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FMCOMMS1 GSM Sample Rates

Question asked by wmaguire on Jun 5, 2013
Latest reply on Jun 19, 2013 by wmaguire

Hi all,

 

Just wondering if anyone out there has configured this device to work for GSM sample rates.  The default ADC clock is set to 245.76MHz which has an irrational relationship to the GSM symbol rate of 270.8333333' KHz.    A sample rate of 260MHz would be better but this is beyond the ADC9643 250MHz limit. 

 

I suppose a value of 36*6.5MHz or 234MHz might work.    At this stage I don't know if 234MHz can be synthesized using the AD9523-1.

 

so we have the following potential decimation / interpolation values

 

234MHz/30 = 7.8MHz *10 = 78MHz / 12 = 6.5MHz

 

Note the 6.5MHz needs to be decimated by 6 to give 1.0833333'MHz which is 4 times the GSM symbol rate.

 

I note the Wiki mentions "

." An anti-alias filter is used to remove harmonics and other out of band signals before the signal is digitized with the AD9643."  Do you have details for this filter as we need to determine if it will have sufficient image rejection at the lower sample rate.

 

Regards

 

 

Walter

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