Paging Michael Terrell, video router design query

[msg]

On 14 Oct 2006 in sci.electronics.components, Michael Terrell suggested using
MAX435x parts to build a video router; I am awaiting delivery of several Maxim
video crosspoint ICs for just this purpose and wonder if anyone has prototyped
a router/switch using them and could share any caveats or design tips
(trace routing, surface area issues, dead-bug solder-up, need for external
buffers or not, etc.). I intend to control the chips at first using only
a PC <-> SPI interface but I also will add vertical interval switching
(gating of the /update pin on the device).

Regards,

Michael

 

[No Spam]

On Mon, 01 Dec 2008 15:51:04 -0600, msg wrote:

On 14 Oct 2006 in sci.electronics.components, Michael Terrell suggested
using MAX435x parts to build a video router; I am awaiting delivery of
several Maxim video crosspoint ICs for just this purpose and wonder if
anyone has prototyped a router/switch using them and could share any
caveats or design tips (trace routing, surface area issues, dead-bug
solder-up, need for external buffers or not, etc.). I intend to control
the chips at first using only a PC <-> SPI interface but I also will add
vertical interval switching (gating of the /update pin on the device).

Use a differential input buffer to reduce noise and hum between equipment

 

[Michael A. Terrell]

msg wrote:

On 14 Oct 2006 in sci.electronics.components, Michael Terrell suggested using
MAX435x parts to build a video router; I am awaiting delivery of several Maxim
video crosspoint ICs for just this purpose and wonder if anyone has prototyped
a router/switch using them and could share any caveats or design tips
(trace routing, surface area issues, dead-bug solder-up, need for external
buffers or not, etc.). I intend to control the chips at first using only
a PC <-> SPI interface but I also will add vertical interval switching
(gating of the /update pin on the device).

Regards,

Michael

Have you looked at the evaluation kit?
<http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3297>


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[msg]

Michael A. Terrell wrote:

msg wrote:

On 14 Oct 2006 in sci.electronics.components, Michael Terrell suggested using
MAX435x parts to build a video router; I am awaiting delivery of several Maxim
video crosspoint ICs for just this purpose and wonder if anyone has prototyped
a router/switch using them and could share any caveats or design tips
(trace routing, surface area issues, dead-bug solder-up, need for external
buffers or not, etc.). I intend to control the chips at first using only
a PC <-> SPI interface but I also will add vertical interval switching
(gating of the /update pin on the device).

Regards,

Michael



Have you looked at the evaluation kit?
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3297

Yeah, that would be nice, but Maxim won't give _that_ away <grin>; I should
be seeing the samples in a few days.

Michael

 

[Michael A. Terrell]

msg wrote:

Michael A. Terrell wrote:

msg wrote:

On 14 Oct 2006 in sci.electronics.components, Michael Terrell suggested using
MAX435x parts to build a video router; I am awaiting delivery of several Maxim
video crosspoint ICs for just this purpose and wonder if anyone has prototyped
a router/switch using them and could share any caveats or design tips
(trace routing, surface area issues, dead-bug solder-up, need for external
buffers or not, etc.). I intend to control the chips at first using only
a PC <-> SPI interface but I also will add vertical interval switching
(gating of the /update pin on the device).

Regards,

Michael



Have you looked at the evaluation kit?
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3297



Yeah, that would be nice, but Maxim won't give _that_ away <grin>; I should
be seeing the samples in a few days.

They never gave away any evaluation kits, but all of the
documentation & sample software is online for free. You can etch your
own PC board, or just look at their board design & schematic to built a
useable test circuit. Then expand that into your full blow switcher.

The main layout problems are keeping short ground traces t the 75 ohm
ports, and keeping both power supply & digital switching noise out of
the video.

What configuration are you looking at building? The inputs have to be
terminated at 75 ohms and you have to put it at the furthest chip from
the input, or feed it back to another connector for external
termination, for future expansion. Some early video switchers/routers
had a switch at the input, or both connectors connected with a short
jumper. This isn't a good idea in a complex design, because the HF roll
off will vary and get worse the farther you are from the input.
Depending on the bandwidth you need, and your budget you may want to use
sub miniature 75 ohm coax connectors on the PC board and equal length
cables to the rear panel connectors to equalize the phase shift for
critical color applications.

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listed, or I will not see your messages.

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your account: http://www.usenettools.net/ISP.htm


There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.

 

[msg]

Michael A. Terrell wrote:

msg wrote:

Michael A. Terrell wrote:

<snip>

Have you looked at the evaluation kit?
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3297


Yeah, that would be nice, but Maxim won't give _that_ away <grin>; I should
be seeing the samples in a few days.



They never gave away any evaluation kits, but all of the
documentation & sample software is online for free. You can etch your
own PC board, or just look at their board design & schematic to built a
useable test circuit. Then expand that into your full blow switcher.

Indeed, the parallel-port control program is useful and will help me
with initial testing. I can't afford a four-layer board, but hope that
prototyping on double-layer epoxy stock, using mini-mills to make islands,
and hand soldering to the TQFPs will suffice for now. What I can't do
is guarantee 75 ohm lines for the short runs from the i/o pins to the
islands on the pcb with the connections to external coax runs. I imagine
the longest of these lines will be about three inches (of kynar 30ga wire
laid flat on the ground plane).

The main layout problems are keeping short ground traces at the 75 ohm
ports, and keeping both power supply & digital switching noise out of
the video.

Agreed; power supply noise has been my bane in recent projects and also
on commodity PCI video capture boards.

What configuration are you looking at building? The inputs have to be
terminated at 75 ohms and you have to put it at the furthest chip from
the input, or feed it back to another connector for external
termination, for future expansion.

In my case, the switcher will terminate all inputs; for fanout an input
can be routed to several outputs.

<snip>

Depending on the bandwidth you need, and your budget you may want to use
sub miniature 75 ohm coax connectors on the PC board and equal length
cables to the rear panel connectors to equalize the phase shift for
critical color applications.

Well I will have to solder mini coax to the pcb and hope for no big
impedance bumps, but I _will_ be careful to maintain equal lengths measured
from IC pins to rear panel connectors (through 75 ohm series resistors at the
output pins; each output will run at 2V/V).

Regards,

Michael