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Re: [Xylo-SDR] A/D anti-aliasing filters
Specifically: the TI / Burr Brown PCM1804 has a built in "linear phase
antialias digital filter" that is fairly sharp and very deep. Does it
require any additional filtering when connected to the capacitors of a
quadrature sampling detector, like on Flex Radio? It almost seems like
it will do more harm than good. Does anyone have practical experience on
this?
The anti-aliasing filter in the 1804 is an integral part of the overall
ADC design. Remember that this is a sigma-delta converter, and the
filter characteristics are part of how TI achieves such excellent
performance for this part.
The QSD is by nature a filter as well. The 1804 filter won't get in
your way as long as you are operating in its intended bandwidth. But I
think you'll find the cutoff of the 1804 is much sharper than the QSD.
To get the rated performance from the 1804, you must interpose a
differential amplifier as outlined in the TI data sheet using very low
noise amplifiers. Not doing so will likely degrade the noise
performance of the part.
73,
Lyle KK7P