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AD7767 Digital Filter - plot vs data

Question asked by bolerm on Apr 8, 2014
Latest reply on Aug 17, 2016 by bolerm

Hi,

 

We have used the AD7767 for many, many applications over the last few years very successfully.  For the latest project, some questions have arisen about the transition region of the digital filter from pass band to stop band.

 

The data sheet (Rev C | page 4) lists the following characteristics: 

 

Pass Band = 0.453 × ODR Hz

-3 dB Bandwidth = 0.49 × ODR Hz

Stop-Band Frequency = 0.547 × ODR Hz

 

Further, the text on page 15 last paragraph states the filter provides 6 dB of attenuation at Nyquist.  However, the plot of Figure 34 doesn't really reflect these values.  At Nyquist the plot looks more like 15 dB of attenuation.  Can you resolve the differences for me?  Which is more accurate?  Can I have data showing the actual mag vs frequency in this transition region?

 

Thanks

Eric

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