Sinusoidal oscillator electronic circuit diagram

A simple sinusoidal oscillator can be made using this electronic circuit diagram.
Oscillator consists of two parts: IC1, R1, R5, C1 and C2 forms second order a low-pass filter , while IC2 is connected as an integrator.
Sinusoidal signal at the output of IC2 becomes trapezoidal after passing through the limiter, then low-pass filter is applied. Meaning that the reaction amplitude is constant, so the peak value of sinusoidal signal from the oscillator output is also constant.
The circuit provides two sinusoidal signals at port A, respectively B, which are out of phase with each other by 90 °.
Using electronic components specified in the schematic below circuit generates a signal frequency of 3.3 kHz, the peak to peak voltage of 11 V.
Frequency change is obtained by changing the values of C1, C2 and C3 in proportion.
At a supply voltage of 15 V circuit current is 3 mA.