><br />
To demodulator<br />
Bandgap ref<br />
Rectifier Charge_pump<br />
Modulator<br />
Env_detector<br />
Bias Gen<br />
LDO Regulator Reset<br />
Comparator<br />
R<strong>in</strong>g Oscillator<br />
7
Power Generation <strong>Circuit</strong> (Rectifier & Charge_Pump)<br />
Large capacitor implemented with<br />
MosVar to make slow charge-pump<br />
8
Power Management <strong>Circuit</strong> (LDO voltage regulator)<br />
from bandgap<br />
- +<br />
9
Power Management <strong>Circuit</strong> (LDO Test)<br />
10
Power Management <strong>Circuit</strong> (Reset)<br />
1 : m<br />
11
Power Management <strong>Circuit</strong> (Reset test)<br />
12
Demodulator <strong>Circuit</strong><br />
To demodulator<br />
Bandgap ref<br />
Rectifier Charge_pump<br />
Modulator<br />
Env_detector<br />
Bias Gen<br />
LDO Regulator Reset<br />
Comparator<br />
R<strong>in</strong>g Oscillator<br />
13
Demodulator <strong>Circuit</strong> (top level)<br />
14
Demodulator <strong>Circuit</strong> (Envelope detector)<br />
Implemented with a two stage charge pump circuit<br />
15
Demodulator <strong>Circuit</strong> (Comparator)<br />
With hysteresis for better performance<br />
<strong>in</strong> a noisy environment.<br />
16
12.5us<br />
Demodulated Signals<br />
1 Tari<br />
RTCal = 2.75*Tari<br />
Data-0 Data-1<br />
17
Demodulator <strong>Circuit</strong> (R<strong>in</strong>g Oscillator)<br />
Replica Feedback<br />
Differential Delay Block<br />
Comparator<br />
18
R<strong>in</strong>g Oscillator Output<br />
R<strong>in</strong>g Oscillator output<br />
Freq =4.0MHz<br />
19
Demodulator <strong>Circuit</strong> (Bias and Control)<br />
Bipolar Core<br />
BandGap<br />
Ref Voltage<br />
BandGap<br />
Ref Voltage<br />
VT sensor<br />
Constant Current<br />
Source<br />
20
Modulator <strong>Circuit</strong><br />
To demodulator<br />
Bandgap ref<br />
Rectifier Charge_pump<br />
Modulator<br />
Env_detector<br />
Bias Gen<br />
LDO Regulator Reset<br />
Comparator<br />
R<strong>in</strong>g Oscillator<br />
21
Modulator <strong>Circuit</strong> for PSK<br />
22
Tag’s Overall <strong>Radio</strong><br />
Simulation and Verification<br />
23
Input Impedance Simulation for Tag’s <strong>Radio</strong><br />
Under the condition of<br />
large signal <strong>in</strong>put !<br />
Z<br />
total<br />
=<br />
Y<br />
tag<br />
⇒ Y<br />
⇒ Z<br />
1<br />
=<br />
Y<br />
tag<br />
tag<br />
1<br />
+ 0.<br />
01<br />
=<br />
total<br />
1<br />
Z<br />
=<br />
Y<br />
total<br />
=<br />
⎛ 1<br />
⎜<br />
⎝ Z<br />
total<br />
tag<br />
1<br />
+ Y<br />
− 0.<br />
01<br />
src _ imp<br />
1<br />
⎞<br />
− 0.<br />
01 ⎟<br />
⎠<br />
Yellow traces <strong>in</strong><br />
the next slide<br />
red traces <strong>in</strong><br />
the next slide<br />
24
25<br />
Input Impedance Simulation for Tag’s <strong>Radio</strong><br />
---- mod_<strong>in</strong> to AVDD<br />
---- mod_<strong>in</strong> to AGND<br />
~ 1.5V regulated supply generation<br />
@900MHz
Cont<strong>in</strong>uous Wave (CW) Input (Transient)<br />
Only transient solver can solve<br />
this region..<br />
