EP2S130F1020I4 Datasheet, PDF (743/768 Pages) List of Unclassifed Manufacturers – Stratix II Device Handbook, Volume 1

High-Speed Board Layout Guidelines
Figure 11–6. Stripline Trace Impedance with Changing Trace Width
80
70
60
50
Z0 (Ω) 40
30
20
10
0
4
4.5
5
5.5
6
6.5
7
7.5
8
8.5
9
10
W (mil)
Z0
T = 1.4 mils
H = 24.0 mils
Figure 11–7 shows stripline trace impedance with changing dielectric
height using the stripline impedance equation, keeping trace width and
trace thickness constant.
Figure 11–7. Stripline Trace Impedance with Changing Dielectric Height
80
70
60
50
Z0 (Ω) 40
30
20
10
0
16
20
24
28
32
36
40
H (mil)
Z0
T = 1.4 mils
W = 9.0 mils
44
As with the microstrip layout, the stripline layout impedance also
changes inversely proportional to line width and directly proportional to
height. However, the rate of change with trace height above GND is much
slower in a stripline layout compared with a microstrip layout. A stripline
layout has a signal sandwiched by FR-4 material, whereas a microstrip
layout has one conductor open to air. This exposure causes a higher
effective dielectric constant in stripline layouts compared with microstrip
Altera Corporation
May 2007
11–7
Stratix II Device Handbook, Volume 2