2. 2
In pulse modulation, various properties of pulse signals are varied according the analog
message signal
A. Pulse Amplitude Modulation (PAM)
a. Natural Sampling (Follow class lecture)
b. Instantaneous sampling/Flat-topped
A. Pulse Time Modulation (PTM)
i) Pulse Width Modulation (PWM) / Pulse Duration Modulation (PDM)
ii) Pulse Position Modulation (PPM)
C. Pulse Code Modulation (PCM)
D. Delta Modulation (DM)
Pulse Modulation
3. 3
Pulse Amplitude Modulation (PAM) (1)
๏ฑ In PAM, the amplitudes of regularly spaced pulses are varied in proportion to the
corresponding sample values of a continuous message signal
๏ฑ Pulses can be of a rectangular form or some other appropriate shape
Two operations involved in the generation of the PAM
signal:
1. Instantaneous sampling of the message signal
every Ts seconds (sampling rate is chosen in
accordance with the sampling theorem)
2. Lengthening the duration of each sample, so that it
occupies some finite value T
5. 5
Pulse Amplitude Modulation (PAM) (3)
Comments on PAM:
1. The transmission of a PAM signal imposes stringent requirements on the amplitude and
phase responses of the channel, because of the relatively short duration of the
transmitted pulses
2. The noise performance of a PAM system can never be better than direct (i.e., base band)
transmission of the message signal
3. Thus, for transmission over long distances, PAM would be used only as a means of
message processing for time-division multiplexing
6. 6
Pulse Time Modulation (1)
๏ฑ The samples of the message signal are used to vary the duration of the individual pulses
๏ฑ Also known as as pulse-width modulation (PWM) or pulse-length modulation (PLM)
๏ฑ PDM is wasteful of power, in that long pulses expend considerable power during the
pulse while bearing no additional information
In PPM, the position of a pulse relative to its unmodulated time of occurrence is varied in
accordance with the message signal
Pulse Duration Modulation (PDM)
Pulse Position Modulation (PPM)
