I would suggest that LTSpice gets LT repsonisble for a huge share of its high margin business. It's the way they support smaller companies (where the margins are higher). There is no other way to justify their prices.
We had a team of LTC folks visit us last Wednesday, partly to tell us about the expected effects of the ADI acquisition. They agreed with me that LT Spice is going to be important to ADI, and that LT Spice has probably sold gigabucks of parts so far.
Some of their parts are good deals. Not gumdrop opamps or regulators, but things like fast ADCs and multi-channel serial DACs.
We've used thousands of their LTM micro-brick switchers. Nice quiet little things.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Way too expensive. When we can buy SMPS regulator chips for well less than $.50 (and add another $.20 for passives), these sorts of things don't hold the interest much.
"Expensive" depends on the context. They are small, convenient, and as I noted, very quiet. Two inches away from a 250 MHz, 12 bit ADC, I don't want a lot of switching spikes in my ground plane.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
You've just stated my point about LTSpice, and LT in general. Great stuff, if you're making tens or hundreds a month. Not so great if you're making thousands or hundreds of thousands. TI doesn't give much support for people making tens or hundreds but...
It's a matter of market. LTSpice allows LT to go after the high margin business, where they want to play. TI, for instance, has a completely different marketing model.
If I post a question to one of the TI forums, somebody generally answers it pretty promptly, and usually fairly well. I actually have some support contacts at TI, but I think the forums work about as well in most cases. My question and answer get googl indexed for the rest of the world to see.
Distributor FAEs work for small companies too.
Sure. We average about 20% overall parts cost compared to selling price. Half of that is PC boards and packaging. So I don't worry much about parts cost. I do use cheap TI synchronous switchers and external Ls and Cs when it's reasonable, and when I have a lot of them on a board.
On a production run of, say, 50 or 100 pieces, it's good to minimize the number of line items on the BOM. Every part has to be loaded into feeders and such.
Hey, I use LT Spice for non-LT sims. UniversalOpamp2 is handy.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
May be it looks a little bit home made and uses odd shortcuts but it has one feature that makes entering schematics as fast as no second program I know: There is no need to place wires from pin to pin! Just place a few parts, then draw a wire right through them and when you end the wire (right click or escape) all lines that would short a component magically disappear. Also, if you place a component right over a wire, the piece of wire under the component is automatically deleted. Frequently used components like resistors, inductors, diodes or ground symbols can be inserted without moving the mouse to a menu by typing r, l, d or g. Rotate is ctrl-r but mirror is _not_ ctrl-m :-( Anyhow, very nice imho!
Robert
Simply not true. I wrote SS for *ME*. I wrote it after evaluation all available spices at the time around 1996. Other than, PSpice, they all had shit GUIs. Any money I get from SS, goes straight to my 80 year old mother, not me.
I give an accurate, non biased view, as an engineer. Period. Believe what you want.
I have repeatedly stated that LTSpice, to my knowledge, has the fastest and best convergence of any PC Spice. However, its GUI, is a joke. Seriously. For me, its the twilight zone how anyone can find its GUI ok. If the GUI was usable, I would be using it. I want the best speed and convergence and features myself. Dah...
LTSpice simply does not have the core features that I *need* and use *every* day, as a companion to Cadence Virtuoso in my professional IC design work.
Having to press a menu/function key just to move a component, is just insane....
-- Kevin Aylward
This claim makes no sense. LTSpice is *only* a *simulation* program. A simulation program can't "allow" them to sell parts.
LTSpice is, essentially, an advertising tool. It simply puts the name LT on the desktop. Sure, this has value, but purchasing departments don't buy parts based on simulating LT chips on a computer, its, does the part meet the performance required, at a cost I am willing to be, with an acceptable lead time .
-- Kevin Aylward
And just what would you expect them to say about LTSpice?
LTSpice, is essentially, advertising. Its not easy to work out the effect of advertisement on profits, however, one can try different campaigns over time to see if there is any correlation.
Without supplying LTSpice for a time, then cutting it off over several periods, I don't see how its possible to validly quantify any value to it all, although I agree that LTSPice has some value.
"probably sold gigabucks of parts", is just a fantasy claim.
I do remember when Bruce Springteen's "Born In The USA" album came out, it apparently boosted Levi's jean sales
-- Kevin Aylward
Maybe, maybe not. How do know? What physical evidence is there of that?
-- Kevin Aylward
I will expand on that, in part this will give a bit of general knowledge as to what "pro ic design is all about" that readers here may find useful.
Key parameters in producing a commercial IC product are.
1 It takes several months to get a design back from the fab after tapeout. 2 ICs, typically today, are complicated, 10,000s of transistors for an analog ASIC 3 A 0.18u process might take $100k in prototype fab costs 4 Fab process have extensive variations 5 Millions sold per month must work, reliably, for many years.So, prior to tapeout, an ic designs are required to have extensive design effort and verification.
The process of designing, say a BiCMOS chip, involves going through a range of design optimisations and simulations. This consists of designing for DC, AC TRAN, NOISE, in an iterative manner.
The details of the design involve selecting, for example, gate lengths and widths, and how many in parallel and series, and emitter areas. For example, shorter gate lengths get you faster speed. Maximising headroom may be achieved by reducing the Vdsat of the transistor, by reducing its overdrive voltage, Vgst (Vgs-Vth), this means say, increasing the ratio of W/L. However, reducing Vgst, makes matching worse, so compromises have to be made. Better matching means larger W x L, however, this means a slower circuit, which could mean instability in a feedback loop. etc...etc... all to satisfy specifications of power consumption, noise, die size, etc...etc...
