This is a voltage controller oscillator that was designed as a wide range oscillator to generate clock pulses for a stepper motor drive system. It does however have some interesting features. The original application used a stepper motor for its ability to operate over a very wide speed range, so this oscillator is also designed for a very wide frequency range.
Clocks and Oscillators - An Introduction To Digital Electronics - PyroEDU
#60: Basics of Phase Locked Loop Circuits and Frequency Synthesis