automatic length compensation for analog integrated circuit routing
TRANSCRIPT
Automatic Length Compensation for Analog Integrated Circuit Routing
Matthew A. Smith (Foley & Lardner LLP)Lars Schreiner (Cadence Design Systems, Inc.)Erich Barke (University of Hannover)Volker Meyer-zu-Bexten (ATMEL Germany GmbH)
3Matthew Smith
Overview
Approach
Problems to be Solved
Results
Summary
4Matthew Smith
Overview
Approach
Problems to be Solved
Results
Summary
5Matthew Smith
One goal (of many): balance parasitic loads on interconnects
Analog Router
During routing length differences between bus traces occur
PARSY
GLOBALLOCAL
Terminal: Beginning of a “Net Bundle”
6Matthew Smith
Length Compensation
Create a Geometry Equalizes Trace Lengths
L=100L=110L=120
7Matthew Smith
Length Compensation
Create a Geometry Equalizes Trace Lengths
L=100L=110L=120
8Matthew Smith
Length Compensation
Create a Geometry Equalizes Trace Lengths
L=100L=110L=120
9Matthew Smith
Length Compensation
Create a Geometry Equalizes Trace Lengths
L=100L=110L=120
10Matthew Smith
Length Compensation
Create a Geometry Equalizes Trace Lengths
L=120L=110L=120
11Matthew Smith
Length Compensation
Create a Geometry Equalizes Trace Lengths
L=120L=110L=120
12Matthew Smith
Length Compensation
Create a Geometry Equalizes Trace Lengths
L=120L=110L=120
13Matthew Smith
Length Compensation
Create a Geometry Equalizes Trace Lengths
L=120L=110L=120
14Matthew Smith
Length Compensation
Create a Geometry Equalizes Trace Lengths
L=120L=120L=120
15Matthew Smith
Length Compensation
Create a Geometry Equalizes Trace Lengths
L=120L=120L=120
16Matthew Smith
A More Difficult Case
L=100
L=200
L=120
L=200L=150
17Matthew Smith
A More Difficult Case
L=100
L=200
L=120
L=200L=150
•Find the longest trace(s)
18Matthew Smith
A More Difficult Case
L=100
L=200
L=120
L=200L=150
•Make all lengths 200
19Matthew Smith
A More Difficult Case
L=100
L=200
L=120
L=200L=150
20Matthew Smith
A More Difficult Case
L=100
L=200
L=120
L=200L=150
21Matthew Smith
A More Difficult Case
L=100
L=200
L=120
L=200L=150
22Matthew Smith
A More Difficult Case
L=100
L=200
L=120
L=200L=150
23Matthew Smith
A More Difficult Case
L=100
L=200
L=120
L=200L=200
24Matthew Smith
A More Difficult Case
L=100
L=200
L=120
L=200L=200
25Matthew Smith
A More Difficult Case
L=100
L=200
L=120
L=200L=200
26Matthew Smith
A More Difficult Case
L=100
L=200
L=120
L=200L=200
27Matthew Smith
A More Difficult Case
L=100
L=200
L=120
L=200L=200
28Matthew Smith
A More Difficult Case
L=100
L=200
L=200
L=200L=200
29Matthew Smith
A More Difficult Case
L=100
L=200
L=200
L=200L=200
30Matthew Smith
A More Difficult Case
L=100
L=200
L=200
L=200L=200
• Middle trace uncompensated
31Matthew Smith
A More Difficult Case
L=100
L=200
L=200
L=200L=200
• Middle trace uncompensated
• Needs room for compensation geometry
32Matthew Smith
A More Difficult Case
L=100
L=200
L=200
L=200L=200
• Middle trace uncompensated
• Needs room for compensation geometry
HOWEVER
33Matthew Smith
A More Difficult Case
L=100
L=200
L=200
L=200L=200
• Middle trace uncompensated
• Needs room for compensation geometry
HOWEVER• To make room, other traces must be moved (lengthened)
34Matthew Smith
Problem To Be Solved
35Matthew Smith
General Length Compensation Problem for Parallel Traces
Problem To Be Solved
36Matthew Smith
Arbitrary Number of Traces
General Length Compensation Problem for Parallel Traces
Problem To Be Solved
37Matthew Smith
Arbitrary Number of Traces
General Length Compensation Problem for Parallel Traces
