# Signal distorted after CIC filter

1. ## Signal distorted after CIC filter

Can anyone here let me know why the amplitude of the signal get distorted after it go through the CIC filter?

Is is due to the passband of the CIC filter is not flat?

I had try to cascade the CIC filter with compensator filter and i see the passband quite flat (+/- 4dB) but i still see the same problem. Can anyone help? Thanks.

Thanks.

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2. ## Signal distorted after CIC filter

What do you mean with distorted amplitude?

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3. ## Re: Signal distorted after CIC filter

Hi FvM,

The amplitude of the sine wave is not equal. Some of the sine wave doesn't reach the neccesary peak value.

Thanks

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4. ## Signal distorted after CIC filter

Sorry, that's no sufficient information.

5. ## Re: Signal distorted after CIC filter

Hi FvM,

Let's say i pump in a input sine wave of 10kHz to the filter.

The amplitude of this sine wave input is a constant.

And the output sine wave from the filter is not constant. That why i say the output signal is distorted. Hope this clear.

Thanks.

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6. ## Re: Signal distorted after CIC filter

Still unclear without knowing the CIC filter parameters and sampling frequency. But I think, it can happen with a low order CIC, if the decimated sampling frequency is near to an integer multiply of signal frequency. I would designate it an interference rather than a distortion.

P.S.: The decimated sampling rate is possibly too low to reproduce the sine waveform correctly. The numerical magnitude is probably constant or at least much less varying.

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