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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