I tried
.step param r1 490 10 -10
and
R2 set to {500 - {r1}}
output seems to be all-right...
cheers
AG
toggle quoted message
Show quoted text
On 9/14/2011 12:06 PM, John Fields wrote:
Hello,
I'd like to simulate a 500 ohm pot by using a voltage divider: (View
using a fixed-pitch font)
CW
|
[Ra]
|
+---COM
|
[Rb]
|
CCW
and stepping Ra from 499 ohms to 1 ohm in one ohm steps while
simultaneously stepping Rb from one ohm to 499 ohms in one ohm steps.
I tried .STEP PARAM {Rx} 1 499 1 for the ascending resistance, and
that works, but for the descending: .STEP PARAM {Rx} 499 1 -1 doesn't
work.
Matter of fact, it gives me the same result as the ascending!
Help, please?
--
JF
No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 9.0.914 / Virus Database: 271.1.1/3896 - Release Date: 09/14/11 01:34:00
|
Thanks
A. Ganesan
toggle quoted message
Show quoted text
On 9/14/2011 12:25 PM, Howard Hansen wrote:
Both Octave and Scilab are freeware.
Howard
On 9/14/2011 9:25 AM, Ganesan wrote:
Thanks.. What freeware will meet my needs..? (I am a windows XP guy)
cheers
AG
On 9/14/2011 9:18 AM, Howard Hansen wrote:
LTspice doesn't have any built in capability for merging data. However,
you can export the data and then use a program like Octave, Scilab or
Matlab to merge the data. The data would be represented as vectors in
these programs and vectors can be concatenated. With either Octave or
Scilab you are working with ASCII data. Whereas with NAtlab you could
use LTspice2Matlab, keep the data in binary format and gain the benefit
of smaller file sizes. In addition you can zoom in and out in plots in
Matlab.
Howard
On 9/13/2011 10:38 PM, Ganesan wrote:
I am re posting this since I didn't get aye or nay...
Cheers
AG
On 9/10/2011 6:46 PM, Ganesan wrote:
I can run different ac simulations with different frequency resolutions
and range..
Is there a way to merge the plot files.?
Cheers
A. Ganesan
===================================================================================
On 9/10/2011 6:41 PM, Ganesan wrote:
The list seems to work..But the interpolated output on the plot
looks
funky... I can live with it..
Cheers
A. Ganesan
On 9/10/2011 6:16 PM, Helmut wrote:
--- In LTspice@... <mailto:LTspice%40yahoogroups.com>
<mailto:LTspice%40yahoogroups.com><mailto:LTspice%40yahoogroups.com>
<mailto:LTspice%40yahoogroups.com>
<mailto:LTspice%40yahoogroups.com>,
Ganesan<dg1@...> wrote:
I forgot to add, I don't know how to do variable resolution for
transient analysis either...
Cheers
A. Ganesan
On 9/10/2011 4:43 PM, Apparajan wrote:
I have a filter with some sharp notches and flat pass-bands. I want to
be able to simulate it with variable resolution.
For example
.ac lin 10 20 50 lin 1000 50 70 oct 20 70 3k lin 1000 3k 3.8k
(linearly sweep the frequency 10 points from 20 to 50 hz;
high resolution of 1000 points between 50 to 70 HZ ( power supply
rejection notch;
Flat region from 70 to 3 khz and
a high resolution sweep of 1000points between 3k and 3.8k
(transition
band)
How do I do this in LTspice...?
Cheers
A. Ganesan
Hello,
There is only the option of lin, dec, oct and list in the
.AC-command. This means you would have to use "list", but it
would be a big effort to create the 10000 or more frequency
values.
The AC-simulation runs so fast, that you can simulate the
whole span with high resolution, even if you end with 100000
or more frequency-points.
I also don't know of any simple solution for .TRAN.
A possible workaround may be a dummy-source creating bursts.
This may force the automatic timestep calculator in LTspice
to reduce the time step.
Best regards,
Helmut
------------------------------------
Yahoo! Groups Links
No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 9.0.914 / Virus Database: 271.1.1/3896 - Release Date:
09/14/11 01:34:00
|
Both Octave and Scilab are freeware.
Howard
toggle quoted message
Show quoted text
On 9/14/2011 9:25 AM, Ganesan wrote: Thanks.. What freeware will meet my needs..? (I am a windows XP guy)
cheers
AG
On 9/14/2011 9:18 AM, Howard Hansen wrote:
LTspice doesn't have any built in capability for merging data. However,
you can export the data and then use a program like Octave, Scilab or
Matlab to merge the data. The data would be represented as vectors in
these programs and vectors can be concatenated. With either Octave or
Scilab you are working with ASCII data. Whereas with NAtlab you could
use LTspice2Matlab, keep the data in binary format and gain the benefit
of smaller file sizes. In addition you can zoom in and out in plots in
Matlab.
