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aaron_do

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linear distortion due to RF filtering
May 15^th, 2011, 10:39pm

Hi all,

it is my understanding that linear distortion (in the form of ISI) usually occurs due to group delay variation in baseband/IF filters and not in the RF filters. This is because RF filters used in FDMA systems generally have a significantly wider bandwidth than the desired signal.

My question is, are there any common systems where the group delay performance of the RF filters (in the GHz range) can have a significant impact on the desired signal? The only systems which occur to me are impulse based UWB systems.

thanks,
Aaron

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loose-electron

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Re: linear distortion due to RF filtering
Reply #1 - May 16^th, 2011, 5:29pm

Generally, the critical poles are farther away for the signal of interest in the RF circuits, and closer in the baseband filters.

Think about it, the RF front end passes a wide group of channels, and the baseband is generally designed to pass a single channel.

UWB and anything that is not a narrow channel moduilation scheme (like 99% of whats out there) would be the small group of exceptions, perhaps.

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Jerry Twomey
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Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical

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aaron_do Senior Fellow Offline Posts: 1398	Re: linear distortion due to RF filtering Reply #2 - May 23^rd, 2011, 5:04am Thanks. That's what I was thinking, but I'm just wondering if there are any common systems that do require good group delay performance in the RF section. Two-way radios, cordless telephones, GPS maybe? (just throwing out some wild guesses since i'm not familiar with all the standards). thanks, Aaron
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loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: linear distortion due to RF filtering Reply #3 - May 23^rd, 2011, 7:23pm Read channels in disk drive read channels (older designs needed this)
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