Digital Signal Processing Reference
In-Depth Information
w
b
t
h
Microstrip
Stripline
Figure 7.1
Microstrip and stripline traces of width
w
, thickness
t
, and distance
h
or
b
.
Field solvers sometimes use conductivity (the reciprocal of resistivity, with units
of Siemens-meter) rather than resistivity to specify the metal characteristics. De-
pending on the alloy, at room temperature the conductivity of copper is about 5.7
×
10
7
S-m.
Figure 7.2 shows the room temperature resistance for half-ounce and 1-ounce
perfectly rectangular copper traces. The resistance increases dramatically for half-
ounce traces under 10 mils and 1-ounce traces less than 15 mils. The resistance is
higher than shown if the trace is trapezoidal. Equations for calculating trace resis-
tance appear in Chapter 17.
7.3
Stripline and Microstrip Capacitance
As illustrated in Figure 7.3, a parallel plate capacitor is formed between the mi-
crostrip trace (as the upper plate of the capacitor) and the ground plane (as the
Trace Width (mm)
0.00
0.13
0.25
0.38
0.51
0.63
0.35
0.14
Half-ounce
0.30
0.12
0.25
0.10
0.20
0.08
0.15
0.06
One-ounce
0.10
0.04
0.05
0.02
0.00
0.00
0
5
10
15
20
25
Trace Width (mils)
Figure 7.2
Room temperature (25°C) DC resistance of half-ounce (0.65-mil-thick) and 1-ounce
(1.2-mil-thick) rectangular copper traces.