Howard
On 9/13/2011 10:38 PM, Ganesan wrote:
I am re posting this since I didn't get aye or nay...
Cheers
AG
On 9/10/2011 6:46 PM, Ganesan wrote:
I can run different ac simulations with different frequency resolutions
and range..
Is there a way to merge the plot files.?
Cheers
A. Ganesan
===================================================================================
On 9/10/2011 6:41 PM, Ganesan wrote:
The list seems to work..But the interpolated output on the plot looks
funky... I can live with it..
Cheers
A. Ganesan
On 9/10/2011 6:16 PM, Helmut wrote:
--- In LTspice@...
<mailto:LTspice%40yahoogroups.com><mailto:LTspice%40yahoogroups.com>
<mailto:LTspice%40yahoogroups.com>
<mailto:LTspice%40yahoogroups.com>,
Ganesan<dg1@...> wrote:
I forgot to add, I don't know how to do variable resolution for
transient analysis either...
Cheers
A. Ganesan
On 9/10/2011 4:43 PM, Apparajan wrote:
I have a filter with some sharp notches and flat pass-bands. I want to
be able to simulate it with variable resolution.
For example
.ac lin 10 20 50 lin 1000 50 70 oct 20 70 3k lin 1000 3k 3.8k
(linearly sweep the frequency 10 points from 20 to 50 hz;
high resolution of 1000 points between 50 to 70 HZ ( power supply
rejection notch;
Flat region from 70 to 3 khz and
a high resolution sweep of 1000points between 3k and 3.8k
(transition
band)
How do I do this in LTspice...?
Cheers
A. Ganesan
Hello,
There is only the option of lin, dec, oct and list in the
.AC-command. This means you would have to use "list", but it
would be a big effort to create the 10000 or more frequency
values.
The AC-simulation runs so fast, that you can simulate the
whole span with high resolution, even if you end with 100000
or more frequency-points.
I also don't know of any simple solution for .TRAN.
A possible workaround may be a dummy-source creating bursts.
This may force the automatic timestep calculator in LTspice
to reduce the time step.
Best regards,
Helmut
------------------------------------
Yahoo! Groups Links
No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 9.0.914 / Virus Database: 271.1.1/3896 - Release Date: 09/14/11 01:34:00
------------------------------------
Yahoo! Groups Links
|
Hello,
I'd like to simulate a 500 ohm pot by using a voltage divider: (View
using a fixed-pitch font)
CW
|
[Ra]
|
+---COM
|
[Rb]
|
CCW
and stepping Ra from 499 ohms to 1 ohm in one ohm steps while
simultaneously stepping Rb from one ohm to 499 ohms in one ohm steps.
I tried .STEP PARAM {Rx} 1 499 1 for the ascending resistance, and
that works, but for the descending: .STEP PARAM {Rx} 499 1 -1 doesn't
work.
Matter of fact, it gives me the same result as the ascending!
Help, please?
--
JF
|
Hi all,
I've started playing around with the awesome TIA model (TIA_universalopamp_shotnoise.asc) and have a couple of questions or perhaps statements that I'd like verified so I can understand I'm going the right way about things.
I'm designing a low speed (~kHz) high sensitivity photodiode circuit. Initial testing suggest that the optical signals are very low so I'm going to need a high gain, and want to understand the limiting noise components in the circuit so I can choose the correct photodiode and op amp for my circuit.
From what I understand, the main inputs into the model are:
A) The feedback cap & resistor (C1, R1). Used to adjust such that the noise spectrum is flat around frequency of operation, and the gain is sufficient.
B) The photodiode specs: the shunt resistance (Rsh), the photocurrent itself (I1) and the junction capacitance (Cjo in DP)
C) and obviously the cable capacitance, Ccable and actual op amp model.
A few queries:
1. I'm a little confused about the presence of D2, I2, C2 & V3 and how shot noise can be included in this model.
2. Also, what other parameters can be set that define the photodiode?
3. To work out the dark current contribution to the output voltage of the TIA, can I simply put as I1?
Thanks in advance!
|
Re: Caps smaller than 0.5 uF?
--- In LTspice@..., "Tony Casey" <tony@...> wrote:
--- In LTspice@..., Philip Bellingham <rmhc78a@> wrote:
Tony,
You wrote, "I believe it is more efficient to use the parasitics included in
LTspice inductors and capacitors than to have explicit discrete parasitic
components, even though you lose the convenience of being able to see them at a
glance on a schematic".
If I understand correctly what you said, you believe that you cannot see the
values of the parasitic components. While it is true that you will not see the
schematic configuration of the parasitic components, you can make their values
visible on the schematic by Ctrl+right click on the component and making the
attribute SpiceLine visible.
???? - Philip
________________________________
From: Tony Casey <tony@>
To: LTspice@...
Sent: Wed, September 14, 2011 3:08:43 AM
Subject: [LTspice] Re: Caps smaller than 0.5 uF?