To save time and get more <strong>in</strong>sightful<br />
<strong>in</strong>formation:<br />
• Better use HB Eng<strong>in</strong>e<br />
26
Cont<strong>in</strong>uous Wave (CW) Input (Harmonic Balanced: HB)<br />
The results are from Nexxim’s HB eng<strong>in</strong>e<br />
27
28<br />
System/Nexxim Co-simulation<br />
NSAMP=sample_num<br />
SAMPLE_RATE=sample_rat<br />
PERIOD=20/sample_rat<br />
A=1V<br />
DUTY=0.61<br />
T1=0s<br />
T2=0s<br />
NSAMP=sample_num<br />
SAMPLE_RATE=sample_rat<br />
PERIOD=20/sample_rat<br />
A=1V<br />
DUTY=0.81<br />
T1=0s<br />
T2=0s<br />
VTHRESHOLD=0.5V<br />
SP<br />
PWM_out<br />
PRBS<br />
NB=sample_num/10<br />
BR=sample_rat/20<br />
T=1V<br />
F=0V<br />
V0=0V<br />
TS=1/sample_rat<br />
TR=0s<br />
TF=0s<br />
SEED=0<br />
AMMOD<br />
FC=fc<br />
P=-35dBm<br />
REF=-0.01<br />
SAMPREP<br />
NOR=NOR<br />
SP<br />
AM_out<br />
SP<br />
env_p<br />
SP<br />
env_n<br />
SP<br />
avdd<br />
SP<br />
rst<br />
SP<br />
agnd<br />
antp<br />
env_p<br />
env_n<br />
agnd<br />
rst<br />
avdd<br />
mod_<strong>in</strong><br />
U1<br />
rfid_tag8102008<br />
0<br />
antp<br />
env_p env_n<br />
agnd<br />
rst<br />
avdd<br />
mod_<strong>in</strong><br />
Env_Det<br />
<strong>in</strong>n<br />
<strong>in</strong>p<br />
opn<br />
opp<br />
antn<br />
antp<br />
rect_o<br />
rect_on<br />
rect_so<br />
rect_son<br />
rect_sso<br />
rect_sson<br />
agnd<br />
avdd r_avdd<br />
ref<br />
agnd<br />
avdd rst<br />
agnd<br />
antn<br />
antp<br />
avdd<br />
mod_<strong>in</strong><br />
agnd avdd<br />
mr_bias<br />
vref<br />
E42<br />
agnd<br />
rect_o<br />
agnd
System/Nexxim Co-simulation<br />
Worst case for supplied voltage generation duty cycle = 47.5%<br />
29
System/Nexxim Co-simulation<br />
Worst case for supplied voltage generation duty cycle = 47.5%<br />
--- Generated Supplied Voltage<br />
--- Detected Evlelope<br />
--- Reset Signal<br />
30
System/Nexxim Co-simulation<br />
Worst case for envelope detection: duty cycle = 13.25%<br />
31
System/Nexxim Co-simulation<br />
Worst case for envelope detection: duty cycle = 13.25%<br />
--- Generated Supplied Voltage<br />
--- Detected Evlelope<br />
--- Reset Signal<br />
32
System/Nexxim Co-simulation<br />
Typical case: RTcal = 2.75*Tari, PW = 0.4*Tari � Average duty cycle = 71%<br />
33
System/Nexxim Co-simulation<br />
Typical case: RTcal = 2.75*Tari, PW = 0.4*Tari � Average duty cycle = 71%<br />
--- Generated Supplied Voltage<br />
--- Detected Evlelope<br />
--- Reset Signal<br />
34
UHF <strong>RFID</strong> Antenna<br />
<strong>Design</strong> and Simulation<br />
35
<strong>Design</strong> Method<br />
• The method follows recently<br />
published work on <strong>RFID</strong> tag<br />
design.<br />
Reference: K.V. Rao, P.V. Nikit<strong>in</strong>, and S.F. Lam, “Antenna design for UHF <strong>RFID</strong> tags: a review and a<br />
practical application,” IEEE Trans. on Antennas Propagat. Dec. 2005.<br />
36
<strong>Design</strong> Goals<br />
• Primary goal is to design an antenna that maximizes <strong>RFID</strong><br />
read range<br />
