1 “Design, Analysis and Simulations of a Si Schottky Diode Based Sampling Circuit for 40 Gbps ETDM Demultiplexer Circuit“ Supervisors: Prof. Dr. techn. Peter Russer Jung Han Choi, M.S. Master Thesis: Septiaji Eko Nugroho Master of Science in Microwave Engineering (MSMWE) Program Institute for High Frequency Engineering
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1
“Design, Analysis and Simulations of a Si Schottky Diode Based Sampling Circuit
for 40 Gbps ETDM Demultiplexer Circuit“
Supervisors:Prof. Dr. techn. Peter RusserJung Han Choi, M.S.
Master Thesis:
Septiaji Eko Nugroho
Master of Science in Microwave Engineering (MSMWE) ProgramInstitute for High Frequency Engineering
2
Layout1. Sampling Circuit for Demultiplexer
Multiplexing Overview The Demultiplexer Circuit The Sampling Theory and The Undersampling Technique for
Demultiplexer Sampling Circuit for Demultiplexer
2. Driving Requirements and Components Driving Requirements The Components
3. Design, Analysis and Simulations The Rule of the Design Bandwidth Optimization: Analytic and Simulation Layout Design and Simulation Flip Chip Bonding Effect Effect of Oscillator Phase Difference
4. Conclusions and Future Works
3
1. Sampling Circuit for Demultiplexer
Multiplexing/Demultiplexing OverviewThe Demultiplexer Circuit in ETDM systemThe Sampling Theory and The Undersampling Technique for DemultiplexerSampling Circuit for Demultiplexer
4
Multiplexing/Demultiplexing Overview
Backgrounds:
•Optical fiber is able to transmit THz of signal
•The bit rate in the fiber was limited, caused by the speed of electronic components (i.e. 10 Gbps at 1995)
To increase the operation speed of the fiber : Multiplexing technique is introduced:
Time Division Multiplexing (TDM)
ETDM: Electronic TDM
OTDM: Optical TDM
Frequency Division Multiplexing (FDM)/Wavelength Division Multiplexing (WDM)
1. Sampling Circuit for Demultiplexer
C hannel 1A G bps
M U X D E M U X
C hannel NA G bps
C hannel 2A G bps
C hannel 1A G bps
C hannel NA G bps
C hannel 2A G bps
Optical L inkN x A Gbps
5
The Demultiplexer Circuit for ETDM system
1. Sampling Circuit for Demultiplexer
4-W ayP owerD iv ider
4 x A Gbps
D ecision C ircu it
D ecision C ircu it
D ecision C ircu it
D ecision C ircu it
A Gbpsunquantized data A Gbps
Digital Data
SamplingCircuit A GHz
Diagram of 4-Way Demultiplexer
Diagram of Optical Receiver
The Demultiplexer Circuit for ETDM system
P hotodiode A m plifierDemultiplexer
1:N
N x A Gbpsoptical signal
A Gbps
Channel 1
Channel 2
Channel 3
Channel N
61. Sampling Circuit for Demultiplexer
n
ssinout nTtTtvtv )()()(
xvin (t) vout(t)
D iracDe lta
The Sampling Theory and The Undersampling Technique for Demultiplexer (1)
7
t im e
A m p litude
"1" "1"
P eriod o f the s igna lT
"1""1" "1" "1""1""0" "0""0" "0"
Input : Ideal NRZ signal
NRZ pulse:
001_ )
2(.)
2(.)(
nss
l
kkchout
TnTtT
TkTtgatv
Output of the first channel:
is “1” or “0”ka
The Sampling Theory and The Undersampling Technique for Demultiplexer (2)
1. Sampling Circuit for Demultiplexer
otherwise
Ttfor
Ttfor
tg
,0
22
12
1
)(
8
For 1:2 Demultiplexer:Output of the first channel:
TTs 2
001_ )
22(.)
2(.)(
ns
l
kkchout
TnTtT
TkTtgatv
002_ )
2
32(.)
