# TUTORIAL - Example 1, Using Femm to Calculate Component Values of Simple Microstrip to use in LTspice/PSpice

Started by May 5, 2015
```I offer to share with you a TUTORIAL but don't know how to get it into

The TUTORIAL is about 15kB, zipped, and describes the step-by-step process
of using FREE femm 4.2 to analyze a simple PCB structure to calculate
values to then use in circuit simulation, LTspice/PSpice. The sequence can
be modified for use in analyzing really complex structures, structures
where there are NO formulas. [I know there are many formulas and online
calculators for 'normal' structures that can provide similar values, BUT
they deprive you of gaining any understanding.]

The simple structure in this example is a 50 ohm microstrip implemented
using 1 oz copper on a four layer 1 inch wide 5 inch long FR4 PCB
operating at 10MHz. The trace is 16 mils wide, copper 1.4 mils thick, and
dielectric separations of 9 mils each with the overall PCB thickness
approx 32 mils. The stack up is:
Layer 1  Trace
Layer 2  GND
Layer 3  Vcc
Layer 4  Trace

An exmaple, of gaining insight:

If the microstrip uses only the top two layers, evrything is 'normal' and
as expected. Current flows into the SIGANL trace and is RETURNed through
the GND plane. Of course no one would do that, you would always keep the
next layer, Vcc, and use it as a pseudo-ground plane.

BUT! Now something very interesting happens. The RETURN current splits
between GND plane and Vcc plane, where the current in GND plane is in the
correct direction, but slightly MORE than what you put intn SIGNAL! and
there is a slight bit of that 'extra' current flowing in the Vcc plane,
BUT IN THE SAME DIRECTION AS THE SIGNAL??!!

No book formula I've ever found will show you this, so there is
'education' in getting down into details.

As I said, this is a step-by-step tutorial, with descriptions,
explanations, and dedicated femm drawings for each step culminating in
LTspice schematics of the final model. Hopefully, educational/useful for
someone out there.

Regards,
Robert
```
```This sounds very interesting and I guess a lot of good karma is headed your way for collaborating in this way

How do I get the 15kB file?

Thanks

Klaus
```
```How about putting it on Dropbox or someplace like that?

ABSE would work for many of us as well.

Cheers

Phil Hobbs
```
```On a sunny day (Tue, 05 May 2015 03:36:33 -0700) it happened RobertMacy
<robert.a.macy@gmail.com> wrote in <op.xx5rq8hc2cx0wh@ajm>:

>An exmaple, of gaining insight:

Ms. Maple?

```
```On Tuesday, May 5, 2015 at 6:33:18 AM UTC-4, Robert Macy wrote:
> I offer to share with you a TUTORIAL but don't know how to get it into
>
> The TUTORIAL is about 15kB, zipped, and describes the step-by-step process
> of using FREE femm 4.2 to analyze a simple PCB structure to calculate
> values to then use in circuit simulation, LTspice/PSpice. The sequence can
> be modified for use in analyzing really complex structures, structures
> where there are NO formulas. [I know there are many formulas and online
> calculators for 'normal' structures that can provide similar values, BUT
> they deprive you of gaining any understanding.]
>
> The simple structure in this example is a 50 ohm microstrip implemented
> using 1 oz copper on a four layer 1 inch wide 5 inch long FR4 PCB
> operating at 10MHz. The trace is 16 mils wide, copper 1.4 mils thick, and
> dielectric separations of 9 mils each with the overall PCB thickness
> approx 32 mils. The stack up is:
> Layer 1  Trace
> Layer 2  GND
> Layer 3  Vcc
> Layer 4  Trace
>
> An exmaple, of gaining insight:
>
> If the microstrip uses only the top two layers, evrything is 'normal' and
> as expected. Current flows into the SIGANL trace and is RETURNed through
> the GND plane. Of course no one would do that, you would always keep the
> next layer, Vcc, and use it as a pseudo-ground plane.
>
> BUT! Now something very interesting happens. The RETURN current splits
> between GND plane and Vcc plane, where the current in GND plane is in the
> correct direction, but slightly MORE than what you put intn SIGNAL! and
> there is a slight bit of that 'extra' current flowing in the Vcc plane,
> BUT IN THE SAME DIRECTION AS THE SIGNAL??!!
>
> No book formula I've ever found will show you this, so there is
> 'education' in getting down into details.
>
> As I said, this is a step-by-step tutorial, with descriptions,
> explanations, and dedicated femm drawings for each step culminating in
> LTspice schematics of the final model. Hopefully, educational/useful for
> someone out there.
>
> Regards,
> Robert

Dropbox?  Or send me an email attachment and I'll stick it up in my dropbox.

@teachspin or ggherold at sign gmail

George H.
```
```On Tue, 05 May 2015 04:26:26 -0700, Klaus Kragelund
<klauskvik@hotmail.com> wrote:

> This sounds very interesting and I guess a lot of good karma is headed
> your way for collaborating in this way
>
> How do I get the 15kB file?
>
> Thanks
>
> Klaus

Hi, Klaus,

