On 3/12/25 4:38 PM, John Waugaman via groups.io wrote: The LM121 is shown as a preamplifier IC in the 1976 National Semiconductor Linear Data Book, but it's not listed in the 1980 edition. Strange, my yellowing copy of the 1980 edition has the LM121/221/321 on page 4-11. -- David Schultz "The cheeper the crook, the gaudier the patter." - Sam Spade
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Indeed; many web sites offering its data sheet
do not in fact include LM121, only LM221 and LM321, which do not
have two outputs.
On 2025-03-12 21:38, John Waugaman via
groups.io wrote:
The
LM121 is shown as a preamplifier IC in the 1976 National
Semiconductor Linear Data Book, but it's not listed in the
1980 edition.? I will look to see if I still have the 1976
data book or any other data for this device.? The LM321 is?not?the
same device!
John
--
OOO - Own Opinions only
If something is true:
* as far as we know - it's science
*for certain - it's mathematics
*unquestionably - it's religion
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The LM121 is shown as a preamplifier IC in the 1976 National Semiconductor Linear Data Book, but it's not listed in the 1980 edition.? I will look to see if I still have the 1976 data book or any other data for this device.? The LM321 is?not?the same device!
John
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The old National Semi numbering system was LM1xx for Mil-temp devices, LM2xx for industrial temp, and LM3xx for commercial temp. Then the LMyx1 was for the single version, LMyx2 for dual and LMyx4 for the quad.?
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The LM121 I am looking for is unique as it has a differential output and is paired with another opamp such as the LM118 to become a low-drift, high-gain set.
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On Wed, Mar 12, 2025 at 11:59 AM, DerekK wrote:
I am trying to work out some old schematic and circuit issues and am looking for a model for the old LM121 opamp. Anyone have such a thing? I found the LM118, as I can use the LTSpice LT118A model. Now for the front end.
If you meant LM321, it is a single version of an LM324.
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The LM121 has a differential output. Pinout is?
1: output 2
2: IN-
3: IN+
4: V-
5: balance
6: balance
7: V+
8: output 1
?
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All the models do not show the proper LM121 differential output configuration. Andy, you are correct about the LM121 being special. The old National Semi Apps Handbook has the LM121 and LM118 used as a high-gain, low-drift amplifier set. Hence, the differential output of the LM121 is fed into the LM118 directly.
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It looks like the LM121/LM321 was a very ordinary 1 MHz GBP op-amp, but maybe with somewhat lower operating power (lower supply current).? It is capable of +/-16 V supplies, but optimized for 5 V (+/-2.5 V) power.
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T.I. has a product webpage for it: .? Near the bottom of that page, they include some PSpice and TINA-TI models? for it, which, oddly enough, are the SAME models as for the LM158/LM358/LM2904 garden-variety op-amps.
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This suggests that you can substitute almost any generic 50-year-old op-amp for the part, including the bad-old 741 - at least for your SPICE simulations.
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Andy
?
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... I found the LM118, as I can use the LTSpice LT118A model. ...
As I say, it's been too many years.? But I do not remember that the LM121 was anything like the LM118.? The latter was optimized for high slew rate and bandwidth, unusually high in its day.
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Andy
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On Wed, Mar 12, 2025 at 02:59 PM, DerekK wrote:
I am trying to work out some old schematic and circuit issues and am looking for a model for the old LM121 opamp. Anyone have such a thing?
Remember that LM121, LM221, and LM321 are the same, just with different worst-case ratings.
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There is something that claims to be an LM321 SPICE model, here:
It is a text file.? You can rename it if you feel like it.
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There is a test schematic that uses it, here:
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All you need is LTspice's built-in "opamp2" symbol, with the name changed to match that of the .SUBCKT model, and add a ".lib" or ".inc" command to include the model itself.? It's easy.
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CAUTION:? That model is actually for Maxim's LMX321, which is a low-voltage version of the LM321.? I don't have a LM121/LM321 datasheet handy, but I suspect the original was not a low-voltage op-amp, like the LMX321 is.? So, caution is called for.
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Turning now to the PSpice model at the previously-referenced T.I. webpage for their LM321LV - it is not an encrypted model, so chances are good-to-excellent that it works in LTspice.? Most PSpice models are SPICE, and LTspice understands SPICE and most PSpice models quite well.? Forget about all that Orcad stuff.? The .lib file is the SPICE model so it is the only one needed.? Once again, use the "opamp2" schematic symbol.
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The TINA model there is not SPICE, so don't try that in LTspice.
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Now I wonder whether an LM321LV is a suitable replacement for the LM121/LM321.? The "LV" in the part number suggests that it is not.? It is indeed a low-voltage op-amp, so it might not work on your old schematics.
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Can you tell us, what made the LM121 unique?? It's been so long....
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Andy
?
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Derek,
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There is a PSPICE version on that list.? I use it all of the time in LTspice.
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If it's a Tina model, it might be compatible
with LTspice, but might need some tweaks.
