Technical question about NOX sensor communication

How does the NOX outlet sensor communicate its readings to the ECU?

Is it just a simple variable volatage? Or is it something weird like frequency modulation or digital encoding?

Asking for... reasons...

 

What about between the sensor itself and the electronic module that comes attached to the other side of the sensor wire? That's got to be something simple and analog, right? An electronic encoder probably wouldn't survive the extreme heat in the actual sensor..

 

So, two questions...

1: as you know, the nox sensor (at least for dd15s) comes with the actual probe and the little electronic box on the other side that mounts on the onebox and plugs into the emissions harness...

I am guessing the box is the encoder? And the signal between the box and the probe is analog? Because no microchip could survive the high temperatures of the probe end? Or is it all 1s and 0s all the way through?

2: if it is all digital, where does one procure those sensor emulators?