>I was just looking at a few oscilloscope data sheets and, you are right,
>many of these scopes sample at repetitive rates to achieve their peak
>performance. However, several can do flat-out 1GS/s rates, the HP Infinium,
>is one example.

Yep, some can, some can't.  Another technique used in some of the older
digital scopes was to clock the analog data into a fast ccd, and then clock
it out to an adc at a much slower rate.  Philips and Tek both used this
method, but they also had the ability to custom manufacture the required
devices.

Tek also made some digitizers using a video-camera like device that sweeped
an electron beam across a 512 * 512 pixel diode target.  The charge on each
'pixel' of the target could then be read out after the trace and either
displayed (analog) or digitized and stored.  This topped out at something
like the equivalent of 500 GSamples/second!

As far as I know, all the newer scopes have gone to using fast flash ADCs.

Seems to me the problem for the individual builder isn't finding fast ram
(after all, you could interleave 16 sets of common 15 ns cache sram), but
the front end and adc circuits.  Even a 300-400 MHz analog bandwidth is
going to require some pretty 'tweaky' amps and attenuators, and lots o'
gain-bandwidth product in the active devices.  Very fast flash converters
aren't likely to be inexpensive, and their high (and variable) input
capacitance isn't trivial to drive.


Good luck,
newell