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Explain of LVDS driver for RapidIO AC specification

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Warlike

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Hello,

In the RapidIO standard DC specs for Driver is similar to TIA-644-A standard (Vohd = 247...454 mV, Vold = -454...-247 mV).

But AC specs are:
Vohd = 200...540 mV,
Vold = -540...-200 mV.

What from appear this specs? Does it appear on acount of reflections in transmission line?

What is testbench to measure AC Vohd and Vold? Should it include receiver, transmission line, capacitance load (at the line end)?
 

Sounds like: with/without termination
 

erikl, can you explain clearly?

I don't understand why there are 454 mV in DC specs and 540 mV in AC specs. If I use in testbench of driver 100 Ohm res and capacitance load (receiver give only additional cap load) I would never get AC Vohd larger than DC Vold, only smaller (depend on cap. load). And why AC Vohd = 540 mV?

I have only one idea - reflections in tline. If we have bad termination there would be reflection and AC Vod can be larger than DC Vod. Does it seems right?
 

Warlike said:
erikl, can you explain clearly?
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Oh sorry, this was a misinterpretation. I just figured a factor of about 2, which isn't true, sorry!

Warlike said:
I don't understand why there are 454 mV in DC specs and 540 mV in AC specs. If I use in testbench of driver 100 Ohm res and capacitance load (receiver give only additional cap load) I would never get AC Vohd larger than DC Vold, only smaller (depend on cap. load). And why AC Vohd = 540 mV?

I have only one idea - reflections in tline. If we have bad termination there would be reflection and AC Vod can be larger than DC Vod. Does it seems right?
Click to expand...
Yes, this seems possible. I don't know better, though. Sorry!
 

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