ATTENUATION IN PCB TRACES DUE TO PERIODIC DISCONTINUITES · 2009-04-19 · TRACES DUE TO PERIODIC...
Transcript of ATTENUATION IN PCB TRACES DUE TO PERIODIC DISCONTINUITES · 2009-04-19 · TRACES DUE TO PERIODIC...
ATTENUATION IN PCB TRACES DUE TO PERIODIC DISCONTINUITESGustavo Blando, Jason R. Miller, Istvan Novak, Cheryl PrestonSun MicrosystemsJim DeLapAnsoft Corporation
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Outline• Introduction• Background theory and simulation methodology• Test board definition and measurements• Measurement to simulation correlation• Periodic discontinuities characteristics• Parameterization studies• Summary and conclusions• Q & A
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• Periodic discontinuities, what are they?• Refers to the loading of some element, for example, a
transmission line, at periodic intervals• Many kinds can be found in practice, ranging from the
periodic loading in multi-drop busses, to the periodic loading of plate capacitors
• Which ones are we going to study and why?• Traces routed over perforated planes.
We will present parametric studies on realistic cases and will show its effects
Introduction
Connpin-field
BGA pin-field
In most cases, a great percentage of the PCB trace length has to be routed over perforated areas
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Lumped discontinuity
⎥⎦
⎤⎢⎣
⎡⎥⎦
⎤⎢⎣
⎡⎥⎦
⎤⎢⎣
⎡⎥⎦
⎤⎢⎣
⎡⎥⎦
⎤⎢⎣
⎡⎥⎦
⎤⎢⎣
⎡⎥⎦
⎤⎢⎣
⎡
4
4
11
11
3
3
2
2
11
11
1
1
IV
DCBA
IV
DCBA
IV
DCBA
IV
dd
dd
Background theory and simulation methodology
• Periodically loaded transmission lines can be analyzed by identifying a unit cell, which is repeated along the structure, and calculating the loaded propagation delay.
• Unit cell length -> half wave resonance• Number of unit cells -> size of the resonance• Discontinuity size/kind -> size of the resonance
dip
00
00
0
/}]1)){cosh(2/()[sinh(}]1)){cosh(2/()[sinh(
)sinh()2/()cosh(
ZdZZdCdZZdZBdZZdDA
d
d
d
−+=++=
+==
γγγγγγ
).sinh().2/().cosh().cosh( 0 dZZdd dp γγγ +=
Length of one unit cell
Unit Cell
• From a practical stand point, we could, for example, get the unit cell from a field-solver
• Or, do different type of analysis, for example
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Design guidelines
Simulation plan
Real case simulations, definitions andparameterization
Resultsand conclusions
TransmissionLine generation
Simulation of:● Saturation● Frequency dependency
Gain modelingconfidence level
HFSS:● Solve a single unit cell
Same?
