Re: FFT spectrum calculation algorithm ?
Hi, John:
?
I didn't see it in the help, but I saw it in the pop-up menu when doing FFT.
?
I upload the screenshot of this pop-up menu.
?
?
Thank you very much.
Best regards.
?
On Thu, Mar 27, 2025 at 04:15 PM, John Woodgate wrote:
Yes. Look at the Help for Waveform Arithmetic. At the end you can see an FFT set-up pane that allows start and end times for the FFT to be set up.
--
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
|
Re: FFT spectrum calculation algorithm ?
Yes. Look at the Help for Waveform Arithmetic.
At the end you can see an FFT set-up pane that allows start and
end times for the FFT to be set up.
On 2025-03-27 08:00, ericsson.sunshine
via groups.io wrote:
Hi, :
?
May I ask about FFT feature ?
?
If in a waveform viewer, I want to do FFT analysis of a
chosen node, which may has multiple frequency components varying
during whole simulation time interval.
Can it be done to separate the whole simulation time into
several intervals by eg: zoom-in feature, then run the FFT
feature only for the "zoom-in"ed waveform data, to see what's
the freq component in these data ?
I say so, because, some applications , eg: OFDM modulation,
may have the multiple freq components in modulated signal, and
may vary the amplitude depending on transmitted data in
different time interval.
?
It helps to analyze if FFT could do analyzing of separated
time interval in a single waveform.
?
Is this feature supported ?
?
Thank you very much.
Best regards.
--
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
|
FFT spectrum calculation algorithm ?
Hi, :
?
May I ask about FFT feature ?
?
If in a waveform viewer, I want to do FFT analysis of a chosen node, which may has multiple frequency components varying during whole simulation time interval.
Can it be done to separate the whole simulation time into several intervals by eg: zoom-in feature, then run the FFT feature only for the "zoom-in"ed waveform data, to see what's the freq component in these data ?
I say so, because, some applications , eg: OFDM modulation, may have the multiple freq components in modulated signal, and may vary the amplitude depending on transmitted data in different time interval.
?
It helps to analyze if FFT could do analyzing of separated time interval in a single waveform.
?
Is this feature supported ?
?
Thank you very much.
Best regards.
|
Re: Sawtooth waveform by simple BJTs, but dips at the top.
Hi, Andy:
?
Your suggestions are absolutely correct!
?
I just tried,?
1. Modify the PWL's Trise = 1u (from 10n), Tfall = 1u (from 10n), the peaks are eliminated.
2. modify R1 = 5.1K, C1=10nf with unchanged Trise, Tfall, the V(vout) has no peaks phenomemon ,too.
?
Both works . Heil ! Viva! Banzai! Hooray! Live Looooooooong!
?
Wish you happy & good healthy!
Best regards.
?
On Thu, Mar 27, 2025 at 09:48 AM, Andy I wrote:
On Wed, Mar 26, 2025 at 04:46 AM, <ericsson.sunshine@...> wrote:
It looks like, different modeling topology of OPA will maybe show different behavior.
Quite probably not.
?
Let's consider what makes these two integrators different.? ?I'm talking about U1 = LT1220 in "Lab 4 Integrator Square 500us with PWL.asc", versus U1 = MCP6001 in "triangle_gear.asc".
?
In the first case, the square wave comes from a PWL voltage source with Tr = Tf = 10 ns.? In the second case, the square wave comes from a saturated op-amp comparator, with Tr = Tf = 7.7 us, nearly 1000 times slower.? One sends a 10 ns, 10 mA (1 MegAmp/us) current step to the integrator.? The second sends a 7.7 us, 10 uA (0.0000013 MegAmp/us) current step to its integrator.? That is 770 times slower and 1000 times smaller amplitude, or nearly 1,000,000 times smaller di/dt.? The slower speed gives the op-amp more chance to respond and recover.? If you plot the second integrator's d(V(tri_1)), you can see a combination of BOTH a ramp in its dv/dt (causing the peak to round), and smaller glitches at the start and end of the square wave's edges.? It is a mixture of effects.
?
It should also be noted that the two circuits employ vastly different op-amps.? One uses a high-speed op-amp with 45 MHz GBP and SR = 250 V/us, and the other is a low-power op-amp with 1 MHz GBP and SR = 0.6 V/us.? It's like apples and oranges.? They do not compare well.
