Last time I tested several 2N7000 Spice models (2005), there was huge variance between them, and some down-right non-physical behavior.
Has anyone found a better 2N7000 model since then? ...Jim Thompson
Last time I tested several 2N7000 Spice models (2005), there was huge variance between them, and some down-right non-physical behavior.
Has anyone found a better 2N7000 model since then? ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et |
The 2N7000/2N7002 parts themselves vary a lot between manufacturers, which is why some of our products specify a specific manufacturer for these parts.
What non-physical behavior are you seeing?
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com
I would hope to see some electrical behaviour!
-- Mike Perkins Video Solutions Ltd
I really don't understand the confusion here. The number 2N7000 is a JEDEC registered number, how can there be a variance at all ?
I admit I have very little experience with Spice, but JEDEC is JEDEC, no ?
Going into this "given samples" shit is one thing, but should not be an iss ue in design usually. Tolerances are one thing. Current sharing amond MOSFE Ts is another, but I doubt anyone has to match a 2N7000 for that purpose.
In fact I would like to see the scenario in which that would be necessary. Well not really in practice, what I mean is for one of the seasoned enginee rs around here to actually explain why the $^%#@ #$$&* you owuld have to do that. I thought the thing was a simple switcher, maybe use it linear somet imes, but only if you bought a truckload of them. At least that's what I th ink.
Typical behaviors could be radically better than the Jedec requirements. Some 2N7002s are ten times as fast as you'd expect from the max rise/fall time specs. Gate leakages can be 8 or so orders of magnitude below the specs.
I suspect that one fabbed wafer gets sold as a lot of different part numbers. Nobody really needs 7000+ different transistors.
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com
All but the Supertex model failed to model ANY behavior below threshold, and the Supertex model had discontinuities in the ID/VDS curve blending... guaranteed to cause simulator convergence issues. ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et |
I forgot to reference my old post (4/6/2005)...
Second page tells it all. ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et |
Fairchild FQD2N100 model attached.
If you're actually designing boards with 2N7000s, any of those curves is about as good as any other. Real-life parts will be all over the map.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com
You didn't notice the discontinuities? ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et |
Sure, but they are down in the "noise" of part-part differences.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com
So let me get this straight. If any little thing happens this is smoked, right ?
Refer back in the history of this group, and Win Hill's concern about operation in the subthreshold region. Use as a low noise amplifier is quite different from just using the device as a switch. ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et |
Here's a graph that I found in our PDATA folder for the 2N7000. I don't know where it came from, possibly from Win.
(people should sign and date everything that they create)
What does "subthreshold" mean anyhow? It seeme to me that specified gate thresholds are based on arbitrary drain currents. That curve above has no threshold.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com
No model level higher then Level=3... that is, early school-boy text-book complexity.
The problem is that it is quite rare to see discrete MOS devices modeled properly as BSIM3v3. ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et |
That's not "leakage", it's the natural square-law behavior of MOS devices below "threshold"... sometimes used to make faux bandgaps with MOS ;-)
I suspect Joerg regularly works down in this region.
I recently participated in the design of a medical device (chip) where _everything_ operated subthreshold... the oscillators I mentioned before... 1kHz at 6nA, 1MHz at 1.2uA
The definition of "threshold" is a vague. I have these papers that I can share, if any are interested...
...\ModelingIssues\ThresholdModeling_SalcedoEtAl.pdf
...\MOS-GateCharge\WinHill_subthreshold_mosfet_model.pdf (graphs)
...\MOS-GateCharge\Win Hill Data\2n7000_data_graphs.xls (data)
...\SubthresholdEffects\CurrentMirror_Novel_SubthresholdRegion.pdf
...\SubthresholdEffects\ExploitingSubthresholdMOSFET_Behavior.pdf
...\SubthresholdEffects\ReferencesFromSubthreshold MOSFETs.pdf
...\SubthresholdEffects\SubthresholdDeviceModeling.pdf
...\SubthresholdEffects\SubthresholdMOSforUltra-LowPower.pdf ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et |
Very pretty. What was V_GS?
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant
Not if the board function depends on sub-threshold behavior!
-- Tim Wescott Wescott Design Services
Do you mean Vds? I don't know.
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com
V_DS, right. Ah, well, I'll have to quit snuggling with my computer and actually do some measurements. ;)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant
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