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AD7176-2 Digital Filter / sinc5 + sinc1

Question asked by da_lundi on Jul 14, 2015
Latest reply on Jul 31, 2015 by da_lundi

Hi, concerning the AD7176-2 Digital Filters I run into the spreadsheet AD7176_2_filter_model.xls provided by Analog Devices.

The spreadsheet results always varied from my understanding of a sinc5 + sinc1 filter.

The equation showed that the sinc5 + sinc1 filter is

3 x Moving average filter of the length 32

+ 1 x Moving average filter of the length of 16

+ 1 x Moving average filter of variable length depending on the output data rate.


Here is the Excel Code Analog Devices uses. 20*log(abs(  

    (1/f_dec *SIN(f_dec *$A44/Fm*PI())/SIN($A44/Fm*PI()))^(order-2)
*   (1/f_dec2*SIN(f_dec2*$A44/Fm*PI())/SIN($A44/Fm*PI()))
*   (1/(f_dec*n_avg)*SIN((f_dec*n_avg)*$A44/Fm*PI())/SIN($A44/Fm*PI()))



For example


MCLK FrequencyMclk16,00MHz1 ..16.384
Sinc Filter Orderf_ord53 or 5
Single Cycle / Multiple-Channels10 or 1
SINC3_MAPs3_map00 or 1
FILTER[14:0]FilterReg50001 to 32767


results in order = 5  and n_avg = 2 and f_dec = 32 and f_dec2 = 16



So is the sinc5 part in reality a sinc3 + sinc1 filter? Or is there an error in the spreadsheet?