开云体育

Hi Shivesh,

I have not a great deal of understanding of Laplace transforms but I have a niggling feeling of the transform of an increasing ramp is (1/s**2). Which definition of L-tranform are you usiing ?

Best regards

Michael




To: LTspice@...
From: shivesh_sl@...
Date: Wed, 14 Sep 2011 20:01:53 +0000
Subject: [LTspice] Re: Freqeucny Dependent resistor






Hi George,

Laplace transform for ramp in increasing values is (1/s). Yuo search we for this. Since we have decreasing function hence inverse of previous case, you get (s).

since s is complex no. with value of containing (w)=2*PI()*freq hence for R_eq you multiply 2*PI() to compensate for one coming in from (w).

I hope this explanation helps. I know it is not great but probably you get gits of it.

Regards,
Shivesh

--- In LTspice@..., "George Evans" <george.evans@...> wrote:

Shivesh

many thanks - however I find the laplace expression syntax needs a bit of explanation. How can it be generalised say to model an R proportional to square_root of frequency?

George

_____

From: shivesh_sl [mailto:shivesh_sl@...]
To: LTspice@...
Sent: Mon, 12 Sep 2011 16:47:00 +0100
Subject: [LTspice] Re: Freqeucny Dependent resistor






Hi George,

I have uploaded LTSpice schematic to our group. It should be under msg:49523 heading. Please look it up. If you look up impedance i.e. Voltage at R2/ Current R1 it should give nice linear slope 20db per decade slope.

If you any more question please let me know.

Regards,
Shivesh.

--- In LTspice@..., "George Evans" <george.evans@> wrote:

Hi Shivesh
Interesting. Can you indicate where you placed the Laplace function definition please? The expression I need is one where R_Freq is proprotional to sqare root of Freq. e.g. R_Req=R_eq*K*sqrt(s). Can this go in as a spice directive?

George


_____

From: shivesh_sl [mailto:shivesh_sl@]
To: LTspice@...
Sent: Wed, 07 Sep 2011 16:28:04 +0100
Subject: [LTspice] Freqeucny Dependent resistor






Recently I had had been trying to simulate frequency dependent resistor in LTSpice. But was did not find solution on internet. Then I tried performing simulation by inserting behavioral voltage and current sources. But was having problems with it. Following solution was achieved after reading that Laplace transform can be used for behavioral sources.

To simulate you will need value of resistor at 1Hz =R_1
R_eq= R_1 * 2 * Pi()[3.142...]

R_Freq=R_eq Laplace (s)

Please leave space between R_eq & Laplace, Laplace & (s).

You can use this either as part of your sub circuit model (SPICE Model) or you use them with default resistor by inserting the equation in value field.

Same method can be used for other capacitor and inductors. I have tested all of them and does provide with good replications.

I hope this helps.








----------------------------------------------------------

This email and any files transmitted with it are confidential and
intended solely for the use of the individual or entity to whom
they are addressed. If you have received this email in error
please notify the system manager. Please note that any views or
opinions presented in this email are solely those of the author
and do not necessarily represent those of the company. Finally,
the recipient should check this email and any attachments for
the presence of viruses. The company accepts no liability for
any damage caused by any virus transmitted by this email.


Gill Research & Development Ltd is a limited company registered
in England and Wales. Registered number: 3154453.
Registered office: The George Business Centre, Christchurch
Road, New Milton. BH25 6QJ


[Non-text portions of this message have been removed]

----------------------------------------------------------

This email and any files transmitted with it are confidential and
intended solely for the use of the individual or entity to whom
they are addressed. If you have received this email in error
please notify the system manager. Please note that any views or
opinions presented in this email are solely those of the author
and do not necessarily represent those of the company. Finally,
the recipient should check this email and any attachments for
the presence of viruses. The company accepts no liability for
any damage caused by any virus transmitted by this email.


Gill Research & Development Ltd is a limited company registered
in England and Wales. Registered number: 3154453.
Registered office: The George Business Centre, Christchurch
Road, New Milton. BH25 6QJ


[Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]

--- In LTspice@..., Andy <Andrew.Ingraham@...> wrote:

Naive question. Why would you want to do that? If you have s-parameter
files, presumably they came from measurements of a real circuit. So why
ask Spice (or anything else) to generate a circuit?

Often you have s-parameters for a component (a transistor or MMIC),
which you get from the component vendor, and you want to use it in a
circuit.

Andy

Indeed. And for passive products, such as SAW filters or isolators, S-parameters are the only data you're ever likely to get from vendors.

Also for capacitors and inductors, vendors such as Murata and ATC also provide S-parameter data for use at frequencies at which the simple equivalent circuits we're used to in SPICE are hopelessly inadequate to describe the performance.