??
--- In LTspice@..., "sepulchre10" <sepulchre10@> wrote:
When I look in the list the smallest shown is 0.5uF. When putting together a
schematic with smaller caps, eg. 470pF I don't know any of the info on them
other than the value. I see that the ones in the list have all the needed data.
Is there a database or other info on smaller caps?
Thanks,
Ken
Hello Ken,
That's probably for two reasons: because LTspice was/is primarily intended to
evaluate switchmode power supply chips, capacitors appropriate to that
application are supplied. The other reason, I suspect, is that for lower value
capacitors, i.e. small ceramics, their parasitics are often not significant for
typical applications - I'm thinking particularly of tuned circuits that are
dominated by the inductors' Q.
However, for some other applications too, it is vital that the capacitor
parasitics are explicitly entered. You will have to find the data yourself, and
enter it for each capacitor. To assist me, I have an ESR and ESL calculator that
I wrote in Excel that uses equations derived from a best fit to published data
from Kemet and Murata to estimate these values on a component by component
basis. It's not perfect, but it's close enough for starters.
Unfortunately, sometimes there is just no substitute for some getting your hands
dirty and doing the grunt work yourself.
Incidentally, I believe it is more efficient to use the parasitics included in
LTspice inductors and capacitors than to have explicit discrete parasitic
components, even though you lose the convenience of being able to see them at a
glance on a schematic. Does keep it neater and less cluttered though, although
some folk don't seem to be too bothered by schematics that look like they were
drawn by a drunken spider. But that's getting off-topic. :-)
Regards,
Tony
[Non-text portions of this message have been removed]
Hello Philip,
Thanks for that, I had forgotten. In fact, I'm ashamed to admit it had never occurred to me to try ctrl-right-click on Ls and Cs, even though I routinely do it for other components. Thanks again.
Regards,
Tony
This jolt of fallibility reminded me of analogspiceman's tip of pressing ctrl-alt-shift-h to reveal all hidden text in schematics. Of course, if you can only use the fingers of one hand for any reason, it takes quite some effort - I just tried it :-) Regards, Tony
|
Re: Simple model for diffin-diffout amp
Thanks.. I model offset by dial ling some mismatch, so it includes
temperature effects..
I can understand Microchip having poor models.. But TI, LTC and ADI have
way too complex models for the job they seem to do.
I thought these models are simple representations of the real device
intended to give the board level designer something to simulate his
circuit with.. The way these commercial models are, it looks like they
took the schematic from the chip design engineer and did a poor job of
obscuring proprietary information.
cheers
AG
=====================================================================================================================
toggle quoted message
Show quoted text
On 9/14/2011 9:52 AM, RobertTalty wrote:
I'm not sure I understand
How do you model offset?
I model it by adding a DC source in series with the In+ or IN- gate.
some value between 100uV and 10mV depending on the expected mismatch
of the input pair.
Model PSRR requires that you model the power supply, which a simple
G/R model does not have, also the typical sources of non-ideal opamp
performance that results in power supply variation transferring to the
output signal neesd to be correctly modeled. simple things like the
variations in current sources with power supply voltage, the correct
model for this depends on weather you cascode the mirrors or not.
Same thing with Cmrr? A differential G with perfect R load has
infinite CMRR, modeling CMRR requires that you include errors that
cause CMRR. in your model. This requires some knowledge of the Input
pair type and the cascode bias levels.
BTW most commercial device level spice models are very badly written.
I mean VERY BADLY written. so they are unlikely to include these
effects, heck Microchips opamp models usually don't even converge
properly.
The Microchip opamp spic models are very complex and attempt to model
all types of errors and their Temp variations, but in the end these
models cause convergence problems, so what is the point of a complex
model that causes beginners convergence problems. Convergence can be
hard for experienced spice users to solve, so it is the last thing
that beginners need.
So if you want to see some complex models go to Microchip and download
some of their spice models.
regards
Robert
--- In LTspice@... <mailto:LTspice%40yahoogroups.com>,
Ganesan <dg1@...> wrote:
Thanks for the suggestions.. I will get back in a few days..
My more complicated models which I did not post are Gm and R based..
However my most complicated model seems to be much simpler than what is
commercially available? They also have a disclaimer that they don't
model offset, psrr, cmrr etc.? What gives..
This question still remains unanswered..
Cheers
ag
--- In LTspice@...
<mailto:LTspice%40yahoogroups.com> <mailto:LTspice%40yahoogroups.com>,
"Apparajan" <dg1@> wrote:
I have uploaded my model
Temp-->File-->>E_model_for_diffamp.asc
It is a very simple model that models the differential and common
mode loop gains. I have other more complicated models that model
slew-rate, bandwidth, etc. However my most complicated model seems to be
much simpler than what is commercially available? They also have a
disclimer that they don't model offset, psrr, cmrr etc.? What gives...
