Re: Problem of plotting (TI) log112 curve (Vo vs. I1/I2) (log112 model in file folder)
mmm....
I think the equation in the datasheet "(TI) log112" could possibly be wrong, there is NOT "negative" relation between Vlogout & Vo3. But the simulation shows they are "negative", possibly in the "k" factor.
"VLOGOUT = (0.5V)LOG (I1/I2)"
"VO3 = K (0.5V)LOG (I1/I2), K = 1 + R2/R1"
Maybe someone should inform (TI) to fix this. If it's really wrong or there is a better explanation.
Best regards.
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Re: Problem of plotting (TI) log112 curve (Vo vs. I1/I2) (log112 model in file folder)
ericsson.sunshine?wrote:
? ?"Is it possible to plot the curve similiar to the datasheet ?"
Yes.
Sorry, after a few false starts ... I uploaded the file "20160801_log amp (TI) log112_DC.zip" to the Temp folder.
Run the simulation in that file.? Then after the simulation finishes, click in the plot window to select it, then go to Plot Settings -> Open Plot Settings File, and open the .PLT file again.? This should re-scale the axes so that the plot looks similar to the curve in the datasheet.? The difference is that the log amp runs out of positive range when the input current is too large.
? ?"And says the log amp is utilized to measure the physical quantities which has exponential characteristic (varies large.) ? ? I don't know how to show this characteristic in the waveplot of LTspice."
The plot shows it.? The log amp is able to handle input signals over a 5 to 8 decade range of values, or more, which is significant.
Stay away from negative values of input current.? Also avoid very small input values (less than about 100pA).? Either of those can cause the output of the log amp to deviate significantly from a log() response.
Also, the current Iref through the external resistor seems to no longer be 100uA when the input current is much out of range, and this can also mess up the plot. ?(This might be a problem in the SPICE model?? Or maybe not.)
? ?"The equation's simple to understand, but it's hard to plot the curve of "Vout vs. I1/I2". I don't why"
It works for a .DC sweep.? It doesn't work if the input current is not within the range where the log amp follows a log() curve.
I think the reasons it didn't work well in a .TRAN simulation, are (1) the input current went outside the range where the log amp fits the equation, (2) the log amp's response time gets to be ridiculously slow (even a 10 second ramp might be too fast), and (3) there might be some oscillation (instability) going on.
Andy
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Re: Problem of plotting (TI) log112 curve (Vo vs. I1/I2) (log112 model in file folder)
Hi, Andy:
Ok, now I see what's the difference, the Vout definition of the datasheet referred to Vlogout NOT Vo3.
Vlogout vs. I1/I2 curve is same with the datasheet curve.
But Why it can't be shown in the .TRANS simulation with a ramp voltage source ? I am still confused.
Thank you
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Re: Problem of plotting (TI) log112 curve (Vo vs. I1/I2) (log112 model in file folder)
Hi, Andy:
Actually, I don't need to consider frequency response this time. I had plot the DC sweep curve, but the slop is negative (Vout decrease while I1/I2 increase).
In fact, I used op amp almost in the linear amplifier of the signal and very low frequency. This is the first time I heard about log amp. I had updated the DC sweep file.
Best regards.
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Re: Problem of plotting (TI) log112 curve (Vo vs. I1/I2) (log112 model in file folder)
? ?"I don't know what the "uni-polar" means"
?It means one polarity.
Andy
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Re: Problem of plotting (TI) log112 curve (Vo vs. I1/I2) (log112 model in file folder)
Hi, Andy:
I had fixed the value (time, amplitude) of DC sweep source (.TRAN) to lower speed, smaller scale. And I found in a very small range, it has exp behavior, but output a DC bias about 4.2V.
Is it possible to plot the curve similiar to the datasheet ? in the datasheet it says these equations: "VLOGOUT = (0.5V)LOG (I1/I2)"
"VO3 = K (0.5V)LOG (I1/I2), K = 1 + R2/R1"
And says the log amp is utilized to measure the physical quantities which has exponential characteristic (varies large.) I don't know how to show this characteristic in the waveplot of LTspice.
I don't know what the "uni-polar" means, if you meant that it shouldn't have the negative value, I had fixed it ,it came from this ,at the beginning I used the negative value because I couldn't show the curve, so I simply thought maybe I could enlarge the scale of the waveplot to see what's different.
The equation's simple to understand, but it's hard to plot the curve of "Vout vs. I1/I2". I don't why, and not sure whether it's caused by the model mismatch or other reasons.
Thank you for the reply
Best regards.
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Re: Problem of plotting (TI) log112 curve (Vo vs. I1/I2) (log112 model in file folder)
I re-ran it as a DC sweep, keeping I1 sufficiently positive.
I get pretty good agreement with the datasheet's plot, noting the polarity inversion of your circuit, up to about 4 or 5 mA.? At that point, the core log circuit runs out of steam and clips.? That is higher than the specified input dynamic range (3.5mA max), so I think it is good -- even though the ratio I1/Iref is not as high as it is shown on the datasheet plot.? Obviously, they used a smaller value for Iref in that part of the datasheet plot.
This is the first time I simulated (or even used) a log amp so I'm not an expert.
Andy
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Re: Problem of plotting (TI) log112 curve (Vo vs. I1/I2) (log112 model in file folder)
Since it is a log amp, shouldn't the input current (I1, I2) be uni-polar?
Andy
?
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Re: Problem of plotting (TI) log112 curve (Vo vs. I1/I2) (log112 model in file folder)
ericsson.sunshine?asked about a Log amp from T.I.