2(.)(
ns
l
kkchout
TnTtT
TkTtgatv
Output of the second channel:
The Sampling Theory and The Undersampling Technique for Demultiplexer (3)
(Undersampling Technique)
1. Sampling Circuit for Demultiplexer
9
t im e
A m p litude
"1 " "1 "
P eriod o f the s igna lT
"1 ""1 " "1 " "1 ""1 ""0 " "0 ""0 " "0 "
P eriod o f the sam p le r
T s
tim e
A m p litude
"1 " "1 ""1 " "0 " "0 "
Channel 1
t im e
A m p litude
"1 " "1 " "1 " "1 ""0 "
tim e
A m p litude
"1 " "1 "
P eriod o f the s igna lT
"1 ""1 " "1 " "1 ""1 ""0 " "0 ""0 " "0 "
P eriod o f the sam p le r
T s
Channel 2
"0 "
Output
The Sampling Theory and The Undersampling Technique for Demultiplexer (4)
1. Sampling Circuit for Demultiplexer
10
Sampling Circuit Topology:
-Based on Sampling Circuit of the Oscilloscope
-Using Double Diode Configuration
-Very Symmetric
The Sampling Circuit for Demultiplexer (1)
1. Sampling Circuit for Demultiplexer
Zo =50 Oh m
In p u tS ig n al
Ch arg eAm p lifier
Ch arg eAm p lifier
Ou tp u tS ig n al
Vb ias
Vb ias
Stro b eG en erato r
S tro b eG en erato r
50Oh m
11
0
-0.2
0.4
0.5
DiodeVoltage
(V)
T im e (ps)
T S
Turn OnPoint
Zo=50 Ohm
InputSignal
ChargeAm plifier
ChargeAm plifier
OutputSignal
Vbias
Vbias
StrobeGenerator
StrobeGenerator
50Ohm
Chold
Chold
Basic operation:
-Vbias will charge Chold so that the diode will be in reverse bias
-The strobe turn on the diode in a very small span time
-In this span time, the charge will be transferred from the input into the Chold
The Sampling Circuit for Demultiplexer (2)
1. Sampling Circuit for Demultiplexer
12
Driving RequirementsCircuit Components
2. Driving Requirements and Circuit Components
132. Circuit Requirements and Components
Driving Requirements
20 40 60 800 100
-90
-80
-70
-60
-50
-40
-30
-20
-10
-100
0
freq, GHz
dB
(mag_fft_
vin
)
Broadband Characteristic is Important
Circuit bandwidth > 40 GHz is necessary
Spectrum of 40 Gbps NRZ signal PRBS 27-1
142. Circuit Requirements and Components
The Components in the Design
1. Infineon Schottky Diode Double Configuration
2. Oscillators 20 GHz max 1 Vpp
3. DC Bias
4. Alumina (Al2O3) Substrates
5. Hold Capacitors
152. Circuit Requirements and Components
General Properties:
-Using Flip-Chip Interconnections
-Cjo=30 fF, Rs=10 Ohm
-Max forward current = 25 mA
Modeled by Root Diode Model in the ADS:
•Large signal table based model
•Generated from measured DC and small signal S-Parameters
Infineon Schottky Diode Double Configuration
162. Circuit Requirements and Components
0.1 0.2 0.3 0.4 0.5 0.6 0.70.0 0.8
-05
10152025
-5
30
Vbias
IC.i,
mA
We define turn-on point of the diode is 480 mV
DC Characteristic of the Diode Model
172. Circuit Requirements and Components
Equivalent Model
)2(1
2
122o
sp
psres Z
LC
CLf
Resonance frequency *):
*)Chun-Long Wang and Ruey-Beei Wu, “A Locally matching Technique for Broadband Flip-chip Transition Design,” IEEE Trans. Microwave Theory Tech., pp. 1399, February 2002.
Using L=103 pH, C=45 fF, Zo=50 Ohm
fres=76.9 GHz
Height= 5 um
Diameter=50 um
Flip-Chip Bonding AuSn (1)
182. Circuit Requirements and Components
Equivalent Model*)
The double diode pad C=20 fF
Flip-Chip Bonding AuSn (2)
*)Jung Han Choi, C.-J. Weiske, G.R. Olbrich, P. Russer, “Flip-chip bonded Si Schottky Sampling Circuits for High Speed Demultiplexer”, Microwave Symposium Digest, 2003 IEEE MTT-S International, vol. 3, pp. 1515-1518, 8-13 June 2003.
