For the QPSK modulator shown in FIGURE Q2c, change the +90? phase-shift network to -90? and sketch the new constellation diagram. Binary input data fb Bit splitter Bit clock I Q ÷2 I channel fb/2 Logic 1 = +1 V Logic 0 = -1 V Q channel fb/2 Balanced modulator sin ?ct Reference carrier oscillator (sin ?ct) 90º phase shift cos ?ct Balanced modulator Bandpass filter Linear summer Bandpass filter BPF QPSK output FIGURE Q2c
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In the original QPSK modulator, the 90° phase shift network creates a phase difference between the two channels (I and Q) so that the constellation points are separated by 90°. Show more…
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