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Jak navrhnout pulsní amplitudovou modulaci?

Date:2018/10/11 15:03:59 Hits:


Before we go into the design of pulse amplitude modulation let us know about the concept of modulation and different types of modulations.

Co je modulace?


Modulation is a process of changing the characteristics of a carrier signal like amplitude, frequency and width, etc. It is the process of adding information to the carrier signal. A carrier signal is a steady waveform with constant amplitude and frequency.



Modulation is normally applied to electromagnetic signals like radio laser and optical signals. The Audio, video, images and text data are added to the carrier signal for transmission over telecommunication.


Types of Modulation


Modulation is categorized into two types depending on the type of signal.

* Continuous-wave Modulation
* Pulse Modulation


Continuous-wave modulation and Pulse modulation are further categorized as shown below.



Continuous-wave Modulation


In continuous wave modulation signal is used as a carrier signal which modulates the message signal. There are three parameters that can be altered to achieve modulation namely, frequency, amplitude and phase. Thus, there are three types of modulations.


1. Amplitude Modulation
2. Frequency Modulation
3. Phase Modulation


Pulse Modulation



Pulse modulation is a technique in which the signal is transmitted with the information by pulses. This is divided into Analog Pulse Modulation and Digital Pulse Modulation.

Analog pulse modulation is classified as

* Pulse Amplitude Modulation (PAM)
* Pulse Width Modulation (PWM)
* Pulse Position Modulation (PPM)


Digital modulation is classified as

* Pulse Code Modulation
* Delta Modulation



Pulse Amplitude Modulation


Pulse amplitude modulation is a technique in which the amplitude of each pulse is controlled by the instantaneous amplitude of the modulation signal. It is a modulation system in which the signal is sampled at regular intervals and each sample is made proportional to the amplitude of the signal at the instant of sampling. This technique transmits the data by encoding in the amplitude of a series of signal pulses.


There are two types of sampling techniques for transmitting a signal using PAM. They are:

* Flat Top PAM

* Natural PAM


Flat Top PAM: The amplitude of each pulse is directly proportional to modulating signal amplitude at the time of pulse occurrence. The amplitude of the signal cannot be changed with respect to the analog signal to be sampled. The tops of the amplitude remain flat.

Natural PAM: The amplitude of each pulse is directly proportional to modulating signal amplitude at the time of pulse occurrence. Then follows the amplitude of the pulse for the rest of the half cycle.



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