Still waiting for a Ltspice expert answer.

Jamie
Guest

Wed Jan 18, 2012 4:32 am

Does the wires assume real life situations to some
degree or do we need to add stray inductance, Resistors
and caps to act like a board?

I would of thought it would assume an average lay out of one
persons worse nightmare and the actual real live circuit would
just work better, seeing that this designer would engineer proper
protocols on the board.

It just seems that I don't see many of the small defects the
sim may show, when it is on a real board assembled using common
practices.

Which leads me to my question, does the sim assume a worse case
scenario or maybe the sim just over exaggerates now and then?

This would be LTspice I am referring to. I was thinking of looking at
Pspice to see how that goes.

Jamie

Jim Thompson
Guest

Wed Jan 18, 2012 4:32 am

On Tue, 17 Jan 2012 22:32:53 -0500, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa__at_charter.net> wrote:

Quote:

Does the wires assume real life situations to some
degree or do we need to add stray inductance, Resistors
and caps to act like a board?

I would of thought it would assume an average lay out of one
persons worse nightmare and the actual real live circuit would
just work better, seeing that this designer would engineer proper
protocols on the board.

It just seems that I don't see many of the small defects the
sim may show, when it is on a real board assembled using common
practices.

Which leads me to my question, does the sim assume a worse case
scenario or maybe the sim just over exaggerates now and then?

This would be LTspice I am referring to. I was thinking of looking at
Pspice to see how that goes.

Jamie

Tim Williams
Guest

Wed Jan 18, 2012 4:41 am

I've heard of a few simulators which assumed the designer indicated wire
resistance proportional to the length of the traces on the schematic
drawing. Which often have no relation to actual board traces, and
certainly have no relation to their widths.

As far as I know, most professional environments (SPICE based) assume all
nets are ideal. If the models themselves include parasitics, they will
necessarily be limited to package parasitics. It's always the user's
responsibility to include realistic wiring parasitics.

I don't remember if LTSpice includes package parasitics. I seem to recall
they mostly use MODELs rather than SUBCKTs, but they may've expanded the
MODEL definition to include simple series or parallel elements.

In short, no, SPICE tends to assume ideal conditions. It's a model, not a
reality simulator, and it's your duty to construct a model that has any
useful representation at all.

If you insist on reality simulation, there are suites out there which
attempt to do such things. Ansoft makes such a system, including
electromagnetic (which can do static, AC and transient 3D simulations on
real board layouts, and generate approximate SPICE models for the
circuit), mechanical (stress/strain) and thermal (including fluid flow,
expansion, tempcos to feed back into the circuit). A few others make
similar suites; all are horrifically expensive, only something worthwhile
if you're either making millions of top-quality, moderately complex
products (cars maybe??), or a few very, VERY critical systems (avionics,
aircraft, spacecraft?).

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa__at_charter.net> wrote in
message news:i%qRq.2757$FH7.1429_at_newsfe09.iad...

Quote:

Does the wires assume real life situations to some
degree or do we need to add stray inductance, Resistors
and caps to act like a board?

I would of thought it would assume an average lay out of one
persons worse nightmare and the actual real live circuit would
just work better, seeing that this designer would engineer proper
protocols on the board.

It just seems that I don't see many of the small defects the
sim may show, when it is on a real board assembled using common
practices.

Which leads me to my question, does the sim assume a worse case
scenario or maybe the sim just over exaggerates now and then?

This would be LTspice I am referring to. I was thinking of looking at
Pspice to see how that goes.

Jamie

Jamie
Guest

Wed Jan 18, 2012 5:43 am

Jim Thompson wrote:

Quote:

On Tue, 17 Jan 2012 22:32:53 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa__at_charter.net> wrote:

Does the wires assume real life situations to some
degree or do we need to add stray inductance, Resistors
and caps to act like a board?

I would of thought it would assume an average lay out of one
persons worse nightmare and the actual real live circuit would
just work better, seeing that this designer would engineer proper
protocols on the board.

It just seems that I don't see many of the small defects the
sim may show, when it is on a real board assembled using common
practices.

Which leads me to my question, does the sim assume a worse case
scenario or maybe the sim just over exaggerates now and then?

This would be LTspice I am referring to. I was thinking of looking at
Pspice to see how that goes.

Jamie

Do the math... by hand... then use the sim to VERIFY!

...Jim Thompson
Well that just sounds counter productive.

Why waste my time using a sim if I am going to do it by hand in the
first place?

You can haggle all you want Jim, It does not work on me..

