[sdiy] sample and (infinite) hold

[Scott Juskiw]

>One technique is to use two S/H in series.
>the first is set for a fast acquisition time
>(small S/H cap) and the second a long time
>(large cap).  One shot multivibrators control
>the relative sample apertures.   I think National
>Semi might have had this as an app note but I don't
>remember for sure.

This is mentioned in the app note for the LF398. I tried it and it 
works better than just having one S/H, but it will droop eventually 
(as we all do with age).