On Thu, 04 Aug 2011 18:21:58 -0500, "
wrote:

On Thu, 04 Aug 2011 07:16:49 -0700, John Larkin
wrote:

On Wed, 03 Aug 2011 23:38:45 -0500, "
wrote:

On Wed, 03 Aug 2011 20:56:57 -0700, John Larkin
wrote:

On Wed, 03 Aug 2011 22:35:35 -0500, "
wrote:

On Wed, 03 Aug 2011 19:25:05 -0700, John Larkin
wrote:

On Wed, 03 Aug 2011 19:22:36 -0500, "
wrote:

On Wed, 03 Aug 2011 17:06:22 -0700, John Larkin
wrote:

On Wed, 03 Aug 2011 18:56:30 -0500, "
wrote:

On Wed, 03 Aug 2011 16:46:11 -0700, John Larkin
om wrote:

On Wed, 03 Aug 2011 15:07:32 -0400, Archon
wrote:

On 8/3/2011 11:39 AM, Lanny wrote:

but this resistence have a polarity?
---
No.

--
JF

They have a particular name these little resistance?

Regards


They do when I drop one and can't find it
JC


They work better at high frequencies if you install them upside down.
Less inductance.

Less inductance or higher capacitance (resistive element closer to the plane)?

What I see in a TDR setup is less series inductance. The context is a
coplanar waveguide PCB trace with a gap that's bridged by the
resistor.

ftp://jjlarkin.lmi.net/0805_res_fix.JPG

The impedance bump at cm 3.5 is inductive...

ftp://jjlarkin.lmi.net/0805_normal.JPG

and if you flip it over, it's a lot smaller

ftp://jjlarkin.lmi.net/0805_flipped.JPG

But that's telling you that the sqrt(L/C) is closer to the transmission line
Z0, no? C will certainly be higher with the resistor closer to the plane.


I'd have to think about that. The normal way, you'd have the substrate
(alumina, Er around 10) down, and then the PCB, Er more like 4.6
maybe, and air on top. Inverted, the resistance element sees the PCB
looking down, and alumina+air looking up. Too complex for my tiny
brain, especially after the day I've had.

But the alumina is the same in both orientations. Down adds the PCB plane
capacitance.

But the TDR sure looks inductive in both cases. Effective bandwidth is
around 12 GHz. 1-cent 0805 resistors are pretty good way up into the
GHz.

Less inductive or more capacitive (canceling a constant inductance) = higher
impedance?

I'm an engineer, not a philosopher. What I see here is inductance. I
assume that the issue is loop area, and less area is less L.

The mechanics matter. Understanding the physics matters.

"One measurement is worth a thousand expert opinions."

Measurements, alone, don't lead to understanding.

But reality exists. The resistors behave the way I measured them. No
amount of theorizing is going to make them behave any different.

It wouldn't take a lot of math to reconcile the dimensions with the
amounts of capacitance and inductance to explain the things I've
measured. That's interesting, but as an engineer I now know that
mounting the resistors upside-down makes them more ohmic at high
frequencies, and that's useful. People's theorizing about resistors
here wasn't especially useful, in the sense of being predictive to
behavior.

Strictly speaking, I don't need to understand it. I use lots of things
I don't understand.

John