I am not one of your goal post. You have JL for that :)

Jamie

Tim Wescott
Guest

Wed Jan 18, 2012 6:23 am

On Tue, 17 Jan 2012 22:32:53 -0500, Jamie wrote:

Quote:

Does the wires assume real life situations to some degree or do we need
to add stray inductance, Resistors and caps to act like a board?

I would of thought it would assume an average lay out of one
persons worse nightmare and the actual real live circuit would just work
better, seeing that this designer would engineer proper protocols on the
board.

It just seems that I don't see many of the small defects the
sim may show, when it is on a real board assembled using common
practices.

Which leads me to my question, does the sim assume a worse case
scenario or maybe the sim just over exaggerates now and then?

This would be LTspice I am referring to. I was thinking of looking at
Pspice to see how that goes.

Wires in LTSpice (and PSpice, as far as I know), are made of Magic
Stuff. A node is a node is a node (in Spice-land) and has no voltage
variations across it.

Jim's right, although I would state it differently: the simulation is
help for those who already know what's up; try something that the
simulation isn't prepared to give a correct answer for, and you'll get a
wrong answer.

It _is_ handy for complex, nonlinear circuits (like switchers), but you
still have to pose questions that it can answer sensibly.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

Robert Macy
Guest

Wed Jan 18, 2012 12:42 pm

On Jan 17, 8:32 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Quote:

Does the wires assume real life situations to some
degree or do we need to add stray inductance, Resistors
and caps to act like a board?

I would of thought it would assume an average lay out of one
persons worse nightmare and the actual real live circuit would
just work better, seeing that this designer would engineer proper
protocols on the board.

It just seems that I don't see many of the small defects the
sim may show, when it is on a real board assembled using common
practices.

Which leads me to my question, does the sim assume a worse case
scenario or maybe the sim just over exaggerates now and then?

This would be LTspice I am referring to. I was thinking of looking at
Pspice to see how that goes.

Jamie

Don't forget to add, "delay" All these simulators keep forgetting
about that pesky quirk of reality, "It takes time for a signal to go
from here to there." And, oh, yes, don't forget to add that even
peskier term, "radiation loss" That way when you simulate charging a
cap from another cap, you can reconcile the apparent loss of energy.

Jim Thompson
Guest

Wed Jan 18, 2012 4:06 pm

On Tue, 17 Jan 2012 23:43:42 -0500, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa__at_charter.net> wrote:

Quote:

Jim Thompson wrote:

On Tue, 17 Jan 2012 22:32:53 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa__at_charter.net> wrote:

Does the wires assume real life situations to some
degree or do we need to add stray inductance, Resistors
and caps to act like a board?

I would of thought it would assume an average lay out of one
persons worse nightmare and the actual real live circuit would
just work better, seeing that this designer would engineer proper
protocols on the board.

It just seems that I don't see many of the small defects the
sim may show, when it is on a real board assembled using common
practices.

Which leads me to my question, does the sim assume a worse case
scenario or maybe the sim just over exaggerates now and then?

This would be LTspice I am referring to. I was thinking of looking at
Pspice to see how that goes.

Jamie

Do the math... by hand... then use the sim to VERIFY!

...Jim Thompson
Well that just sounds counter productive.

Why waste my time using a sim if I am going to do it by hand in the
first place?

You can haggle all you want Jim, It does not work on me..

I am not one of your goal post. You have JL for that :)

Jamie

qrk
Guest

Wed Jan 18, 2012 7:57 pm

On Tue, 17 Jan 2012 23:43:42 -0500, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa__at_charter.net> wrote:

Quote:

Jim Thompson wrote:

On Tue, 17 Jan 2012 22:32:53 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa__at_charter.net> wrote:

Does the wires assume real life situations to some
degree or do we need to add stray inductance, Resistors
and caps to act like a board?

I would of thought it would assume an average lay out of one
persons worse nightmare and the actual real live circuit would
just work better, seeing that this designer would engineer proper
protocols on the board.

It just seems that I don't see many of the small defects the
sim may show, when it is on a real board assembled using common
practices.

Which leads me to my question, does the sim assume a worse case
scenario or maybe the sim just over exaggerates now and then?

This would be LTspice I am referring to. I was thinking of looking at
Pspice to see how that goes.

Jamie

Do the math... by hand... then use the sim to VERIFY!

...Jim Thompson
Well that just sounds counter productive.

Why waste my time using a sim if I am going to do it by hand in the
first place?

You can haggle all you want Jim, It does not work on me..

I am not one of your goal post. You have JL for that :)

Jamie

If you don't understand your circuit maths, how do you know if the

simulation is close to reality???? Many times, you can do this in your
head, but sometimes you need to write down a bunch of maths to
understand issues you may run in to. As an excercise, try to
temperature stabilize a simple one transistor amplifier without
understanding the basic transistor equations.

