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Re: Freqeucny Dependent resistor

 

Hi again Tony,

My starting question was whether radiation impedance actually held up as
only real - his example of a possibility. John then slightly moved the
goalposts in response by saying that they were by definition only real; look
no further than the power response (and we know that nothing can be
dissipated reactively). This was not so damning an argument as it looked, I
said, because power is not a vector quantity.

I don't care where the power goes. I just wanted to know if there was a
direction associated with the amplitude.

To keep this on track - perhaps Nigel can tell us whether this was what he
had in mind as a VCVS type f dependent resistor. I think we would know
about it if it could be done.

Christian

On 15 September 2011 23:14, Tony Casey <tony@...> wrote:

**




--- In LTspice@..., Christian Thomas <ct.waveform@...> wrote:

That's a pretty damning point!

But does it hold? You've squared up a vector quantity to get something
that
by definition has no direction. Telling me that power is a scalar is
surely
a starting point, not a proof that nothing reactive is there.

CT



On 15 September 2011 21:46, John Woodgate <jmw@...> wrote:

**


In message
<CANj54jz_C3C0wTdO5kkCRbVh3qDQsrda9qatksP5h1bX+ohtqA@...>,
dated Thu, 15 Sep 2011, Christian Thomas <ct.waveform@...>
writes:

But are you sure that radiation resistances are only real?
By definition: they are notionally responsible for the real power that
is radiated. Reactive elements cannot be responsible.

--
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.




Christian,

I don't think John was stating that there is no reactive part, only that
power cannot be dissipated in it.

Regards,
Tony
Re: Ideal Swich Model missing

 

--- In LTspice@..., Michael Stuarts wrote:

The model for SW appears to missing. If anyone can help me create
a .model statement for schematic that would be great. I could not
figure out how to do it from the help file alone.
Why not? Do you have a reading comprehension problem? This is a
serious question because Help both clearly explains that you must
provide a model statement to define your switch and gives you a
link to an example schematic that you may run if you are too
unfamiliar with the correlation between the netlist notation
example provided and how it derives from the schematic.

Perhaps English is not your native language? Or perhaps you really
didn't read Help? I am curious because I really would like to
understand why Help (which seems perfectly fine to me) does not
seem to work for so many users (so there is no wrong answer on
your part other than a less than honest one).

Regards -- analogspiceman

PS: Here is the relevant section from Help.
-----------------------------------------------------------
S. Voltage Controlled Switch

Symbol Names: SW

Syntax: Sxxx n1 n2 nc+ nc- <model> [on,off]

Example:

S1 out 0 in 0 MySwitch

.model MySwitch SW(Ron=.1 Roff=1Meg Vt=0 Vh=-.5 Lser=10n Vser=.6)

The voltage between nodes nc+ and nc- controls the switch's
impedance between nodes n1 and n2. A model card is required
to define the behavior of the switch. See the schematic file
.&#92;examples&#92;Educational&#92;Vswitch.asc to see an example of a model
card placed directly on a schematic as a SPICE directive.
-----------------------------------------------------------
Re: Freqeucny Dependent resistor

Tony Casey
 

--- In LTspice@..., Christian Thomas <ct.waveform@...> wrote:

That's a pretty damning point!

But does it hold? You've squared up a vector quantity to get something that
by definition has no direction. Telling me that power is a scalar is surely
a starting point, not a proof that nothing reactive is there.

CT



On 15 September 2011 21:46, John Woodgate <jmw@...> wrote:

**


In message
<CANj54jz_C3C0wTdO5kkCRbVh3qDQsrda9qatksP5h1bX+ohtqA@...>,
dated Thu, 15 Sep 2011, Christian Thomas <ct.waveform@...>
writes:

But are you sure that radiation resistances are only real?
By definition: they are notionally responsible for the real power that
is radiated. Reactive elements cannot be responsible.

--
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.



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

I don't think John was stating that there is no reactive part, only that power cannot be dissipated in it.

Regards,
Tony
Re: Ideal Swich Model missing

Tony Casey
 

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

The model for SW appears to missing.
If anyone can help me create a .model
statement for schematic. That would be great.
I could not figure out how to do it from
the help file alone.

Thanks,

//Michael
Hello Michael,

From the Help:

S1 out 0 in 0 MySwitch
.model MySwitch SW(Ron=.1 Roff=1Meg Vt=0 Vh=-.5 Lser=10n Vser=.6)

You don't say what your switch will be used for, but I'm betting that if you deleted the last three terms in the model above, it would do what you wanted.

