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Design >> Mixed-Signal Design >> Understanding "dB per bin" unit
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Message started by neoflash on Jan 21^st, 2010, 8:00am

Title: Understanding "dB per bin" unit
Post by neoflash on Jan 21^st, 2010, 8:00am

In sigma-delta modulator's result showing, I often see units defined as
"dB per bin". Sometimes as "dBFs per bin"

How to understand this unit?

Title: Re: Understanding "dB per bin" unit
Post by wave on Jan 22^nd, 2010, 3:57pm

neoflash wrote on Jan 21^st, 2010, 8:00am:

In sigma-delta modulator's result showing, I often see units defined as
"dB per bin". Sometimes as "dBFs per bin"

How to understand this unit?

FS - Full Scale.
Critical as some converters may clip or distort with large signals.
http://en.wikipedia.org/wiki/DBFS

Bin is usually related to the DFT used to measure the spectral response.
How many points taken relates to the width of a Frequency Bin.
http://www-inst.eecs.berkeley.edu/~ee247/fa05/lectures/L14_f05.pdf

Title: Re: Understanding "dB per bin" unit
Post by thechopper on Jan 25^th, 2010, 5:02pm

Since in sigma delta modulators you deal with noise (quantization noise in this particular case) it is necessary to talk about spectral densities rather than spectra.
Thus dB/bin is a spectral density unit for the noise processed in the sd modulator, pretty much the same way it is done for "continuous time" noise where the PSD in dB/Hz.

In the dB/bin case, you can think of the amount of noise power in each bin, although you cannot tell how it is distributed "inside a bin". That asks for a higher resolution DFT.

Best
Tosei