Page 192 - Fundamentals of Communications Systems

6.14 Chapter Six

Envelope Detector

y t () A m t()
c
0
DC Remover

Figure 6.16 Circuit implementation of an LC-AM demodulator.

phase shift induced by the propagation delay in the channel is entirely limited
to shifting the phase of the bandpass signal and has no impact on the amplitude
of bandpass signal.

EXAMPLE 6.6
Consider again affine modulation with
m(t) = β sin(2π f m t)
with
x z (t) = A c (1 + aβ sin(2π f m t))
The vector diagram of x z (t) is shown in Figure 6.17(a) and it is obvious from this plot
that only the real part of the complex envelope is used in producing a LC-AM signal and

2 2 2 2
1.5 1.5 1.5 1.5
1 1
1 1
0.5 0.5
x Q (t) 0 y Q (t) 0 0.5 0.5

−0.5 −0.5
0 0
−1 −1 x (t) y (t)
A
−0.5 A −0.5
P
−1.5 −1.5 x (t) y (t)
P
−2 −2 −1 −1
−2 −1 0 1 2 −2 −1 0 1 2 0.08 0.084 0.09 0.08 0.084 0.09
x (t) y (t) Time, t Time, t
I
I
(a) The transmitted and received (b) The transmitted and received amplitude
vector diagram and phase signals
Figure 6.17 The signals for a sinusoidal message signal. φ p =−49 .
◦