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)|
|MCLK Frequency||Mclk||16,00||MHz||1 ..16.384|
|Sinc Filter Order||f_ord||5||3 or 5|
|Single Cycle / Multiple-Channels||1||0 or 1|
|SINC3_MAP||s3_map||0||0 or 1|
|FILTER[14:0]||FilterReg||5000||1 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?