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Design >> Analog Design >> SNDR calculation in a delta sigma DAC
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Message started by polyam on Dec 19^th, 2018, 8:59pm

Title: SNDR calculation in a delta sigma DAC
Post by polyam on Dec 19^th, 2018, 8:59pm

Hi,

I've designed a delta-sigma DAC. My reconstruction filter has a pass-band frequency of 10 MHz and a stop-band frequency of 100MHz. My delta-sigma is clocked at 800 MHz for an OSR of 128. So the BW is about 3MHz. Now the question is that in which bandwidth I should calculate the SNDR? 3MHz of fs/2=400MHz. If I calculate it over 3MHz I'll have SNDR=101 dB. If I calculate it over 400 MHz it will be 38 dB. Which one is correct?

tnx

Title: Re: SNDR calculation in a delta sigma DAC
Post by polyam on Dec 19^th, 2018, 9:00pm

I added the output spectrum after the reconstruction filter.

Title: Re: SNDR calculation in a delta sigma DAC
Post by jdp on Jan 13^th, 2019, 4:51am

Integrate the noise till the half the Nyquist rate of the desired input signal freq band. If the desired signal can lie in dc to say 4MHz, then you should integrate till Nyquist rate/2=4MHz.