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Current flow in Ethernet driver

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Below is an example of an Ethernet PHY - current mode PHY driver.

The voltage given to the Vcc of the PHY is 3.3 V. Image for reference on page 3 of this doc

I want to understand how does the current flow on the TXP/RXP pins of the PHY in the current mode driver? Since, in a current mode driver, external pull-up termination resistors are there.

My questions:

  1. enter image description here
Can someone tell me the current flow path in the above image when Ethernet signals are present on the TX lines? How will the current flow be through the transformer and the PHY? And like what would be the voltage on the ethernet lines?

  1. Since there are 50 Ω termination resistors, the impedance of the ethernet traces TX/RX should able be 50 Ω on the PCB for impedance matching, correct?
 
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Imagine TX pins as unidirectional current sources that are sinking current to ground.

As for the differential current respectively voltage magnitude, refer to datasheet and IEEE 802.3.
 
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FvM said:
Imagine TX pins as unidirectional current sources that are sinking current to ground.

As for the differential current respectively voltage magnitude, refer to datasheet and IEEE 802.3.
Click to expand...
Can you please explain a bit more on the current flow with image or direction, please?
--- Updated ---

FvM said:
Imagine TX pins as unidirectional current sources that are sinking current to ground.

As for the differential current respectively voltage magnitude, refer to datasheet and IEEE 802.3.
Click to expand...
Also, how can a current source, sink current to the ground?
 
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What exactly is unclear?
* The transformer_CT is supplied by 3.3V.
* TXP/TXN are pulled up with 50 Ohms.
* TXP as well as TXN consists of a current sink to GND (IC internal)
A current source (more correct: current sink) is high impedance, thus it won´t change the 50 Ohms, independent whether it sinks current or not.

******

Wikipedia says:

A current source is an electronic circuit that delivers or absorbs an electric current which is independent of the voltage across it.

A current source is the dual of a voltage source. The term current sink is sometimes used for sources fed from a negative voltage supply.
Click to expand...

There is no Wikipeda article for "current sink".

Klaus
 
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