On 03/28/2011 02:36 PM, Bruce Griffiths wrote:
Martyn Smith wrote:
Hello,
I'm trying to compare the stability specifications of two oscillators.
The first spec is 2 x 10E-11 Allan Variance.
The second spec is 3 x 10E-11 Allan Deviation.
As Allan deviation (ADEV), is the square root of Allan variance, I
thought the first spec is the better of the two, but a collegue
disagrees, saying 3x10E-11 Allan Deviation is a better spec than 2 x
10E-11 Allan Variance.
I'm sure the million experts at there will give me the correct answer
Regards
Steve Jones
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Strictly you are correct, however some early datasheets (eg Crystek, )
say Allan variance whilst they actually tabulated its square root or
Allan deviation.
It's also common to have plots saying "Allan Variance" and plotting the
Allan Deviation.
Since Allan Deviation is the square root of Allan Variance, 2E-11 Allan
Variance is about 4.5E-6 in Allan Deviation so an Allan Deviation of
3E-11 is better than an Allan Variance of 2E-11... by far.
Use Allan Deviation through-out.
Cheers,
Magnus
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