On Fri, 10 Mar 2006, Herbert Graf wrote:

>> Only while sending.
>
> Nope. More while sending yes, but even idle the analog portion of a PHY
> capable of dealing with long lines can consume a good amount of power.
>
> That's why alot of power saving these days actually deals with shutting
> power off to parts of chips. Stopping the clocks no longer helps as much
> as it used to.

I do not agree. I made a phy repeater using switching transistors a long 
time ago. It came nowhere near such power figures.

Remember the ether phy is ac coupled so there is NO need to hold the 
state after sending a transition. It is exactly like bipolar pulse 
signalling for telco. The latter gets by with 100 mW power to go up to 
1.5 km utp (after duplexing) (this is ~7.5Vpp into 600 ohms). The 
average power is much lower, as with ether phy.

The normal 'low power' way to hold state on the sending end of a 
balanced transmission line is to terminate it with a mosfet whose Rdson 
= Zcable. When the sender sends neither + nor - pulses the mosfet is on. 
This consumes zero power, as you know (there is no voltage across the 
mosfet, and if there is any, it is crosstalk from the line).

Peter
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