End-to-End Capacitance of SMD Resistors

Are you sure the meter can distinguish the capacitive impedance from the resistive impedance?

A Q-Tip has a plastic pin and its dielectric constant isn't favorable. Got zinged by that once. I prefer bone-dry toothpicks. Just don't use them for picking teeth afterwards if you touched leaded parts too much.

Got to check out that Aade meter. Missed the tax curfew, dang. So far I am using a HP4191 but that thing is so freaking bulky and heavy. It does measure to 1GHz though.

This is where an almost forgotten tool comes in handy: The dipmeter. Hang a well known inductor in parallel and dip the resonance. Then whip out the old HP calculator or slide rule ...

I used an "industrial" single-ended wooden q-tip, and pushed the resistor with the sharp corner edge of the non-cotton end. If one end makes contact, I get about 0.15 pF; push harder to make both ends contact and it jumps to about 0.32.

I suppose I could TDR a resistor, too.

The AADE thing is great, especially at the price. But only for small-valued Ls and Cs.

John

Unlikely, knowing how the AADE thing works. But I'll try some higher values to make sure.

John

Spent a few weeks trying to do that for a class. We had brand-new VNAs to use, but I got the impression that no one had experience with board- level RF work. In the end we couldn't reliably model the parasitics in simulation and, for lack of time and effort, resorted to tweaking.

I'd be interested in what the folks here think about the lab procedure, which is at the end of the filter lab document:

Thanks, Mike

Wait, you earlier wrote 0.32pF (see above), now you say 0.15pF, could you please spell this out for us?

The AADE meter is a toy compared to an HP 4191. :-) While a useful tool -- I've had one for a handful of years now -- a somewhat more sophisticated (if still not close to a 4191) is this:

One downside of the M^3 meter there is that it only has a DC power input jack whewreas the AADE is battery-powered. With some creative shoehorning one might be able to get a bunch of "AA"s into it, though. Both the M^3 and AADE meters are almost entirely through-hole components -- they could both be about

---Joel

I couldn't say for sure, without a full e-m simulation, but it appears that some capacitors may demonstrate more capacitance when the measuring instrument connects to both ends.

John

Some of the HP (Agilent) network analyzers have surface mount component test fixtures and software to create LCR models. It wouldn't be the first time that someone asked Agilent to loan a unit for evaluation, ran their tests, then said they weren't interested in the box.

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.

Anyhow, I applaud you guys for providing such hands-on training for future engineers. Seems not many universities are doing such a good job of it these days.

Yeah, but the 4191 is so freaking heavy. Last time I had to repair it (it's out of support, of course ...) I paid for that with a fair amount of back pain. Before that repair I had split four cords of wood - no back pain then.

The M^3 looks nice but with 15.625kHz being the highest frequency it doesn't seem to offer much of an advantage. For intermediate frequency work this seems to be a good deal:

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

Big SEG ;-)

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

Isn't that like "disembodied" ?:-)

...Jim Thompson

Nope. De-embedded is what happens if the girlfriend don't like you no more. Disembodied is what happens when the extended family finds out.

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.

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

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

robert

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!