Re: using LTSPICE symbols for representation of spice netlist of OPAMP
Hello Andy,I managed to do it as shown in the attached file.
added the whole netlist as a directive and deleted the last pin number of the title.
Is it Ok?
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Thanks.
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/g/LTspice/files/Temp/op-amp%20AD797%20%281%29.asc
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Re: using LTSPICE symbols for representation of spice netlist of OPAMP
Hello Andy,I did what you said it still gives a netlist bug which says pin mismatch.
Ltspice file and the errotr is attached.
Where did I go wrong?
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/g/LTspice/files/Temp/ad797_cir.zip
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LLC schematic from "flyback" with mistakes
Group member "flyback" (massey2) uploaded a schematic earlier today "LLC to compare.asc".? ?But she or he may have forgotten to read the group's guidelines.? Files should be uploaded into the "Temp" directory only.? (I fixed that for you.)? Uploaded files must be accompanied by a message from you, telling us why you uploaded it, or what is your question.
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The file she or he uploaded does not run without errors.? There were mistakes in the schematic.? I corrected some (not all) of them, and uploaded "LLC to compare AI1.asc".
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But it is still not right.? "flyback" attempted to make parameters depend on a voltage in the circuit, and that can never work.? Parameter values are fixed during any simulation run, and their values must be known before the simulation begins.? I substituted a dummy value for the first one that was supposed to track a voltage.
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If you want to make the parameters (not .PARAMs but circuit element parameters) depend on your voltage at node EA, you must find another way to do it.
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The extensive use of Rser with your voltage sources is somewhat troubling.? Attempting to power an op-amp that way, with no bypass capacitors, might lead to failure, although Rser was small enough so it's probably OK.? Also be more careful with your typing.? Numbers such as "0..01" might not work.? (I fixed that too.)
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Andy
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Re: Build spice model of transimpedance amplifier
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Re: Build spice model of transimpedance amplifier
So.. what? bandwidth are You looking for?
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Re: Looking for advice on TRAN timing
#FFT
Thank you for your reply and the test file, Andy.
Indeed, splitting v(out) into v(out)@1 and v(out)@2 clearly revealed the missing part at the end,
and so the crazy fft plot makes perfect sense. Specifying a time range solved the fft problem.
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--
Ryu
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Re: Estimating Base spreading resistance for a bipolar transistor via LTspice
"In that case I would suggest capturing waveforms on a transistor driving a dummy load, and matching them by modifying Rb for a model that is known to already have correct high-frequency behavior. One step further would be to get the low-current Rb with the noise method and then adjusting Rbm and Irb to match the waveform."
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A practical & useful suggestion. Thank you!
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Re: Estimating Base spreading resistance for a bipolar transistor via LTspice
In that case I would suggest capturing waveforms on a transistor driving a dummy load, and matching them by modifying Rb for a model that is known to already have correct high-frequency behavior. One step further would be to get the low-current Rb with the noise method and then adjusting Rbm and Irb to match the waveform.
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Re: 12AU7 tube heater model
It’s a somewhat obscure figure of merit in statistical analysis.
An R^2 of 1.00 is as near perfect fit as possible, of a formula to a set of data.
Anything close to that, is “close enough!”
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Dave
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From: [email protected] <[email protected]>
On Behalf Of Carlo
Sent: Saturday, February 22, 2025 9:38 AM
To: [email protected]
Subject: EXTERNAL: Re: [LTspice] 12AU7 tube heater model
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On Sat, Feb 22, 2025 at 08:14 AM, John Woodgate wrote:
A bit of Excel work gives a resistance trend line (for voltages between 3.0 and 6.5)? R = 0.22*V^2 + 3.61*V + 6.50. The R^2 (accuracy measure) = 0.9993, good enough for government work.
Sorry, what does R^2 accuracy measure of 0.9993 actually mean ?
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Re: Estimating Base spreading resistance for a bipolar transistor via LTspice
Hi Jerry, I am investigating a NMOSFET based class E oscillator. The BJT will be used as a driver for the mosfet and part of the feedback loop will include the rbb and the cap_be of the BJT in series with the input capacitance of the mosfet. Hence I am after the high current version of the rbb.
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Re: Estimating Base spreading resistance for a bipolar transistor via LTspice
Thank you keantoken. I am interested in the Rbb at high current values. Would the s-parameters help for this estimation? If if does, then please provide some guidelines on how to do so. I am already familiar with deriving s-parameters for a bjt in LTspice.
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Re: 12AU7 tube heater model
IIRC, we've been told that v24.1.3? restores LTspice's ability to generate the netlist, but the netlist it generates is no longer usable as the input to new simulations?