no
yes
Concatenate “N” unit cells
Create a test board:● Easily modifiable●Simple to measure●With “N” unit cells
HFSS:● Solve a single unit cell
Same? Concatenate
“N” unit cellsManyvariations
Periodical-disc effects study
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TDR response (rho)
-0.04
-0.02
0
0.02
0.04
0.06
0.08
0.1
0.0E+0 2.0E-10 4.0E-10 6.0E-10 8.0E-10 1.0E-9 1.2E-9
Time [sec]
Half wave resonance1/ 2*500mils*150ps/in=6.6GHz
Test board 2.5 mm wide, 6in long microstrip on top of a 800 mil wide, 63 mil thick FR4 dielectric
500mils pitch
Fixed 125 mils from the edge of the trace to center of the hole
Hole diameter increased from: 125,164,194,250mils
Edge launch SMA
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Test board measurementsS21 magnitude [dB]
-2.5E+01
-2.0E+01
-1.5E+01
-1.0E+01
-5.0E+00
0.0E+00
0.0E+0 5.0E+9 1.0E+10 1.5E+10 2.0E+10
Frequency [Hz]
164-mil194-mil250-mil
Solid plane125-mil
Half wave resonance
Full wave resonance
Baseline
Dip
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Simulation setup• Ansoft HFSS, v10• Unit cell approach used• Material: FR4
• Dk = 4.5• Tand = 0.03
• The hole diameters were progressively increased to match the test board
• MATLAB was used to perform the concatenation
12 un
it cell
s
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Measurement correlation (1)
0 0 10 20-25
-20
-15
-10
-5
0
Frequency [GHz]
dB
0 10 20-14
-12
-10
-8
-6
-4
-2
0
Frequency [GHz]
dB
250mils holediameter
Simulated
194mils holediameter
Used a frequencyindependent dK
Goodcorrelation
Measured
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Measurement correlation (2)
0 10 20-14
-12
-10
-8
-6
-4
-2
0
Frequency [GHz]
dB
Measured
Sim
164 mil holediameter
0 10 20-14
-12
-10
-8
-6
-4
-2
0
Frequency [GHz]
dB
Measured
Sim
125 mil holediameter
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Periodically loaded line characteristics• Doing some mathematical post-processing, several
periodic discontinuity effects can be studied.• Study 1: Examine how the location of the
resonance dip changes as a function of unit cell length
• Study 2: Examine the first resonance amplitude as a function of the number of cascaded cells for a 500-mil long unit cell
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Frequency vs. pitch dependency12
unit c
ells
0 5 10 15 20-45
-40
-35
-30
-25
-20
-15
-10
-5
0
frequency[GHz]
dB
0 5 10 15 20200
300
400
500
600
700
800
frequency[GHz]
leng
ht[m
ils]
1/(2*tpd)
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Saturation effect
0 25 50 75 100-0.18
-0.16
-0.14
-0.12
-0.1
-0.08
-0.06
-0.04
-0.02
0
Number of Cells
dB
5.9 6.1 6.3 6.5 6.7
-0.18
-0.16
-0.14
-0.12
-0.1
-0.08
-0.06
-0.04
-0.02
0frequency[GHz]
dB
(Bas
eline
–Di
p)/ (
numb
ers o
f Cell
s)
0.5in
Incre
asing
numb
er of
cells
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Parameterization• Examine the impact of additional losses introduced
by the periodic discontinuities in real-world designs• Large number of variables including:
• Number of periodic discontinuities• Distance between the discontinuities• Separation between the discontinuity and the
trace• Size of the discontinuity
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Parameterization cases
• Case 1: Trace routed through a pin field, such as a connector, where the trace would periodically encounter a hole located on either side of a trace
ws
• Case 2: Trace routed near to a single cutout but due to misregistration and manufacturing tolerances, the trace gets routed over a portion of the plane cutout
-s
Example: 4 mil line width, BGA (1mm, 39.37 mil), 30 mil antipadRange Antipad edge to trace edge separation
Different core misregistration +/-5 mils+/-3 mils
-3.315 mils (-82%)Same core misregistration -1.315 mils (-33%)
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Parameter ranges
