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Visitor jrrguzman
Visitor
3,034 Views
Registered: ‎02-27-2017

Interpolation filter using FIR compiler

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Hi everyone,

 

I'm using the FIR compiler to create an interpolation filter for my design.

 

As far as I know the gain of an interpolation filter should be set to the interpolation value to achieve unity gain in the new sampling domain. I was expecting that the FIR compiler was smart enough to identify the interpolation feature and adjust the gain (or at least give me a warning or show the system overall gain in the frequency response plot which comes along with the filter). As far as I know, if I define the filter coefficients for unity gain, I get an attenuated signal.

 

On the other hand, if I specify a filter with gain equal to the interpolation factor, the coefficient output starts to grow (even if I know that the system will have unity gain and maybe one extra bit might be needed).

 

Is this a known issue in the FIR compiler tool or am I missing something important here?

 

Thanks in advance.

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1 Solution

Accepted Solutions
Moderator
Moderator
4,013 Views
Registered: ‎08-01-2007

Re: Interpolation filter using FIR compiler

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The filter gain displayed on the FIR Compiler GUI is for a single rate implementation and does not take into account the zero insertion between output samples in the up-sampling processes in a interpolating filter. Therefore, following the zero insertion the average filter gain is reduced by the up-sampling rate.

 

For a single rate filter, the coefs and the coefs settings in the GUI define the gain of the filter.

 

If you are designing the interpolation filter, the filter type should be set to Interpolation, otherwise the FIR Compiler IP could not recognize it as an interpolation filter.

 

There is not an issue with the gain of interpolation filter. Hope the above clarify the things.

 

 

 

 

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2 Replies
Moderator
Moderator
4,014 Views
Registered: ‎08-01-2007

Re: Interpolation filter using FIR compiler

Jump to solution

The filter gain displayed on the FIR Compiler GUI is for a single rate implementation and does not take into account the zero insertion between output samples in the up-sampling processes in a interpolating filter. Therefore, following the zero insertion the average filter gain is reduced by the up-sampling rate.

 

For a single rate filter, the coefs and the coefs settings in the GUI define the gain of the filter.

 

If you are designing the interpolation filter, the filter type should be set to Interpolation, otherwise the FIR Compiler IP could not recognize it as an interpolation filter.

 

There is not an issue with the gain of interpolation filter. Hope the above clarify the things.

 

 

 

 

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Visitor jrrguzman
Visitor
2,654 Views
Registered: ‎02-27-2017

Re: Interpolation filter using FIR compiler

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Hi,

 

Thanks for the answer. I would have expected the GUI to take that into account if I select the interpolation option.

 

I did generate the coefficients to match the gain I need to cope with 0 insertion but the x80 gain I was seeing at the plot was a bit misleading.

 

Cheers

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