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Stupid.? Er, Bummer.? No, it IS stupid.
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Andy
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Re: Estimating Base spreading resistance for a bipolar transistor via LTspice
Do you want to experiment with this in relation with noise
voltage?
You could probably build a theoretical model circuit of your
transistor and adjust an explicit Rbb' until you have coincidence
between the simulation and the real-life behavior.
Le 22/02/2025 à 18:31, Kamran Ahmed via
groups.io a écrit?:
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Show quoted text
Hello friends,
?
Is there a way of estimating the base spreading resistance of
a bipolar transistor by using LTspice? Perhaps via getting the
transistor's S-parameters?
Many thanks in advance!
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Re: Estimating Base spreading resistance for a bipolar transistor via LTspice
I meant to say the fall in transconductance as frequency increases.
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Re: Estimating Base spreading resistance for a bipolar transistor via LTspice
For a BJT model, the parameters Rb, Rbm and Irb determine the base spreading resistance. The resistance is Rb at low currents and falls to the value of Rbm as current increases past the value of Irb.
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The base spreading resistance is not present in LTspice unless it has been specified in the model. Many models use Rb=10 as a default value. There are many thousands of garbage models in existence which bear only a passing resemblance to the BJTs they are named after (likely the result of a failed attempt to batch process a dataset into SPICE models).
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Rb can be estimated by measuring the base voltage noise of a transistor at the collector current you plan to use it at. This does not always give the same value of Rb as the high frequency estimation method where you determine Rb based on the rise in transconductance as frequency approaches Ft (this is possible with s-parameters).
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There are still other methods of extracting Rb that are given in multiple long PDFs about the SGP model, although I can't find any of them at the moment.
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Here is a page with a calculator for using the noise method:
http://www.dicks-website.eu/low_noise_amp_part4/part4.html
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Re: 12AU7 tube heater model
I think it's a question that's no often asked:
people just accept it as a magic number. I did a web search,
which led to a URL about half a km long, so I can't post it.
Instead, do a web search for 'Coefficient
of Determination, R-squared'. It's a measure of the accuracy of
the trend line, based on RMS deviations from the curve. A
perfect match is a value of 1.
On 2025-02-22 17:38, Carlo wrote:
On Sat, Feb 22, 2025 at 08:14 AM, John Woodgate wrote:
A bit of Excel work gives a resistance trend line
(for voltages between 3.0 and 6.5)? R = 0.22*V^2 + 3.61*V +
6.50. The R^2 (accuracy measure) = 0.9993, good enough for
government work.
Sorry, what does R^2 accuracy measure of 0.9993 actually mean ?
?
Thanks.
--
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: 12AU7 tube heater model
On 22/02/2025 16:30, Andy I via
groups.io wrote:
I believe that this
has been somewhat restricted now, in LTspice version 24.1.?
Previous versions generated a SPICE Netlist file when they ran,
which was saved on your drive but deleted when LTspice is closed.?
Version 24.1 no longer generates a runnable SPICE Netlist file.? I
believe it can still run (process) a Netlist file if you have one,
but saving one might no longer be an option.? I could be wrong.
I haven't yet tried other than 24.1.0, but View > SPICE Netlist
> Right-click > Edit as Independent Netlist > Save, is
still available from the Schematic menu.
I hope that feature remains, otherwise how about if you wanted to
use batch mode (with -b) to run a netlist? (Assuming batch mode,
itself, is still available.)
--
Regards,
Tony
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Re: 12AU7 tube heater model
On Sat, Feb 22, 2025 at 08:14 AM, John Woodgate wrote:
A bit of Excel work gives a resistance trend line (for voltages between 3.0 and 6.5)? R = 0.22*V^2 + 3.61*V + 6.50. The R^2 (accuracy measure) = 0.9993, good enough for government work.
Sorry, what does R^2 accuracy measure of 0.9993 actually mean ?
?
Thanks.
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Estimating Base spreading resistance for a bipolar transistor via LTspice
Hello friends,
?
Is there a way of estimating the base spreading resistance of a bipolar transistor by using LTspice? Perhaps via getting the transistor's S-parameters?
Many thanks in advance!
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Re: 12AU7 tube heater model
FYI - My advice about adding GMIN across current sources, is that you should specifically add them to your current sources, by adding a resistor in parallel with them.
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The checkbox in the Control Panel's Hacks! tab is not permanent (it goes away when you close and then re-start LTspice), and it does not solve any topology problems and won't eliminate that error you had.? If you think you need a conductance added across your current sources, do it by adding resistors to the schematic!? That is my advice.
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Andy
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Bell, Dave
John Woodgate
Tony Casey
Carlo