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kilian987654321

Anti-Aliasing Filter on Analog Discovery 2

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Hi @kilian987654321

There is no adjustable filter available in the device only the averaging of N samples = 100MHz ADC rate / sample rate
The scope input bandwidth +30MHz acts as an aliasing filter.

In the WaveForms application you can enable oversampling under the Time options and add Math filter channel like this:

image.thumb.png.9105eb796581781b675a5c0a221d5d97.png

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Thank you, this is very helpful. As a follow-up question, this also means that there is no anti-aliasing filter to filter out frequencies higher that the maximum bandwidth, correct (a 6MHz signal for example)? It's fine for me if not, just curious.

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Dear,

 

I really surprise about the absence of adaptative anti-aliasing filter (depending on sample rate configuration).

Is there any Reason of it ?

 

The solution you give is not a really one because the spectrum is still altered in the low frequencies.

Just try to Watch the Spectrum of a 110kHz square wave… It is awfull… That mean, your device is unusable exept for special frequency (or use a large oversampling which limits the bandwidth of the Spectrum analyser).

Sans titre-1.jpg

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Hi @TTL

The 'Reason" for not having adjustable filter are the device size and price.
It would require additional components and larger processing unit to handle software filtering.

If you use a high order low pass filter Math channel, the low frequencies won't be affected.
You can select the 2nd device configuration, under Settings/ Device Manager, to double the scope buffer, to double the resolution.
For lower frequencies, below 1-2MHz, you can record more samples in the Scope.

Here you have shown the most extreme situation with a square waveform.
With typical sine waves modulated in a way or other, or distorted, you don't have that many significant harmonics which could cause alias.

Even with expensive tools I use to analyze the signals at different ranges, sampling frequencies.
This to identify which components in the view may be alias of a different frequency domain.

 

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