No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 9.0.914 / Virus Database: 271.1.1/3896 - Release Date: 09/14/11 01:34:00
|
Re: Caps smaller than 0.5 uF?
--- In LTspice@..., Philip Bellingham <rmhc78a@...> wrote:
Tony,
You wrote, "I believe it is more efficient to use the parasitics included in
LTspice inductors and capacitors than to have explicit discrete parasitic
components, even though you lose the convenience of being able to see them at a
glance on a schematic".
If I understand correctly what you said, you believe that you cannot see the
values of the parasitic components. While it is true that you will not see the
schematic configuration of the parasitic components, you can make their values
visible on the schematic by Ctrl+right click on the component and making the
attribute SpiceLine visible.
???? - Philip
________________________________
From: Tony Casey <tony@...>
To: LTspice@...
Sent: Wed, September 14, 2011 3:08:43 AM
Subject: [LTspice] Re: Caps smaller than 0.5 uF?
??
--- In LTspice@..., "sepulchre10" <sepulchre10@> wrote:
When I look in the list the smallest shown is 0.5uF. When putting together a
schematic with smaller caps, eg. 470pF I don't know any of the info on them
other than the value. I see that the ones in the list have all the needed data.
Is there a database or other info on smaller caps?
Thanks,
Ken
Hello Ken,
That's probably for two reasons: because LTspice was/is primarily intended to
evaluate switchmode power supply chips, capacitors appropriate to that
application are supplied. The other reason, I suspect, is that for lower value
capacitors, i.e. small ceramics, their parasitics are often not significant for
typical applications - I'm thinking particularly of tuned circuits that are
dominated by the inductors' Q.
However, for some other applications too, it is vital that the capacitor
parasitics are explicitly entered. You will have to find the data yourself, and
enter it for each capacitor. To assist me, I have an ESR and ESL calculator that
I wrote in Excel that uses equations derived from a best fit to published data
from Kemet and Murata to estimate these values on a component by component
basis. It's not perfect, but it's close enough for starters.
Unfortunately, sometimes there is just no substitute for some getting your hands
dirty and doing the grunt work yourself.
Incidentally, I believe it is more efficient to use the parasitics included in
LTspice inductors and capacitors than to have explicit discrete parasitic
components, even though you lose the convenience of being able to see them at a
glance on a schematic. Does keep it neater and less cluttered though, although
some folk don't seem to be too bothered by schematics that look like they were
drawn by a drunken spider. But that's getting off-topic. :-)
Regards,
Tony
[Non-text portions of this message have been removed]
Hello Philip, Thanks for that, I had forgotten. In fact, I'm ashamed to admit it had never occurred to me to try ctrl-right-click on Ls and Cs, even though I routinely do it for other components. Thanks again. Regards, Tony
|
Re: Simple model for diffin-diffout amp
I'm not sure I understand
How do you model offset?
I model it by adding a DC source in series with the In+ or IN- gate. some value between 100uV and 10mV depending on the expected mismatch of the input pair.
Model PSRR requires that you model the power supply, which a simple G/R model does not have, also the typical sources of non-ideal opamp performance that results in power supply variation transferring to the output signal neesd to be correctly modeled. simple things like the variations in current sources with power supply voltage, the correct model for this depends on weather you cascode the mirrors or not.
Same thing with Cmrr? A differential G with perfect R load has infinite CMRR, modeling CMRR requires that you include errors that cause CMRR. in your model. This requires some knowledge of the Input pair type and the cascode bias levels.
BTW most commercial device level spice models are very badly written. I mean VERY BADLY written. so they are unlikely to include these effects, heck Microchips opamp models usually don't even converge properly.
The Microchip opamp spic models are very complex and attempt to model all types of errors and their Temp variations, but in the end these models cause convergence problems, so what is the point of a complex model that causes beginners convergence problems. Convergence can be hard for experienced spice users to solve, so it is the last thing that beginners need.
So if you want to see some complex models go to Microchip and download some of their spice models.
regards
Robert
toggle quoted message
Show quoted text
--- In LTspice@..., Ganesan <dg1@...> wrote:
Thanks for the suggestions.. I will get back in a few days..
My more complicated models which I did not post are Gm and R based..
However my most complicated model seems to be much simpler than what is
commercially available? They also have a disclaimer that they don't
model offset, psrr, cmrr etc.? What gives..
This question still remains unanswered..
Cheers
ag
> > --- In LTspice@... <mailto:LTspice%40yahoogroups.com>,
"Apparajan" <dg1@> wrote:
> > >
> > > I have uploaded my model
> > > Temp-->File-->>E_model_for_diffamp.asc
> > > It is a very simple model that models the differential and common
mode loop gains. I have other more complicated models that model
slew-rate, bandwidth, etc. However my most complicated model seems to be
much simpler than what is commercially available? They also have a
disclimer that they don't model offset, psrr, cmrr etc.? What gives...
