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Alan Walsh

# Challenges & Requirements: Voltage Reference Design for Precision Successive-Approximation ADCs, Part 3

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AlanWalsh
6/19/2014 8:32:20 AM
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Re: Vrms=Vp-p/2√2
@amrutah : Your welcome. You are correct. The 2√2*rms= Vp-p applies to a sinusoidal waveform. The 6.6 factor is for a gaussian random noise distribution.

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amrutah
6/18/2014 6:06:44 PM
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Re: Vrms=Vp-p/2√2
Alan: Thanks for the Appnote pdf, its nice.

Please correct me if I go wrong .  Nominally 2√2*rms= Vp-p, but if we consider another dimension of time, then rms noise will increase as mentioned in table on page 5 of the pdf.  To consider the effect of the time-bound random noise, a factor of 6.6 (more margin) is considered.

Thanks.

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etnapowers
6/12/2014 4:39:09 AM
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Re: effective bandwidth
@Alan, thank you for the useful link , I found this interesting sentence:

"The noise in the spectrum above the single pole filter cutoff frequency,fc, extends the corner frequency to 1.57fc.Similarly, a two pole filter has an apparent corner frequency of approximately 1.2fc."

The two pole approximation should correspond to a cover factor of 5/6 pi. It may be interesting to evaluate the error for both of the approximations.

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AlanWalsh
5/27/2014 9:54:05 AM
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Re: effective bandwidth
The pi/2 factor is to convert the 3dB BW of the reference to an effective noise BW. This is an approximation and assumes the BW rolloff is first order. See this app note for a better explanation.

http://www.analog.com/static/imported-files/tutorials/MT-048.pdf

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AlanWalsh
5/27/2014 9:45:50 AM
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Re: Vrms=Vp-p/2√2
The equation you are using is valid if you are considering a sine wave signal. 1/f noise is random so to convert from pk-pk to rms you use a statistical number thats based on a gaussian noise distribution. Its explained better here but 6.6 is a standard number thats used. Sorry this should have been explained better, see page 5 of this app note.

http://www.analog.com/static/imported-files/tutorials/MT-048.pdf

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etnapowers
5/26/2014 6:44:40 AM
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effective bandwidth
"The effective bandwidth will be given by:
"

Why the cover factor of π/2?

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5/26/2014 5:27:55 AM
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Re: Vrms=Vp-p/2√2
@amrulah: Thank you for helping me to clarify on this formula. Even I was thinking the other way round.

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amrutah
5/24/2014 10:24:58 AM
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Vrms=Vp-p/2√2
@Alan:  This is such a nice series of post.  Thanks.

"To convert the 1/f noise from peak-to-peak to rms, divide by 6.6 to get..."

I though that Vrms=Vp2p/(2√2), why is a factor of 6.6 used instead of 2√2?

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