Regarding Drive Strength

[sandeepkumar]

Hello everybody,

I want to know how this drive strength is selected for simulation. is it depends on the board impedance like (50 ohm or 55 Ohm for single ended what we maintain) or something else.

here we have 34 ohm 40 ohm and 60 ohm? which one is best  for simulation .Any one having more insight on drive strength kindly share the link.

[sandeepkumar]

Thanks Yuri,

But I want to know do we have to match the driver Impedance with the characteristic impedance of the trace ? is there any relationship between Driver impedance and the characteristic impedance of the trace. suppose we have to maintain 50 Ohm on the board is it good to chose 40 ohm driver impedance and 10 ohm series resistor or the driver impedance of IC has nothing to take with the board impedance ..............?

do we have to do like that Driver impedance of IC + Series Resistor = Trace characteristic impedance?

or based on the simulation we will choose the driver impedance?

[Yuri]

Sandeep Kumar !

  Yes, it is true – at least theoretically – “we have to match the driver Impedance
with the characteristic impedance of the trace”. But this is one of advantages
of simulation – it is possible to try different configurations in order to be sure
PCB design is fine. Moreover, later we can try again different drive strength
settings on real board.

~Yuri.

[sandeepkumar]

Thanks Yuri,

So i think better to go with sweep simulation and choose the best from it.

[Yuri]

Sure !

[Yuri]

  It makes sense to try different Drive Strength configurations during simulation,

in order to select most suitable : where signals have proper waveforms, 
without voltage under / overshoots, "eye" meet specifications.  

Have a great day,
Yuri

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