[time-nuts] An (unknown?) nasty feature of the DDS principle for time nuts applications

[pablo alvarez]

Hi,

The AD9850 has a 10bit DAC. If the AD9850 does not dither the 10bit ADC
output the zero crossings for a 1MHz signal will have an aprox resolution of
2^-10*1us~1ns on average. If the lookup table feeding values to the dac has
10 address lines (just guessing, I do not see any anything on it on the
datasheet), you will have an additional uncertainty of 1ns to the phase
error. Adding these two we have the ~2ns Ulrich is measuring.

What do you think?

Pablo


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