What is the relation between voltage and speed in USB.

In USB 2.0 voltage = 4.4V speed=480Mbps,but
In USB 3.0 voltage = 4.0V speed=upto 3.2Gbps.


How is this achieved, as speed is increased voltage is decresed...

 

Where did you get this information?

As for speed, usb3.0 uses a full-duplex (talks and listens at the same time) to get increased bandwidth.

The voltages look off to me. The signal voltages have never been that high.. As far as I know.

 

Read down to the "Signaling" section for some mention of the signal voltages - http://en.wikipedia.org/wiki/Universal_Serial_Bus

They are very different from the ones in your post. You might check your source.