User's Manual

Intel
®
820 Chipset Design Guide 3-19
Advanced System Bus Design
3.4 More Details and Insight
3.4.1 Textbook Timing Equations
The “textbook” equations used to calculate the propagation rate of a PCB are the basis for
spreadsheet calculations for timing margin based on the component parameters. These equations
are:
Equation 3-6. Intrinsic Impedance
(Ω)
Equation 3-7. Stripline Intrinsic Propagation Speed
(ns/ft)
Equation 3-8. Microstrip Intrinsic Propagation Speed
(ns/ft)
Equation 3-9. Effective Propagation Speed
(ns/ft)
Equation 3-10. Effective Impedance
(
Ω
)
Equation 3-11. Distributed Trace Capacitance
(pF/ft)
Equation 3-12. Distributed Trace Inductance
(nH/ft)
Z
L
C
0
0
0
=
S
STRIPLINE
r
0
1017
_
.*=
ε
S
MICROSTRIP
r
0
1017 0475 0 67
_
.*.* .=+
ε
S
EFF
S
C
D
C
=∗+
0
1
0
Z
EFF
Z
C
D
C
=
+
0
1
0
C
S
Z
0
0
0
=
LZ
S
0
12
00
=∗
∗