> > >
[Non-text portions of this message have been removed]
|
Re: Sensitivity Anlysis..
--- In LTspice@..., "Apparajan" <dg1@...> wrote:
Let s take a simple 2 resistor divider and a battery
I want to step one of the resistors by 1% or 10%.(small
change sensitivity v. large change sensitivity ) I want
to plot "(Delta(Vout)/Vout)/(Delta(R)/R)"...
How do I do this?
Or has this question been already answered..?
Cheers
AG
Hello AG, Maybe this will work. Let's assume you have the non modified divider on the schematic too. .step param TOL 0 0.01 0.1 .param RX=1k*(1+TOL) V1 100 0 {TOL} Then plot the following. (V(out)-V(outref))/V(TOL) Best regards, Helmut
|
Thanks.. What freeware will meet my needs..? (I am a windows XP guy)
cheers
AG
toggle quoted message
Show quoted text
On 9/14/2011 9:18 AM, Howard Hansen wrote:
LTspice doesn't have any built in capability for merging data. However,
you can export the data and then use a program like Octave, Scilab or
Matlab to merge the data. The data would be represented as vectors in
these programs and vectors can be concatenated. With either Octave or
Scilab you are working with ASCII data. Whereas with NAtlab you could
use LTspice2Matlab, keep the data in binary format and gain the benefit
of smaller file sizes. In addition you can zoom in and out in plots in
Matlab.
Howard
On 9/13/2011 10:38 PM, Ganesan wrote:
I am re posting this since I didn't get aye or nay...
Cheers
AG
On 9/10/2011 6:46 PM, Ganesan wrote:
I can run different ac simulations with different frequency resolutions
and range..
Is there a way to merge the plot files.?
Cheers
A. Ganesan
===================================================================================
On 9/10/2011 6:41 PM, Ganesan wrote:
The list seems to work..But the interpolated output on the plot looks
funky... I can live with it..
Cheers
A. Ganesan
On 9/10/2011 6:16 PM, Helmut wrote:
--- In LTspice@...
<mailto:LTspice%40yahoogroups.com><mailto:LTspice%40yahoogroups.com>
<mailto:LTspice%40yahoogroups.com>
<mailto:LTspice%40yahoogroups.com>,
Ganesan<dg1@...> wrote:
I forgot to add, I don't know how to do variable resolution for
transient analysis either...
Cheers
A. Ganesan
On 9/10/2011 4:43 PM, Apparajan wrote:
I have a filter with some sharp notches and flat pass-bands. I want to
be able to simulate it with variable resolution.
For example
.ac lin 10 20 50 lin 1000 50 70 oct 20 70 3k lin 1000 3k 3.8k
(linearly sweep the frequency 10 points from 20 to 50 hz;
high resolution of 1000 points between 50 to 70 HZ ( power supply
rejection notch;
Flat region from 70 to 3 khz and
a high resolution sweep of 1000points between 3k and 3.8k
(transition
band)
How do I do this in LTspice...?
Cheers
A. Ganesan
Hello,
There is only the option of lin, dec, oct and list in the
.AC-command. This means you would have to use "list", but it
would be a big effort to create the 10000 or more frequency
values.
The AC-simulation runs so fast, that you can simulate the
whole span with high resolution, even if you end with 100000
or more frequency-points.
I also don't know of any simple solution for .TRAN.
A possible workaround may be a dummy-source creating bursts.
This may force the automatic timestep calculator in LTspice
to reduce the time step.
Best regards,
Helmut
------------------------------------
Yahoo! Groups Links
No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 9.0.914 / Virus Database: 271.1.1/3896 - Release Date: 09/14/11 01:34:00
|
LTspice doesn't have any built in capability for merging data. However, you can export the data and then use a program like Octave, Scilab or Matlab to merge the data. The data would be represented as vectors in these programs and vectors can be concatenated. With either Octave or Scilab you are working with ASCII data. Whereas with NAtlab you could use LTspice2Matlab, keep the data in binary format and gain the benefit of smaller file sizes. In addition you can zoom in and out in plots in Matlab.
Howard
toggle quoted message
Show quoted text
On 9/13/2011 10:38 PM, Ganesan wrote: I am re posting this since I didn't get aye or nay...
Cheers
AG
On 9/10/2011 6:46 PM, Ganesan wrote:
I can run different ac simulations with different frequency resolutions
and range..
Is there a way to merge the plot files.?
Cheers
A. Ganesan
===================================================================================
On 9/10/2011 6:41 PM, Ganesan wrote:
The list seems to work..But the interpolated output on the plot looks
funky... I can live with it..
Cheers
A. Ganesan
On 9/10/2011 6:16 PM, Helmut wrote:
--- In LTspice@...<mailto:LTspice%40yahoogroups.com>
<mailto:LTspice%40yahoogroups.com>
<mailto:LTspice%40yahoogroups.com>,
Ganesan<dg1@...> wrote:
I forgot to add, I don't know how to do variable resolution for
transient analysis either...
