SV: Re: [sdiy] Simulating SW?

[Grant Richter]

A continuos input function produces a discrete FFT.
A discrete input produces a continuous FFT.

That is to say the results of discrete input to an FFT produce  
results in the FFT from the quantizing, sampling and windowing.
The output is a line function that has various amount of "bleed"  
between frequency bins based on the windowing function.
So you have to consider the effects of a single sine versus a  
continuos sine from - infinity to + infinity.
The face that it is a single cycle produces artifacts in the FFT itself.

On Nov 18, 2005, at 3:20 PM, karl dalen wrote:

> Thanks for the spice sugestion Jim!
> I downloaded it and now trying to use it properly!:)
>
> However i havent simulated before!
> (oh, that was a bad one) :)
>
> When i run the FFT on a single sine wave i get spurious harmonics,  
> first harmo
> are displayed 60db below fundamental
> and so on.
>
> Is this due to the number of samples in the AC sine
> model or the number of FFT points or what?
>
> The more FFT sample points i use the worser the result gets!
> Im used to get one spike in the diagram showing the fundamental
> and spurious noise a 140db below! And no harmonics!!
>
> And the signal floor are constantly changing due
> to number of FFT sample points set? Really wierd!
>
> KD
>
> --- James Patchell <patchell at cox.net> skrev:
>
>> I use the Linear Technology Switcher Cad...they promote it as a  
>> way to
>> simulate switching power supplies, but you can use it as a general  
>> purpose
>> SPICE as well...and the best thing...it is free....there are similar
>> packages available from other vendors as well...I think TI also has
>> one.  Take your pick...use the one that works for you.
>>
>> http://www.linear.com/company/software.jsp
>>
>>
>> At 07:55 AM 11/18/2005 +0000, tom.adam at telenet.be wrote:
>>> What simulation software you guys use for trying out new idea's?
>>> Or is this "not done".....
>>>
>>> Looking for a lite version, preferably freeware ;-)
>>>
>>> Cheers,
>>>
>>> --
>>> Tom Adam
>>> The Big Ear
>>> http://users.pandora.be/the-big-ear/
>>> Check out the download section!
>>
>>          -Jim
>> ***************************************************************
>> http://www.oldcrows.net/~patchell
>>
>> ***************************************************************
>>
>>
>>