Questions about SAR ADC dynamic characteristics

[vergilpjl]

hello guys.
I just have desined a SAR ADC with a 12-bit resolution and 1mhz sampling rate.
but i find some problem with it :

when i simulated the ENOB with it and i found the enob droped when the frequency of the input sinewave rises.

can anyone tell me why this happens and how i can make it solved?

thank you all!

 

[KlausST]

Hi,

How can we help without seeing your design?
We don´t see your simulation, too.
And we don´t see how much your ENOB drops.. maybe it´s just 0.01dB, maybe it is 20dB?
We don´t see the frequency range of your input sine wave.
We don´t see the amplitude of your input sine wave.

Give us informations, so that we have at least a chance to help.

1 milliHertz sampling rate is very slow....


Klaus

 

[dick_freebird]

ENOB will always drop as frequency rises.

You will have issues with the front end S/H amplifier
tracking a faster-slewing signal. You could quantify
the error at the hold node / A-D comparator front
end.