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TUTORIAL - Example 1, Using Femm to Calculate Component Values of Simple Microstrip to use in LTspice/PSpice
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RobertMacy
May 5, 2015, 6:33:17 AM5/5/15
to
I offer to share with you a TUTORIAL but don't know how to get it into
your hands.
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
your hands.
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
Jan Panteltje
May 5, 2015, 9:22:37 AM5/5/15
to
On a sunny day (Tue, 05 May 2015 03:36:33 -0700) it happened RobertMacy
<robert...@gmail.com> wrote in <op.xx5rq8hc2cx0wh@ajm>:
>An exmaple, of gaining insight:
Ms. Maple?
<robert...@gmail.com> wrote in <op.xx5rq8hc2cx0wh@ajm>:
>An exmaple, of gaining insight:
RobertMacy
May 5, 2015, 11:39:40 AM5/5/15
to
On Tue, 05 May 2015 03:36:33 -0700, RobertMacy <robert...@gmail.com>
wrote:
>> ...snip....
ARRRGGGG!!!!
I sent the WRONG file to any of you!
should have been the
TUTORIAL_Example01.zip
Throw away the TUTORIAL_StepByStep.zip !!!
I'll go back and do again!
...sigh
Regards to all,
Robert
wrote:
>> ...snip....
ARRRGGGG!!!!
I sent the WRONG file to any of you!
should have been the
TUTORIAL_Example01.zip
Throw away the TUTORIAL_StepByStep.zip !!!
I'll go back and do again!
...sigh
Regards to all,
Robert
Jim Thompson
May 5, 2015, 7:23:36 PM5/5/15
to
...Jim Thompson
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