If you're having trouble relating that to your schematic, do this:
1. Place a sw from the parts chooser, and change its value to MySwitch.
2. Add a SPICE directive, and paste in the .model text.

If you're trying to control it from something like TTL or CMOS, change Vt to 1.8V, or something between the logic levels.

Regards,
Tony
Re: Freqeucny Dependent resistor

Tony Casey
 

<snip>
I believe it is impossible to have a physically realizable resistor that is frequency dependent and has no reactive component. A transmission line comes close in that its resistance is almost constant for a range of frequencies, but as you know at very low frequencies, neglecting any series resistive components, its reactance is largely capacitive.

Hubert
</snip>
Hello Hubert,

You are of course correct: the only resistor possible that had no reactive component would also have zero size. Any conductor of finite size inevitably has both inductance and capacitance, even if it has no resistance, like a superconductor.

I think the salient point of the discussion really is whether we can legitimately model part of a system, in which the reactive part doesn't significantly change as a consequence - with a notional frequency-dependent resistor.

I think there are converse examples too, where the reactive part changes without a consequential change to the resistive part: a capacitor where the real part of permittivity reduces with frequency without significant change to the imaginary part. A good example of this is an FR4 PCB trace. It's capacitance reduces with frequency, whilst its resistance increases, albeit for a completely unconnected reason. I'm sure there are many more.

(I detect the red pen of the moderator twitching, so had better stop here.)

Regards,
Tony
Re: Freqeucny Dependent resistor

 

That's a pretty damning point!

But does it hold? You've squared up a vector quantity to get something that
by definition has no direction. Telling me that power is a scalar is surely
a starting point, not a proof that nothing reactive is there.

CT



On 15 September 2011 21:46, John Woodgate <jmw@...> wrote:

**


In message
<CANj54jz_C3C0wTdO5kkCRbVh3qDQsrda9qatksP5h1bX+ohtqA@...>,
dated Thu, 15 Sep 2011, Christian Thomas <ct.waveform@...>
writes:

But are you sure that radiation resistances are only real?
By definition: they are notionally responsible for the real power that
is radiated. Reactive elements cannot be responsible.

--
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.



[Non-text portions of this message have been removed]
Ideal Swich Model missing

 

The model for SW appears to missing.
If anyone can help me create a .model
statement for schematic. That would be great.
I could not figure out how to do it from
the help file alone.

Thanks,

//Michael
Re: About impedance

 

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

Tony,

All valid points. I agree that creating SPICE models for s-parameter
characterized passive parts using only native SPICE passives (C, L, and R) is an
art and the native models are often inadequate even with the provision for
adding parasitics. The same is true for modeling active components. Therefore, I
agree that creating SPICE models that can be used for all types of analysis
(TRAN, AC, etc.) is a daunting task when the only data you have is s-parameters.
My experience has been that frequency domain characterization and simulation is
often sufficient. To that end, the utility, in our group files, that converts an
s-parameter file to a set frequency dependent controlled sources in SPICE,
creates models that are quite acceptable when performing AC network
analysis.??This does limit you to AC analysis, and for active devices you are
constrained to the bias conditions present??when the s-parameters were measured.


Regards,

???? - Philip
All,

By definition s-parameters are small signal linear AC parameters, and in most cases the parameters are a function of frequency. Usually, one is interested in only a single frequency or a mall range of frequencies. The work fine for their intended purpose.

Rick
Re: Freqeucny Dependent resistor

John Woodgate
 

In message <CANj54jz_C3C0wTdO5kkCRbVh3qDQsrda9qatksP5h1bX+ohtqA@...>, dated Thu, 15 Sep 2011, Christian Thomas <ct.waveform@...> writes:

But are you sure that radiation resistances are only real?
By definition: they are notionally responsible for the real power that is radiated. Reactive elements cannot be responsible.
--
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.
Re: About impedance

 

Tony,

All valid points. I agree that creating SPICE models for s-parameter
characterized passive parts using only native SPICE passives (C, L, and R) is an
art and the native models are often inadequate even with the provision for
adding parasitics. The same is true for modeling active components. Therefore, I
agree that creating SPICE models that can be used for all types of analysis
(TRAN, AC, etc.) is a daunting task when the only data you have is s-parameters.
My experience has been that frequency domain characterization and simulation is
often sufficient. To that end, the utility, in our group files, that converts an
s-parameter file to a set frequency dependent controlled sources in SPICE,
creates models that are quite acceptable when performing AC network
analysis.?This does limit you to AC analysis, and for active devices you are
constrained to the bias conditions present?when the s-parameters were measured.


