sensor - How do Dualshock 4 pressure sensitive buttons work?

I'm doing a reverse engineering research about the PlayStation 4 controller. I want to know how do the analog buttons work (the triggers in the bottom, not the analog sticks). I've found a nice teardown album and, there, I've seen this image:

I know from this page that the flexible film pins for each analog trigger are these:

• Common: Oscillating between 0 and 3.3V.


• Sig: Voltage divider output, active low.

I want to know if it is:

• A capacitive sensor.


• A piezoelectric film.


• A force-sensitive resistor


• Other

And, by the way, how does the circuit attached work? I suppose it will have some kind of Analog Digital Converter, filtering, amplification...