Circuit simulation software

Who cares?

You haven't been around here very long, so I will clue you in......

In Kevin's view, only Kevin is worth quoting. I think it is 95% because he is usually correct and 5% because he argues to win even when he is wrong, and knows it. It's kind of like trying to discuss things with his Texan alter ego.

Don

Reply to
Don Bowey
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Well, I was thinking that Anasoft might not want to repel potential customers, if Anasoft is in business to make money.

Ah. True, I haven't been reading this group regularly for several months.

Reply to
mc

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

Reply to
John Larkin

See...

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

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

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

"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.

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

Reply to
John Larkin

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

Yep, absolutely!

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.

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

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

AHMEN :))

Reply to
fpga_toys

I think only for some modern programmers ... many of us learned to design software when you might get a few test runs a week on batch systems.

Others only get one shot at a production run ... aerospace guys for one ... and a lot of others, where you reall do have to have your software right first time.

There are an equally sloppy number of FPGA/CPLD HW guys these days.

Reply to
fpga_toys

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

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? :-)

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

Reply to
Joel Kolstad

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

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

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

John

Reply to
John Larkin

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

--
Rick
Reply to
rick H

Only if your models are brain dead.

--
  Keith
Reply to
Keith

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

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

Pretty useless then, eh? All of the models I've ever used specify such things (though I've never used any opamp models).

Well, there ya' go.

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.

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
Reply to
Keith

Looked at any SiGe recently, fT > 35GHz+

...Jim Thompson

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

well, I have recently used verliloga models supplied by cadence, and they have offsets, slews etc all parametized. You need to set them of course!

And more importantly, how to correct/set them up so that they can be trusted.

Kevin Aylward B.Sc. snipped-for-privacy@anasoft.co.uk

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SuperSpice, a very affordable Mixed-Mode Windows Simulator with Schematic Capture, Waveform Display, FFT's and Filter Design.

"There are none more ignorant and useless,than they that seek answers on their knees, with their eyes closed"

Reply to
Kevin Aylward

That's only if one is too inexperienced to know how to use models that address 1st order errors.

Of course if people are clueless its GIGO. However, people that correctly understand analogue and the simulater, simulation is trully wonderfull. No one is suggesting driving a simulater in ignorance. As I have already mentioned, the only way to gain a true genuine

*understanding* of the physics of colliding black holes is to use simulation programs. The equations are just too complicated to "see" what they mean without doing *experimental* simulations, and this is done by people with PhDs and 20 years direct experience. Its just the way it is. Most modern technology is way too complicated to understand by pen and paper anymore, no matter how much we delude ourselves. Sure, we all like to imagine that we are Steven Hawking doing grand calculations in our head, but even he cant actually get the answers without running simulations.

Kevin Aylward B.Sc. snipped-for-privacy@anasoft.co.uk

formatting link
SuperSpice, a very affordable Mixed-Mode Windows Simulator with Schematic Capture, Waveform Display, FFT's and Filter Design.

"There are none more ignorant and useless,than they that seek answers on their knees, with their eyes closed"

Reply to
Kevin Aylward

No, you didnt design it then, you just copied (replicated) something else you already knew worked. The *only* way to know if something actually works, is to measure if it works. Even then you could be fooled.

Kevin Aylward B.Sc. snipped-for-privacy@anasoft.co.uk

formatting link
SuperSpice, a very affordable Mixed-Mode Windows Simulator with Schematic Capture, Waveform Display, FFT's and Filter Design.

"There are none more ignorant and useless,than they that seek answers on their knees, with their eyes closed"

Reply to
Kevin Aylward

Pardon? So you think that praying to gods is worthwhile? Yeah, right on dude. Many your gods have mercy on your souls.

Kevin Aylward B.Sc. snipped-for-privacy@anasoft.co.uk

formatting link
SuperSpice, a very affordable Mixed-Mode Windows Simulator with Schematic Capture, Waveform Display, FFT's and Filter Design.

"There are none more ignorant and useless,than they that seek answers on their knees, with their eyes closed"

Reply to
Kevin Aylward

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