Regards,

?? - Philip


________________________________
From: Tony Casey <tony@...>
To: LTspice@...
Sent: Thu, September 15, 2011 12:42:09 PM
Subject: [LTspice] Re: About impedance

?


--- 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




[Non-text portions of this message have been removed]
Re: Freqeucny Dependent resistor

 

John

I put my caveat in for good reason ...

The way I thought about it was to think what I would do to design one. I
would need a reactive component somewhere, to do it easily, and then I would
cancel out that component's phase shift with an all-pass. I am fairly
certain that can't be done perfectly (though for the moment I can't quite
think why not for a first order original. I suppose because it has to add,
so you can never get a perfect time delay.)

But are you sure that radiation resistances are only real? I'm fairly
certain that acoustic radiation impedances aren't naturally real and that
it's only because drivers are mass controlled that they appear so. (I
suspect that means masses in the f = ma sense rather than an equivalent C.)

Christian



On 15 September 2011 20:32, John Woodgate <jmw@...> wrote:

**


In message
<CANj54jwDGEMhNQA5E=DD=cMmYJTwDN=mMCrX2FaMfB4YgiLxuw@...>,
dated Thu, 15 Sep 2011, Christian Thomas <ct.waveform@...>
writes:


In which case the answer needed is "No, you can't. Or at least you
can't have a full solution. (I think that must be right).
I'm not sure. We have real resistances that change with frequency -
radiation resistances for example, There are definitely resistances - at
any fixed frequency they are consistent with Ohm's and Joule's Laws.

So why can't I define a resistor R(f), such that R(f) = kf, or K*F(f)? k
and K have dimensions, of course, but that doesn't seem to be a problem.
--
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.



[Non-text portions of this message have been removed]
Re: Freqeucny Dependent resistor

 

I believe it is impossible to have a physically realizable resistor that is frequency dependent and has no reactive component. A transmission line comes close in that its resistance is almost constant for a range of frequencies, but as you know at very low frequencies, neglecting any series resistive components, its reactance is largely capacitive.

Hubert

----- Original Message -----
From: Tony Casey
To: LTspice@...
Sent: Thursday, September 15, 2011 12:43 PM
Subject: [LTspice] Re: Freqeucny Dependent resistor



<snip>
--- In LTspice@..., Christian Thomas <ct.waveform@...> wrote:
>
> Well, that's a question AG.
>
> Might we not be looking at a naive question here? Ie. Can I please have a
> resistor that changes with frequency but with none of those nasty reactive
> elements? If that's the case then looking in the s-plane is not the answer
> being sought.
>
> In which case the answer needed is "No, you can't. Or at least you can't
> have a full solution. (I think that must be right). But we do have some
> useful reactive components that perform that function, and that's what
> everyone else uses. C and L in LTSpice; and their s-plane behaviour is
> built in."
>
> CT
</snip>
Hello Christian,

I'm sure you ask the question tongue-in-cheek, because you surely must be aware of instances where the real part of an impedance changes with frequency without significant change in the reactance.

What about the resistance of straight length of wire? This increases due to the skin effect, whereby as the frequency rises more and more of the current travels closer to the outer (indeed for circular cross-section, the only) surface of the wire, so in effect reducing the cross-sectional area of the wire. In the limit, there is also a change in the inductance per unit length too, but it is not significant compared to the change in resistance.

And although not strictly a "component", there is the free space acoustic radiation resistance of a diaphragm, which also rises with frequency up to the frequency where the circumference is approximately equal to the wavelength. I will concede in this example that the reactive part of the impedance also changes at a fair rate of knots over the same frequency interval.

I'm sure you already knew all that. But it does illustrate why it is perfect legitimate to seek frequency-dependent resistance models.

Regards,
Tony
Re: Freqeucny Dependent resistor

Ganesan
 

There is a whole field of active filter synthesis based on FDNR
(Frequency Dependent Negative Resistance).... LTspice makes it easier to
synthesize...


