What is PAM?
The modulation of the amplitude of the individual pulses with reference to the amplitude of an analog signal to encode the information analog signal into the digital signal is known as PAM. Therefore, this kind of pulse modulation forms an optimal way to transmit analog data through digital information channels, so it is popularly applied in the data transmission technology, signal processing, and communications fields.
Modulation
Channel Bandwidth of PAM
Now let us consider the N baseband signals that carries the message information. Every signal is represented by m1(t), m2(t),……..,mn(t) and is bandlimited to FM. A bandwidth greater than NFM is not necessary for the communication channel. The time interval Ts = 1/2FM is not exceeded by the baseband signal m1(t) sampling. This indicates that samples of the subsequent signals are taken at the same time interval (1/2FMN). The difference between the two succeeding signals, such as m1(t) and m2(t), is what it is. A high channel bandwidth would make demultiplexing simpler and more straightforward to do. However, if the channel bandwidth is restricted, crosstalk between the baseband signals might occur, reducing the signal’s quality.
Now, let us assume that the first baseband signal is transmitted at time t=0, thus the output response of the system is given by:-
S1 = I1ωc sin ωct/πωct , The response shows a peak at t = 0 that is proportional to the message signal m1(t).
At t= 1/2FC, the second baseband signal is required to transmitted, and is given by
S2 = I2ωc sin ωc (t – 1/2FC)/πωc(t – 1/2FC)
Thus the response of both the basebands in waveform is represented in the diagram below:
Channel Bandwidth Representation
Pulse Amplitude Modulation
Pulse Amplitude Modulation (PAM) is a key modulation technique used in digital communication for transmitting analog data and is one of the most widely used types of analog-to-digital conversion. Its process is simple where the amplitude of a sequence of pulses changes with the instantaneous amplitude of the analog message signal. The analog signal that is to be modulated is sampled by a sequence of pulses that are amplitude-modulated on the carrier to produce the amplitude-modulated pulses.
The analog signal is sampled at regular intervals to enable the amplitude of pulses due to be produced by the carrier to be varied. The sampled values are quantized to a specific number of quantization levels or discrete levels whereupon the process is repeated. Due to its simplicity of implementation and analysis, PAM is often employed in many applications including digital communication, audio transmission, and instrumentation among others. One of the biggest drawbacks of PCM is its sensitivity towards channel errors, as poor-quality channels will introduce noise and distortion, particularly over larger distances and lower data rates.
Table of Content
- What is PAM?
- PAM Block Diagram
- Types
- Mathematical expression
- Construction
- PAM Circuit
- Solved Examples on PAM
- Applications
- Advantages
- Disadvantages