Noise Spectral Density and Fouier Analysis
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godfrey
diyAudio Member

Join Date: Nov 2009
Location: Cape Town
Hi Karl

I use an old "Student" version of Circuitmaker.
On the output screen there's a button that brings up a "Settings" screen, where you can select "Decibels" for the vertical scale. Perhaps your version has something similar?

Btw, I wouldn't recommend the old "Student" version as it's more than slightly buggy (but very easy to use). In comparison LTSpice is very good, but an absolute pain to use.

Cheers - Godfrey
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DF96
diyAudio Member

Join Date: May 2007
Quote:
 what does fV2^2/Hz translate into?
I don't think anyone has answered this question.

White noise has a uniform power spectrum - to find the noise power within a particular bandwidth you multiply the noise power density by the bandwidth. Noise power goes like voltage squared (like all power with a fixed resistance). Often in electronics we are more interested in voltage than power, so noise spectral density can be expressed as V^2 instead of watts. So NSD in V^2/Hz means that to get the RMS noise voltage you multiply by the bandwidth (that is the /Hz part), then take the square root (the V^2 part).

I'm not sure what the f and the first 2 are for.

 8th April 2012, 01:50 PM #13 kbeist   diyAudio Member   Join Date: Sep 2010 Location: Grove, Ok. Thank you for that explaination. At least that gives me a the basics for the noise density>voltage correlation. And yes, bypassing a generic 'power' reading has more than one advantage. As everyone should know: 1) Power is a relative term. 2)Power is only meningful if most, if not all parameters are known and/or specified. The student version that you have a scr-shot of is definitly more limited. CM2K pro has a few more user friendly buttons. I lost the reg# after a few years and several moves and now I have to deal with the trial period, then reload MSWin, trial, reload, trial, relo... PITA. LTSpice is definitly nice but no where near being user friendly. When I say friendly I mean (create component - import spice data - Save component with inherant spice data - create new circuit - sim it). It would be really nice if a developer designed a cross-platform program that could extract user defined data from PDF's to be used in spice. I know Adobe would probably loose multi-billions of dollars letting another program access data points within their pdf structure. However, it would benifit many, for the common advancement of our human race. Design Spark V3 is really nice as a Sch/pcb freebee with 3D modeling and the ability to only export to LTSpice. But it would be a really robust program if the import and export could be a 2-way freeway! (12 lane Interstate standards ) Last edited by kbeist; 8th April 2012 at 02:17 PM.

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