Problem with Spice - it won't allow me to change bounds of g

[Michael Noone]

Hi - I'm trying to simulate a circuit with spice (which I'm very new to). I
first set a DC sweep on the input (V3):

https://netfiles.uiuc.edu/mnoone/www/Electronics/iviewcapture_date_30_03_
2005_time_11_38_36.jpg

Then I hit the run button and choose node 6 (the output) when it prompts
me, giving me this graph:

https://netfiles.uiuc.edu/mnoone/www/Electronics/iviewcapture_date_30_03_
2005_time_11_39_02.jpg

Then I try to change the horizontal axis bounds:

https://netfiles.uiuc.edu/mnoone/www/Electronics/iviewcapture_date_30_03_
2005_time_11_39_15.jpg

Which for some odd reason does not work:

https://netfiles.uiuc.edu/mnoone/www/Electronics/iviewcapture_date_30_03_
2005_time_11_39_19.jpg

Any idea as to what I am doing wrong? Thanks for your help!

-Michael J. Noone

 

[Robert Monsen]

Michael Noone wrote:

Hi - I'm trying to simulate a circuit with spice (which I'm very new to). I
first set a DC sweep on the input (V3):

https://netfiles.uiuc.edu/mnoone/www/Electronics/iviewcapture_date_30_03_
2005_time_11_38_36.jpg

Then I hit the run button and choose node 6 (the output) when it prompts
me, giving me this graph:

https://netfiles.uiuc.edu/mnoone/www/Electronics/iviewcapture_date_30_03_
2005_time_11_39_02.jpg

Then I try to change the horizontal axis bounds:

https://netfiles.uiuc.edu/mnoone/www/Electronics/iviewcapture_date_30_03_
2005_time_11_39_15.jpg

Which for some odd reason does not work:

https://netfiles.uiuc.edu/mnoone/www/Electronics/iviewcapture_date_30_03_
2005_time_11_39_19.jpg

Any idea as to what I am doing wrong? Thanks for your help!

You are posting this question to the wrong newsgroup.

-Michael J. Noone

Try the cad newsgroup. However, once you've done the sweep, if you put
the cursor over circuit nets, it'll turn into a little probe. If you
then right click, it shows the voltage on that node. If you hover over a
component, another cursor shows up, and you can find the current.
Holding down the alt key while clicking on a component gives you the
power dissipated in that component.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.

 

[Michael Noone]

Robert Monsen <rcsurname@comcast.net> wrote in
news:xpqdnbzqRcIJ7NbfRVn-rA@comcast.com:

Try the cad newsgroup. However, once you've done the sweep, if you put
the cursor over circuit nets, it'll turn into a little probe. If you
then right click, it shows the voltage on that node. If you hover over
a component, another cursor shows up, and you can find the current.
Holding down the alt key while clicking on a component gives you the
power dissipated in that component.

I don't think you understand - the problem is that it will only display on
the x axis v3=9.9-10, even though it's set to range from 0-10.

-M. Noone

 

[Robert Monsen]

Michael Noone wrote:

Robert Monsen <rcsurname@comcast.net> wrote in
news:xpqdnbzqRcIJ7NbfRVn-rA@comcast.com:

Try the cad newsgroup. However, once you've done the sweep, if you put
the cursor over circuit nets, it'll turn into a little probe. If you
then right click, it shows the voltage on that node. If you hover over
a component, another cursor shows up, and you can find the current.
Holding down the alt key while clicking on a component gives you the
power dissipated in that component.


I don't think you understand - the problem is that it will only display on
the x axis v3=9.9-10, even though it's set to range from 0-10.

-M. Noone

Perhaps I wasn't paying attention.

If you select an area, it will only show that area. If you then right
click on the waveform display window, and select "Zoom to Fit" from the
popup, it'll show the entire waveform.

If you right click on the waveform window, and select 'Autorange' it may
be better. Perhaps you got into manual limit mode somehow.

There is a manual that talks about this stuff. Use the help menu. There
is also a yahoo group devoted to LTSpice, which may have more answers
for you.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.

 

[Michael Noone]

Robert Monsen <rcsurname@comcast.net> wrote in
news_idnUl_CrcFMdbfRVn-rg@comcast.com:

Perhaps I wasn't paying attention.

If you select an area, it will only show that area. If you then right
click on the waveform display window, and select "Zoom to Fit" from
the popup, it'll show the entire waveform.

If you right click on the waveform window, and select 'Autorange' it
may be better. Perhaps you got into manual limit mode somehow.

There is a manual that talks about this stuff. Use the help menu.
There is also a yahoo group devoted to LTSpice, which may have more
answers for you.

Hi again mr Monsen - I read through the pertaining sections in the
LTSpice manual, but I couldn't find anything about what I was doing.

