# AD7176-2 Digital Filter / sinc5 + sinc1

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

 Name Symbol Value Unit Range MCLK Frequency Mclk 16,00 MHz 1 ..16.384 ODR[4:0] ODR 1 0..20 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

Questions:

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

Parents
• Hi Jonathan

thank you for the answer, however it is still not absolutly clear to me:

You are saying that

... It is a combination of 4 x Moving average of length 32 + ......

and

... The first part contains three of the Sinc5 moving average terms. ..

that is a conflict, or is it not?

Thank you for your Help!

Sören

Reply
• Hi Jonathan

thank you for the answer, however it is still not absolutly clear to me:

You are saying that

... It is a combination of 4 x Moving average of length 32 + ......

and

... The first part contains three of the Sinc5 moving average terms. ..

that is a conflict, or is it not?

Thank you for your Help!

Sören

Children
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