At 05:29 PM 12/12/97 +1300, you wrote:
>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.
>
>

Thanks for the tip. I am still wondering, though, what in general do people
think of my idea? What am I forgetting? Any suggestions? Is it worth it?

Thanks,

Sean


>> ----------
>> 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
>>
>
+--------------------------------+
| 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