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 > > > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > 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. -- Principal Investigator Shirleys Bay Radio Astronomy Consortium http://www.sbrac.org
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