– Range is limited by tag response threshold (tag power<br />
absorption):<br />
range<br />
λ<br />
4π<br />
PtG<br />
tGrτ<br />
P<br />
– where<br />
λ = wavelength<br />
P t = Power of transmitter<br />
G t = Ga<strong>in</strong> of transmit (reader) antenna<br />
G r = Ga<strong>in</strong> of receive (tag) antenna<br />
P th = Tag response threshold power<br />
τ = mismatch factor (0 ≤ τ < 1)<br />
=<br />
th<br />
=<br />
4R<br />
c a τ Mismatch<br />
2<br />
Z<br />
c<br />
Z = R +<br />
Z = R +<br />
Goal: maximize power absorption by design<strong>in</strong>g tag antenna<br />
impedance that resonates with chip impedance<br />
a<br />
c<br />
a<br />
c<br />
+<br />
jX<br />
R<br />
Z<br />
a<br />
jX<br />
a<br />
c<br />
Factor<br />
Chip impedance<br />
37<br />
Antenna impedance
Simulation and Optimization<br />
Dimensions Taken From Reference Paper<br />
Adjust parameters l, w, s, d, a, b to achieve desired antenna<br />
<strong>in</strong>put impedance<br />
Note: This antenna was<br />
designed for<br />
Z a = 16 + j 350 Ω<br />
38
Target Impedance From <strong>Circuit</strong><br />
Simulation<br />
Re(Z <strong>in</strong>_tag )<br />
Capacitive<br />
Im(Z <strong>in</strong>_tag )<br />
Ω<br />
Small signal chip impedance<br />
is Z c = 35 - j 155 Ω<br />
Rectifie<br />
r<br />
Modulator<br />
Envelope Detector<br />
Th<strong>in</strong> traces <strong>in</strong><br />
the next slide<br />
Thick traces <strong>in</strong><br />
the next slide<br />
Voltage Regulator<br />
2V<br />
39
Simulation <strong>in</strong> Ansoft <strong>Design</strong>er<br />
Provides <strong>in</strong>ductive reactance<br />
Load<strong>in</strong>g Bar Reduces Resistance<br />
Optimize to Match Target Impedance<br />
40
Optimized<br />
Result<br />
New<br />
<strong>Design</strong><br />
Removed load<strong>in</strong>g bar<br />
Reduced <strong>in</strong>ductive<br />
meanders<br />
Results<br />
Z a = 12.5 + j 148 Ω<br />
l = 77.7 mm<br />
b = 7 mm<br />
s = 5 mm<br />
Goal<br />
Small signal chip impedance<br />
is Z c = 35 - j 155 Ω<br />
Too low<br />
Z a = 34.3 + j 155 Ω<br />
l = 121 mm<br />
b = 2.85 mm<br />
Meets goal but<br />
larger <strong>in</strong> size<br />
41
Swept Frequency Performance<br />
Imag<strong>in</strong>ary Part of Impedance<br />
Real Part of Input Impedance<br />
Antenna design provides relatively flat response across UHF <strong>RFID</strong> band<br />
42
Far-field Radiation Performance<br />
1.95 dB Ga<strong>in</strong><br />
Broad Omnidirectional Pattern<br />
43
Conclusions<br />
• UHF <strong>RFID</strong> tag RF/analog circuits have<br />
been designed and tested at circuit and<br />
system levels us<strong>in</strong>g Ansoft tools with<strong>in</strong> the<br />
Cadence environment.<br />
• Meandered (<strong>in</strong>ductive) dipole antenna was<br />
designed for this specific tag.<br />
• Ansoft team has comprehensive<br />
understand<strong>in</strong>g of EPC Global Standard<br />
44
Thank you!<br />
45
Appendix: Entry for Nexxim/Cadence Integration<br />
“Netlist & Run”<br />
46
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