?
I think it is likely that "different modeling topology" of the op-amps is not related to the different behaviors of the two circuits.
?
Andy
?
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Re: Sawtooth waveform by simple BJTs, but dips at the top.
On Thu, Mar 27, 2025 at 07:06 AM, Andy I wrote:
?
I have little practical use for them anymore, but about fifty years ago I started studying and collecting them and quickly had assembled a collection of several dozen circuits to generate accurate triangle waves.
?
?
Andy
?
?
Hi, Andy:
?
Sorry, forgot it.
?
May I ask, how old are you ?
|
Re: Sawtooth waveform by simple BJTs, but dips at the top.
Hi, Andy:
?
Thank you for the reply.
At the first, the purpose is to seek a good C/P solution, to generate a varying, mostly sawtooth or triangle waveform and inject it into some Vref pin of PWM IC.
The Vref which I think, is utilized for the internal reference voltage of comparators of the IC. Thus to give the varying frequency of PWM in a fixed frequency designed IC.
?
So, the instant change of frequency means, the duty cycle or period will significantly vary , if consider the load, mostly inductance loading, this peak , I think , normally, would be likely avoided.
?
And, while talking about the good choice of C/P, I think the more choices considered , the better solutions should come out.
?
Thank you very much for the helpful opinions.
?
Best regards.
?
On Thu, Mar 27, 2025 at 07:06 AM, Andy I wrote:
ericsson.sunshine,
?
Allow me to ask.? What is this for?? Is the plan to build one of these circuits (not just to simulate it) where it has a useful purpose?
?
The first few circuits you uploaded were not oscillators; they were circuits to convert something like a square wave into a triangular or sawtooth wave.? As such, they were only one-half of the circuit you would need to design and build.
?
Triangle or sawtooth wave oscillator circuits are very plentiful.? Is this your first venture into making sawtooth waves?? You should be able to find hundreds of them.
?
I have little practical use for them anymore, but about fifty years ago I started studying and collecting them and quickly had assembled a collection of several dozen circuits to generate accurate triangle waves.
?
If this were for simulations only, I'm sure you know that a PULSE voltage source makes an accurate sawtooth, with no artifacts.
?
Have you considered other waveforms besides sawtooth, for dithering?
?
In the last photo you uploaded (3 of 3), the peak of the sawtooth is rounded.? Is that any better than the other ones with the glitch near the peak?? Either waveform has a flawed derivative, dv/dt.
?
Andy
?
?
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Re: Sawtooth waveform by simple BJTs, but dips at the top.
On Wed, Mar 26, 2025 at 04:46 AM, <ericsson.sunshine@...> wrote:
It looks like, different modeling topology of OPA will maybe show different behavior.
Quite probably not.
?
Let's consider what makes these two integrators different.? ?I'm talking about U1 = LT1220 in "Lab 4 Integrator Square 500us with PWL.asc", versus U1 = MCP6001 in "triangle_gear.asc".
?
In the first case, the square wave comes from a PWL voltage source with Tr = Tf = 10 ns.? In the second case, the square wave comes from a saturated op-amp comparator, with Tr = Tf = 7.7 us, nearly 1000 times slower.? One sends a 10 ns, 10 mA (1 MegAmp/us) current step to the integrator.? The second sends a 7.7 us, 10 uA (0.0000013 MegAmp/us) current step to its integrator.? That is 770 times slower and 1000 times smaller amplitude, or nearly 1,000,000 times smaller di/dt.? The slower speed gives the op-amp more chance to respond and recover.? If you plot the second integrator's d(V(tri_1)), you can see a combination of BOTH a ramp in its dv/dt (causing the peak to round), and smaller glitches at the start and end of the square wave's edges.? It is a mixture of effects.
?
It should also be noted that the two circuits employ vastly different op-amps.? One uses a high-speed op-amp with 45 MHz GBP and SR = 250 V/us, and the other is a low-power op-amp with 1 MHz GBP and SR = 0.6 V/us.? It's like apples and oranges.? They do not compare well.
?
I think it is likely that "different modeling topology" of the op-amps is not related to the different behaviors of the two circuits.
?
