Scott Newell wrote:
> 
> >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.

A nice trick if you want to fill up memory fast, is to use a PR counter
on the address line instead of binary counter.

-- 
Friendly Regards

Tjaart van der Walt
mailto:tjaart@wasp.co.za
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