```
```On Tue, 05 May 2015 05:17:57 -0700, Phil Hobbs <pcdhobbs@gmail.com> wrote:

> How about putting it on Dropbox or someplace like that?
>
> ABSE would work for many of us as well.
>
> Cheers
>
> Phil Hobbs

websites, Dropbox, etc. Dropbox and all those 'free' websites sell
something to somebody ...else, Their customers are NOT the users. Those
websites start 'poking' around inside our PC's, causing hangs, and worst
of all, total crashes that require Power OFF reboots! And the times I sit
and wait and wait and they didn't crash us, they didn't even give me
access to what somebody dropped there. So, NO I now NEVER you those 'free'
websites.

```
```On Tue, 05 May 2015 08:05:52 -0700, RobertMacy
<robert.a.macy@gmail.com> wrote:

>On Tue, 05 May 2015 05:17:57 -0700, Phil Hobbs <pcdhobbs@gmail.com> wrote:
>
>> How about putting it on Dropbox or someplace like that?
>>
>> ABSE would work for many of us as well.
>>
>> Cheers
>>
>> Phil Hobbs
>
>websites, Dropbox, etc. Dropbox and all those 'free' websites sell
>something to somebody ...else, Their customers are NOT the users. Those
>websites start 'poking' around inside our PC's, causing hangs, and worst
>of all, total crashes that require Power OFF reboots! And the times I sit
>and wait and wait and they didn't crash us, they didn't even give me
>access to what somebody dropped there. So, NO I now NEVER you those 'free'
>websites.

Send it to me and I'll put it on the S.E.D/Schematics Page of my
website.  No scripts, no nutting, just look/see ;-)

...Jim Thompson
--
| James E.Thompson                                 |    mens     |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

I love to cook with wine.     Sometimes I even put it in the food.
```
```On Tue, 05 May 2015 06:43:45 -0700, George Herold <gherold@teachspin.com>
wrote:

>>> ...snip...
> Dropbox?  Or send me an email attachment and I'll stick it up in my
> dropbox.
>
> @teachspin or ggherold at sign gmail
>
> George H.

Just sent to your 'teachspin' address: you did NOT set me up to accept any
.zip files, but at least YOUR server has the courtesy to tell someone it
threw away the email.

got this error:
Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server
for the recipient domain teachspin.com by mx0.managemyspam.com.
[72.88.83.109].

The error that the other server returned was:
552 Filename not allowed: 'TUTORIAL_StepByStep.zip' (#5.7.1)

Will try again to ggherold at sign gmail dot sign com
```
```On Tue, 05 May 2015 08:11:19 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@on-my-web-site.com> wrote:

>> ...snip...
>
> Send it to me and I'll put it on the S.E.D/Schematics Page of my
> website.  No scripts, no nutting, just look/see ;-)
>
>                                         ...Jim Thompson

Will do, it's small at only 15kB
```