Radio Frequency Integrated Circuit Design - Webs

132 Radio Frequency Integrated Circuit Design
lators need dimensions specified in mils (thousandths of an inch), where a mil
is equal to 25.4 �m. A typical substrate thickness for a double-sided printed
circuit board is 40 to 64 mils. Multilayered boards can have effective layers
that are 10 mils or even less. Surface material is often copper with a thickness
typically specified by weight; for example, half-ounce copper translates to 0.7
mil. In simulators, the conductivity � is typically specified relative to the conductivity
of gold. Thus, using Table 5.2, � Au = 1.42 � Cu, or� Cu = 0.70 � Au.
Table 5.4 shows parameters for a variety of materials, including on-chip material
(SiO2, Si, GaAs) printed circuit board material (FR4, 5880, 6010), and some
traditional substrate material for microwave, for example, ceramic.
Example 5.9 Calculation of Transmission Lines
Using a simulator, determine line impedance at 1.9 GHz versus dielectric
thickness for microstrip lines, coupled microstrip lines, and coplanar waveguide
with a ground plane. Use FR4 material with a dielectric constant of 4.3, and
0.7-mil copper with a line width of 20 mils and a 20-mil gap or space between
the lines.
Solution
Calculations were done and the results are shown in Figure 5.34. It can be seen
that 50� is realized with a dielectric thickness of about 11 mils for the microstrip
line and the coplanar waveguide and about 14 mils for the coupled microstrip
lines. Thus, the height is just over half of the line width. It can also be seen
that a microstrip line and a coplanar waveguide with ground have very similar
behavior until the dielectric height is comparable to the gap dimension.
Example 5.10 Transmission Lines
Using a simulator, determine line impedance at 1.9 GHz versus line width,
gap, and space for microstrip lines, coupled microstrip lines, and coplanar
waveguide with a ground plane. Use material with a dielectric constant of 2.2
and height of 15 mils, and 0.7-mil copper.
Table 5.4
Properties of Various Materials
Material Loss Tangent Permittivity Material Loss Tangent Permittivity
SiO 2 0.004–0.04 3.9 Al 2O 3 (ceramic) 0.0001 9.8
Si 0.015 11.9 Sapphire 0.0001 9.4; 1.6
GaAs 0.002 12.9 Quartz 0.0001 3.78
FR4 0.022 4.3 6010 0.002 10.2
5880 0.001 2.20