Arbitrary Lengths, Widths and Spacings
Problem To Be Solved
38Matthew Smith
Characteristics of a Good Solution
39Matthew Smith
Compensates Trace Lengths
Characteristics of a Good Solution
40Matthew Smith
Compensates Trace Lengths
Introduces Minimal Extra Trace Length
Characteristics of a Good Solution
41Matthew Smith
Compensates Trace Lengths
Introduces Minimal Extra Trace Length
Keeps Footprint Small
Characteristics of a Good Solution
42Matthew Smith
Compensates Trace Lengths
Introduces Minimal Extra Trace Length
Keeps Footprint Small
Introduces Few Additional Bends
Characteristics of a Good Solution
43Matthew Smith
Compensates Trace Lengths
Introduces Minimal Extra Trace Length
Keeps Footprint Small
Introduces Few Additional Bends
Flexible and Easy to Implement
Characteristics of a Good Solution
44Matthew Smith
Overview
Approach
Problems to be Solved
Results
Summary
45Matthew Smith
Overview
Approach
Problems to be Solved
Results
Summary
46Matthew Smith
Ripple Compensation
47Matthew Smith
Ripple Compensation
Multiple copies of a simple compensation geometry
48Matthew Smith
Ripple Compensation
RH
Multiple copies of a simple compensation geometry
49Matthew Smith
Ripple Compensation
A fixed height RH is chosen for the compensation geometry
Multiple copies of a simple compensation geometry
RH
50Matthew Smith
Ripple Compensation
A fixed height RH is chosen for the compensation geometry
Number of ripples determined by dividing length to be added by 2RH
Multiple copies of a simple compensation geometry
RH
51Matthew Smith
Example
52Matthew Smith
One ripple („storage ripple“) is extended in bus direction
Example
53Matthew Smith
One ripple („storage ripple“) is extended in bus direction
Example
Storage Ripples
54Matthew Smith
One ripple („storage ripple“) is extended in bus direction
Within the storage ripples are the ripples for other traces
Example
Storage Ripples
55Matthew Smith
Leftover Ripples
56Matthew Smith
Leftover Ripples
Ripples can be made smaller in case the compensation length
is not evenly divisible by 2RH
57Matthew Smith
Leftover Ripples
Ripples can be made smaller in case the compensation length
is not evenly divisible by 2RH
Leftover ripple
58Matthew Smith
Algorithm
59Matthew Smith
L=100 µmL=120 µmL=110 µmL=130 µm
1234
Algorithm
RH=5 µm
60Matthew Smith
L=100 µmL=120 µmL=110 µmL=130 µm
1234
Algorithm
RH=5 µm
Step 1: compute the compensation lengths
61Matthew Smith
L=100 µmL=120 µmL=110 µmL=130 µm
1234
Algorithm
RH=5 µm
Step 1: compute the compensation lengths
compensation length is the length of the longest trace minus the length of the current trace
62Matthew Smith
L=100 µmL=120 µmL=110 µmL=130 µm
1234
Algorithm
RH=5 µm
Step 1: compute the compensation lengths
compensation length is the length of the longest trace minus the length of the current trace
63Matthew Smith
L=120 µmL=110 µmL=130 µm
1234
Algorithm
L=30 µm
RH=5 µm
64Matthew Smith
L=110 µmL=130 µm
1234
Algorithm
L=30 µmL=10 µm
RH=5 µm
65Matthew Smith
L=130 µm
1234
Algorithm
L=30 µmL=10 µmL=20 µm
RH=5 µm
66Matthew Smith
1234
Algorithm
L=30 µmL=10 µmL=20 µmL=0 µm
RH=5 µm
67Matthew Smith
Starting at the top, calculate the number of ripples A needed
RH=5 µm
Algorithm
L=30 µm
68Matthew Smith
Starting at the top, calculate the number of ripples A needed
RH=5 µm
Algorithm
A = L / 2RH A = 30 / 10 = 3
L=30 µm
69Matthew Smith
Generate (A-1) ripples and half of the Ath ripple
RH=5 µm
Algorithm
70Matthew Smith
Repeat for the second trace. A = 10 / 10 = 1
RH=5 µm
Algorithm
71Matthew Smith
RH=5 µm
Algorithm
