CIC compensation filter design
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I have a CIC filter as below:
- Decimation factor: 20
- Differential Delay: 1
- Number of sections: 4
I created cicDecim object by
cicDecim = dsp.CICDecimator(DecimationFactor = 20,...
DifferentialDelay = 1,...
NumSections = 4,...
FixedPointDataType = "Full precision")
The CIC filter has an input with sample rate of 10 MHz and the output of the CIC has the sample rate of 500 kHz (e.g., 10 MHz/20). Now, I want to design a compensation filter after the CIC but am having a hard time to configure the some of parameters. I have the following compensation filter requirements
- Passband Frequency: 200 kHz
- Stopband Frequency: 250 kHz
- Passband Ripple: 1 dB
- Sample Rate: 500 kHz (The rate of the compensation filter)
I assumed the Passband Frequency and Stopband Frequency as based on the input of the compensation filter (e.g., 500 kHz not 10 MHz).
cicCompDecim = dsp.CICCompensationDecimator('CICDifferentialDelay',1,... % Defined in the cicDecim above
'CICNumSections', 4,... % Defined in the cicDecim above
'CICRateChangeFactor', 20,... % Defined in the cicDecim above
'DecimationFactor', 1,... % The compensation filter is a single rate
'PassbandFrequency', 200000, ... % Passband Frequency 200 kHz
'StopbandFrequency', 250000, ... % Stopband Frequency 250 kHz
'PassbandRipple', 1,... % Passband ripple
'SampleRate', 500000) % Sample rate of the compensation filter = 500 kHz
I checked the combined filter response by cascading the CIC and the compensation filters:
filtCasc = dsp.FilterCascade(cicDecim, cicCompDecim);
Fs = 500e3;
f = fvtool(cicDecim, cicCompDecim, filtCasc, 'Fs', [20*Fs Fs 20*Fs]);
I have the following response from the code above.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1601856/image.png)
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1601861/image.png)
I'm wondering if the compensation filter design I've done is correct? Or other suggestion that I can improve or optimize the compensation filter?
3 Comments
Paul
on 1 Feb 2024
You're quite welcome.
What is the concern with the compensation filter as designed? What about it should be optimized or improved?
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