This is just a very first impression, and may or may not be meaningful.
You are doing this as a transient analysis. ?It's possible you are sweeping the input current too fast.? At some signal levels, and depending on external components, the part's bandwidth can be as low as 1 Hz or less, so the step response could be quite slow, maybe too slow for a 10ms step.
Did you try a .DC sweep analysis?
Over some of the range, I think it is oscillating.
All the negative values in the X-axis should be discarded, to correspond to the datasheet's plots. ?(Now, why are there negative values at all, I wonder?)
Regards, Andy
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Problem of plotting (TI) log112 curve (Vo vs. I1/I2) (log112 model in file folder)
Hi, :
Here is a pure technical problem. I had found a log amp model (TI) LOG112 at the file folder. When I was trying to plot the "Vo vs I1/I2" curve mentioned in the datasheet, I can't work it out. The plot is unexpected.
I had uploaded the example file at? 20160801_log amp (TI) log112.zip
Thank you for any opinion Simplicity brings fun & satisfaction.
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Re: Looking for a IDT74CBTLV3253 model.
Gunoiar?wrote:
? ?"Also, I observe that the logic library contains only the graphical description on certain ?devices but lacks the simulation definitions."
I am confused what you mean by that.
Are you talking about the logic parts in the [Digital] section of the library?? They all have actual models already.? What's missing are the parameters that MAY need to be set, to get realistic performance.
I am not aware of logic parts in the LTspice library that are graphical symbols only.
Some analog parts, e.g., MESFETs, SCRs, IGBTs, valves/tubes, and varistors, are symbols only and you must provide the model.
Regards, Andy
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Re: Looking for a IDT74CBTLV3253 model.
Hello,
You could use the basic AND, NAND from the folder [Digital] plus a NMOS and PMOS transistor. See the circuit diagram in the datasheet.?
?
I recommend to make a hierarchical schematic. This means you make top-level schematic with your circuit and a lower level schematic with the IDT74CBTLV3253.
Best regards, Helmut
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Looking for a IDT74CBTLV3253 model.
Hello one and all. it's time to bite the bullet. Do some digital simulation on an analog simulator :) I need to design a four channel sequential track and hold. Part of this contains a 2 bit digital counter stirring 4 switches. it appears the the ?? IDT74CBTLV3253? integrates these functions well.
Does any one have a model for it? please include an example how to use it.
Also, I observe that the logic library contains only the graphical description on certain? devices but lacks the simulation definitions. Is that meaning that I have to develop an entire library?
Sincerely
G.
??????????????????????????????????????????????????????????????????????????????????????
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Dear Andy,
the Standard Ferrite Bead symbol in LTspice of Wurth is not encrypted.
Once you selected a particular P/N and right click on the symbol,
you can see the datas used for the simulation model.
And can also edit them- if needed.
The current dependent Ferrite bead Ferrite Bead (I)? model of Wurth is encrypted.
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Indeed, fine LTspice group, I am, most times, happiest to take the advice that one "learns more with mouth closed" ;-)
Thanks to all of you who proffer your experience in both LTspice and electronics, generally!
I try to find my way, using available web resources and the many thread topics to be found in the archives, thus do not, often, need to ask too basic a question ....
Vielen Dank, Helmut, especially, but also many thanks to the "usual suspects"
Barry Rowland
Bayern (that's near Germany ;-) )
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Re: Doing the SYNC update with LTSPICEXVII 64/32 and LTSPICEIV
Hello wms121
You wrote :
"
Check your primary files in LTSPICEXVII where you should find the "scad.exe" files in LTSPICEIV. "
I have XVIIx86.exe on 32 bits system and XVIIx64;exe on 64 bits on 64b systems.
When I run? LTspiceXVII;exe the choice between 32 and 64b is not active.
But it's not a problem. for me. All is clear and fine.
So I don't understand your problem.
Regards
PhB
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Re: Doing the SYNC update with LTSPICEXVII 64/32 and LTSPICEIV
Maybe I didn't read well enough, but what is the purpose of all this? Because if it's about doing sync updates for IV and XVII, all you have to do is fire up the desired version and do a normal sync update -- it will correctly update its version, IV to IV, XVII to XVI, 32 or 64 bit.
Vlad
______________________
-- holding, among others:
a universal analog/digital filter, block-level models
for power electronics (and not only), math blocks
with a more stream-lined approach, some digital
ADC, DAC, (synchronous-)counter, JKflop, etc.
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Re: Doing the SYNC update with LTSPICEXVII 64/32 and LTSPICEIV
theeten,
Check your primary files in LTSPICEXVII where you should find the "scad.exe" files in LTSPICEIV.
You should see a 64 bit .exe file and a 32bit .exe file listed.
Follow the procedures I gave for each program.
IF something happens doing this please post (even if you just had to use the "administrator options" or similar).
So far everyone who uses a decent workaround has not had a serious issue.
W. Warren
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Re: Doing the SYNC update with LTSPICEXVII 64/32 and LTSPICEIV
Hello wms121
I also use W7 32 and W7 64 and W10 64.
The LTspiceXVII installation does not let me to choose between 32 or 64 bits.
But I always do complete installations.
I don't like sync update.
Regards
PhB
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Re: Doing the SYNC update with LTSPICEXVII 64/32 and LTSPICEIV
...just Windows 10 and Windows 7, although I have tested LTSPICEIV on WinXP and OpenSuse13 via WINE.
If I have any difficulties using Linux, OpenBSD or Solaris* I will post that info here.
W. Warren
*( haven't gotten WINE to work under Solaris 10)
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