VCA Using JFET and Op Amp
Note that U1 has a signal gain of 2 and its input is Vout/4, so it applies Vout/2 to the JFET gate, essential to cancelling out most of the second harmonic. 

This is a classic basic configuration known since at least the 1970s, though the detail around U1 may be novel.

Figure 7B on this page has some similarities. The opamp has a gain of 11. and feeds back 1/22 of its output to the gate (again driving the gate with 0.5 of the drain voltage)