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manodipan

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Posts: 83

DFT and windowing
Apr 08^th, 2009, 3:34am

Hi all,
I am confused about how many bins to be taken in SNDR measurement....let's say no. of bins=1024 and OSR=64 for a delta sigma modulator....now for hanning window no. of nonzero signal bins=3 ...but what about no. of bins for offset and distortion components....normally how many bins are taken and how it's related to window type and length.....
Thanks a lot...
regards,
Manodipan

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ywguo Community Fellow Offline Posts: 943 Shanghai, PRC	Re: DFT and windowing Reply #1 - Apr 15^th, 2009, 8:42pm Hi Manodipan, The no. of bins need to be large enough in order to discern the offset, signal, and distortions. Saying no. of bins = 1024 and OSR = 64, there are 16 bins in the signal band. For hanning window no. of nonzero signal bins = 3, that setup is barely enough. Yawei
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sheldon

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Posts: 751

Re: DFT and windowing
Reply #2 - Apr 18^th, 2009, 9:44pm

Manodipan,

� There are some additional considerations if you want to get
a good estimate of the noise, see the Appendix A in Schrier's
book, "Understanding Delta-Sigma Data Converters". My
reading of Schrier is that you will need additional bins in the
FFT to get a good estimation of the noise. Also, if you are simulating
then the noise will only include the quantatization noise unless
you run a transient noise analysis.

� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �Best Regards,

� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � Sheldon

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manodipan Community Member Offline Posts: 83	Re: DFT and windowing Reply #3 - Apr 22^nd, 2009, 3:28am Hi Sheldon, yes you are right...because oversampling reduces no. of bins available in signal band.....also transient noise analysis reveals the information about noise floor...thanks for your reply.....
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