Regards,
Tony

In message <CALBs-ThF7REAcCQEOUOw2A8J1qBi752gUcHTrqUnBUatD03Scg@...>, dated Thu, 15 Sep 2011, Andy <Andrew.Ingraham@...> writes:

Naive question. Why would you want to do that? If you have s-parameter
files, presumably they came from measurements of a real circuit. So why
ask Spice (or anything else) to generate a circuit?

Often you have s-parameters for a component (a transistor or MMIC), which you get from the component vendor, and you want to use it in a circuit.

I said it was naive! The data are s-parameter values as functions of frequency, I suppose? Synthesising circuits from impedance values in any form is difficult but only very nearly impossible unless the functions of frequency are rather simple.
--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
When I point to a star, please look at the star, not my finger. The star will
be more interesting.

Naive question. Why would you want to do that? If you have s-parameter
files, presumably they came from measurements of a real circuit. So why
ask Spice (or anything else) to generate a circuit?

Often you have s-parameters for a component (a transistor or MMIC),
which you get from the component vendor, and you want to use it in a
circuit.

Andy

Ah. Got it. It was "Edit->Edit Attributes..." I was missing.
Thanks again.

<snip>
However, some clever contributor to this group has provided a means to

plot the graticule of a Smth chart and impedance curves with frequency markers
(Files > Examples > Apps > SmithLTspice.zip).

??
With respect to LTspice handling s-parameters, it certainly can. The .NET
command computes network parameters in an AC sweep. The HELP files says in part,

??
"This statement is used with a small signal(.AC) analysis to compute the input
and output admittance, impedance, Y-parameters, Z-parameters, H-parameters, and
S-parameters of a 2-port network. It can also be used to compute the input
admittance and impedance of a 1-port network. This must be used with a .AC
statement, which determines the frequency sweep of the network analysis."
??
There is an entire section in the tutorial section of this groups files devoted
to s-parameters in LTspice (Files> Tut> S-Parameter).
??
All the best,
??
???? - Philip

Hello Philip,

Thanks for the info.

I'm aware of the Smith chart add-on, which is why I said native. It's clever as you said, but not slick enough for serious design work; even the author concedes it's crude.

</snip>
Other folk might like to be aware that also exist several ways of plotting Smith charts in Excel by using similar kludges. This is one of several:


Regards,
Tony

In message <j4t6tu+4c59@...>, dated Thu, 15 Sep 2011, Tony Casey <tony@...> writes:

There are also various utilities that claim to generate SPICE subcircuits from S-parameter files, but this is something of a holy grail, which is why the only commercial product that really claims to have cracked this with multiport demonstrable accuracy over decades of frequency range costs thousands of dollars.

Naive question. Why would you want to do that? If you have s-parameter files, presumably they came from measurements of a real circuit. So why ask Spice (or anything else) to generate a circuit? To track down parasitics?
--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
When I point to a star, please look at the star, not my finger. The star will
be more interesting.

So, here it is:

.model 1N6628 D(Is=20.73u N=2.871 Rs=11.4m Ikf=.269 Xti=3 Eg=1.11 Cjo=97p
+ Isr=49.6E-30 Bv=660 Ibv=50u Tt=74n Iave=2.3 Vpk=600 mfg=Microsemi type=Silicon)

Best regards,

Gerhard

--- In LTspice@..., Philip Bellingham <rmhc78a@...> wrote:

Tony,

While LTspice may not be the ideal tool for RF design, it can still be quite
useful.

You are correct that it does not have native support for producing a Smith
chart. However, some clever contributor to this group has provided a means to
plot the graticule of a Smth chart and impedance curves with frequency markers
(Files > Examples > Apps > SmithLTspice.zip).

??
With respect to LTspice handling s-parameters, it certainly can. The .NET
command computes network parameters in an AC sweep. The HELP files says in part,

??
"This statement is used with a small signal(.AC) analysis to compute the input
and output admittance, impedance, Y-parameters, Z-parameters, H-parameters, and
S-parameters of a 2-port network. It can also be used to compute the input
admittance and impedance of a 1-port network. This must be used with a .AC
statement, which determines the frequency sweep of the network analysis."
??
There is an entire section in the tutorial section of this groups files devoted
to s-parameters in LTspice (Files> Tut> S-Parameter).
??
All the best,
??
???? - Philip

Hello Philip,

Thanks for the info.

I'm aware of the Smith chart add-on, which is why I said native. It's clever as you said, but not slick enough for serious design work; even the author concedes it's crude. I'm also aware that adding the .net directive enables an .ac analysis to generate S-parameters; and indeed, I make a lot of use of this feature. But you cannot use S-parameters as input data. This was my point, although I admit I didn't make that very clear.

