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384
AM, FM, and Digital Modulated Systems Chap. 5
m(t)
input
FM transmitter
F=(1/4)R
s(t)
FFSK signal
(a) Generation of Fast Frequency-Shift Keying (FFSK)
x data
x(t)
cos(∏t/2T b )
m(t)
input
Serial-toparallel
converter
(2 bit)
Sync
output
y data y(t)
A c cos( c t)
Oscillator
Carrier
f 0 =F=1/4R
oscillator, f c
Sync
input
90°
90°
phase shift
phase shift
sin(∏t/2T b )
A c sin( c t)
s(t)
MSK
signal
(b) Parallel Generation of Type I MSK (This will generate FFSK if a differential encoder is inserted at the input.)
m(t)
input
BPSK signal at
carrier frequency f 2
A c sin( 2 t)
MSK bandpass
filter about f 1
H(f)
s(t)
MSK signal
at carrier
frequency f c
Carrier oscillator
at frequency
f 2 =f c -F
(
|H(f)| 2 sin[∏(f-f 2 2
1 )T b ] sin[∏(f+f 1 )T b ]
= +
∏(f-f 1 )T b ∏(f+f 1 )T b
(
(
(
(c) Serial Generation of MSK
Figure 5–36
Generation of MSK signals.