yes, but couldn't you interleave A/Ds as well. i.e each A/D handles the
nth sample?. In front of the A/Ds we have a bunch of high-speed sample
and hold circuits, and we route the input signal to the appropriate A/D
in a 'round-robin' fashion.

Our friends at Los Alamos would have needed this sort of thing - as
someone at TEK said 'our customers needed scopes which would capture
events with a repetition rate of one every month, or so'.

> ----------
> From:         Scott Newell[SMTP:newell@CEI.NET]
> Reply To:     pic microcontroller discussion list
> Sent:         Friday, December 12, 1997 4:16 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: Very Fast RAM
>
> >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
>