[問題] CIC decimation filter

[gggould (evanescent)]

Hi all,

Lst say a input signal IP with 0~200KHz bw is sampled at fs=16MHz (lets call
it X), then pass through a 1st order CIC decimation filter (R=8, M=1) to get
2MHz output (lets call it Y).

Let define Δf as shifting the signal to center at f, so

X = IPΔ0 + IPΔ16M + IPΔ32M ...
and sinc is the sinc function without alias

1. What does the Y spectrum now look like ???

Should it be  (X* sincΔ0)Δ0 + (X* sincΔ0)Δ2M +(X* sincΔ0)Δ4M ...
or                 X* sincΔ0 + X* sincΔ2M + X* sincΔ4M ...

2. How about the  output spectrum if (R=4, M=2) ???

3. There is a function called mfilt.cicdecim in matlab. Does
Y=mfilt.cicdecim*X ??? By multiplying IP with this transfer function, I am
just not sure if the alias part would be taken into account.

4. How to calculate the SNR?


I am new to the signal processing world, and these kind of frequency
conversion really confuse me...


Thanks a lot

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推 jsp0520:Y should be a sinc function response. You can refer to
→ jsp0520:to the book "CMOS Mixed-Signal Circuit Design" by
→ jsp0520:Jacob Baker for more details.
→ gggould:謝謝 我看過那本書 也知道Y會是SINC+ALIAS 但是不確定
→ gggould:是輸入先ALIAS在乘SINC 還是先乘SINC在ALIAS
→ gggould:還是輸入跟SINC各自ALIAS再相乘