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Paging Michael Terrell, video router design query

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

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

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No Spam

Have you looked at the evaluation kit?

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Michael A. Terrell

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

Michael

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Maxim

prototyped

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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Michael A. Terrell

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).

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

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

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

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