One of the most basic forms of digital modulation is called Amplitude Shift Keying (ASK). In amplitude shift keying, the carrier has two possible states, On and Off, On representing a digital 1, and ...

In Figure 5-9 (b), we have used M = 4, giving four signal points and a system called quadruple phase shift keying (QPSK) or 4PSK . In Figure 5-9 (c) M = 8, i.e. the signal constellation 8PSK , etc.

4. The constellation diagram shows the end points of the invisible phasors. Sixteen different phase and amplitude combinations are produced, one for each 4-bit code. 8-PSK uses eight different ...

U1, U2, and U3 form the quadrature oscillator. U4 provides the necessary amplitude gain required for ASK. U5 and U6 are configured as inverters to provide a phase shift of 180°.