• 50-ohm microstrip was simulated using a 4-mil wide trace and a 4-mil thick dielectric (2%, εr=4.5)
• Number of periodic discontinuities : 10• Distance between the discontinuities: 500 mils
(λ/2=6.6 GHz)• Trace to hole separation: -4 (-100%) mils to 6 mils
(+150%)• Size of the discontinuity (antipad diameter) : 50mils
to 150 mils
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0 (0%)2 (50%)
4 (100%)6 (150%)50
100
1500 (0%)
0.5 (6%)
1 (11%)
1.5 (16%)
2 (22%)
2.5 (27%)
3 (32%)
edge-to-edge [mils(%line whole-diam [mils]
extra
-loss
[dB
(%ba
selin
e)]
Case 1, third resonanceParameterization
(20.23 GHz)
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0 (0%)2 (50%)
4 (100%)6 (150%)50
100
1500 (0%)
0.5 (8%)
1 (16%)
1.5 (23%)
2 (31%)
edge-to-edge [mils(%line whole-diam [mils]
extra
-loss
[dB
(%ba
selin
e)]
Case 1, second resonanceParameterization
(13.44 GHz)
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Case 1, first resonanceParameterization
0 (0%)
2 (50%)
4 (100%)
6 (150%)4060
80100
120140
0 (0%)
0.1 (3%)
0.2 (6%)
0.3 (9%)
0.4 (11%)
0.5 (14%)
0.6 (17%)
edge-to-edge [mils(%line width)]hole-diam [mils]
extra
-loss
[dB
(%ba
selin
e)]
(6.89 GHz)
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Case 1, etch to antipad separationParameterization
0 (0%)2 (50%)
4 (100%)6 (150%)50
100
1500 (0%)
0.5 (6%)
1 (11%)
1.5 (16%)
2 (22%)
2.5 (27%)
3 (32%)
edge-to-edge [mils(%line whole-diam [mils]
extra
-loss
[dB
(%ba
selin
e)]
0% 50% 100% 150%-0.5
0
0.5
1
1.5
2
2.5
3
edge-to-edge [%line-width]
extra
-loss
[dB
]
0 1 2 3 4 5 6
-0.5
0
0.5
1
1.5
2
2.5
3
edge-to-edge [mils]
f3
f2
f1
100 mil antipad diameter
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Case 1, antipad diameter changeParameterization
60 70 80 90 100 110 120 130 140
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
2.2
hole diameter [mils]
extra
-loss
[dB
]f3
f2
f1
0 mil separation0 (0%)
2 (50%)4 (100%)
6 (150%)50
100
1500 (0%)
0.5 (6%)
1 (11%)
1.5 (16%)
2 (22%)
2.5 (27%)
3 (32%)
edge-to-edge [mils(%line whole-diam [mils]
extra
-loss
[dB
(%ba
selin
e)]
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-4 (-100%)-2 (-50%)
0 (0%)2 (50%)40
6080
100120
0 (0%)
2 (22%)
4 (43%)
6 (64%)
8 (85%)
10 (106%)
edge-to-edge [mils(%line widhole-diam [mils]
extra
-loss
[dB
(%ba
selin
e)]
Case 2, third resonanceParameterization
(20.23 GHz)
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-4 (-100%)-2 (-50%)
0 (0%)2 (50%)40
6080
100120
0 (0%)
1 (16%)
2 (31%)
3 (46%)
4 (61%)
5 (77%)
6 (92%)
edge-to-edge [mils(%line widthole-diam [mils]
extra
-loss
[dB
(%ba
selin
e)]
Case 2, second resonanceParameterization
(13.44 GHz)
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-4 (-100%)-2 (-50%)
0 (0%)2 (50%)40
6080
100120
0 (0%)
0.5 (14%)
1 (28%)
1.5 (41%)
2 (55%)
edge-to-edge [mils(%line widhole-diam [mils]
extra
-loss
[dB
(%ba
selin
e)]
Case 2, first resonanceParameterization
(6.89 GHz)
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Case 2, etch to antipad separationParameterization
-100% -80% -60% -40% -20% 0% 20% 40%0
1
2
3
4
5
6
7
edge-to-edge [%line-width]
extra
-loss
[dB
]
-4 -3 -2 -1 0 1
0
1
2
3
4
5
6
7
edge-to-edge [mils]
f3
f2
f1
58 mil antipad diameter-4 (-100%)
-2 (-50%)0 (0%)
2 (50%)4060
80100
1200 (0%)
2 (22%)
4 (43%)
6 (64%)
8 (85%)
10 (106%)
edge-to-edge [mils(%line widhole-diam [mils]
extra
-loss
[dB
(%ba
selin
e)]
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Case 2, antipad diameter changeParameterization
50 60 70 80 90 100 110 1201
2
3
4
5
6
7
8
9
10
hole diameter [mils]
extra
-loss
[dB
]
f3
f2
f1
-4 mil separation-4 (-100%)
-2 (-50%)0 (0%)
2 (50%)4060
80100
1200 (0%)
2 (22%)
4 (43%)
6 (64%)
8 (85%)
10 (106%)
edge-to-edge [mils(%line widhole-diam [mils]
extra
-loss
[dB
(%ba
selin
e)]
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Conclusions (1)• Due to periodic discontinuity the slope of transfer function
