End-to-End Capacitance of SMD Resistors

[John Larkin]

I like the term "de-embedded"

I have seen mixed results with port extensions and other compensation
mechanisms of analyzers. At least I'd use the good stuff such as rigid
coax. But in order to estimate the stray capacitance of a package I
always use resonance with a known inductor. Mostly a known LC circuit to
which the DUT gets paralleled, watching the change in resonance. That
takes a whole lot of compensation tricks out of the equation. In my
younger days I even had a "broom stick oscillator", a circuit that would
oscillate upon finding an ever so light resonance. But after a move
across an ocean it and the schematic was gone, probably tossed with
mountains of packaging paper.

I know this suggestion sounds pre-historic: Teach your students how to
use of a dip meter. No idea where to buy them these days but they are
cheap and can be built. Really practical for finding resonances,
especially in circuits that others have designed but not documented too
well.

We have a 3 GHz spectrum analyzer with tracking generator. I'm
thinking that some sort of diplexer and a loop, or maybe just a pair
of (orthogonal?) loops, would make a sort of mega-dipper.

John

 

[Robert Latest]

One more non-trivial issue, how to test these beasts.
If a signal-generator test is desired, one shouldn't
depend on simply using a high-value resistor to create
the TIA's test current, because that resistor also has
self capacitance, which could make the amplifier look
better than it really is, etc. Instead, you can make
a corrected resistor this way,

R1 Rs, high-value
---/\/\---+---/\/\/-----
_|_
--- C <-- I like to use adjustable capacitors
|
gnd

Or you can use a Keithley model 6221. Accurate AC and DC current source. I
wonder how it works though. Any idea?

robert

 

[Joel Koltner]

I know this suggestion sounds pre-historic: Teach your students how to use
of a dip meter. No idea where to buy them these days but they are cheap and
can be built.

MFJ still makes them... both a standalone unit (MFJ-201) and as a set of coils
(MFJ-66) for the well-known MFJ-259B impedance meter... although there seem to
be mixed reports on how well that setup works, as the '259B was never intended
initially to work as a DIP meter!

 

[Joel Koltner]

http://radio.tentec.com/Amateur/vna

Goes to about 100MHz and can also do one-port measurements. Not bad at all
for $655. But no audio and such.

Last time I looked at one of those in person (about 9 months ago) the software
was still a bit flaky and S11 measurements weren't as good as the AIM 4170
(http://www.arraysolutions.com/Products/AIM4170.htm -- 100kHz -170MHz, and
only does one port measurements... somewhere there's a report where a guy
rounded up all the cheap impedance network analyzers he could and compared
them), but still... for $665 it's a phoenomenal deal.

 

[Joerg]

I love my AADE, but IMHO one each 4191A, 4192A, 4193A, 4194A,
and 4195A is a necessity. With HP's test fixtures, plus ones
that we can fabricate ourselves, the world can be our oyster.


Yes, they're heavy, but so is your upper body (or at least
mine is). Handling an axe or sledgehammer and little pieces
of wood is nothing. Lifting the hp4191's 53 pounds should be
a snap, if you expect to properly handle your own upper-body
weight in various awkward situations. When I realized I was
beginning to have some trouble, I started spending serious
time at the gym with the weights and machines. Recommended.
I can lift my 4191A on and off the table and to the floor and
carry it around, no problem. Did it yesterday. Go for it.

Well, the 4191 is rarely used here so it's in the far back of a corner
table.

Those "little pieces of wood" were actually 2-3 foot rounds of pine. And
then the four cords where gone before the winter was gone :-(

 

[Joerg]

We have a 3 GHz spectrum analyzer with tracking generator. I'm
thinking that some sort of diplexer and a loop, or maybe just a pair
of (orthogonal?) loops, would make a sort of mega-dipper.

In a pinch a resistive-T will do. Set to 1dB/div the analyzer will show
an ever so slight dip. Of course mine still has a real CRT, none of
those pixely LCDs. Which unfortunately also means that it's really heavy.

BTW, does anyone know where to get a decently priced CRT for a HP3585A?
A client of mine had one go dim on them. Probably the cathode has become
tired.

 

[Joerg]

MFJ still makes them... both a standalone unit (MFJ-201) and as a set of coils
(MFJ-66) for the well-known MFJ-259B impedance meter... although there seem to
be mixed reports on how well that setup works, as the '259B was never intended
initially to work as a DIP meter!

A real dip meter has to be a loosely coupled oscillator. Anything else
makes it a tough job. An analyzer works, too, but it should ideally have
an old-fashioned CRT for very slight dips.

 

[john jardine]

Last time I looked at one of those in person (about 9 months ago) the software
was still a bit flaky and S11 measurements weren't as good as the AIM 4170
(http://www.arraysolutions.com/Products/AIM4170.htm -- 100kHz -170MHz, and
only does one port measurements... somewhere there's a report where a guy
rounded up all the cheap impedance network analyzers he could and compared
them), but still... for $665 it's a phoenomenal deal.

There's a clever, low cost design here and some comparisons ...
http://homepages.ipact.nl/~pa1are/Antenna_Analyzer.html

 

[Joel Koltner]

There's a clever, low cost design here and some comparisons ...
http://homepages.ipact.nl/~pa1are/Antenna_Analyzer.html

Nice. That design is largely the same approach as the AIM4170 takes, with
extra emphasis on reducing the cost (keeping the frequency span to just HF
helps there), it would seem. I like the standalone operation aspect of it.

 

[Joerg]

Nice. That design is largely the same approach as the AIM4170 takes, with
extra emphasis on reducing the cost (keeping the frequency span to just HF
helps there), it would seem. I like the standalone operation aspect of it.

I don't understand why there still is nobody who makes a spectrum
analyzer in that cost range. Something simple that goes to 1GHz for
pre-compliance, fits in a briefcase and talks over USB. But not those
drifty TV-tuner thingies. If I just had the time ...