J
Joel Kolstad
- Jan 1, 1970
- 0
I have a design on an FR-4 PCB that has a few long traces on it, about 12"
each. When I examine those trace's responses on a network analyzer, they
have significant (>15dB) dips at 30MHz, then 90MHz, 150MHz, etc... this led
me to suspect that the traces were behaving like quarter wave transformers
(the traces have various components connected to them, but they're all
supposed to be pretty high impedances), but if I assume an effective
dielectric constant of ~2.35, I compute lambda/4 as ~60 inches. Indeed, the
trace lengths were originally set such that I would (hopefully) be able to
assume the system was behaving as a lumped network up to at least 30MHz!
Anyone have suggestions on what else might cause periodic resonances such as
the ones described?
Thanks,
---Joel Kolstad
each. When I examine those trace's responses on a network analyzer, they
have significant (>15dB) dips at 30MHz, then 90MHz, 150MHz, etc... this led
me to suspect that the traces were behaving like quarter wave transformers
(the traces have various components connected to them, but they're all
supposed to be pretty high impedances), but if I assume an effective
dielectric constant of ~2.35, I compute lambda/4 as ~60 inches. Indeed, the
trace lengths were originally set such that I would (hopefully) be able to
assume the system was behaving as a lumped network up to at least 30MHz!
Anyone have suggestions on what else might cause periodic resonances such as
the ones described?
Thanks,
---Joel Kolstad