Jack Carroll wrote:
On Tue, Mar 21, 2006 at 05:23:32AM -0700, James Richard Tyrer wrote:
Dieter wrote:
<SNIP>
Hopefully the DVI will turn out to be good enough. I like coax
as much as the next guy, but I assume that whatever chip the
signals come out of doesn't have a coax connector on the side.
Answers.com states that the bandwidth is 400 MHz without any
citation:
http://www.answers.com/topic/digital-visual-interface
AMP data sheets indicate that the rise time would be 840 ps which
would be 416.6 MHz. That is 700 ps rating for the connector and
140 ps degradation for a cable.
So the 400 MHz figure may have validity.
This sounds like the DVI analog pins are good enough for now, though
the dotclock rate is approaching its limits. It should be just
about able to handle the 330 MHz rate, and that would meet the
requirement for 75 ohm lines on OGD1.
One of the DVI jacks (J6) is for the LoRes head, and one of them (J7) is
for the HiRes Head. 400 MHz is adequate for the 330 MSPS head although
495 MHz would be better. The issue is with the HiRes head. Clearly,
400 MHz is not adequate for the HiRes head, so if the 400 MHz figure is
correct then DVI is not adequate for the HiRes head.
This might leave us with making a choice between having a HiRes head and
having two DVI connections. If the 400 MHz figure is correct, there is
no point connecting a 500 MSPS analog video head to a DVI connector, we
would be better to just have two LoRes heads if we want two DVI connectors.
As far as hydra cables go, SI carries them.
To clarify, I was talking about Sun 13W3 Hydra cables. Yes, I have
found these as well as 13W3 to HD25 adapters and other stuff.
In summary: since OGD1 can't accommodate multiple 75 ohm connectors,
DVI still likes the choice that will suit the most users directly,
and adapter cables are commercially available for everybody else.
Since the 500 MHz signals are going to 50 ohm coax anyway, DVI isn't
an issue there.
This is a good question. The DVI connector *is* 75 ohm so for the 50
ohm option, it isn't going to work. However, most monitors are 75 ohm,
even the high resolution ones such as the Sony 20 inch.
The 13W3 probably isn't suitable either, because it's 75 ohms.
To add further confusion to the issue: actually the coax inserts are 50
ohm according to the Amphenol catalog. They are rated for 1 GHz with a
VSWR of 1.44:1 for 1 GHz, not as good as individual connectors but OK.
That leaves either 5 50 ohm BNCs,
This is best from a price/performance consideration but requires space.
5 smaller-size 50 ohm coax connectors such as SMAs,
These can be rather expensive.
or a multi-pin 50 ohm connector in a D shell.
The 13W3 would do for the D shell. But, a 50 ohm Hydra cable would be
needed.
Unless there is some issue with additional pins to handle
plug-and-play configuration,
Yet another issue. The 13W3 does have these.
coax connectors look like the simple choice.
In all cases, the analog connections would be in addition to a DVI-D
connection.
Adapters to interface different type 50 ohm connectors are stock
items, so if panel space is insufficient for 5 BNCs, that's not a
problem. Somebody mentioned running coax through holes in the case.
DON'T!! The outer conductor should enter the case through a flange
that gives it 360 degree grounding to the case wall.
Yes, that is what bulkhead connectors are for. :-)
Otherwise you let ESD in and RF interference out. Also, a
low-reflection stripline-to-coax transition is a lot easier to make
with a right angle connector designed for the purpose.
IIRC, you can also get fittings to connect coax to a PCB without
requiring a connector or you can use a board to board connector.
--
JRT
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