Tektronix AWG 2021 Manual do Utilizador descarregar pdf (Página 19)

Digital Phase Modulation — PSK

The modulating signals in the

foregoing examples have been

sinusoidal or continuous wave-

forms. A simple step to digital

modulation is made with a slight

variation to sinusoidal modula-

tion. Figure 21 shows one cycle

of a sinewave that has been

quantized into steps between

–0.5 and +0.5. The equation

defining these steps is shown in

Figure 22. The second line

simply quantizes a cosine wave

by rounding and scaling the

continuous waveform to the

nearest eighth. This quantized

modulating pattern is then

directly inserted in the phase

argument of a cosine carrier.

Thus, the phase argument takes

on values between –π to +π in

π/4 steps. If the polar graphical

representation of the signal is

used, a family of eight points of

equal magnitude is defined,

spaced around the circle in π/4

or 45° phase increments.

Figure 21. The sinusoidal modulating pattern is

quantized into discrete steps. The steps are

equally spaced in amplitude and will shift the

phase of the carrier in π/4 or 45° increments.

Digital Modulation

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Tektronix AWG 2021 Manual do Utilizador Página 19