Andy
?
|
Re: Sawtooth waveform by simple BJTs, but dips at the top.
ericsson.sunshine,
?
Allow me to ask.? What is this for?? Is the plan to build one of these circuits (not just to simulate it) where it has a useful purpose?
?
The first few circuits you uploaded were not oscillators; they were circuits to convert something like a square wave into a triangular or sawtooth wave.? As such, they were only one-half of the circuit you would need to design and build.
?
Triangle or sawtooth wave oscillator circuits are very plentiful.? Is this your first venture into making sawtooth waves?? You should be able to find hundreds of them.
?
I have little practical use for them anymore, but about fifty years ago I started studying and collecting them and quickly had assembled a collection of several dozen circuits to generate accurate triangle waves.
?
If this were for simulations only, I'm sure you know that a PULSE voltage source makes an accurate sawtooth, with no artifacts.
?
Have you considered other waveforms besides sawtooth, for dithering?
?
In the last photo you uploaded (3 of 3), the peak of the sawtooth is rounded.? Is that any better than the other ones with the glitch near the peak?? Either waveform has a flawed derivative, dv/dt.
?
Andy
?
?
|
Re: Sallen Key Filter Capacitor at feedback network
Pity; I was looking forward to dissecting
that.
On 2025-03-26 16:48, Andy I via
groups.io wrote:
FYI - Antonios deleted the files already, before their
message was approved.
?
I'm guessing they answered their own question already.?
Perhaps no follow-up is needed anymore.
?
Andy
--
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
|
Re: Sallen Key Filter Capacitor at feedback network
FYI - Antonios deleted the files already, before their message was approved.
?
I'm guessing they answered their own question already.? Perhaps no follow-up is needed anymore.
?
Andy
|
Re: Sallen Key Filter Capacitor at feedback network
You should not have uploaded to Files. Uploads
go into Files/Temp. I can't find your upload in Files, or in
Temp. Please upload it to Files/Temp.
Hello everyone,
I am designing an Analog Front-End for biosignals (EMGs). You
can find the corresponding circuit here /g/LTspice/files/EMG_AFE.asc.
I have selected INA317 as an instrumentation amplifier and I am
trying to design a 2nd order low pass filter after the InAmp
stage. The problem is at Capacitor C3. If I remove the capacitor
and connect the path to ground, the circuit behavior is not as
expected. However the classic Sallen Key circuit topology does
not contain this capacitor. Should someone has any idea why is
it necessary in this particular configuration with the INA317, I
would be very grateful. Thank you in advance.?
?
--
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
|
Sallen Key Filter Capacitor at feedback network
Hello everyone,
I am designing an Analog Front-End for biosignals (EMGs). You can find the corresponding circuit here /g/LTspice/files/EMG_AFE.asc. I have selected INA317 as an instrumentation amplifier and I am trying to design a 2nd order low pass filter after the InAmp stage. The problem is at Capacitor C3. If I remove the capacitor and connect the path to ground, the circuit behavior is not as expected. However the classic Sallen Key circuit topology does not contain this capacitor. Should someone has any idea why is it necessary in this particular configuration with the INA317, I would be very grateful. Thank you in advance.?
?
|
On 25/03/2025 19:07, pilou via
groups.io wrote:
thanks a lot for your reply.
Indeed, it's an inverting amplifier.
But if you look closer, no need to negative supply as the
amplifier positive input is connected to mid-supply: it acts as
a "virtual ground".
I first tested the whole schematic without PTC and it "works"
:)
Update:
Change V2 from 13VDC to:
PULSE(0 13 0 100u 0 1 2 1)
.. and the whole simulation works OK in both 24.0.12 and 24.1.5. You
might also try using the "startup" switch in the .TRAN directive,
which also works:
.TRAN 1 startup
--
Regards,
Tony
|
On 25/03/2025 19:07, pilou via
groups.io wrote:
Thanks a lot for your reply.
Indeed, it's an inverting amplifier.
But if you look closer, no need to negative supply as the
amplifier positive input is connected to mid-supply: it acts as
a "virtual ground".
