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Re: Circuit simulation software


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ROTFLMAO! Thats wonderful Rich, I may well pinch it.

Cheers
Terry

Re: Circuit simulation software


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You're lucky you didn't try that in my Jesus Freak days.  I would have
looked you straight in the eye, and said "Bring it on!" or whatever the
70s equivalent would have been....

Charlie

Re: Circuit simulation software


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What, luck? All I'd have to do is give you or him the Evil Eye (I can do
that - I'm an empath), and either of you would have withered, because all
I would do is evoke the denied essence in your own self. >:->

Cheers!
Rich
for further information, please visit http://www.godchannel.com


Re: Circuit simulation software


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Or, more likely, I would have broken out in laughter from the funny
face... 8-)

Charlie

Re: Circuit simulation software


On Tue, 20 Jun 2006 21:28:27 GMT, "Kevin Aylward"


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Cool. I can design something that I *know* will work in a few hours,
and then I can goof off the other 37 hours of the work week.

John



Re: Circuit simulation software


On Wed, 21 Jun 2006 07:09:08 -0700, John  Larkin

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Cool.  Show me your 40 pages of schematic that you designed without
any preliminary breadboarding or simulation.

                                        ...Jim Thompson
--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Re: Circuit simulation software


On Wed, 21 Jun 2006 07:49:28 -0700, Jim Thompson

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I could show you a thousand. The last project I did, a temperature
controller/pulsed gradient driver, had no sim or breadboarding. This
week's gadget, a sub-ns singlemode laser driver, will have none
either.

About the only time I ever breadboard is when a part is poorly
characterized, and then I only test a single part or a very simple
circuit involving the part, like when I TDRd a trimpot last week to
see just how high a frequency signal can be trimmed with a pot. Ditto
simulation, just little snippets, usually for nonlinear control loop
tweaking, based on idealized component models. I never breadboard or
simulate an entire product. I design maybe 10 products a year and fire
up a simulator two or three times a year at most.

I do appreciate that it makes sense to simulate an IC design, but I
don't do IC design. I do FPGA design, but don't simulate that either.

Really, designing is a good investment in time. That especially
applies to software, where most programmers spend four times as long
debugging ("breadboarding") as they do coding, and have the same
problem as hardware breadboarders have, namely that ad-hoc debugging
never finds all the bugs. My ratio is more like 4:1 in the other
direction, not because I'm so smart, but because I *know* I'm not
smart enough to speed-type reliable code without looking back.

I think that the worst part of design by simulation/breadboarding is
the bad-habits-training loop that results.

John





Re: Circuit simulation software


On Wed, 21 Jun 2006 08:34:39 -0700, John  Larkin

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I design on paper, then test by simulation.

I do note that you admit to regular failures.  My rate of need for
debug is under 1%... usually due to the customer's failure to spec
what he really wanted.

                                        ...Jim Thompson
--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Re: Circuit simulation software


On Wed, 21 Jun 2006 08:49:39 -0700, Jim Thompson

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I have no design "failures" since I started designing professionally
at the age of 18. I often change parts values on a new first-article,
and sometimes add a kluge, usually a cut/jumper and sometimes an added
resistor, cap, or even a diode, like if we find a latchup mode in a
chip or something like that. Sometimes we think of an improvement or a
feature, and squeeze it in if possible. It's very rare around here
that we can't sell a presentable rev "A" board. I do design a *lot* of
stuff.

How careful you need to be depends on the consequences of defects and
how hard they are to fix. An IC is expensive to turn, so a lot of
simulation is justified. Software is the other extreme, easy to hack
and easy to edit, so programmers are the sloppiest of designers. The
point is for everyone to optimize his particular design process, and I
believe my optimum involves careful design and checking and very
little breadboarding or simulation.

But the flat statement that complex analog design can't be done
without simulation may be mostly true for IC design, but it's sure not
universal. I wonder how much the uA709 was simulated.

The current educational paradigm, design by simulation, seems very bad
news to me. For Pete's sake, guys are simulating battery-resistor-LED
circuits and the most basic transistor switches.

