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3 Inductance Screening Accurate modeling the inductance is expensive Only include inductance effect when necessary How to identify?
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Inductance Screening and Inductance Matrix Sparsification
1
Outline
• Inductance Screening• Inductance Matrix Sparsification
2
3
Inductance Screening
• Accurate modeling the inductance is expensive
• Only include inductance effect when necessary
• How to identify?
4
Off-chip Inductance screening
• The error in prediction between RC and RLC representation will exceed 15% for a transmission line if
CL is the loading at the far end of the transmission line
l is the length of the line with the characteristic impedance Z0
oDRV
o
nZZZRl
Cl
12
CL
5
Conditions to Include Inductance
• Based on the transmission line analysis, the condition for an interconnect of length l to consider inductance is
R, C, L are the per-unit-length resistance, capacitance and inductance values, respectively
tr is the rise time of the signal at the input of the circuit driving the interconnect
CL
Rl 2
LC2t r
6
On-chip Inductance Screening
• Difference between on-chip inductance and off-chip inductance– We need to consider the internal inductance for on-chip
wires– Due to the lack of ground planes or meshes on-chip, the
mutual couplings between wires cover very long ranges and decrease very slowly with the increase of spacing.
– The inductance of on-chip wires is not scalable with length.
7
Self Inductance Screening Rules
• The delay and cross-talk errors without considering inductance might exceed 25% if
where fs = 0.34/tr is called the significant frequency4
)(2
281CL
DRVs
ZRlLlf
CL
Rl
Cl
8
Mutual Inductance Screening Rules
• SPICE simulation results indicates that most of the high-frequency components of an inductive signal wire will return via its two quiet neighboring wires (which may be signal or ground) of at least equal width running in parallel
• The potential victim wires of an inductive aggressor (or a group of simultaneously switching aggressors) are those nearest neighboring wires with their total width equal to or less than twice the width of the aggressor (or the total width of the aggressors)
Outline
• Inductance Screening• Inductance Matrix Sparsification
9
C Matrix Sparsification
10
433810047.3309.3285.3342.83310042605134634.8548.3394.16
7.33013463047126923.619.249.23834.8512693047126327.875.33448.3323.611263304813402.83394.169.2427.8713402411
10C 12
• Capacitance is a local effect• Directly truncate off-diagonal small elements produces a sparse matrix.• Guaranteed stability.
433810040002.8331004260513460094.16013463047126909.240012693047126327.87000126330481340
2.83394.169.2427.871340241110C 12
L Matrix Sparsification
• Inductance is not a local effect• L matrix is not diagonal dominant• Directly truncating off-diagonal elements cannot guarantee stability
11
11= 1010.8 8.51 7.22 6.45 5.90 5.47 5.138.51 10.8 8.51 7.22 6.45 5.90 5.477.22 8.51 10.8 8.51 7.22 6.45 5.906.45 7.22 8.51 10.8 8.51 7.22 6.455.90 6.45 7.22 8.51 10.8 8.51 7.225.47 5.90 6.45 7.22 8.51 10.8 8.515.13 5.47 5.90 6.45 7.22 8.51
L
,
10.8
12
Direct Truncation of
11= 10
10.8 8.51 7.22 6.45 5.90 5.47 5.138.51 10.8 8.51 7.22 6.45 5.90 5.477.22 8.51 10.8 8.51 7.22 6.45 5.906.45 7.22 8.51 10.8 8.51 7.22 6.455.90 6.45 7.22 8.51 10.8 8.51 7.225.47 5.90 6.45 7.22 8.51 10.8 8.515.13 5.47 5.90 6.45 7.22 8.51
L
,
10.8
1
1 10= 102.53 1.67 0.12 0.12 0.08 0.05 0.111.67 3.63 1.60 0.04 0.07 0.04 0.050.12 1.60 3.64 1.59 0.04 0.07 0.080.12 0.04 1.59 3.64 1.59 0.04 0.120.08 0.07 0.04 1.59 3.64 1.60 0.120.05 0.04 0.07 0.04
L
,
1.60 3.63 1.670.11 0.05 0.12 0.12 0.12 1.67 2.53
1 10= 102.53 1.671.67 3.63 1.60
1.60 3.64 1.59,1.59 3.64 1.59
1.59 3.64 1.601.60 3.63 1.67
1.67 2.53
L
1L
13
Direct Truncation of
1L
next
11= 106.74 4.21 2.50 1.49 0.90 0.57 0.384.21 6.35 3.77 2.25 1.36 0.86 0.572.50 3.77 5.96 3.55 2.15 1.36 0.901.49 2.25 3.55 5.85 3.55 2.25 1.490.90 1.36 2.15 3.55 5.96 3.77 2.500.57 0.86 1.36 2.25 3.77 6.35 4.210.38 0.57 0.90 1.49 2.50 4.21
L
,
6.74
11= 1010.8 8.51 7.22 6.45 5.90 5.47 5.138.51 10.8 8.51 7.22 6.45 5.90 5.477.22 8.51 10.8 8.51 7.22 6.45 5.906.45 7.22 8.51 10.8 8.51 7.22 6.455.90 6.45 7.22 8.51 10.8 8.51 7.225.47 5.90 6.45 7.22 8.51 10.8 8.515.13 5.47 5.90 6.45 7.22 8.51
L
,
10.8
14
Direct Truncation
• Resulting inductance matrix quite different• Large matrix inversion.• No stability guarantees.