Zoom to fit is greyed out for some odd reason:

https://netfiles.uiuc.edu/mnoone/www/Electronics/iviewcapture_date_31_03
_2005_time_07_58_48.jpg

There are "autorange Y axis" and "autoranging" menu items when I right
lick on the waveform window. The autoranging item seems not to do
anything, while the other just auto ranges the y axis.

If you want to try it out for yourself (I've duplicated this same
problem on 2 computers now), this is the schematic:

https://netfiles.uiuc.edu/mnoone/www/Electronics/linear%20amplifier.asc


Thanks again,

-Michael

 

[Larry Brasfield]

"Michael Noone" <mnoone.uiuc.edu@127.0.0.1> wrote in message
news:Xns962A5250173C4mnooneuiucedu127001@204.127.199.17...

Robert Monsen <rcsurname@comcast.net> wrote in
news_idnUl_CrcFMdbfRVn-rg@comcast.com:

Perhaps I wasn't paying attention.

If you select an area, it will only show that area. If you then right
click on the waveform display window, and select "Zoom to Fit" from
the popup, it'll show the entire waveform.

If you right click on the waveform window, and select 'Autorange' it
may be better. Perhaps you got into manual limit mode somehow.

There is a manual that talks about this stuff. Use the help menu.
There is also a yahoo group devoted to LTSpice, which may have more
answers for you.

Hi again mr Monsen - I read through the pertaining sections in the
LTSpice manual, but I couldn't find anything about what I was doing.

Zoom to fit is greyed out for some odd reason:

https://netfiles.uiuc.edu/mnoone/www/Electronics/iviewcapture_date_31_03
_2005_time_07_58_48.jpg

There are "autorange Y axis" and "autoranging" menu items when I right
lick on the waveform window. The autoranging item seems not to do
anything, while the other just auto ranges the y axis.

If you want to try it out for yourself (I've duplicated this same
problem on 2 computers now), this is the schematic:

https://netfiles.uiuc.edu/mnoone/www/Electronics/linear%20amplifier.asc

Using that source, I cannot replicate your problem. (I did
use my finger on the mouse rather than my tongue!) Zoom-
to-fit is active. Zooming works as Mr. Monsen describes.

Maybe it would help to describe what you are actually
expecting to see. The trouble may reside there.

Looking at your circuit, I find myself wondering if you
have dropped your 1 mS response time requirement.
What that unreal when you mentioned it awhile back?

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Michael Noone]

"Larry Brasfield" <donotspam_larry_brasfield@hotmail.com> wrote in
news:0bX2e.28$oI2.743@news.uswest.net:

Using that source, I cannot replicate your problem. (I did
use my finger on the mouse rather than my tongue!) Zoom-
to-fit is active. Zooming works as Mr. Monsen describes.

Maybe it would help to describe what you are actually
expecting to see. The trouble may reside there.

Looking at your circuit, I find myself wondering if you
have dropped your 1 mS response time requirement.
What that unreal when you mentioned it awhile back?

Hmm this is odd indeed. I was expecting for the x axis to have a range of
V3=0-10 volts in 01.V increments. I was then hoping to see a nice little
linear line that would be something like Y=30X. Is this what you are
seeing? Instead - All I see is the x axis having a range of v3 = 9.9-10V,
in 0.1V increments.

I am still hoping for 1ms response time though. I was hoping the simulator
could tell me if that was a possibility - but I can't seem to get it to
show me anything besides V3=9.9-10V!

Any suggestions?

Best regards,

-Michael

 

[Larry Brasfield]

"Michael Noone" <mnoone.uiuc.edu@127.0.0.1> wrote in message
news:Xns962A84F71647Dmnooneuiucedu127001@63.240.76.16...

"Larry Brasfield" <donotspam_larry_brasfield@hotmail.com> wrote in
news:0bX2e.28$oI2.743@news.uswest.net:
Using that source, I cannot replicate your problem. (I did
use my finger on the mouse rather than my tongue!) Zoom-
to-fit is active. Zooming works as Mr. Monsen describes.

Maybe it would help to describe what you are actually
expecting to see. The trouble may reside there.

This still seems to be the case, but maybe it will clear
up once you get a time-varying source per below.

Looking at your circuit, I find myself wondering if you
have dropped your 1 mS response time requirement.
What that unreal when you mentioned it awhile back?

Hmm this is odd indeed. I was expecting for the x axis to have a range of
V3=0-10 volts in 01.V increments. I was then hoping to see a nice little
linear line that would be something like Y=30X. Is this what you are
seeing? Instead - All I see is the x axis having a range of v3 = 9.9-10V,
in 0.1V increments.

I am still hoping for 1ms response time though. I was hoping the simulator
could tell me if that was a possibility - but I can't seem to get it to
show me anything besides V3=9.9-10V!

