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AM, FM, and Digital Modulated Systems Chap. 5
m(t)
V p
t
(a) Sinusoidal Modulating Signal
f c +∆F
f i (t)
f c
f c -∆F
0
t
(b) Instantaneous Frequency of the Corresponding FM Signal
A c
s(t)
t
(c) Corresponding FM Signal
Figure 5–9
FM with a sinusoidal baseband modulating signal.
Note that ∆F is a nonnegative number. In some applications, such as (unipolar) digital modulation,
the peak-to-peak deviation is used. This is defined by
¢F pp = max e 1
(5–43)
2p c du(t) df - min e 1
dt
2p c du(t) df
dt
For FM signaling, the peak frequency deviation is related to the peak modulating voltage by
¢F = 1
(5–44)
2p D fV p
where V p = max [m(t)], as illustrated in Fig. 5–9a.