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ADC Type of filter ? - RF Cafe Forums
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gui076
Post subject: ADC Type of filter ? Posted: Thu Jun 12, 2008
5:20 am
Captain
Joined: Mon May 05, 2008 9:56 am
Posts:
15
Location: France
Hello,
I have an IQ demod before
an ADC. After the IQ demod i would like to use direct conversion or
low-if (70/140 MHz). My question is what type of filter i have to insert
between the IQ demod and the ADC ? LPF,BPF ? SAW for 70/140 MHz ?
Thank you.
Guillaume
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IR
Post subject: Posted: Fri Jun 13, 2008 4:06 pm
Site Admin
Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location:
Germany
Hello gui076,
The filter has to be LPF to limit
the frequency of the sampled signal and by this to prevent aliasing.
I would use a lumped LC filter and not SAW, which has a high insertion
loss and thus will reduce the ADC's dynamic range.
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gui076
Post subject: Posted: Sat Jun 14, 2008 7:56 am
Captain
Joined: Mon May 05, 2008 9:56 am
Posts: 15
Location: France
So if i have to put a filter it's better to have
a LPF until 160 MHz instead of a bandpass at 140 MHz and about 40 MHz
of bandwidth. The noise won't be too high ?
Guillaume
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IR
Post subject: Posted: Sun Jun 15, 2008 6:19
am
Site Admin
Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
The choice of filter also depends
on your system architecture: Do you plan to use undersampling? If yes,
then you will require a LPF to allow sampling in lower frequencies.
If not, then a BPF is adequate.
Both filters can be implemented
by lumped components which will provide lower insertion loss than SAW
technology.
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gui076
Post subject: Posted:
Sun Jun 15, 2008 8:18 am
Captain
Joined: Mon May 05,
2008 9:56 am
Posts: 15
Location: France
Hello,
Maybe
i will try to implement some switche if i want to test some kind of
sampling.
So thank you for your answer
Guillaume
Posted 11/12/2012
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