increases and sharp dips appear in the loss profile • Extra attenuation varies almost linearly with frequency
Increases linearly with frequencySimplified discontinuitymodel
Z = jωL(ω)
Decreases weakly with frequency• Due to this effect, at lower frequencies (less than ~3 GHz),
for the type of discontinuities studied here, the additional loss is not too pronounced
• The extra attenuation starts to sharply increase as the separation between antipad and trace approaches zero
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Conclusions (2)• Due to misregistration the loss can increase dramatically• Loss has a close to linear relationship to antipad diameter• Loss scales with the number of discontinuities until it
saturates• Distance between the discontinuities determines the lowest
resonance frequency
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Next steps• Understand different types of discontinuities
> Including a complete via structure (some studies have already been done)
> Understand the crosstalk effect between same layers and adjacent layers due to perforated planes
> Understand the same effect on stripline structures, (all the measurements and simulations have been done on microstrips)
> Create behavioral models to account for these effects
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Eye mask degradation due to periodic discontinuities (1)• Four cases have been created:
> Six inch trace without perforation: F-6in, (Baseline)> Six inch trace formed by twelve, 500mils perforated unit
cells: D-6in (Dip)> Eighteen inch trace with no perforation: F-18in> Twenty seven inch trace without perforations: F-27in
• Different bit times have been used• Internal differential eye contour, area and UI have
been computed for every simulated bit time
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Eye mask degradation due to periodic discontinuities (1)• Simulations have been run using a 10ps rise-time.• The discontinuity has been generated fitting the half
wave resonance of the 250mils hole diameter using a RLC T-network
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Frequency domain channel characteristics
0 2 4 6 8 10 12 14 16 18
x 109
-50
-40
-30
-20
-10
0
Freq
FULL-6in[1,2]D-194mils,6",500mils-sep[1,2]FULL-27in[1,2]FULL-18in[1,2]
• Notice the cases have been created to study the difference between:> Baseline> Discontinuity> Longer uniform line,
presenting the same attenuation than the periodic discontinuity case at the resonance frequency
> Medium line length, falling in between the baseline and the long case
D-250mils
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Back-Up-Slides
0.2 0.4 0.6 0.80
0.05
0.1
0.15
0.211.1111GB/s
0.2 0.4 0.6 0.80
0.05
0.1
0.15
0.2
10GB/s
0.2 0.4 0.6 0.80
0.05
0.1
0.15
0.2
9.0909GB/s
0.2 0.4 0.6 0.80
0.05
0.1
0.15
0.2
8.3333GB/s
0.2 0.4 0.6 0.80
0.05
0.1
0.15
0.2
7.1429GB/s
0.2 0.4 0.6 0.80
0.05
0.1
0.15
0.2
5GB/s
0.2 0.4 0.6 0.80
0.05
0.1
0.15
0.2
4GB/s
0.2 0.4 0.6 0.80
0.05
0.1
0.15
0.2
3.125GB/s
0.2 0.4 0.6 0.80
0.1
0.2
2.5GB/s
UI
V
F-6inD-6inF-27inF-18in
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Horizontal eye opening• Note how the
periodical discontinuity case is closely following the 18” case. Maybe a shorter line, 12” would be closer.
• The 27” has by far the biggest horizontal eye closure as seen on the eyes in the previous page
2 4 6 8 10 120.4
0.5
0.6
0.7
0.8
0.9
1
UI
f[GHz]
F-6inD-6inF-27inF-18in
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Eye area• The area
computation, follows the same trend as the horizontal eye opening computation
• Clearly in all these cases, the line with periodic discontinuities is the one that have more fluctuations
2 4 6 8 10 120
0.05
0.1
0.15
0.2
0.25
area
,UI*V
f[GHz]
F-6inD-6inF-27inF-18in