Re: Sallen Key Filter Capacitor at feedback network
FYI - Antonios deleted the files already, before their message was approved.
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I'm guessing they answered their own question already.? Perhaps no follow-up is needed anymore.
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Andy
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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
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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.?
?
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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
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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
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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!
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Jim
Hi, Jim:
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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.
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/g/LTspice/files/z_yahoo/Files%20sorted%20by%20message%20number/msg_62836/MCP_6001_triangle_ic.zip
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The ran result is as below:
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It looks like, different modeling topology of OPA will maybe show different behavior.
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Thank you very much.
Best regards.
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Re: Sawtooth waveform by simple BJTs, but dips at the top.
Please label plotted nodes. Nothing shows where node n001 is!
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Jim
On 03/25/2025 11:49 PM PDT ericsson.sunshine via groups.io <ericsson.sunshine@...> wrote:
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Hi, :
?
I'm sorry...
I miss this, in the following two examples, they shows same phenomemon , there are peaks at the top.
?
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The ran result shows in the image,?
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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!
?
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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!
?
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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
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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
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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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Re: LTspice non-inverting Opamp loop gain.
Hi, Victor. Perhaps I should say 'Salve,
Victor'! I think you need to explain a bit more about your
question. What is it about the Tian method that you need more
information on? In the first place, with no external input, the
opamp doesn't 'know' whether it is inverting or non-inverting;
that is just a matter of how the external signal is fed in. In
the inverting case, it is fed through a resistor, but in the
non-inverting case, that resistor is between the inverting input
and ground, while the external input is applied, either via a resistor or directly, to the non-inverting input of the opamp, which may
have near-infinite internal impedance or a value defined in the
data sheet.
On 2025-03-25 21:46, LV via groups.io
wrote:
This one?
Read youself what you sent.
I ask about stability, open loop modelling (Tian method), NOT
how to build non-inverting opamp circuit.
--
Kind regards,
Victor
--
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: LTspice non-inverting Opamp loop gain.
This one?
Read youself what you sent.
I ask about stability, open loop modelling (Tian method), NOT how to build non-inverting opamp circuit.
--
Kind regards,
Victor
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Re: LTspice non-inverting Opamp loop gain.
*Actually*, Dave (me) is not a purist about this side topic!
I expected one of the real purists to chime in before this.
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I pointed Victor towards a tutorial on the subject he was asking about.
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Dave
toggle quoted message
Show quoted text
From: [email protected] <[email protected]>
On Behalf Of John Woodgate
Sent: Tuesday, March 25, 2025 2:28 PM
To: [email protected]
Subject: EXTERNAL: Re: [LTspice] LTspice non-inverting Opamp loop gain.
?
Dave is a wee bit purist on what is on-topic. The list has very many members , so we can expect differences of opinion, and accept them.
On 2025-03-25 21:15, BRUCE108 wrote:
You will soon be told this forum is for LTspice-specific questions, not for electronic design.? :{)
But I would suggest:
?
What's your point Dave? Should we not be doing what we are doing? Should we be doing something else? The information exists all over the web and is not hard to find.?
I'm just sayin'
?
--
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: LTspice non-inverting Opamp loop gain.
I asking exactly about LTspice example and how to modify open loop probes and input for non-inverting amp.
Sorry, I no need empty answers. If you dond`t know how - skip my question and drink tea.
--
Kind regards,
Victor
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Re: LTspice non-inverting Opamp loop gain.
Dave is a wee bit purist on what is on-topic.
The list has very many members , so we can expect differences of
opinion, and accept them.
On 2025-03-25 21:15, BRUCE108 wrote:
Dave Bell wrote:
You
will soon be told this forum is for LTspice-specific
questions, not for electronic design.? :{)
But
I would suggest:
?
What's
your point Dave? Should we not be doing what we are doing?
Should we be doing something else? The information exists
all over the web and is not hard to find.?
I'm
just sayin'
?
--
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: LTspice non-inverting Opamp loop gain.
Dave Bell wrote:
You will soon be told this forum is for LTspice-specific questions, not for electronic design.? :{)
But I would suggest:
?
What's your point Dave? Should we not be doing what we are doing? Should we be doing something else? The information exists all over the web and is not hard to find.?
I'm just sayin'
?
|
Re: LTspice non-inverting Opamp loop gain.
You will soon be told this forum is for LTspice-specific questions, not for electronic design.? :{)
But I would suggest:
?
?
Dave
?
toggle quoted message
Show quoted text
From: [email protected] <[email protected]>
On Behalf Of LV via groups.io
Sent: Tuesday, March 25, 2025 1:34 PM
To: [email protected]
Subject: EXTERNAL: [LTspice] LTspice non-inverting Opamp loop gain.
?
There is example for open loop gain simulation for inverting Opamp:
C:\Users\...\AppData\Local\LTspice\examples\Educational\LoopGain2.asc
How to modify probes circuit and connection for Non-inverting Opamp?
Especially how I should connect non-inverting input?
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On Tue, Mar 25, 2025 at 10:44 AM, Tony Casey wrote:
Are you sure? U2 and J2 are correct?
U2 is configured as an inverting amplifier and is connected to node OUT, which must always be positive. Therefore, U2's output should go negative, but it can't because it doesn't have a negative power rail, it is grounded.
Hi Tony,
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" :)
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On 25/03/2025 17:40, pilou via
groups.io wrote:
I'm very sorry. I forget to correct paths into symbol and
indeed I forget a lib too.
For R3, it wasn't connected to VCC: the wire was too long ;)
I just re-upload the whole schematic:
Are you sure? U2 and J2 are correct?
U2 is configured as an inverting amplifier and is connected to node
OUT, which must always be positive. Therefore, U2's output should go
negative, but it can't because it doesn't have a negative power
rail, it is grounded.
Did you test each stage before connecting it all together?
--
Regards,
Tony
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John Woodgate
Tony Casey
LV
DerekK
Bell, Dave