Cheers
A. Ganesan
On 9/10/2011 4:43 PM, Apparajan wrote:
I have a filter with some sharp notches and flat pass-bands. I want to
be able to simulate it with variable resolution.
For example
.ac lin 10 20 50 lin 1000 50 70 oct 20 70 3k lin 1000 3k 3.8k
(linearly sweep the frequency 10 points from 20 to 50 hz;
high resolution of 1000 points between 50 to 70 HZ ( power supply
rejection notch;
Flat region from 70 to 3 khz and
a high resolution sweep of 1000points between 3k and 3.8k
(transition
band)
How do I do this in LTspice...?
Cheers
A. Ganesan
Hello,
There is only the option of lin, dec, oct and list in the
.AC-command. This means you would have to use "list", but it
would be a big effort to create the 10000 or more frequency
values.
The AC-simulation runs so fast, that you can simulate the
whole span with high resolution, even if you end with 100000
or more frequency-points.
I also don't know of any simple solution for .TRAN.
A possible workaround may be a dummy-source creating bursts.
This may force the automatic timestep calculator in LTspice
to reduce the time step.
Best regards,
Helmut
------------------------------------
Yahoo! Groups Links
|
Re: Caps smaller than 0.5 uF?
Tony, You wrote, "I believe it is more efficient to use the parasitics included in LTspice inductors and capacitors than to have explicit discrete parasitic components, even though you lose the convenience of being able to see them at a glance on a schematic". If I understand correctly what you said, you believe that you cannot see the values of the parasitic components. While it is true that you will not see the schematic configuration of the parasitic components, you can make their values visible on the schematic by Ctrl+right click on the component and making the attribute SpiceLine visible. ?? - Philip ________________________________ From: Tony Casey <tony@...> To: LTspice@... Sent: Wed, September 14, 2011 3:08:43 AM Subject: [LTspice] Re: Caps smaller than 0.5 uF? ? --- In LTspice@..., "sepulchre10" <sepulchre10@...> wrote:
When I look in the list the smallest shown is 0.5uF. When putting together a
schematic with smaller caps, eg. 470pF I don't know any of the info on them
other than the value. I see that the ones in the list have all the needed data.
Is there a database or other info on smaller caps?
Thanks,
Ken
Hello Ken, That's probably for two reasons: because LTspice was/is primarily intended to evaluate switchmode power supply chips, capacitors appropriate to that application are supplied. The other reason, I suspect, is that for lower value capacitors, i.e. small ceramics, their parasitics are often not significant for typical applications - I'm thinking particularly of tuned circuits that are dominated by the inductors' Q. However, for some other applications too, it is vital that the capacitor parasitics are explicitly entered. You will have to find the data yourself, and enter it for each capacitor. To assist me, I have an ESR and ESL calculator that I wrote in Excel that uses equations derived from a best fit to published data from Kemet and Murata to estimate these values on a component by component basis. It's not perfect, but it's close enough for starters. Unfortunately, sometimes there is just no substitute for some getting your hands dirty and doing the grunt work yourself. Incidentally, I believe it is more efficient to use the parasitics included in LTspice inductors and capacitors than to have explicit discrete parasitic components, even though you lose the convenience of being able to see them at a glance on a schematic. Does keep it neater and less cluttered though, although some folk don't seem to be too bothered by schematics that look like they were drawn by a drunken spider. But that's getting off-topic. :-) Regards, Tony
|
Re: Simple model for diffin-diffout amp
Thanks for the suggestions.. I will get back in a few days..
My more complicated models which I did not post are Gm and R based..
However my most complicated model seems to be much simpler than what is
commercially available? They also have a disclaimer that they don't
model offset, psrr, cmrr etc.? What gives..
This question still remains unanswered..
Cheers
ag
> > --- In LTspice@... <mailto:LTspice%40yahoogroups.com>,
"Apparajan" <dg1@> wrote:
> > >
> > > I have uploaded my model
> > > Temp-->File-->>E_model_for_diffamp.asc
> > > It is a very simple model that models the differential and common
mode loop gains. I have other more complicated models that model
slew-rate, bandwidth, etc. However my most complicated model seems to be
much simpler than what is commercially available? They also have a
disclimer that they don't model offset, psrr, cmrr etc.? What gives...
> > >
|
Thanks..will get back in a few days..
Cheers
AG
On 9/14/2011 3:28 AM, RobertTalty wrote:I am re posting this since I
didn't get aye or nay...
Cheers
AG
toggle quoted message
Show quoted text
On 9/10/2011 6:46 PM, Ganesan wrote:
I can run different ac simulations with different frequency resolutions
and range..
Is there a way to merge the plot files.?
Cheers
A. Ganesan
===================================================================================
On 9/10/2011 6:41 PM, Ganesan wrote:
The list seems to work..But the interpolated output on the plot looks
funky... I can live with it..