There are also various utilities that claim to generate SPICE subcircuits from S-parameter files, but this is something of a holy grail, which is why the only commercial product that really claims to have cracked this with multiport demonstrable accuracy over decades of frequency range costs thousands of dollars.

Regards,
Tony

Oh, I just noticed that you wrote in the subject line 1N6628 and in the text 1N6618. Which one is your favourite? If you need 1N6628, I will try to create a model, too.

Gerhard

Hello Dan,

these are approximate models for the requested diodes, newly created from the datasheets' curves/values:

.model 1N5811 D(Is=850n N=1.938 Rs=4.235m Ikf=2.584 Xti=3 Eg=1.11 Cjo=146p
+ Isr=378E-30 Bv=160 Ibv=100u Tt=43.3n Iave=6 Vpk=160 mfg=Microsemi type=Silicon)

.model 1N6618 D(Is=620.6u N=5.430 Rs=15.4m Ikf=.662 Xti=3 Eg=1.11 Cjo=192p
+ M=.414 Vj=.184 Isr=372E-30 Bv=800 Ibv=1u Tt=173n Iave=3 Vpk=800 mfg=VMI type=Silicon)


Best regards,

Gerhard Kaufmann

--- In LTspice@..., "stm6823@..." <stevemorris@...> wrote:

I opened the AD8336.asy you had in the zip file with FILE OPEN in LTspice but I don't find any attributes.
When I open it in notepad the only attributes are pin references.

Version 4
SymbolType BLOCK
RECTANGLE Normal -80 -104 80 104
WINDOW 0 0 -104 Bottom 2
WINDOW 3 0 104 Top 2
SYMATTR Value AD8336
SYMATTR Prefix X
SYMATTR SpiceModel ad8336.cir
SYMATTR Value2 AD8336
PIN -80 -64 LEFT 8
PINATTR PinName GNEG
PINATTR SpiceOrder 1
PIN -80 -32 LEFT 8
etc.

How do I open the others to see what you set?
Thanks,
STM

Hello STM,

You can see my attributes in the text file above.
It's different from what you had in your your symbol.
Normally you don't look with a text editor. You should open
my symbol with LTspice and then "Edit->Edit Attributes...".

Modelfile: ad8336.cir
Value: AD8336
Value2: AD8336

Best regards,
Helmut

--- In LTspice@..., "Helmut" <helmutsennewald@> wrote:

--- In LTspice@..., "stm6823@" <stevemorris@> wrote:

Helmut,
Thank you very much for your time and help. So much for me to learn. I integrated all your schematic changes into mine and it works great. I put the changes in one at a time to observe the effect. Lots of subtle stuff like the series resistance in the supplies messing things up that I don't get.
I am curious about your reference to correcting the symbol because I am still using mine and it works OK. I had LTspice make it from the netlist editor. I tried to open yours to see what you changed but it is not editable. What did you change?
Thanks again,
STM

Hello STM,

I made a specific symbol which isn't editable.
All symbol of the LTC-opamps are made this way.
Please open the symbol(.asy) with LTspice to see which
attributes I have set.

Best regards,
Helmut

--- In LTspice@..., Dan Chamberlin <dachamberlin16@...> wrote:

Could someone let me know where I can find spice models for both 1N5811 and 1N6618?
?
Thanks,
?
Dan

[Non-text portions of this message have been removed]

Hello Dan,

If you can't find models for your diodes, it's not the end of the world, but it will involve more work. (But think of the satisfaction.)

Firstly, for a tutorial, start here:


Then, you can download Hendrik's Diode Modeler from here:


Read the instructions, if necessary, then brew you own models. Create an LTspice test jig and check the curves against those in the datasheet, and you're good to go.

Now you're equipped to tackle almost any diode job regardless of whether there already exists a SPICE model for the device.

Note: many manufacturers' models are garbage anyway, so it's always good practice to check them in a test jig before using on anything important.

There is also a VMOS modeler from the same author in the Files section.

Regards,
Tony

Hello Again,

Just to finish this topic out, today I generated the "Skip" file successfully. Since this is an SMPS circuit whose inductor currents are not zero, I edited the "Skip" file to change its .nodeset command to a .ic command, and set the initial conditions of the 2 inductors to their approximate values at the time the .savebias command executed. This changes the inductor characteristics for initial convergence from short circuits to ideal current sources with the specified initial conditions. This must be done to prevent the circuit from converging to a highly erroneous state with 0V across the inductors.

The simulation picked up very close to where I expected it to, and settled quickly so I can do the load transient analysis without waiting minutes to get to a settled condition.

