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About front -end design for SAR

Question asked by Tarzan on Mar 25, 2013
Latest reply on Mar 31, 2013 by Tarzan

Hi everyone,

Some questions came up while I was reading a following article from Analog Dialog.

Could anyone give me some advice on it?

Here are my questions.

#1, This article says; "When using a multiplexed input in the above example, the required filter bandwidth for linear response would increase to 3.93 MHz (step size = 5 V vs. 1.115 V with a single channel)."

But I just wondered where 3.93MHz comes from. Could you tell me about about it?

#2, According to Figure 6 "Effect of source resistance on THD vs. input frequency", I  can see that input impedance affects THD peformance.

But I'm not sure why input resistance affects THD peformanc.  Could you help me to underdand it? It would be great if there a material to support this idea. 

Thank you for your help.