problem with coefficients when simulating Sigma first-order high pass
Hi,
I am facing a problem with the coefficients of a first-order high pass filter in SigmaStudio.
I am trying to simulate the filter in Matlab.
In order to do so, I am using the formulas provided in the help of SigmaStudio, but it seems that the implementation that is suggested for the highpass filter there is not correct.
using the implementation when the gainLinear factor is 1 then apparently a1 = b0 and b1 = -b0.
However, this is not the case for a highpass filter of (for example) 1000 Hz cut-off frequency and a Gain of 0 as seen below.
It seems that the implementation is following the formulas:
b0 = (1+x)/2
b1 = -(1+x)/2
a1 = x
when I am using these formulas I get correct results in Matlab, and my results match (approximately) what I see in SigmaStudio.
Is this a mistake in the help file of SigmaStudio?
thank you,
Dimitris
Hello Dimitris,
Thanks for pointing this out. Yes the built-in help is wrong. ADI stopped supporting this help file a few years ago, leaving it frozen where it's been. Thus, newer blocks aren't represented there, and any errors persist.
The Online Wiki at: https://wiki.analog.com/resources/tools-software/sigmastudio/toolbox
has been much improved, making it the preferred help source. Its First-Order Filter entry is correct:
https://wiki.analog.com/resources/tools-software/sigmastudio/toolbox/filters/general1storder
Any registered user can edit and improve the wiki. I'm happy to see how easy this has become -- now it works much like typing posts here. Previously you had to (gasp!) slough through HTML-like code.
Best regards,
Bob
KJBob,
thank you very much for this information.
I have been blindly following the help file and have had problems at times.
I will be using the link from now on.
One small remark only here. Do you think that in future releases of SigmaStudio we can get a message or indication that the integrated help support is obsolete and for more updated information we should use the online wiki instead?
I work in a corporation with many people using SigmaStudio and I can see how fresh users might face conflicts with it.
best regards,
Dimitris
Hello Dimitris,
Yours is a good idea -- hopefully one of the SigmaStudio programmers will see your post and respond. I believe ADI was at least experimenting with doing away with the internal help file altogether. Instead, SigmaStudio's Help function would automatically link to the wiki. With Internet access so commonplace nowadays, this should work fine even for laptops.
Best regards,
Bob
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EZ Admin
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