Repeat for the third trace. A = 20 / 10 = 2
72Matthew Smith
RH=5 µm
Algorithm
Repeat for the fourth trace. A = 0 / 10 = 0
73Matthew Smith
RH=5 µm
Stepping back up through the traces, construct the last half of each storage ripple and complete the trace
Algorithm
74Matthew Smith
RH=5 µm
Algorithm
Stepping back up through the traces, construct the last half of each storage ripple and complete the trace
75Matthew Smith
RH=5 µm
Algorithm
Stepping back up through the traces, construct the last half of each storage ripple and complete the trace
76Matthew Smith
RH=5 µm
Algorithm
Stepping back up through the traces, construct the last half of each storage ripple and complete the trace
77Matthew Smith
Problems
78Matthew Smith
Problems
Consumption of space in bus direction
79Matthew Smith
Problems
Consumption of space in bus direction
Introduction of bends
80Matthew Smith
Problems
Consumption of space in bus direction
Introduction of bends
Introduction of serpentine structures
81Matthew Smith
Problems
Consumption of space in bus direction
Introduction of bends
Introduction of serpentine structures
Compensation of parasitic capacitances
82Matthew Smith
Problem: Space Consumption
83Matthew Smith
Space Consumption
Vertical space consumption small, but
84Matthew Smith
Space Consumption
Geometries increase in length with the square of the number of traces
Vertical space consumption small, but
85Matthew Smith
Space Consumption
Geometries increase in length with the square of the number of traces
Example: with n=16 traces, width = 4 µm und spacing = 1 µm,
to compensate for a 90º turn in the bus
total length of the required module = 1,2 mm !
Vertical space consumption small, but
86Matthew Smith
Partial solution 1: Compensation by group
Differential pair 1
Differential pair 2
Ground
Trace Length
87Matthew Smith
Implementation of Groups
88Matthew Smith
Implementation of Groups
User can give every trace a group number
89Matthew Smith
Implementation of Groups
User can give every trace a group number
Length compensation only within each group
90Matthew Smith
Solution 2: Total Length Fitting
91Matthew Smith
Partial solution 2: Total Length Fitting
Ripple Height increased to make geometries shorter.
RH=5
92Matthew Smith
Partial solution 2: Total Length Fitting
Ripple Height increased to make geometries shorter.
RH=5
RH=10
93Matthew Smith
Problem: Resistance Compensation
94Matthew Smith
Problem: Resistance Compensation
The same length does not guarantee the same resistance
95Matthew Smith
Problem: Resistance Compensation
90º corners are problematic
The same length does not guarantee the same resistance
96Matthew Smith
Partial solution: No 90º Corners
Decreases electromigration as well
45º bends rounded corners
97Matthew Smith
Resistance in leftover ripples
Difficult to estimate the resistance of small ripples.
98Matthew Smith
Resistance in leftover ripples
Difficult to estimate the resistance of small ripples.
Partial solution: introduce a minimum ripple height RHmin
99Matthew Smith
Resistance in leftover ripples
Difficult to estimate the resistance of small ripples.
Partial solution: introduce a minimum ripple height RHmin
Recommended at least two times the trace width
100
Matthew Smith
Resistance in leftover ripples
Difficult to estimate the resistance of small ripples.
Partial solution: introduce a minimum ripple height RHmin
Recommended at least two times the trace width
Also necessary for 45º angle ripples
101
Matthew Smith
Introduction of the minimum ripple height (RHmin).
