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Re: Freqeucny Dependent resistor
Ganesan
Should Laplace be turning in his grave?
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On 9/15/2011 12:51 PM, Michael Peter Kiwanuka wrote:
Hi Shivesh, |
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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:
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Re: About impedance
Tony Casey
--- In LTspice@..., Andy <Andrew.Ingraham@...> wrote:
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.Naive question. Why would you want to do that? If you have s-parameterOften you have s-parameters for a component (a transistor or MMIC), 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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Re: About impedance
John Woodgate
In message <CALBs-ThF7REAcCQEOUOw2A8J1qBi752gUcHTrqUnBUatD03Scg@...>, dated Thu, 15 Sep 2011, Andy <Andrew.Ingraham@...> writes:
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.Naive question. Why would you want to do that? If you have s-parameterOften 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. -- 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. |
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Re: About impedance
Naive question. Why would you want to do that? If you have s-parameterOften 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 |
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Re: AD8336 failure
Ah. Got it. It was "Edit->Edit Attributes..." I was missing.
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Thanks again. --- In LTspice@..., "Helmut" <helmutsennewald@...> wrote:
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Re: About impedance
Tony Casey
<snip>
However, some clever contributor to this group has provided a means to </snip>plot the graticule of a Smth chart and impedance curves with frequency markersHello Philip, 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 |
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Re: About impedance
John Woodgate
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. |
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Re: Diode Model Request for 1N5811 and 1N6628
So, here it is:
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.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@..., Dan Chamberlin <dachamberlin16@...> wrote:
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Re: About impedance
Tony Casey
--- In LTspice@..., Philip Bellingham <rmhc78a@...> wrote:
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 |
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Re: Diode Model Request for 1N5811 and 1N6628
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.
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Gerhard --- In LTspice@..., Dan Chamberlin <dachamberlin16@...> wrote:
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Re: Diode Model Request for 1N5811 and 1N6628
Hello Dan,
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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@..., "dachamberlin16" <dachamberlin16@...> wrote:
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Re: AD8336 failure
--- In LTspice@..., "stm6823@..." <stevemorris@...> wrote:
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
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Re: Diode Model Request for 1N5811 and 1N6628
Tony Casey
--- In LTspice@..., Dan Chamberlin <dachamberlin16@...> wrote:
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 |
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Re: .savebias command commented out
g.moberg
Hello Again,
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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 --- In LTspice@..., "g.moberg" <gregory.moberg@...> wrote:
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Re: AD8336 failure
Tony,
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You are right about the path - I messed up, sorry. I will follow the check box suggestion from now on. Thanks again, STM --- In LTspice@..., "Tony Casey" <tony@...> wrote:
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Re: AD8336 failure
I opened the AD8336.asy you had in the zip file with FILE OPEN in LTspice but I don't find any attributes.
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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@..., "Helmut" <helmutsennewald@...> wrote:
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Re: AD8336 failure
--- In LTspice@..., "stm6823@..." <stevemorris@...> wrote:
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 |
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Re: About impedance
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: 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] |
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Re: Hey i am working on a Class D amp project, need help about LT Spice
Tony Casey
--- In LTspice@..., "cukkacan" <mustafa_cukka@...> wrote:
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 |
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