Now, all of this has to be done with process variations, say Vt varying by
200mv, gm of mosfet varing 20%, and over temperatures, say -40 deg to 85deg, over all supply voltages. Typically models are made that reflect the extremes of the process, which I explain in more detail here:Typically, 100,000s of simulations are run to verify a chip before tapeout.
So, no, I do not have "bias". My view is based on the facts.
If a simulator does not directly support worst case analyses, its dead in the water as far as IC design in concerned. Period.
Second, is usability of accessing key data that supports the above design issues. IC design requires spending hours per day, every day, running continually modified simulations. Pissing about for a minute to access each plot *is* a major problem, for serious, professional designers.
For example, in checking that Vds (drain voltage) is greater than Vdsat (when device crushes) over *all* process corners, and over the operating DC ranges, one needs to be able to do this *easily*.
Scroll down to the second screen shot.
This shows a signal list tab to the left where you can ctrl-click and easily display a combination of any signal. For example, plotting Vgs and Vdsat. SuperSpice lists in that signal list all major device parameters such as Vgst, gm, gds, etc... You don't have to hunt about to get the data that you really need to plot.
Even small details can have a *major* effect on usability when your simulating 40 hours per week. For example, SS displays the actual x, y trace data of the graph without cursors, because the mouse cursor *locks* onto the trace, and only displays only the *valid* y with x data. LTSpice just displays apparent x,y data of whether the mouse is on the screen, which has nothing to do with the real trace data. Using LT manual cursers is a major pain.
So, sure, if your not an IC design pro, the LT GUI, may well be adequate for your needs.
-- Kevin Aylward
I've been through the documentation many times and not all of these keystrokes were made apparent to me. Yes, somewhere there is a list of all the hotkeys, but mostly they are control keys and weeding through the list for the few useful ones is not so easy.
I changed one of the hot keys in the settings so cntl-z was undo as is the case in so many windows programs. It was promptly forgotten...
I seem to recall fixing some of the waveform colors so they stood out on a laptop LCD screen... all gone.
If you use the program every day, it can become very familiar. If not, the arcane little idiosyncrasies get on your nerves. Why doesn't cntl-A select all the text in a text field??? There's a million things like this that the few nice features don't make up for.
-- Rick C
I just tried that, and it went and connected up incorrectly. Ahmmm...probably because I am unable to use LTpPice.
It didn't used to do that. Mike copied that from me :-)
But in reality, I hardly ever use that feature
So, you don't see the value in having docked, tabbed sidebars that you can drag any of the component form any library?
To add model libraries, you just drag drop the file from explorer. Symbols for standard models are attached automatically.
There is no rational reason to have the ctrl key as well, SS don't do that, its just "r" "m" "f" to rotate, mirror flip up/down. Zoom in/out is "i" "o"
Double-clicking on component does what you expect in windows, as does right click popping up a menu :-)
-- Kevin Aylward
Great post on a great thread.
Always reminds me of:
Bodacious cowboys Such as your friend Will never be welcome here High in the Custerdome
Steely Dan - Gaucho
PSpice was very good. Where do you think I stole the idea for moving around testpoints on the schematic?
I used PSpice from around 1985 to 1997, whilst I was a board level designer, paid for at the various companies I worked at. I commenced the SS project as
night time work and 150,000 lines of code...
I checked out IntuSoft during that period, and rejected it immediately I discovered that you had to put 0V voltage sources in leads to plot currents. A total no, no. Pspice has .probe, you get everything.
I checked out ALL the spices at the time, none were usable. That's *why* I wrote SS. I needed a usable Spice, personally.
When I got the Berkeley Spice3/XSpice code, around 1997, I discovered that the BSim3 model code did not actually provide terminal currents for the gate, drain and bulk. So, my first task was to spend a week or so, trial and erroring adding up the various terms in the data structures to get the total current from all the individual bits. The issue being, is that its a no documentation, student written bunch of spaghetti.
-- Kevin Aylward
The fact that it is available for download, free. And the fact that other semi makers are offering similar free simulators for their parts.
And because the LTC people physically told me so last week.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Purchasing departments buy what engineers put on the BOM. If the part is sole-source, they have no choice.
In most cases, an engineer can even declare an LM317 to be sole-source. Much less an LTC2242.
My purchasing dept is not allowed to overrule an engineering decision and buy whatever they want. Heaven help companies where they are.
I know lots of engineers who pull a part off the LT Spice parts menu, sim their circuit, and design in the LTC part.
LTC just sold to ADI for $12 billion, about 10x annual sales. That's pretty good.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
[snip]
Monumental BS.
I invite anyone who thinks that the LTspice GUI is "as fast as no second program I know" to drop by, if you're in the East Valley area of the Phoenix 'burbs, and see a demonstration of a real schematic capture.
Bring your laptop.
At that time we'll locate a mutually acceptable schematic image off the web, you can enter it in LTspice, I'll enter with MicroSim PSpice Schematics... you'll get your ass whipped >:-} ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Thinking outside the box... producing elegant solutions.
Right. I only sim or breadboard little snippets of circuit that I have any doubt about; for most designs, that is none. The best prototype is the first production unit.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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