Do you blindly trust your models??? If you do, beware, they are often
wrong. With experience, you will learn a healthy distrust in your
simulator and test equipment.

Jim Thompson
Guest

Wed Jan 18, 2012 9:19 pm

On Wed, 18 Jan 2012 10:57:36 -0800, qrk <SpamTrap_at_spam.net> wrote:

Quote:

On Tue, 17 Jan 2012 23:43:42 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa__at_charter.net> wrote:

Jim Thompson wrote:

On Tue, 17 Jan 2012 22:32:53 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa__at_charter.net> wrote:

Does the wires assume real life situations to some
degree or do we need to add stray inductance, Resistors
and caps to act like a board?

I would of thought it would assume an average lay out of one
persons worse nightmare and the actual real live circuit would
just work better, seeing that this designer would engineer proper
protocols on the board.

It just seems that I don't see many of the small defects the
sim may show, when it is on a real board assembled using common
practices.

Which leads me to my question, does the sim assume a worse case
scenario or maybe the sim just over exaggerates now and then?

This would be LTspice I am referring to. I was thinking of looking at
Pspice to see how that goes.

Jamie

Do the math... by hand... then use the sim to VERIFY!

...Jim Thompson
Well that just sounds counter productive.

Why waste my time using a sim if I am going to do it by hand in the
first place?

You can haggle all you want Jim, It does not work on me..

I am not one of your goal post. You have JL for that :)

Jamie

If you don't understand your circuit maths, how do you know if the
simulation is close to reality???? Many times, you can do this in your
head, but sometimes you need to write down a bunch of maths to
understand issues you may run in to. As an excercise, try to
temperature stabilize a simple one transistor amplifier without
understanding the basic transistor equations.

Do you blindly trust your models??? If you do, beware, they are often
wrong. With experience, you will learn a healthy distrust in your
simulator and test equipment.

I don't think Jamie is even a technician, but he _is_ successfully
becoming a reductive emulation of John Larkin Wink

Simon S Aysdie
Guest

Thu Jan 19, 2012 12:55 am

On Jan 17, 7:32 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Quote:

Does the wires assume real life situations to some
degree or do we need to add stray inductance, Resistors
and caps to act like a board?

No.

Quote:

I would of thought it would assume an average lay out of one
persons worse nightmare...

One persons' nightmare is not "average." WTH?

No, what you suggest -- "average" is whackadoodle. There is no
"average" layout.

Quote:

It just seems that I don't see many of the small defects the
sim may show, when it is on a real board assembled using common
practices.

There may be standards and usual practice for a variety of tasks --
the more simple the more likely it can be handled by standards.
"Simple" is limited. The harder the job, the more diverse opinion
you'll get regarding what is a proper approach.

Quote:

Which leads me to my question, does the sim assume a worse case
scenario or maybe the sim just over exaggerates now and then?

"Worst case" and "one persons' nightmare" doesn't mean "average" or
"common." If your wrong views were more coherent, then they would be
easier to pick apart!

You have 1 pF of pad capacitance, and you think it may matter? then
put it in
You care about 0.7 nH of via inductance? then put it in
You care about the inductance of a long trace? then put it in

The models are just *models* -- not the real thing. How good are
they? After all, that is all spice has to work with. Models are
never perfect -- what should spice assume as "average" about them?
Caveat emptor: you need to have some idea of what you're doing in the
first place.

I think your question is really: Can I get SPICE to think for me? No,
you can't.

Jamie
Guest

Thu Jan 19, 2012 1:30 am

Simon S Aysdie wrote:

Quote:

On Jan 17, 7:32 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Does the wires assume real life situations to some
degree or do we need to add stray inductance, Resistors
and caps to act like a board?

No.

I would of thought it would assume an average lay out of one
persons worse nightmare...

One persons' nightmare is not "average." WTH?

No, what you suggest -- "average" is whackadoodle. There is no
"average" layout.

It just seems that I don't see many of the small defects the
sim may show, when it is on a real board assembled using common
practices.

There may be standards and usual practice for a variety of tasks --
the more simple the more likely it can be handled by standards.
"Simple" is limited. The harder the job, the more diverse opinion
you'll get regarding what is a proper approach.

Which leads me to my question, does the sim assume a worse case
scenario or maybe the sim just over exaggerates now and then?

"Worst case" and "one persons' nightmare" doesn't mean "average" or
"common." If your wrong views were more coherent, then they would be
easier to pick apart!

