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Picotest Injector Teardowns
Wolfgang:
Hi Jay,
in fact I made some bias tees for the very low end (10kHz - 200MHz).
The purpose was to support a transistor device parameter extraction with a VNA, and the bias tees were used to
set the operating point. These bias tees are tricky because of the very broad range.
If you want I send you a schematics.
Higher frequency stuff is easy. Mini-Circuits has parts going up to many GHz.
regards
Wolfgang
Jay_Diddy_B:
Wolfgang,
I don't think that this is a well designed bias tee for high frequencies.
There will be a 'bump' where are all the capacitors are connected in parallel.
I would do a different design with Coplanar Waveguide for high frequencies.
Please share your schematic (you can PM me if you like).
Jay_Diddy_B
Sighound36:
Hindsight being a great thing!
Realistically Wolfgang what do you feel is a lower limited that would be useful in with this particularly application?
Or would designing a seperate bias tee as an add on would be more beneifcal?
Thanks
Sighound
free_electron:
why dont you combine several of these into 1 unit ? or make a 'breakable' circuit board.
Wolfgang:
@ to all
The art of bias tees is complex because all elements (series Cs, Ls, ...) have parasitics
and what you dont want is a high-Q resonance *anywhere* in your passband.
So the trick is to start with the high frequency end, accept some losses to keep resonances low,
and add section per section with larger Ls and Cs until your low frequency corner is acceptable.
The more sections, the lower the frequency, the larger the inductors get and this increases DC
resistance, something you also dont like.
If the lower limit is in the 100s of Hz, you would combine passive LCRs with active bias Tees (Op amp voltage
regulators where the regulator has a cutoff where you need it.
I will put some info on my website the next few days (schematics, photos, VNA measurements, ...).
regards
Wolfgang
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