Overview

Plots of Fourier spectra in SIMetrix are currently displayed with a logarithmic y-axis of the amplitude of the signal. The only option available is to change it to a linear axis.

There is no option to provide the y-axis in dBs with versions up to 5.1. (This is a standard feature from 5.2 onwards). But, the program code that builds the Fourier waveform is written in the SIMetrix script language and it is possible to edit this to provide a dB y-axis.

You need a full production version of SIMetrix to use this feature. It does not work with SIMetrix Intro as user scripts are not permanently available with that product. (But scripts may be enabled for 30 days by using the unlock feature)

Procedure

1. Download one of the following script files according to what version you are using. See menu Help | About... to find out your exact version
   
   

   Version	Download Script
   4.0 to 4.5d	define_fourier_new_db
   5.0 to 5.0h	define_fourier_new_db
   5.1 to 5.1e	define_fourier_new_db
   5.2 onwards	Feature built in

2. Copy the script file to your script directory. The following table tells you where this is located
   
   

   Version	Platform	Path
   4.0 to 5.1a	Windows	ProgFiles\SIMetrixxx\Script
   5.0 to 5.1a	Linux	$HOME/simetrix/script

   
   Where ProgFiles is your "Program Files" directory. This is typically at C:\Program Files. Note that if you installed SIMetrix in non-administrator mode, you will find it located in a different location under your "Documents and Settings" tree. xx is the version number - e.g. 51.
3. To plot a Fourier spectrum with dB axes, type at the command line (the edit box below the menu bar in the Command Shell):
   
   define_fourier_new_db
   
   This will bring up the same dialog box as the menu Probe | Fourier | Arbitrary... and will behave in an identical manner. But you will see that the y-axes are now in dB.