digital filter

[lsullivan]

Dear signal hound,
which filtering algorithm you use in your API in zero-span mode? (design method, response type, filter order, frequency specification, magnitude specification, …)
best regards.

• This topic was modified 3 years ago by lsullivan.

[Andrew]

lsullivan,

The filters used when I/Q streaming are FIR filters. We use 1 or more filters depending on decimation selected. The design method used is the standard windowed sinc method. The bandwidth and filter order is determined by both the decimation and bandwidth chosen by the user during configuration. Additionally, the frequency/magnitude response of the filters are modified by the IF flatness corrections, which are device specific, providing calibrated I/Q output.

Andrew

• This reply was modified 3 years ago by Andrew.

thanks Andrew,
what’s minimum and maximum order of the filter?

lsullivan,

What is the nature of your question? Do you have a specific application in mind, or is there an issue you are having with the I/Q data?

Our API accounts for all filter delays and scaling factors. The size of the filter will primarily only affect the filter transition bandwidth.

Andrew

According to the spectrum of I/Q data on Spike, we can conclude that the applied FIR filter has a fast transition bandwidth, meaning that it is a high ordered filter. I wonder how could this filter work so fast and it does not loose any data? would you mind telling me that if you have used any particular algorithm or library?
best regards.

lsullivan,

The FIR filter uses the standard overlap save algorithm. We do not use a library except for the FFT portion of overlap-save. Everything else is custom implemented. The maximum filter order is 1024 taps.

Regards

[Author]

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