Thanks again for those who looked at this.

Greg Moberg

Tony,
You are right about the path - I messed up, sorry.
I will follow the check box suggestion from now on.
Thanks again,
STM

I opened the AD8336.asy you had in the zip file with FILE OPEN in LTspice but I don't find any attributes.
When I open it in notepad the only attributes are pin references.

Version 4
SymbolType BLOCK
RECTANGLE Normal -80 -104 80 104
WINDOW 0 0 -104 Bottom 2
WINDOW 3 0 104 Top 2
SYMATTR Value AD8336
SYMATTR Prefix X
SYMATTR SpiceModel ad8336.cir
SYMATTR Value2 AD8336
PIN -80 -64 LEFT 8
PINATTR PinName GNEG
PINATTR SpiceOrder 1
PIN -80 -32 LEFT 8
etc.

How do I open the others to see what you set?
Thanks,
STM

--- In LTspice@..., "stm6823@..." <stevemorris@...> wrote:

Helmut,
Thank you very much for your time and help. So much for me to learn. I integrated all your schematic changes into mine and it works great. I put the changes in one at a time to observe the effect. Lots of subtle stuff like the series resistance in the supplies messing things up that I don't get.
I am curious about your reference to correcting the symbol because I am still using mine and it works OK. I had LTspice make it from the netlist editor. I tried to open yours to see what you changed but it is not editable. What did you change?
Thanks again,
STM

Hello STM,

I made a specific symbol which isn't editable.
All symbol of the LTC-opamps are made this way.
Please open the symbol(.asy) with LTspice to see which
attributes I have set.

Best regards,
Helmut

Tony,

While LTspice may not be the ideal tool for RF design, it can still be quite
useful.

You are correct that it does not have native support for producing a Smith
chart. However, some clever contributor to this group has provided a means to
plot the graticule of a Smth chart and impedance curves with frequency markers
(Files > Examples > Apps > SmithLTspice.zip).

?
With respect to LTspice handling s-parameters, it certainly can. The .NET
command computes network parameters in an AC sweep. The HELP files says in part,

?
"This statement is used with a small signal(.AC) analysis to compute the input
and output admittance, impedance, Y-parameters, Z-parameters, H-parameters, and
S-parameters of a 2-port network. It can also be used to compute the input
admittance and impedance of a 1-port network. This must be used with a .AC
statement, which determines the frequency sweep of the network analysis."
?
There is an entire section in the tutorial section of this groups files devoted
to s-parameters in LTspice (Files> Tut> S-Parameter).
?
All the best,
?
?? - Philip





________________________________
From: Tony Casey <tony@...>
To: LTspice@...
Sent: Thu, September 15, 2011 8:55:18 AM
Subject: [LTspice] Re: About impedance

?


--- In LTspice@..., "keantoken" <keantoken@...> wrote:

What is the purpose of Cartesian plot? I'm sure it makes some things more
convenient than a bode plot. What things?

- keantoken

Hello Keantoken,

If you're doing RF design, on oscillators, for example, it is essential to be
able to see both real and imaginary parts clearly and separately without having
to do mental arithmetic for each frequency displayed. The Cartesian presentation
shows this much better for most people, although a few will claim they can glean
everything they need from a polar plot. But then some people are able to write a
complete GUI in one line of C.

For doing serious RF design, LTspice is not the ideal tool, since it does not
have native Smith chart and cannot handle S-parameters, but it is at least
possible.

Regards,
Tony




[Non-text portions of this message have been removed]

--- In LTspice@..., "cukkacan" <mustafa_cukka@...> wrote:

Hey, i am sophomore at the university, and i have a circuit sketch and data sheet. However, i dont know how to use LT Spice effectively. i couldnt build the circuit on LT Spice perfectly. Could you help me about this issue ?

Also, advices about Class D amp are welcome. i need a working class-d amp circuit about 10-20W.i have checked on the web, topics are not live.

Hello,

I don't know which web you checked, but there are thousands of links relating to class D amplifiers, many of them on the semiconductor manufacturers' websites, check there first.

In general, you will only find people here keen to help once you have demonstrated a willingness to try. Start but drawing a schematic, try to make it work, then ask for help when it doesn't. So far, there's no evidence that you have done anything at all.

Regards,
Tony

Helmut,
Thank you very much for your time and help. So much for me to learn. I integrated all your schematic changes into mine and it works great. I put the changes in one at a time to observe the effect. Lots of subtle stuff like the series resistance in the supplies messing things up that I don't get.
I am curious about your reference to correcting the symbol because I am still using mine and it works OK. I had LTspice make it from the netlist editor. I tried to open yours to see what you changed but it is not editable. What did you change?
Thanks again,
STM