Copyright: 1996 - 2024
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
while tying up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
All trademarks, copyrights, patents, and other rights of ownership to images
and text used on the RF Cafe website are hereby acknowledged.
My Hobby Website:
microstrip BP filter from an elliptic prototype - RF Cafe Forums
RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media
platforms dominating public commenting venues. RF Cafe Forums began sometime around
August of 2003 and was quite well-attended for many years. By 2010, Facebook and
Twitter were overwhelmingly dominating online personal interaction, and RF Cafe
Forums activity dropped off precipitously. If the folks at
phpBB would release a version with integrated
sign-in from the major social media platforms, I would resurrect the RF Cafe Forums,
but until then it is probably not worth the effort. Regardless, there are still
lots of great posts in the archive that ware worth looking at.
Below are the old forum threads, including responses to the original posts.
|-- Amateur Radio
Gripes & Humor
-- CAE, CAD, &
Test & Measurement
Post subject: Matching networks for differential design Posted:
Tue Dec 27, 2005 9:12 pm
i need to design an amplifier that has
differential input and output and match it for 50 ohms. however, since
i've differential input/output how do i match for 50 ohms...some one
told me you match it for 100 ohms but that didn't make sense
also, what's the best way to test for matching in the case of differential,
meaning how should the match be tested??
Post subject: Differential ImpedancePosted: Thu Dec 29, 2005 8:29
In the amplifier you're talking about, there will be 3 input
impedances: Input 1 to ground, input 2 to ground, and input 1 to input
2. You can't assume Zdiff = Zin1 + Zin2 at all. Consider a 1:1 transformer
terminated in 50 Ohms - you could ground either input and not affect
the impedance between the two inputs at all. Or you could place, say,
a 1k resistor from one input to ground, and a second 1k resistor from
the other input to ground. Zin1 = 500 Ohms, Zin2 = 500 Ohms, Zdiff =
48.78 Ohms (50 || 2k).
The easiest way to measure differential
input impedance is with a transformer of known behavior. The best way
is with a differential vector network analyzer - and that's $$$$.