VCO with triangle-core phase animator and through zero PM.

PA0 is a voltage controlled triangle core oscillator with a triangle phase animator, producing a second set of waves which is adjustable in phase lag from 0 to 180 degrees from the primary waves. The phase animator may also be pushed past this range to create additional harmonics. PA0 includes TZPM, TZFM, and exponential FM.

https://www.westonaudio.com/pa0.html