"Chapter 1 - The Op Amp's Place in the World" - HTL Wien 10

The Frequency Characteristics of Passive Components
between them (Figure 17–13). The formulas for these parasitic effects can be found in
transmission line and/or microstrip references, but are too complex for inclusion here.
Figure 17–13. Coupling Between Parallel Signal Traces
17.4.4.4 Inductive Vias
Signal lines should not be routed parallel to each other, unless transmission line or microstrip
effects are desired. Otherwise, a gap of at least three times the signal trace width
should be maintained.
Capacitance between traces in an analog design can become a problem if fixed resistors
in the design are large (several MΩ). Capacitance between the inverting and noninverting
inputs of an op amp could easily cause oscillation.
Whenever routing constraints force a via (connection between layers of a PCB, FIgure
17–14), a parasitic inductor is also formed. At a given diameter (d) the approximate inductance
(L) of an via at a height of (h) may be calculated as follows:
L h
5
h (mm)
TRACE
1 ln 4h
d
d (mm)
Figure 17–14. Via Inductance Measurements
nH
TOP LAYER
BOTTOM LAYER
TRACE
Circuit Board Layout Techniques
(17–5)
17-19