You have 1 pF of pad capacitance, and you think it may matter? then
put it in
You care about 0.7 nH of via inductance? then put it in
You care about the inductance of a long trace? then put it in

The models are just *models* -- not the real thing. How good are
they? After all, that is all spice has to work with. Models are
never perfect -- what should spice assume as "average" about them?
Caveat emptor: you need to have some idea of what you're doing in the
first place.

I think your question is really: Can I get SPICE to think for me? No,
you can't.

Well no problem, I'll just continue with how I've been doing it all
these years. Calculator,years of foot notes, engin books, equipment use,
CAD steps and then boards.

I guess spice is good for concept circuit experimenting. Saves on
paper.

I am experimenting with a little tool app I am writing that monitors
the clipboard of a BMP image arriving into it. This tool has FTP code
where I can then hit the default button and send it some where with some
local index to manage them. So far it looks ok. I was thinking to use it
as an uplink tool to send schematics to your web site for the general
public audience instead of dumping spice in the chat areas.

Was thinking of supporting the WMF format too, it would save on
network traffic.

Jamie

Jamie
Guest

Thu Jan 19, 2012 1:48 am

Jim Thompson wrote:

Quote:

On Wed, 18 Jan 2012 10:57:36 -0800, qrk <SpamTrap_at_spam.net> wrote:

On Tue, 17 Jan 2012 23:43:42 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa__at_charter.net> wrote:

Jim Thompson wrote:

On Tue, 17 Jan 2012 22:32:53 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa__at_charter.net> wrote:

Does the wires assume real life situations to some
degree or do we need to add stray inductance, Resistors
and caps to act like a board?

I would of thought it would assume an average lay out of one
persons worse nightmare and the actual real live circuit would
just work better, seeing that this designer would engineer proper
protocols on the board.

It just seems that I don't see many of the small defects the
sim may show, when it is on a real board assembled using common
practices.

Which leads me to my question, does the sim assume a worse case
scenario or maybe the sim just over exaggerates now and then?

This would be LTspice I am referring to. I was thinking of looking at
Pspice to see how that goes.

Jamie

Do the math... by hand... then use the sim to VERIFY!

...Jim Thompson

Well that just sounds counter productive.

Why waste my time using a sim if I am going to do it by hand in the
first place?

You can haggle all you want Jim, It does not work on me..

I am not one of your goal post. You have JL for that :)

Jamie

If you don't understand your circuit maths, how do you know if the
simulation is close to reality???? Many times, you can do this in your
head, but sometimes you need to write down a bunch of maths to
understand issues you may run in to. As an excercise, try to
temperature stabilize a simple one transistor amplifier without
understanding the basic transistor equations.

Do you blindly trust your models??? If you do, beware, they are often
wrong. With experience, you will learn a healthy distrust in your
simulator and test equipment.

I don't think Jamie is even a technician, but he _is_ successfully
becoming a reductive emulation of John Larkin Wink

...Jim Thompson

Yeah, you are correct as usually Jim. I mean, are you ever wrong?

Yes, I am just a back woods inbreed hill billy. Most of the time I
run around with no clothes on, and when I do have them on, they are
hand me downs, full of holes and have not seen what would represent
laundry detergent or anything close to that. Yes, we can't even afford
making our own soaps out of lard from road kill. etc..

I use a chinese abacus because I have found that I can actually
exceed the math skills that requires more than 10 fingers. Yes, I still
have all my fingers. I have not yet lost any of them while fighting with
my sisters, in the sack.

Nothing like having a hole down, especially when its your lady or
boyfriend, what ever your party maybe.

Jamie

Jamie
Guest

Thu Jan 19, 2012 1:50 am

qrk wrote:

Quote:

On Tue, 17 Jan 2012 23:43:42 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa__at_charter.net> wrote:

Jim Thompson wrote:

On Tue, 17 Jan 2012 22:32:53 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa__at_charter.net> wrote:

Does the wires assume real life situations to some
degree or do we need to add stray inductance, Resistors
and caps to act like a board?

I would of thought it would assume an average lay out of one
persons worse nightmare and the actual real live circuit would
just work better, seeing that this designer would engineer proper
protocols on the board.

It just seems that I don't see many of the small defects the
sim may show, when it is on a real board assembled using common
practices.

Which leads me to my question, does the sim assume a worse case
scenario or maybe the sim just over exaggerates now and then?

This would be LTspice I am referring to. I was thinking of looking at
Pspice to see how that goes.

Jamie

Do the math... by hand... then use the sim to VERIFY!

...Jim Thompson

Well that just sounds counter productive.

Why waste my time using a sim if I am going to do it by hand in the
first place?

You can haggle all you want Jim, It does not work on me..

