Where can I find a basic block diagram with descriptions for a typical 10/100BASE-T PHY output driver stage?
I also wonder whether all drivers use "current-mode" outputs that lead to voltage across the external termination resistors (it seems so, because most of the time I see applications with termination resistors to VDD or GND) or are there devices that use voltage output? Why is current output the better choice? It it easier to steer current sources than voltage sources? (and therefore easier to create the different voltage levels)
Best Answer
Below is my guess of what a simplified driver can look like.
When [A1,A2] = 1,1, the output level is positive. When [A1,A2] = 0,0, the output level is negative. When [A1,A2] = 0,1 or 1,0, the output level is zero.
The output impedance is determined by the resistors, which are matched to the cable.
What is completely missing in the diagram is the slew rate control. Which I don't have much idea of how that is actually realized in an IC for this application.
simulate this circuit – Schematic created using CircuitLab