Re: ADC "stacking"


"John Larkin" <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> a écrit dans le
message de news:pegj321k425uauhg5jirrq40bsk6oeqibc@xxxxxxxxxx
On Mon, 10 Apr 2006 01:42:49 GMT, Joerg
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:

Hello John,


What are your targets for clock time trimming and for jitter? And is
cost a big deal here? The adc's must be pretty expensive themselves.


Usually you only have to scoot a slope by a few hundred psec. It's not
just ADCs. This also needs to be done for pulse transmitters and other
things. Cost has to be reasonable, a buck per location would be
acceptable, including the discretes but sans DAC. The main concern is
long term availability and IMHO the situation does not look good for FET
arrays. There must be a reason why their prices crept up and now Arrow
and others carry no stock. The big three prototype caterers don't even
offer them anymore at all.


Designing a scope front-end for somebody?


No, this is just for a publication. But I don't want to present some
elegant academic solution where you can't get the parts.

Jim, or companies like Tektronix that have their own foundries would
just roll their own. Us discrete designers have to be able to find it on
the shelf. Even weak n-channels like the BSS83 (not the p-channel which
unfortunately has the same number) are also becoming rare.

Regards, Joerg

http://www.analogconsultants.com

I was thinking about the opposite problem, muxing dac's. Suppose you
wanted to make a 4 gs/s 12-or-so bit dac. You could make a circle of,
say, 16 250 MHz dacs, which wouldn't be outrageously hard to feed, and
then you'd have to generate a 16-phase clock to load them (from the
equivalent of 16 fifo's) and then - the hard part - mux all of the
analog outputs into a single summing point, one every 250 ps. The
jitter and time alignment problem is identical, for the muxing process
at least.

In my application, I'd like to be kicked off by an external trigger,
so my clock must be externally startable too.


For this, you can (well I think, I've not gone too far into this) just sum
all the ouputs and preprocess the digital datas to obtain the wanted output.

If that works, you owe me a coffee. Or maybe a beer.


--
Thanks,
Fred.


.

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