wideband signal generation and analysis (Tektronix)

Hello,

there is a new class of oscilloscopes from Tektronix, called DIGITAL PHOSPHORE OSCILLOSCOPE (DPO).
With bandwidthes from 4GHz and higher (up to 12 GHz).
E.g. DPO/DSA70000 Series
I am wondering how it is realized. The manual says it is not the normal spectrum analyzer principle (of course).
How do they get 4 GHz down to the baseband in one step.
I dont know any DSP, which is able to digitize 4 GHz at once --- would mean somewhat 8GS/s...

Thanks for any comment. Its quite urgent to me....

I think Agilent has for its fastest real time scopes a 20 or even 40GSps acquisition circuits (working in parallel), so why Tektronix would be any different?

Bandwidth and sampling rate of oscilloscopes are only partly related. The state of the art is about 50 GS/s real-time sampling rate with 15 or 20 GHz analog bandwith at major vendors fastest instruments. Higher analog bandwidths up to 80 GHz are achieved with non-real time sampling scopes.

thank you