Cheers
A. Ganesan
On 9/10/2011 6:16 PM, Helmut wrote:
--- In LTspice@... <mailto:LTspice%40yahoogroups.com>
<mailto:LTspice%40yahoogroups.com>
<mailto:LTspice%40yahoogroups.com>,
Ganesan <dg1@...> wrote:
I forgot to add, I don't know how to do variable resolution for
transient analysis either...
Cheers
A. Ganesan
On 9/10/2011 4:43 PM, Apparajan wrote:
I have a filter with some sharp notches and flat pass-bands. I
want to
be able to simulate it with variable resolution.
For example
.ac lin 10 20 50 lin 1000 50 70 oct 20 70 3k lin 1000 3k 3.8k
(linearly sweep the frequency 10 points from 20 to 50 hz;
high resolution of 1000 points between 50 to 70 HZ ( power supply
rejection notch;
Flat region from 70 to 3 khz and
a high resolution sweep of 1000points between 3k and 3.8k
(transition
band)
How do I do this in LTspice...?
Cheers
A. Ganesan
Hello,
There is only the option of lin, dec, oct and list in the
.AC-command. This means you would have to use "list", but it
would be a big effort to create the 10000 or more frequency
values.
The AC-simulation runs so fast, that you can simulate the
whole span with high resolution, even if you end with 100000
or more frequency-points.
I also don't know of any simple solution for .TRAN.
A possible workaround may be a dummy-source creating bursts.
This may force the automatic timestep calculator in LTspice
to reduce the time step.
Best regards,
Helmut
AG,
I don't know how to do this sort of thing within LTspice However, the
proprietary binary output of LTspice is SpiceExplorer compatible, so
I use SpiceExplorer as the waveform viewer for anything like this.
I know SpiceExplorer is not free, but it is a very useful tool.
regards
Robert
--- In LTspice@... <mailto:LTspice%40yahoogroups.com>,
"Tony Casey" <tony@...> wrote:
<snip>
--- In LTspice@... <mailto:LTspice%40yahoogroups.com>,
Ganesan <dg1@> wrote:
I am re posting this since I didn't get aye or nay...
Cheers
AG
On 9/10/2011 6:46 PM, Ganesan wrote:
I can run different ac simulations with different frequency
resolutions
and range..
Is there a way to merge the plot files.?
Cheers
A. Ganesan
===================================================================================
</snip>
Hello Ganesan,
There at least two ways to do this. The first one is very clunky, and you might not want to do it more than once or twice, depending on
how patient you are. Export the waveform data of each plot
(File>Export), and then combine the data in Excel. You can use
Excel's Data>Sort feature to sort the points into order of increasing
frequency. Be aware, though, that some versions of Excel only support
20,000 points in a chart series.
Alternatively, you can use Helmut's ltsputils program, which can
read and reformat raw files. This is a Perl command line program, but
there is also a GUI front end available for this.
Search the Files section for these and lots of other useful
utilities and add-ons.
Help that helps.
Regards,
Tony
|
--- In LTspice@..., "s35148" <s35148@...> wrote:
Hi,
I'm having a problem with another program that use LTSpice to run the simulation. The schematic have a NAND gate, and I write a ".model" like the one below, but the LTSpice seems don't recognize the "d_nand" expression.
** 2 input NAND schmitt
.model A4093 d_nand ( in_family="4000-5_SCHMITT"
+ out_family="4000-5"
+ out_res=560
+ input_load=5p
+ rise_delay=162n
+ fall_delay=162n
+ max_source = 3.2m
+ min_sink = -1m )
Anyone know how can I solve this?
Best regards,
S.
Hello S, The reason LTspice doesn't recognise your NAND gate is because it isn't a native model. This model is from another flavour of SPICE, and won't work at all. LTspice does not support logic elements from other simulators unless they are transistor level models. I recommend you use a native A source device. Check the help file for the correct syntax. Regards, Tony
|
Re: Starting LTspice GUI from script file loading .sch and .cir - Linux
Hi Tony,
I think you are right. I fear so.
Thanks for the confirmation.
Axel
toggle quoted message
Show quoted text
--- In LTspice@..., "Tony Casey" <tony@...> wrote:
--- In LTspice@..., "Axel K" <axelmklein@> wrote:
Hi *,
In Ubuntu with Wine I want to have a setup of 4 LTSpice GUIs started together. I'd like to have a schematic and a .cir file loaded for every instance of LTspice.
Does anybody know how to load two files, a .sch and a .cir, at the start from a script?
The line
<env WINEPREFIX="/home/xxxx/.wine" wine C:\\Program\ Files\\LTC\\LTspiceIV\\scad3.exe -wine AAAA.sch AAAA.cir &>
does not work.
Thank you in advance.
