563489578934

Sec. 3–11 Pulse Time Modulation: Pulse Width Modulation and PPM 221
Analog input
signal
Instantaneously
sampled PAM
generator
Clock
Sync
Flat-topped
PAM
+
Triangle
+
Triangle
function
generator
+
Comparator
–
V r = reference level
Monostable
multivibrator
PWM
output
PPM
output
PAM
signal
t
Triangle
Clocking
t
V r
PAM
plus
triangle
t
PWM
t
PPM
t
Figure 3–44
Technique for generating instantaneously sampled PTM signals.
multivibrator circuit. In the literature on PTM signals, the comparator level V r is often called
the slicing level.
PWM or PPM signals may be converted back to the corresponding analog signal by a receiving
system (Fig. 3–46). For PWM detection, the PWM signal is used to start and stop the integration
of an integrator; that is, the integrator is reset to zero, and integration is begun when the
PWM pulse goes from a low level to a high level and the integrator integrates until the PWM
pulse goes low. If the integrator input is connected to a constant voltage source, the output will