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| gobruins... |
 Posted: Wed Oct 21, 2009 1:51 am |
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Guest
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Hi, I am learning multi-channel DDC techniques using FFT. My design is
referenced to
http://www.pentek.com/tutorials/15_4/digdown.cfm
Something in this design I do not understand.
The FFT will split the input stream into N(FFT size) bins equally spaced
in frequency. Totally 4 FFTs are used so that the output data rate is
fs/N*4. Followed by the FFT a compensation filter is used to flatten the
frequency droop at the passband edge.
What I do not understand is that after FFT each bin output is a bandpass
signal whose center frequency is fs/N*k (k=0:N-1). Do we need a phase
shifter to translate these bandpass signals down to baseband before
applying the compensation filter?
I am confused on this part, I appreciate for any help. |
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