This circuit is used for converting an analog signal into a digital pulse stream. Such things as class D audio amplifiers, servo amplifiers, A to D converters, or sending an analog signal across a fiber optic link.
The Schematic and explanation here in this webpage.
https://lrak.net/wiki/555_Delta-Sigma_Modulator.html
The output signal is shown as audio modulated onto a triangle wave on the scope in this YouTube video.