I am not one of your goal post. You have JL for that :)

Jamie

If you don't understand your circuit maths, how do you know if the
simulation is close to reality???? Many times, you can do this in your
head, but sometimes you need to write down a bunch of maths to
understand issues you may run in to. As an excercise, try to
temperature stabilize a simple one transistor amplifier without
understanding the basic transistor equations.

Do you blindly trust your models??? If you do, beware, they are often
wrong. With experience, you will learn a healthy distrust in your
simulator and test equipment.

Fucking beginners

What a gas!

Jamie

Jim Thompson
Guest

Thu Jan 19, 2012 1:59 am

On Wed, 18 Jan 2012 19:30:04 -0500, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa__at_charter.net> wrote:

Quote:

Simon S Aysdie wrote:

[snip]

The models are just *models* -- not the real thing. How good are
they? After all, that is all spice has to work with. Models are
never perfect -- what should spice assume as "average" about them?
Caveat emptor: you need to have some idea of what you're doing in the
first place.

I think your question is really: Can I get SPICE to think for me? No,
you can't.

Well no problem, I'll just continue with how I've been doing it all
these years. Calculator,years of foot notes, engin books, equipment use,
CAD steps and then boards.

I guess spice is good for concept circuit experimenting. Saves on
paper.

[snip]

Spice is an absolute necessity for chip design...

(1) You can't breadboard much, if anything.

(2) The expense of building a chip requires checks to make sure you
don't make a dud.

Of course, in the chip-making world, the models are extremely
accurate.

In the PCB-level world, unfortunately, whole-chip models are often not
that wonderful... mostly because the chip manufacturers are so
paranoid of copying that they devise behavioral models that are mostly
created by cretins.

Likewise, in discrete devices, particularly MOSFET's, they don't spend
enough effort to create more than school-boy-level models. You're
lucky if you get a Level=3 representation. In my chip-design world
we're at BSIM3v3 or higher (Level=49+).

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| 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.

John S
Guest

Thu Jan 19, 2012 2:06 am

On 1/18/2012 6:48 PM, Jamie wrote:

Quote:

Jim Thompson wrote:

On Wed, 18 Jan 2012 10:57:36 -0800, qrk <SpamTrap_at_spam.net> wrote:

On Tue, 17 Jan 2012 23:43:42 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa__at_charter.net> wrote:

Jim Thompson wrote:

On Tue, 17 Jan 2012 22:32:53 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa__at_charter.net> wrote:

Does the wires assume real life situations to some
degree or do we need to add stray inductance, Resistors
and caps to act like a board?

I would of thought it would assume an average lay out of one
persons worse nightmare and the actual real live circuit would
just work better, seeing that this designer would engineer proper
protocols on the board.

It just seems that I don't see many of the small defects the
sim may show, when it is on a real board assembled using common
practices.

Which leads me to my question, does the sim assume a worse case
scenario or maybe the sim just over exaggerates now and then?

This would be LTspice I am referring to. I was thinking of looking at
Pspice to see how that goes.

Jamie

Do the math... by hand... then use the sim to VERIFY!

...Jim Thompson

Well that just sounds counter productive.

Why waste my time using a sim if I am going to do it by hand in the
first place?

You can haggle all you want Jim, It does not work on me..

I am not one of your goal post. You have JL for that :)

Jamie

If you don't understand your circuit maths, how do you know if the
simulation is close to reality???? Many times, you can do this in your
head, but sometimes you need to write down a bunch of maths to
understand issues you may run in to. As an excercise, try to
temperature stabilize a simple one transistor amplifier without
understanding the basic transistor equations.
Do you blindly trust your models??? If you do, beware, they are often
wrong. With experience, you will learn a healthy distrust in your
simulator and test equipment.

I don't think Jamie is even a technician, but he _is_ successfully
becoming a reductive emulation of John Larkin ;-)

...Jim Thompson

Yeah, you are correct as usually Jim. I mean, are you ever wrong?

Yes, I am just a back woods inbreed hill billy. Most of the time I
run around with no clothes on, and when I do have them on, they are
hand me downs, full of holes and have not seen what would represent
laundry detergent or anything close to that. Yes, we can't even afford
making our own soaps out of lard from road kill. etc..

I use a chinese abacus because I have found that I can actually exceed
the math skills that requires more than 10 fingers. Yes, I still
have all my fingers. I have not yet lost any of them while fighting with
my sisters, in the sack.

Nothing like having a hole down, especially when its your lady or
boyfriend, what ever your party maybe.

Jamie

So your ladies and boyfriends have their holes down? I guess that would
promote the inbreeding. Try to resist.