I first tested the whole schematic without PTC and it "works"
:)
I tested the whole schematic by removing the PTC and with R2
grounded, in a .OP analysis, and it didn't work in either 24.0.12 or
24.1.5 , although the errors are different:
24.1.5
Convergence Failure:? Time step too small;
initial timepoint: trouble with instance "J2"
24.0.12
Singular matrix:? Check nodes v2#branch and
u2:vn
?? Iteration No. 4
Singular matrix:? Check nodes v2#branch and u2:vn
?? Iteration No. 1
Singular matrix:? Check nodes v2#branch and u2:vn
?? Iteration No. 1
Singular matrix:? Check nodes v2#branch and u2:vn
?? Iteration No. 1
Singular matrix:? Check nodes v2#branch and u2:vn
?? Iteration No. 1
Singular matrix:? Check nodes v2#branch and u2:vn
?? Iteration No. 1
Singular matrix:? Check nodes v2#branch and u2:vn
?? Iteration No. 1
Singular matrix:? Check nodes v2#branch and u2:vn
?? Iteration No. 1
Starting source stepping with srcstepmethod=1
Source Step = 3.0303%
Source stepping failed
Singular matrix:? Check nodes u2:vn and u2:vp
?? Iteration No. 4
Fatal Error: Singular matrix:? check nodes u2:vn and u2:vp
?? Iteration No. 4
You can't conclude much from the errors.
If I also remove J1 as well, the circuit does simulate in 24.1.x,
but not in 24.0.12 and foldback occurs at ~7.7A.
Hope that's helpful.
--
Regards,
Tony
|
Re: Sawtooth waveform by simple BJTs, but dips at the top.
On Wed, Mar 26, 2025 at 03:28 PM, Jim Wagner wrote:
Please label plotted nodes. Nothing shows where node n001 is!
?
Jim
Hi, Jim:
?
Forget the previous files, I found another , which don't neet a PWL source, only DC-supply needed.
Yes, of course, I miss this one, again.? The oscillation's very well.
?
/g/LTspice/files/z_yahoo/Files%20sorted%20by%20message%20number/msg_62836/MCP_6001_triangle_ic.zip
?
The ran result is as below:
?
?
It looks like, different modeling topology of OPA will maybe show different behavior.
?
Thank you very much.
Best regards.
|
Re: Sawtooth waveform by simple BJTs, but dips at the top.
Please label plotted nodes. Nothing shows where node n001 is!
?
Jim
On 03/25/2025 11:49 PM PDT ericsson.sunshine via groups.io <ericsson.sunshine@...> wrote:
?
?
Hi, :
?
I'm sorry...
I miss this, in the following two examples, they shows same phenomemon , there are peaks at the top.
?
?
The ran result shows in the image,?
?
Does this belong to the intrinsic characteristic of the OPA or ... any improving topology/method available ?
?
I appreciate any opinion sharing.
?
Thank you at the beginning.
?
Have nice happiness/day/healthy!
?
|
Re: Sawtooth waveform by simple BJTs, but dips at the top.
Hi, :
?
I'm sorry...
I miss this, in the following two examples, they shows same phenomemon , there are peaks at the top.
?
?
The ran result shows in the image,?
?
Does this belong to the intrinsic characteristic of the OPA or ... any improving topology/method available ?
?
I appreciate any opinion sharing.
?
Thank you at the beginning.
?
Have nice happiness/day/healthy!
?
|
Re: LTspice non-inverting Opamp loop gain.
For inverting amplifier (like LTspice example) input connected with ground for open loop test.
You can test what happened if you short input with ground for non-inverted amplifier (simple Opamp with 2 resistors circuit).
I think you will be surprised looking at negative AOL :)
So, to check AOL, you need to know whether the amplifier is inverting or non-inverting.
--
Kind regards,
Victor
|
On 25/03/2025 19:07, pilou via
groups.io wrote:
thanks a lot for your reply.
Indeed, it's an inverting amplifier.
But if you look closer, no need to negative supply as the
amplifier positive input is connected to mid-supply: it acts as
a "virtual ground".
I first tested the whole schematic without PTC and it "works"
:)
Sorry. Yes, you're right.
--
Regards,
Tony
|
Re: LTspice non-inverting Opamp loop gain.
On Tue, Mar 25, 2025 at 03:22 PM, John Woodgate wrote:
stability, open loop modelling (Tian method
Amazing what Google's AI spits out...
?
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John Woodgate
Tony Casey
LV
DerekK