John



Re: Circuit simulation software


On Wed, 21 Jun 2006 11:56:57 -0700, John Larkin

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See...

http://analog-innovations.com/SED/MC1530-TeachingExercise.pdf

for how I did a similar OpAmp design at about the same time (1963).
Algebra still works, even today.

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You can't design with a simulator, you have to draw something on the
schematic first.

I don't see much design on these newsgroups, just hackers copying
published schematics and then trying to tweak them with no knowledge
aforethought ;-)

                                        ...Jim Thompson
--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Re: Circuit simulation software


On Wed, 21 Jun 2006 12:36:04 -0700, Jim Thompson

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"The MC1530 OpAmp Chip was designed pretty much as outlined in the
above analysis EXCEPT that I worked the
equations backwards from the desired output voltage with some
judicious application of experience."

So, did you simulate the original design? "Worked the equation
backwards" sure sounds like design to me!

Often, design is simpler than analysis. When I design a closed-loop
system, I decide the overall loop dynamics first, then *force* each of
the blocks to do its part. Even simple resistor networks are often
easier to design than they are to analyze.


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Seems to me that a lot of people try. They do start somewhere, and
then fiddle until it seems to work. Some of the results are ghastly,
un-manufacturable messes.

John


Re: Circuit simulation software


On Wed, 21 Jun 2006 13:36:58 -0700, John Larkin

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"Simulate"??  It was *1963*, circuit simulators didn't exist yet ;-)

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Yep, absolutely!

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I knew what I wanted, I just had to try several scenarios until I got
the differential and common-mode performance I wanted.

I then proceeded to breadboard it with "kit parts" (†) and tweaked the
current levels so that the diode drops matched.

(†) "Kit parts" were test devices from process wafers that were bonded
up in DIL packages to allow breadboarding with actual I/C devices.

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I attended a design review about a year ago where another member of
the "design team" used an OpAmp open loop... assuming it had no offset
and that the gain was stable.  Fortunately I spotted it before they
made the presentation to the end customer.

                                        ...Jim Thompson
--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Re: Circuit simulation software


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I suspect Joerg might find that a few pennies could be saved if you needed a
really low performance comparator and can abuse an garden-variety op-amp in
this manner to serve such a purpose? :-)

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...so apparently they weren't trying to build a comparator...



Re: Circuit simulation software


On Wed, 21 Jun 2006 14:16:29 -0700, "Joel Kolstad"

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Nope.  They thought they had a stable gain of 1000X... differential
input, single-ended output, all done in CMOS... ROTFLMAO'd... made 'em
angry... Atmel Germany ;-)

                                        ...Jim Thompson
--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Re: Circuit simulation software


On Wed, 21 Jun 2006 13:52:16 -0700, Jim Thompson


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Spice is great. Put 0 volts into an open-loop opamp and you get 0
volts out.

John


Re: Circuit simulation software


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In much the same way that 0V * Adc/(1 + s*tau) will give you 0V output
on paper?

--
Rick

Re: Circuit simulation software


snipped-for-privacy@highNOTlandTHIStechnologyPART.com says...
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Only if your models are brain dead.

--
  Keith

Re: Circuit simulation software



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Very few vendor-provided models include any offset effects.  

Except for the models provided by I/C foundries, MOST models should be
viewed with a jaundiced eye.

But that's how we separate real engineers from the little boys...
knowing when to trust simulations and when to not.

                                        ...Jim Thompson
--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Re: Circuit simulation software


Use-The-Envelope-Icon@My-Web-Site.com says...
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Pretty useless then, eh?  All of the models I've ever used specify
such things (though I've never used any opamp models).

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Well, there ya' go.  

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Yep, I was using models a friend had once.  I couldn't believe the
speed of the circuit I was designing.  A kept cranking the step
interval down to get a good look.  The idiot had divided all the
cap values by 1000 without telling me.

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Sure, but even I didn't believe the speeds I was getting (the Ft of
the devices I was using were "only" around 7GHz).  ;-)

--
  Keith

Re: Circuit simulation software



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[snip]
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Looked at any SiGe recently, fT > 35GHz+

                                        ...Jim Thompson
--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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