it’s phase shift keying, and a proper implementation uses a phase detection circuit or something similar. [Craig] thought it would be fun to build an analog BPSK31 demodulator and hit upon the ...

Here we report a flexible all-graphene modulator circuit with the ... two types of quaternary modulation schemes: quaternary amplitude-shift keying and quadrature phase-shift keying.

This demodulator is suitable for the quadrature phase-shift keying (QPSK) modulator previously published by the same author, "Novel Low-Cost QPSK Modulator Needs No Adjustments" (electronic design ...