Minimum ripple height
Especially tricky implementation
102
Matthew Smith
Coupling between ripples
Ripples introduce serpentine structures
103
Matthew Smith
Coupling between ripples
Ripples introduce serpentine structures
Coupling between adjacent ripples results (likely) in signal distortion
104
Matthew Smith
Coupling between ripples
Ripples introduce serpentine structures
Coupling between adjacent ripples results (likely) in signal distortion
Serpentine structures are known to have resonant frequencies
105
Matthew Smith
Coupling between ripples
Ripples introduce serpentine structures
Coupling between adjacent ripples results (likely) in signal distortion
Serpentine structures are known to have resonant frequencies
Partial solution: give the designer the flexibility to weaken coupling
Stronger coupling
Weaker coupling
106
Matthew Smith
Cavity Parameter
Introduction of the „Cavity“ Parameter.
A minimum distance between the vertical sides of a ripple
107
Matthew Smith
Modelling capacitances
Extraction of the capacitances via modelling
108
Matthew Smith
Modelling capacitances
Capacitance compensation good with exception of outer traces
Extraction of the capacitances via modelling
109
Matthew Smith
Modelling capacitances
Capacitance compensation good with exception of outer traces
Partial solution: Introduction of shielding elements
Extraction of the capacitances via modelling
110Matthew Smith
Shielding Example
42,847,947,546,942,1
Total C (fF)
111Matthew Smith
Overview
Approach
Problems to be Solved
Results
Summary
112Matthew Smith
Summary
Length compensation module created in C++.
113Matthew Smith
Summary
Solves general length compensation problem
Length compensation module created in C++.
114Matthew Smith
Summary
Solves general length compensation problem
Length compensation module created in C++.
Supports group-based length compensation
115Matthew Smith
Summary
Solves general length compensation problem
Length compensation module created in C++.
Supports group-based length compensation
Can modify own size to fit within specified length parameters
116Matthew Smith
Summary
Solves general length compensation problem
Length compensation module created in C++.
Supports group-based length compensation
Can modify own size to fit within specified length parameters
Creates 90º and 45º geometries
117Matthew Smith
Summary
Solves general length compensation problem
Length compensation module created in C++.
Supports group-based length compensation
Can modify own size to fit within specified length parameters
Creates 90º and 45º geometries
Can use specified constraints on structure size / spacing
118Matthew Smith
Summary
Solves general length compensation problem
Length compensation module created in C++.
Supports group-based length compensation
Can modify own size to fit within specified length parameters
Creates 90º and 45º geometries
Can use specified constraints on structure size / spacing
Use of capacitative shielding supported
119Matthew Smith
Example of Difficult Cases
120
Matthew Smith
End
121
Matthew Smith
Erweiterung der Funktionalität
Benutzer kann jeder Leitung eine Gruppenindex zuordnen
Längenausgleich wird nur innerhalb der jeweiligen Gruppe ausgeführt
Ermöglicht den Einsatz von Shielding.
Gruppenaufteilung und Shielding:
122
Matthew Smith
Erweiterung der Funktionalität
Gesucht wird ein RH, die ein Modul mit einer Gesamtlänge Lg<Lmax
produziert.
Längenanpassungsfähigkeit
Schwierige Aufgabe, wenn auch RHmin eingehalten werden muss.
Einführung des Parameters „Maxlength“ (Lmax)
123
Matthew Smith
Erweiterung der Funktionalität
Längenanpassungsfähigkeit
124
Matthew Smith
Erweiterung der Funktionalität
Längenanpassungsfähigkeit
Änderung des Rippleausgleichs—Höhen „ebnen“
125
Matthew Smith
Erweiterung der Funktionalität
Längenanpassungsfähigkeit
126
Matthew Smith
Erweiterung der Funktionalität
Längenanpassungsfähigkeit
127
Matthew Smith
Erweiterung der Funktionalität
Längenanpassungsfähigkeit
128
Matthew Smith
Erweiterung der Funktionalität
Längenanpassungsfähigkeit
129
Matthew Smith
Erweiterung der Funktionalität
Längenanpassungsfähigkeit