3 stage OP-AMP works as function generator, the first stage produces a square wave which will be integrated by the second stage to produce a tringulare wave which is integrated by the third stage to produce a picewise parabola which resembles sine wave.
The 100 micro volt in the input of the first stage is to simulate the thermal voltage produced by the internal op amp resistors which is needed by the op amp to start the oscillation.
