EP2S90F1020C5 Datasheet, PDF (744/768 Pages) Altera Corporation – Stratix II Device Handbook, Volume 1

Transmission Line Layout
layouts. Thus, to achieve the same impedance, the dielectric span must be
greater in stripline layouts compared with microstrip layouts. Therefore,
stripline-layout PCBs with controlled impedance lines are thicker than
microstrip-layout PCBs.
Figure 11–8 shows stripline trace impedance with changing trace
thickness, using the stripline impedance equation, keeping trace width
and dielectric height constant. Figure 11–8 shows that the characteristic
impedance decreases as the trace thickness increases.
Figure 11–8. Stripline Trace Impedance with Changing Trace Thickness
60
50
40
Z0 (Ω) 30
20
10
0
0.7
1.4
2.8
4.2
T (mil)
Z0
H = 24.0 mils
W = 9.0 mils
Propagation Delay
Propagation delay (t_PD) is the time required for a signal to travel from one
point to another. Transmission line propagation delay is a function of the
dielectric constant of the material.
Microstrip Layout Propagation Delay
You can use the following equation to calculate the microstrip trace layout
propagation delay:
t_PD (microstrip) = ₈₅ 0.475ε_r + 0.67
Stripline Layout Propagation Delay
You can use the following equation to calculate the stripline trace layout
propagation delay.
t_PD (stripline) = 85 ε_r
11–8
Stratix II Device Handbook, Volume 2
Altera Corporation
May 2007