CIC decimator output mirrored

2 次查看（过去 30 天）
Edson Silva
Edson Silva 2020-7-24
回答： Edson Silva 2020-7-24
Hi,
I am trying to use the dsp.CICDecimatior function and comparing the output to a C code algorithm that I have. The CIC decimator is configured as decimation of 8, 3 sections and differential delay equals 1.
below is the code used and attached I have the input vector:
CIC1 = dsp.CICDecimator(8,1,3);
CIC1.SectionWordLengths=[32 32 32 32];
CIC1.FixedPointDataType='Specify word lengths'
k=0;
step1_sig=zeros(1,128);
for i=1:16
step1_sig(1,i)=CIC1(real(normalRx(1+k:8+k)'));
k=k+8;
end
step1_sig'
The output looks mirrored as you can see in the figure below:
I am confident that the C code output is correct, because I have compared it to the following C++ :
https://github.com/EsonJohn/CIC-filter
Both produced the same output, so the issue have to be in my Matlab code.
Any ideas why the Matlab output is mirrored?
  1 个评论
Edson Silva
Edson Silva 2020-7-24
I think the answer to this question is the way the MATLAB block is implemented. In the traditional CIC decimator algorithm, the delay unit in the integrator is used in the feedback path, but in the MATLAB block it uses the unit delay in the feedforward path of the integrators:
https://www.mathworks.com/help/dsp/ref/dsp.cicdecimator-system-object.html#d120e192907
Although the filter will be equivalent (same frequency response), the numerical output of the two implementations are a different (the mirrored look that I mentioned in my question).
I don't know if there is any way of implementing the CIC in Matlab using the unit delay in the feedback.

请先登录，再进行评论。

请先登录，再回答此问题。

回答（1 个）

Edson Silva
Edson Silva 2020-7-24
As it seems that the reason to the problem is the way the CIC filter is implemented in MATLAB with the unit delay in the feedforward path of the integrator, the question now becomes:
Is there a way of implementing the CIC filter with the unit delay on the FEEDBACK path of the integrator?
It should be like this:

类别

在 Help Center 和 File Exchange 中查找有关 Multirate Signal Processing 的更多信息

标签

产品


版本

R2020a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by