Thank you
To make it clear, I use USRP1. Does that mean in common the signals that
come out of ADC chips (in USRP case it is the signals come out of AD9862 before
processed in FPGA) is already filtered and aliasing prior is partly
eliminated ? In the datasheet I do not see anything about that. If I am wrong
please correct me.
Best regards
At 2012-06-19 09:54:11,"Marcus D. Leech" <[email protected]> wrote:
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.
--
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
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