19
The Rule of DesignBandwidth Optimization: Analytic and SimulationLayout Design and SimulationOperation in Lower SpeedFlip Chip Bonding EffectEffect of Oscillator Phase Difference
3. Design, Analysis and Simulation
20
V s(t)
-V s(t)
C hold
C hold
R b
R bV bias
-V bias
R in
R t
50 O hm
F LIP -C H IP B O N D IN G
F LIP -C H IP B O N D IN G
F LIP -C H IP B O N D IN G
Input 40 G bpsP R B S 2 7-1 O utput 20 G bps
R out
R out
•Oscillator is used
•Flip-chip bonding model is included
•Input Bit pattern is PRBS 27-1
Circuit Topology
3. Design, Analysis and Simulation
21
3 .8 3 .93 .7 4 .0
3 0 0
3 5 0
4 0 0
4 5 0
5 0 0
2 5 0
5 5 0
time , nsecV
_dio
de, m
V
T urn O nP o in t
Proper operation
Turn-on point = 480 mV
Basic Operation : Turning On the Diode (1)
outbD
diodeosc
b
bias
diode
RRtZ
dttV
CddtV
CdRV
tV11
)(1
))(
()(
)(
3. Design, Analysis and Simulation
22
Unproper operation:
•Diode voltage always above the turn on point: all bits will be passed
•Caused by too small Rbias (e.g. 15 Ohm)
3.8 3.93.7 4.0
590
600
610
620
630
580
640
time, nsec
V_dio
de, m
V
0.2 0.4 0.6 0.80.0 1.0
0
50
100
150
-50
200
time, nsec
vin, m
Vvo
ut, m
V
Basic Operation : Turning On the Diode (2)
3. Design, Analysis and Simulation
23
Input 40 Gbps PRBS 27-1
Output Channel 1
Output Channel 2
Simulation Results
3. Design, Analysis and Simulation
24
•Vertical Eye opening= 45 mV
Eye Diagram of the 20 Gbps Output Signal
3. Design, Analysis and Simulation
0 20 40 60 80 100 120 140-20 160
-0.01
-0.00
0.01
0.02
0.03
0.04
-0.02
0.05
time, psec
eye_
vout
50 ps
45 mV
25
0)()(213111
DDtin
in
Z
VV
Z
VV
R
V
R
VV
Using KCL on all nodes:
0)()(1222
Dout
out
eq Z
VV
R
VV
Z
V
0)()(1333
Dout
out
eq Z
VV
R
VV
Z
V
050
32
Ohm
V
R
VV
R
VV out
out
out
out
out
b
beq CRj
RZ
1)(
•Flip-chip bonding is neglected
•Diodes are turned-on
Bandwidth Optimization (1) - Analytic
3. Design, Analysis and Simulation
26
Rout
ZRRZ
RZR
RCRjRZRR
RinZV
V
DtinD
outD
out
b
boutDtinD
in
out
2
)(211
)(
21)(
150
)100(150
)100(
1
)(211
)(
2
2
Transfer function:
50
)100(.
)(
211)(
2)(
out
b
DtinD
RR
ZRRRinZ
A
Rb
ZRRZ
RRZB
DtinD
outoutD
.
)(
211)(
2)
100(
1001(
1
)(
11)(
2
Define :
Bandwidth Optimization (2) - Analytic
3. Design, Analysis and Simulation
27
Transfer function:
B
CRjB
AH
b
1
1)(
It has low pass characteristic, with cutoff frequency:
Flip-chip bonding highly affects the 86 Gbps performance.
3. Design, Analysis and Simulation
41
Effect of Asymmetry: Oscillator Phase Difference (1)
Portion of the Oscillators on the output signal:
outoutcb
out
DDin
DD
in
in
c
ss
out
RRtZR
R
tZtZR
tZtZ
R
V
Z
VV
V21
)(
11
50
100
)(
1
)(
12
)(
1
)(
1
'
21
21
The phase difference will add sinusoidal signal as distortion in the output. The greater the phase difference, the greater the distortion
2sin
2cos2)sin(sin'
tAtAtAVV ss
2sin
2cos2
tA
3. Design, Analysis and Simulation
42
0 20 40 60 80 100 120 140-20 160
-0.01
0.00
0.01
0.02
0.03
-0.02
0.04
time, psec
eye_
vout
0 20 40 60 80 100 120 140-20 160
-0.02
-0.01
-0.00
0.01
0.02
0.03
-0.03
0.04
time, psec
eye_vout
0 20 40 60 80 100 120 140-20 160
-0.02
-0.01
-0.00
0.01
0.02
0.03
-0.03
0.04
time, psec
eye_vout
10o phase difference5o phase difference
15o phase difference
Up to 5o difference can be tolerated
Effect of Asymmetry: Oscillator Phase Difference (2)
3. Design, Analysis and Simulation
43
ConclusionsFuture Works
4. Conclusions and Future Works
44
1. Sampling circuit for demultiplexer 1:2 with input ETDM 40 Gbps NRZ has been designed, analyzed and simulated.
2. The bandwidth analysis has excellent agreement with the simulation up to 50 GHz.
3. To avoid resonance in the desired passband, the distance between capacitor and the diode should be minimized.
4. With Chold 0.1 pF, cutoff frequency of 55 GHz with linear phase are achieved. (SC_0110)
5. The output amplitude of 32 mV and eye opening of 18 mV are achieved.
6. The sampling circuit works well in lower bit rate with excellent output eye diagram (20 Gbps and 10 Gbps input).
Conclusions (1)
4. Conclusions and Future Works
45
7. The flip-chip bonding affects the bandwidth of the circuit above 50 GHz. It greatly affects the circuit with 86 Gbps input. But it doesn‘t contribute significant effect to the circuit with 40 Gbps input.
8. The oscillator phase difference of 5o can be tolerated in this circuit.
Conclusions (2)
4. Conclusions and Future Works
46
Future Works
Choosing better diode, which has smaller zero bias junction capacitance, Cj0 lower than 10 fF is recommended for 40 Gbps operation.The real capacitor model with self resonance frequency (SRF) more than 50 GHz should be included, with its interconnectionCompensating the effect of the flip-chip bonding for operation above 40 GbpsExtending the circuit into the desired size of the complete circuit