<>

cheers
A. Ganesan

=================================================================================

On 9/15/2011 2:13 PM, Christian Thomas wrote:
Well, that's a question AG.

Might we not be looking at a naive question here? Ie. Can I please have a
resistor that changes with frequency but with none of those nasty reactive
elements? If that's the case then looking in the s-plane is not the answer
being sought.

In which case the answer needed is "No, you can't. Or at least you can't
have a full solution. (I think that must be right). But we do have some
useful reactive components that perform that function, and that's what
everyone else uses. C and L in LTSpice; and their s-plane behaviour is
built in."

CT



On 15 September 2011 19:28, Ganesan<dg1@...> wrote:

**


Should Laplace be turning in his grave?


On 9/15/2011 12:51 PM, Michael Peter Kiwanuka wrote:
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.








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

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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
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Re: Freqeucny Dependent resistor

Tony Casey
 

<snip>
--- In LTspice@..., Christian Thomas <ct.waveform@...> wrote:

Well, that's a question AG.

Might we not be looking at a naive question here? Ie. Can I please have a
resistor that changes with frequency but with none of those nasty reactive
elements? If that's the case then looking in the s-plane is not the answer
being sought.

In which case the answer needed is "No, you can't. Or at least you can't
have a full solution. (I think that must be right). But we do have some
useful reactive components that perform that function, and that's what
everyone else uses. C and L in LTSpice; and their s-plane behaviour is
built in."

CT
</snip>
Hello Christian,

I'm sure you ask the question tongue-in-cheek, because you surely must be aware of instances where the real part of an impedance changes with frequency without significant change in the reactance.

What about the resistance of straight length of wire? This increases due to the skin effect, whereby as the frequency rises more and more of the current travels closer to the outer (indeed for circular cross-section, the only) surface of the wire, so in effect reducing the cross-sectional area of the wire. In the limit, there is also a change in the inductance per unit length too, but it is not significant compared to the change in resistance.

And although not strictly a "component", there is the free space acoustic radiation resistance of a diaphragm, which also rises with frequency up to the frequency where the circumference is approximately equal to the wavelength. I will concede in this example that the reactive part of the impedance also changes at a fair rate of knots over the same frequency interval.

I'm sure you already knew all that. But it does illustrate why it is perfect legitimate to seek frequency-dependent resistance models.

Regards,
Tony
Re: Solid-state relay model

 

I have made some. They work perfect, except when I put them in a circuit, then they behave unbelievably weird. I'm working the issue.

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

Does anyone have a SPICE model of a solid-state relay, or guidance on how to create one? I'm using the PVA series from International Rectifier.
Thanks

Soumyajit
Re: Freqeucny Dependent resistor

John Woodgate
 

In message <CANj54jwDGEMhNQA5E=DD=cMmYJTwDN=mMCrX2FaMfB4YgiLxuw@...>, dated Thu, 15 Sep 2011, Christian Thomas <ct.waveform@...> writes:

In which case the answer needed is "No, you can't. Or at least you can't have a full solution. (I think that must be right).
I'm not sure. We have real resistances that change with frequency - radiation resistances for example, There are definitely resistances - at any fixed frequency they are consistent with Ohm's and Joule's Laws.

So why can't I define a resistor R(f), such that R(f) = kf, or K*F(f)? k and K have dimensions, of course, but that doesn't seem to be a problem.
--
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.
Re: Freqeucny Dependent resistor

 

Well, that's a question AG.

Might we not be looking at a naive question here? Ie. Can I please have a
resistor that changes with frequency but with none of those nasty reactive
elements? If that's the case then looking in the s-plane is not the answer
being sought.

In which case the answer needed is "No, you can't. Or at least you can't
have a full solution. (I think that must be right). But we do have some
useful reactive components that perform that function, and that's what
everyone else uses. C and L in LTSpice; and their s-plane behaviour is
built in."

CT



On 15 September 2011 19:28, Ganesan <dg1@...> wrote:

**


Should Laplace be turning in his grave?


On 9/15/2011 12:51 PM, Michael Peter Kiwanuka wrote:
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]







[Non-text portions of this message have been removed]
Re: Freqeucny Dependent resistor

Ganesan
 

Should Laplace be turning in his grave?

On 9/15/2011 12:51 PM, Michael Peter Kiwanuka wrote:
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.








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Re: Freqeucny Dependent resistor

 

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]
Re: About impedance

Tony Casey
 

--- 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
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