Any suggestions?

Right click on V3, hit the "Advanced" button, select
the PWL radio button (in "Functions" pane), and fill
in the piece-wise-linear specification of an excitation
function for which you would like to see the transient
response.

As for suggestions about how to deal with the response
you get, I've stated my piece on that in earlier posts.

Best regards,

Likewise.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Larry Brasfield]

"Michael Noone" <mnoone.uiuc.edu@127.0.0.1> wrote in message
news:Xns962A8ABD22482mnooneuiucedu127001@204.127.199.17...

"Larry Brasfield" <donotspam_larry_brasfield@hotmail.com> wrote in
news:y_X2e.30$oI2.843@news.uswest.net:

Right click on V3, hit the "Advanced" button, select
the PWL radio button (in "Functions" pane), and fill
in the piece-wise-linear specification of an excitation
function for which you would like to see the transient
response.

As for suggestions about how to deal with the response
you get, I've stated my piece on that in earlier posts.

Hi - I tried that:

https://netfiles.uiuc.edu/mnoone/www/Electronics/iviewcapture_date_31_03_
2005_time_13_35_28.jpg

And got this:

https://netfiles.uiuc.edu/mnoone/www/Electronics/iviewcapture_date_31_03_
2005_time_13_35_50.jpg

Any idea what I'm doing wrong?

The time at which your PWL input does anything (100 Seconds)
is far beyond the duration of you simulation (100 mSeconds).

Often, a good sanity check is to use the plotting facility to look
at your inputs and verify they are doing what you expected.

Thanks again,

You're welcome.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Michael Noone]

"Larry Brasfield" <donotspam_larry_brasfield@hotmail.com> wrote in
news:eBY2e.33$oI2.918@news.uswest.net:

The time at which your PWL input does anything (100 Seconds)
is far beyond the duration of you simulation (100 mSeconds).

Often, a good sanity check is to use the plotting facility to look
at your inputs and verify they are doing what you expected.

Ah - you're quite right! I changed it to 1 second and it seems to work
fairly well:

https://netfiles.uiuc.edu/mnoone/www/Electronics/iviewcapture_date_31_03_
2005_time_14_40_27.jpg

A couple questions though: First of all - it has a strange spike at the
very beginning. Is that just due to the components initializing? Also - it
looks to me that it takes about 30 ms to stabilize after the input has
changed. Does that seem about right?

Thanks for your continuing help with this project,

-Michael

 

[Larry Brasfield]

"Michael Noone" <mnoone.uiuc.edu@127.0.0.1> wrote in message
news:Xns962A96D5896D8mnooneuiucedu127001@204.127.204.17...

"Larry Brasfield" <donotspam_larry_brasfield@hotmail.com> wrote in
news:eBY2e.33$oI2.918@news.uswest.net:

The time at which your PWL input does anything (100 Seconds)
is far beyond the duration of you simulation (100 mSeconds).

Often, a good sanity check is to use the plotting facility to look
at your inputs and verify they are doing what you expected.

Ah - you're quite right! I changed it to 1 second and it seems to work
fairly well:

https://netfiles.uiuc.edu/mnoone/www/Electronics/iviewcapture_date_31_03_
2005_time_14_40_27.jpg

You PWL spec presents a ramp as the setpoint
for the amplifier to follow. This is not what people
usually use to explore response time. (It can be,
for some systems, but just not often compared to
step response.)

A couple questions though: First of all - it has a strange spike at the
very beginning. Is that just due to the components initializing? Also - it
looks to me that it takes about 30 ms to stabilize after the input has
changed. Does that seem about right?

I observed similar behavior. The circuit appears to
have DC convergence problems in the transient
simulation and AC simulation, so I've attributed
that strange starting behavior to that issue without
studying it closely. I trust the simulator's result
once the transient simulation settles at a believable
operating point. I take that as occuring after the
strange, unrequested initial flailing ceases.

I would suggest an input like this:
PWL(0, 0.1, 40m, 0.1, 40.05m, 10, 200m, 10)
to see your step response past the time taken for
the true initial conditions to be achieved.

Thanks for your continuing help with this project,

You're welcome.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Larry Brasfield]

"Michael Noone" <mnoone.uiuc.edu@127.0.0.1> wrote in message
news:Xns962A9760BEB5mnooneuiucedu127001@204.127.204.17...

"Larry Brasfield" <donotspam_larry_brasfield@hotmail.com> wrote in
news:eBY2e.33$oI2.918@news.uswest.net:
The time at which your PWL input does anything (100 Seconds)
is far beyond the duration of you simulation (100 mSeconds).

Often, a good sanity check is to use the plotting facility to look
at your inputs and verify they are doing what you expected.
Oh - I almost forgot. One last thing: Is there any way to add a time-
varying load in Spice? I clicked around for a good while but couldn't
figure out how to add anything but a constant valued resistor.

