I can see the author mentions that the dual outputs have a 90deg. phase shift between them, how they are opposite in nature and can be shaped to give sine outputs. This could have been used for various wireless communication circuits, like for I and Q generation, for some other type of modulations (phase, BPSK?), etc. Maybe these circuits played an important role back then?
Here's a weird one, that I can't get my head around. It's a dual output triangle wave generator, with adjustable phase shift. I also can't see a purpose for it, but I guess the author must have had a reason!
Another method to generate a triangular waveform from square wave is to use an opamp integrator. However, it is difficult to make a wideband integrator that would give triangular output for all square wave input frequencies.