Axel
Hello Axel,
Running four instances of LTspice from a bash shell is not a problem, but I don't think it's possible to open two files at once, either in Windows or Linux, from the command line. I've tried in both and failed.
It probably depends on the computer (number of cores etc), but when running from a bash shell, I've had up to 20 instances of LTspice running netlists in batch mode before problems set in. This is from a Python script, in which I check how many processes are currently active.
What you want is not possible, as far as I can tell. SCAD3.exe only seems to accept only one target file as a command line argument, even in batch mode. Makes sense, really.
Regards,
Tony
|
AG,
I don't know how to do this sort of thing within LTspice However, the proprietary binary output of LTspice is SpiceExplorer compatible, so I use SpiceExplorer as the waveform viewer for anything like this.
I know SpiceExplorer is not free, but it is a very useful tool.
regards
Robert
toggle quoted message
Show quoted text
--- In LTspice@..., "Tony Casey" <tony@...> wrote:
<snip>
--- In LTspice@..., Ganesan <dg1@> wrote:
I am re posting this since I didn't get aye or nay...
Cheers
AG
On 9/10/2011 6:46 PM, Ganesan wrote:
I can run different ac simulations with different frequency resolutions
and range..
Is there a way to merge the plot files.?
Cheers
A. Ganesan
===================================================================================
</snip>
Hello Ganesan,
There at least two ways to do this. The first one is very clunky, and you might not want to do it more than once or twice, depending on how patient you are. Export the waveform data of each plot (File>Export), and then combine the data in Excel. You can use Excel's Data>Sort feature to sort the points into order of increasing frequency. Be aware, though, that some versions of Excel only support 20,000 points in a chart series.
Alternatively, you can use Helmut's ltsputils program, which can read and reformat raw files. This is a Perl command line program, but there is also a GUI front end available for this.
Search the Files section for these and lots of other useful utilities and add-ons.
Help that helps.
Regards,
Tony
|
Re: Simple model for diffin-diffout amp
Hi AG,
I forgot to mention that there is an A-device OTA (single ended unfortunately)
look LTspice\lib\sub folder at the UniversalOpamps2.sub file
it is a text netlist file, with an example of how to use the OTA
e.g.
A1 2 1 0 0 0 0 out 0 OTA G={Avol/Rout} ref={Vos} linear Cout={Cout}
+ en={en} enk={enk} in={in} ink={ink} incm={incm} incmk={incmk}
+ Vhigh=1e308 Vlow=-1e308 Rout={Rout}
R5 2 3 {2*Rin} noiseless
R6 1 4 {2*Rin} noiseless
R1 3 1 {2*Rin} noiseless
R2 2 4 {2*Rin} noiseless
.param Rout=.1
.param Cout={Avol/GBW/2/pi/Rout}
.param Avol=1Meg GBW=10Meg Slew=10Meg ilimit=25m rail=0 Vos=0
.param en=0 enk=0 in=0 ink=0 incm=0 incmk=0 Rin=1G
regards
Robert
toggle quoted message
Show quoted text
--- In LTspice@..., "RobertTalty" <rtalty@...> wrote:
Hi AG,
I would caution against using a simple E source based fully differential amp model. Usually G source with appropriate resistor results in a much better behaved model.
I believe I suggested you download some ADC models. within that ADC collection are some fully differential CMOS opamp / OTA models.
For a very simple model I would use
.subckt ideal_differential_op_amp Vinm Vinp Outp VCM Outm
R1 Outp N001 1
R2 N001 Outm 1
G1 N001 Outp Vinp Vinm 100MEG
G2 Outm N001 Vinp Vinm 100MEG
G3 0 N001 VCM N001 100MEG
.ends ideal_differential_op_amp
you can also include output caps to limit the bandwidth and change the resistor values to model the output impedance.
I cant give you the exact models I use at work because they don't really belong to me.
regards
Robert
--- In LTspice@..., "Apparajan" <dg1@> wrote:
I am re-posting this since I din't get a boo or an aye or nay..
Cheers
AG
--- In LTspice@..., "Apparajan" <dg1@> wrote:
I have uploaded my model
Temp-->File-->>E_model_for_diffamp.asc
It is a very simple model that models the differential and common mode loop gains. I have other more complicated models that model slew-rate, bandwidth, etc. However my most complicated model seems to be much simpler than what is commercially available? They also have a disclimer that they don't model offset, psrr, cmrr etc.? What gives...
|
Hi,
I'm having a problem with another program that use LTSpice to run the simulation. The schematic have a NAND gate, and I write a ".model" like the one below, but the LTSpice seems don't recognize the "d_nand" expression.
** 2 input NAND schmitt
.model A4093 d_nand ( in_family="4000-5_SCHMITT"
+ out_family="4000-5"
+ out_res=560
+ input_load=5p
+ rise_delay=162n
+ fall_delay=162n
+ max_source = 3.2m
+ min_sink = -1m )
Anyone know how can I solve this?
Best regards,
S.
|
