This circuit, from a documentation from the 1970s, produces two sinusoidal signals given by C2 and R1 with a 90-degree lag. The operating modes used are no longer common, but the same circuit can be implemented with more modern operating systems like the 741. Precision resistors are needed only if precision in the frequency of the generated signal is desired. The supply voltage can also vary, depending on the type of operation with change corresponding to the zener diodes. The power supply must be symmetrical.