15
Window-based Methods
1
11
35.521.421.474.6
10
68.267.11010 1.672.53
11= 106.74 4.21 2.50 1.49 0.90 0.57 0.384.21 6.35 3.77 2.25 1.36 0.86 0.572.50 3.77 5.96 3.55 2.15 1.36 0.901.49 2.25 3.55 5.85 3.55 2.25 1.490.90 1.36 2.15 3.55 5.96 3.77 2.500.57 0.86 1.36 2.25 3.77 6.35 4.210.38 0.57 0.90 1.49 2.50 4.21
L
,
6.74
1 10= 102.53 1.671.67 3.63 1.60
1.60 3.64 1.59,1.59 3.64 1.59
1.59 3.64 1.601.60 3.63 1.67
1.67 2.53
L
1
11
96.577.350.277.335.621.450.221.474.6
10
69.260.1
67.153.21.603.631.67
16
Window-based Methods11= 10
10.8 8.51 7.22 6.45 5.90 5.47 5.138.51 10.8 8.51 7.22 6.45 5.90 5.477.22 8.51 10.8 8.51 7.22 6.45 5.906.45 7.22 8.51 10.8 8.51 7.22 6.455.90 6.45 7.22 8.51 10.8 8.51 7.225.47 5.90 6.45 7.22 8.51 10.8 8.515.13 5.47 5.90 6.45 7.22 8.51
L
,
10.8
44.292.192.144.2
10)2:1,2:1( 101L
48.271.131.071.162.371.131.071.148.2
10)3:1,3:1( 101L
Since the inverse of the original inductance matrix is not exactly sparse, the resulting approximation is asymmetric.
17
Window-based Methods
• Avoid large matrix inversion.• No stability guarantees.• Advanced methods exist to guarantee the stability
but at the cost of
18
Sparsity Pattern for
2
8 9 10
3 4 5
7
1
6
12 13 14 1511
1L
19
Band Matching Method
• Preserve inductive couplings between neighboring wires
L
20
Horizontal layer
Shielding effect by the neighboring horizontal layer is perfect.Inverse of Inductance matrix is block tridiagonal.
2
8 9 10
3 4 5
7
1
6
12 13 14 1511
21
Block Tridiagonal Matching
nnTn
Tn
nT
n
LLL
LLLLLL
L
21
22212
11211
1
,111
111
1 ),(
iiii
iiii
VLU
LUV
LVmmIU
If L has a block tridiagonal inverse,L can be compactly represented by
nnTT
nTT
n
nTT
n
VUUVUV
VUVUUVVUVUVU
L
21
22212
12111
22
Block Tridiagonal Matching
• Sequences and are calculated only from tridiagonal blocks.
• Tridiagonal blocks match those in the original inductance matrix.
• Inverse is a block tridiagonal matrix.
iU iV
23
Properties
• The resulting approximation minimizes the Kullback-Leibler distance to the original inductance matrix.
• The resulting approximation is positive definite.
1)}~det(log)~({1)~,( 11 LLLLTrN
LLd
24
Vertical Layer
Shielding effect by the neighboring vertical layer is perfect.
2
8 9 10
3 4 5
7
1
6
12 13 14 1511
25
Intersection of Horizontal and Vertical Layer
2
8 9 10
3 4 5
7
1
6
12 13 14 1511
26
Multi-band matching method
L
Horizontal Block Tridiagonal band matching
Converge to an unique solution.L~
Vertical Block Tridiagonal band matching
27
Intersection of Horizontal and Vertical Layer
v
L
h
28
has the minimum distance
Optimality
• In every step, the distance to another space is minimized.
(Final solution is optimal.)
L
h
v
29
Stability
• In every step, the resulting matrix is positive definite. Final solution is stable.