AD9057: Aperture uncertainty

Document created by analog-archivist Employee on Feb 23, 2016
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1) Do you have any additional information of the influence of the temperature
over the "Appertur Uncertainty Jitter)?
2) When you apply an input votage of 3V, what is the "shortest" time needed to
"Track-and-Hold" the input signal?

 

1) We wouldn't normally characterize aperture uncertainty over temperature but
you can see the effect of it in figure 9 (showing the variation of SINAD and
SNR over temperature). The aperture uncertainty will contribute to the noise.

2) The speed of the analog input stage is characterized by its -3dB bandwidth
of 120MHz. If you have a fast rising signal at the input, then the ADC front
end will behave like an RC single pole low pass filter with cutoff frequency at
120MHz. The time constant is t= 1/2*pi*f = 1.3ns to reach 63% of the final
value. You can calculate the settling time to any given percentage T =
-ln(%/100)*1.3ns

e.g. to 0.1% the settling time is -ln(0.1/100)*1.3ns = 6.9*1.3ns = 9.0ns.

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