The circuitry to the left of the 3.3 V supply implements a ground-referenced sawtooth labeled "LO", while that to the right forms a 3.3 V-referenced one labeled "HI"
Figure 1. The circuitry to the left of the 3.3 V supply implements a ground-referenced sawtooth labeled "LO", while that to the right forms a 3.3 V-referenced one labeled "HI"