On 2025-03-12 19:27, DerekK wrote:
Now to put it into something that LTSpice can use. Any
suggestions where to start? This looks to be an OrCAD / TINA
thing. I will peruse myself.
--
OOO - Own Opinions only
If something is true:
* as far as we know - it's science
*for certain - it's mathematics
*unquestionably - it's religion
|
Now to put it into something that LTSpice can use. Any suggestions where to start? This looks to be an OrCAD / TINA thing. I will peruse myself.
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I am trying to work out some old schematic and circuit issues and am looking for a model for the old LM121 opamp. Anyone have such a thing? I found the LM118, as I can use the LTSpice LT118A model. Now for the front end.
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Re: More syntax issues with 24.1.x
On 12/03/2025 13:17, Mathias Born via
groups.io wrote:
Hi Tony,
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The next update 24.1.6 will support this again.
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The official syntax for loading table data from a file will
be:
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table(x,
.include "<filename>")
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but yours will also work as is. You will also need not change
the file contents, however the "+" line continuation at the
start of each line will be optional and can be omitted.
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This is a good feature, and now it's official.
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Best Regards,
Mathias
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On Tue, Mar 4, 2025 at 12:06 PM, Tony Casey wrote:
I have many testjigs that import digitised datasheet
characteristic curves. An example of this would be:
.subckt
IB_400u 1 2 3 4
R1 3 4 1G
B1 1 2 I=table(V(3,4)
.inc BC848B_Ic_Vce_400u.inc
+)
Great! I look forward to 24.1.6.
--
Regards,
Tony
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Re: More syntax issues with 24.1.x
Hi Tony,
?
The next update 24.1.6 will support this again.
?
The official syntax for loading table data from a file will be:
?
table(x, .include "<filename>")
?
but yours will also work as is. You will also need not change the file contents, however the "+" line continuation at the start of each line will be optional and can be omitted.
?
This is a good feature, and now it's official.
?
Best Regards,
Mathias
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On Tue, Mar 4, 2025 at 12:06 PM, Tony Casey wrote:
I have many testjigs that import digitised datasheet characteristic curves. An example of this would be:
.subckt IB_400u 1 2 3 4
R1 3 4 1G
B1 1 2 I=table(V(3,4)
.inc BC848B_Ic_Vce_400u.inc
+)
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Re: Brady Ridgway's Fuzz_Face (guitar "fuzz" circuit) simulations
Apologies for the mis-steps. Thank you very much for taking the time to explain everything so clearly. I will restore the standard.bjt file and follow your suggestions with regard to the circuit and simulation.?
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Re: Issue with Nexperia BUK7S1R0-40H PET LTspice model
So I was right about two different data
sources, but both are models, not one model and one measurement
results.? The moral of that is, says the Duchess (not of
Sussex), is 'Caveat Simulator'.
On 2025-03-11 22:47, Andy I via
groups.io wrote:
On Tue, Mar 11, 2025 at 09:52 AM, John Woodgate wrote:
It's quite possible that
the data sheet Figure 13 isn't based on the Spice model,
but on measurements of actual devices? of superior, rather
than average, performance.
That is possible, but I think not likely.? By my read, the
whole purpose of that Application Note is to show you the
results of SPICE simulations.? Therefore, I think none of its
plots were from measurements.? Also, it states that "the
characteristics are always typical values and
do not represent the limits of process variation."? I think it
suggests that everything in that AppNote is average, not
superior performance.
?
I agree with MaticH that the comparison is rather poor.? It
should be much better, if not exact.
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But read on.? I think there are reasons to explain it.
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AppNote AN90034 was published in April 2022.? The LTspice
model used today is dated June or July 2023.? We know it is a
different model file because it lists a different number of
MOSFETs than the ones shown in Figure 1 of the AppNote.
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AN90034 refers specifically to the LTspice model here:
? ?
But the one in MaticH's (and my) simulations is here:
? ?
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I think there was a significant change when they went from
V1.1 to V3, even though it was only one year.
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The older ZIP file is no longer there.??I tried retrieving it
from the Wayback Machine but they did not successfully save it.
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So anyway, that is what I think happened.? Nexperia's model
changed significantly between 2022 and 2023 and this explains
why today's simulations differ so much from the plots in
AN90034.
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To make things even more interesting, Nexperia has yet
another SPICE model for the same part, here:
That one is a non-encrypted generic SPICE model (Level=3
NMOS) and it should work in LTspice as well as most other SPICE
programs.? It lacks the two thermal pins.? I did not try it, but
I do not expect close agreement between that model, and the
AppNote.
?
?
--
OOO - Own Opinions only
If something is true:
* as far as we know - it's science
*for certain - it's mathematics
*unquestionably - it's religion
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Re: Issue with Nexperia BUK7S1R0-40H PET LTspice model
I wrote:
That one, the non-encrypted generic SPICE model, is even older, from 2019 and apparently not updated since.? Who knows what that means.
?
Andy
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John Woodgate
John Waugaman
DerekK
Jay Philippbar
Tony Casey