How to calculate PSD from B-source math and .measure

Question

Hi Group:

Is there direct FFT or DFT and that will lead one to calculate the PSD (pow er spectral density)implementation that could be done with .measure or B-so urce math in LTspice IV? Special Opamps for very low noise figures would ce rtainly have a noise figure and noise spectral density but the data sheet w ill not give you PSD ?

I can only think of signals and systems theory that if the Auto Correlatio n function exist the according to the Fourier Transform Tables it will have the its corresponding Energy Spectral Density which is well known as Wien er-Khinchin Theorem of course.

Perhaps I'll take a look using the idt(x), sdt(x) and idtmod(x) from the B- source functions and options on .measure. Would appreciate some help from t he members out there.

Thanks.

George Herold · Accepted Answer

ower spectral density)implementation that could be done with .measure or B- source math in LTspice IV? Special Opamps for very low noise figures would certainly have a noise figure and noise spectral density but the data sheet will not give you PSD ?

ion function exist the according to the Fourier Transform Tables it will ha ve the its corresponding Energy Spectral Density which is well known as Wi ener-Khinchin Theorem of course.

B-source functions and options on .measure. Would appreciate some help from the members out there.

I'm not sure what you are asking. (And I'm not a LTspice expert... there i s some Yahoo group I hear.) But can't you just square the voltage noise to get the PSD? Or do you need a resistance to get power?

Perhaps multiply the opamp voltage noise by the current noise?

George H.

How to calculate PSD from B-source math and .measure

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