Use a behavioral current source ('bi' in the LTSpice top-level
component listing) with current controlled by the voltage seen
at the current terminals and another voltage of your choosing,
perhaps a PWL source describing your R(t) function.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Michael Noone]

"Larry Brasfield" <donotspam_larry_brasfield@hotmail.com> wrote in
news:VAZ2e.37$oI2.968@news.uswest.net:

You PWL spec presents a ramp as the setpoint
for the amplifier to follow. This is not what people
usually use to explore response time. (It can be,
for some systems, but just not often compared to
step response.)

I understand that - I just wanted to be sure I was getting a linear
(though delayed) output.

I observed similar behavior. The circuit appears to
have DC convergence problems in the transient
simulation and AC simulation, so I've attributed
that strange starting behavior to that issue without
studying it closely. I trust the simulator's result
once the transient simulation settles at a believable
operating point. I take that as occuring after the
strange, unrequested initial flailing ceases.

I already have all the components needed (well, different FETs, but
similar enough that I think they will work) sitting around the lab
anyways, so I'm going to see how it performs in the real world. If I get
similar results, is there any way to modify this circuit so as to
improve response time? I looked back at my original post from two weeks
ago and couldn't find anything along those lines, though it's possible
that I missed something due to the very large size of that topic (over
150 posts! eek)

I would suggest an input like this:
PWL(0, 0.1, 40m, 0.1, 40.05m, 10, 200m, 10)
to see your step response past the time taken for
the true initial conditions to be achieved.

We think alike - That's almost exactly how I found a response time of
30ms

-Michael

 

[Michael Noone]

"Larry Brasfield" <donotspam_larry_brasfield@hotmail.com> wrote in
news:eBY2e.33$oI2.918@news.uswest.net:

The time at which your PWL input does anything (100 Seconds)
is far beyond the duration of you simulation (100 mSeconds).

Often, a good sanity check is to use the plotting facility to look
at your inputs and verify they are doing what you expected.
Oh - I almost forgot. One last thing: Is there any way to add a time-

varying load in Spice? I clicked around for a good while but couldn't
figure out how to add anything but a constant valued resistor.

-Michael

 

[Michael Noone]

"Larry Brasfield" <donotspam_larry_brasfield@hotmail.com> wrote in
news:y_X2e.30$oI2.843@news.uswest.net:

Right click on V3, hit the "Advanced" button, select
the PWL radio button (in "Functions" pane), and fill
in the piece-wise-linear specification of an excitation
function for which you would like to see the transient
response.

As for suggestions about how to deal with the response
you get, I've stated my piece on that in earlier posts.

Hi - I tried that:

https://netfiles.uiuc.edu/mnoone/www/Electronics/iviewcapture_date_31_03_
2005_time_13_35_28.jpg

And got this:

https://netfiles.uiuc.edu/mnoone/www/Electronics/iviewcapture_date_31_03_
2005_time_13_35_50.jpg

Any idea what I'm doing wrong?

Thanks again,

-Michael

 

[Larry Brasfield]

"Michael Noone" <mnoone.uiuc.edu@127.0.0.1> wrote in message
news:Xns962A9A7DFA2BAmnooneuiucedu127001@204.127.204.17...

"Larry Brasfield" <donotspam_larry_brasfield@hotmail.com> wrote in
news:VAZ2e.37$oI2.968@news.uswest.net:

[step vs. ramp cut]

I observed similar behavior. The circuit appears to
have DC convergence problems in the transient
simulation and AC simulation, so I've attributed
that strange starting behavior to that issue without
studying it closely. I trust the simulator's result
once the transient simulation settles at a believable
operating point. I take that as occuring after the
strange, unrequested initial flailing ceases.

I already have all the components needed (well, different FETs, but
similar enough that I think they will work) sitting around the lab
anyways, so I'm going to see how it performs in the real world. If I get
similar results, is there any way to modify this circuit so as to
improve response time?

Here are the changes I would make:
1. Eliminate or greatly reduce R2.
2. Degenerate the M1,R1 gain stage to get a more
stable and predictable gain versus operating point.
A source resistor would be a good addition for this.
3. Set the zero established by C1,R5 to be near the
lowest frequency pole created in the M1,R1,M2 stage.
4. Adjust the M1,R1 gain for best loop response.
(Note this likely interacts with step 3, so it will could
be a little tedious.)

I looked back at my original post from two weeks
ago and couldn't find anything along those lines, though it's possible
that I missed something due to the very large size of that topic (over
150 posts! eek)

Perhaps lost in that maelstrom was a simple circuit I posted
with about 8 uS response time. You should hope to get 1 mS,
perhaps with revision of your current configuration once the
above 4 changes are properly applied.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.