Re: More digitizing stuff

Miroslav Pokorni

You are talking about 50 Msps? That puts your memory cycle to 20 ns, a
pretty tough requirement. Try Cray's gig with memory: butterfly it. Use
registers to store odd samples and on even samples write new sample and odd
one from register into double wide memory; you can extend this scheme to a
four wide memory, if your A/D can hack it. You can also use two A/D with
appropriate sample/holds to butterfly conversion.


Miroslav Pokorni

----- Original Message -----
From: <>
To: <>
Sent: Tuesday, February 18, 2003 4:39 PM
Subject: [TekScopes] More digitizing stuff

Well; I bought a HP 5180A on ebay, and I await it's arrival. It will
(I hope) acomplish what I had wanted: digitize an analog scope so
that I will have digital one-shot capabilty. On the down-side, the
HP5180A is the size of a small compact car, so I'm not sure where
I'm going to put it on my bench if it turns out to actually work.
I'm still working on MY version of a digitizer. I was trying to be
much too complicated with it, after discovering an obvious flaw in
my orginal design. I had first invisioned an A/D D/A , with a latch
in between until I realized that this layout would aquire only ONE
point on my signal display! DUH! No WONDER those DSO's require
memory! Then I went into microcontrollers to read and write the data
which would be my 250 or so samples but came to discover that my
thru-put would be much too slow for any decent signal frequency.
Then I went to a quickly-abandoned idea of using the output of my
THS720 (which goes to a printer to print a stored waveform) into my
analog scope, until Tektronix informed me that the ouput was in the
wrong form for putting into a D/A. Now I'm to a design that I should
have seen sooner: Just use RAM instead of getting overly complicated
with microcontrollers. I have an up-counter (good for 100Mhz)
counting addresses to my RAM, with the same clk used for my A/D. My
counter goes into some NAND gates which, after my count gets high
enough (500 samples), it turns off my read line, resets my counter
and starts writing to my D/A. This is a simple explaination; I have
some latches and buffers in there too. I hope to get 50MPS out of
this contraption if it works! :) The only problem is getting the
spare time at work to work on it! :)

Join to automatically receive all group messages.