On 18/06/12 09:46 PM, signalswdm wrote:
Hello
everyone:
You see in theory there should be a low-pass filter after ADC
for eliminating the image. Also after DDC there should also be a
filter. But in USRP there are not such things. So do the cic
filter and half band filter implement that function besides decimation?
Best regards
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Actually, in typical architectures using I/Q, there are low-pass
filters *in front* of the ADC to eliminate aliasing prior
to sampling. So the CIC decimator "sees" a signal that has already
been band-limited appropriate to the sample
rate of the ADCs.
The CIC decimation process *is* filtering, so out-of-band products
appearing at the output are usually suppressed
by at least 80dB, and usually more.