If you read 'Analogue design, art science and personalities' (I think
this is the name) you'll see quite a bit of material on how TEK designed
high-speed vertical amplifiers.


> ----------
> From:         Sean Breheny[SMTP:shb7@CORNELL.EDU]
> Reply To:     pic microcontroller discussion list
> Sent:         Friday, December 12, 1997 4:36 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: Very Fast RAM
>
> At 09:16 PM 12/11/97 -0600, you 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.
> >
>
> Well, my idea is somewhere in the neighborhood of 100MHz analog BW. I
> realize that I don't have that much design experience to get good
> results
> up to several 100s of MHz., but I don't see why 100MHz would be too
> hard.
> There are lots of video amps and 100MHz op amps out there which are
> not too
> expensive and (so it would seem to me) have BW around 100MHz. I have
> found
> 30MS/s ADCs for $10. I hope, and I don't see why it would be too hard,
> to
> buffer the input of this ADC with a 100MHz op amp,  a (roughly) purely
> resistive attenuator (made from a rotary switch and several
> resistors),
> send the output of the ADC to some SRAM, clock the ADC with a PLL with
> programmable dividing radio (to get adjustable sample rate with very
> accurate time base), read the output either to a PC or to a
> microcontroller
> (PIC :-) ) at a slower rate to feed to an LCD. I could use the
> multiple
> sampling technique to digitize at more than 30MS/s as well as go flat
> out
> at 30MS/s for up to 15MHz non-periodic stuff. I realize that this
> would not
> be as good as a $1000 Fluke scopemeter or similar device, but for my
> budget, I think it would make an interesting project and be able to
> visualize waveforms for most hobby/student applications. Am I
> wrong/wasting
> my money?
>
>
> Thanks for the help,
>
> Sean
> +--------------------------------+
> | Sean Breheny                   |
> | Amateur Radio Callsign: KA3YXM |
> | Electrical Engineering Student |
> +--------------------------------+
> http://www.people.cornell.edu/pages/shb7
> mailto:shb7@cornell.edu
> Phone(USA): (607) 253-0315
>