Lately working on a project for Delta-Sigma modulation. 

From top to bottom we have: input (sinewave), first-order modulator (1-bit) output, second-order modulator (1-bit) output, first-order quantisation error, second-order quantisation error, first-order integrator, second-order second integrator.

The output of the integrators are those going through the quantisers generating the 1-bit stream. Interesting to notice that they look so different and that the pulse-density modulated output is yet so similar.