I was given the following task : 'Implement sine function generator using four different methods: absolute values, table of differences, polynomial approximation and circuit being on stability limit . Parameters of the generators are Amplitude u=255 V, frequency f=50Hz' . The first three ways are already working but now I have problem with 'circuit being on stability limit'. Where to start with here ? I can simulate the whole circuit with PSIM and programm any logics controller with C++.