Objectives:
Understanding the principles of pulse amplitude modulation and demodulation using MATLAB Simulink.
Generating a waveform from an analog signal which looks like pulses and contains the information present in the analog waveform by modulation.
Applying sampling technique to produce a PAM signal.
Performing the demodulation by recovering the original analog waveform from the PAM signal through a low-pass filter.
Preliminary Work:
No preliminary work required.
Theory:
Pulse amplitude modulation (PAM) and demodulation is the process of converting an analog signal to a pulse-type signal in which the amplitude of the pulse denotes the analog information and then recovering the original signal from the pulse amplitude modulated signal. Two types of sampling are used to produce a PAM signal which are natural hertz, the PAM signal that uses natural sampling (gating) is
ωs(t)=ω(t)s(t)
where
s(t)=∑(k=-∞)^(∞)prod((t-kTs)/(τ))
is a rectangular wave switching waveform and fs=(1)/(Ts)≥2B. The duty cycle (ratio) of s(t) is d=τ/Ts where τ is the pulse width and Ts is the sampling time.
(b) Switching Waveform with Duty Cycled d=τ/Ts=1/3
Figure 1. PAM signal with natural sampling
Figure 2. Demodulation of a PAM signal (naturally sampled)
Experimental Procedure:
Switch on the computer and click on the MATLAB icon.
Go to start at the bottom of the command window, then select "Simulink" then go to library browser and drag it into creating file. (or) Once you open the MATLAB, click on the Simulink icon. Go to file and select new: and then select model. You will get a new window.
Arrange the functional blocks as shown in Simulink model.
Assign required parameters to each functional block.
Observe the outputs on scope.
Simulink Model:
Simulation Outputs:
Assignment:
Find and plot as a figure the frequency spectrum of the analog sine wave of the above experiment for the given period and pulse width. Use the time increment dT=(T)/(64*512) and the number of samples M=256.
Which is better, natural sampling or flat topped sampling and why?
Submit your solutions and answers in the report format along with the code, command window parameters and figures as hardcopy within one week from the lab time.
Discussion:
Discuss the outcomes of the experiment and state whether or not there are any deviations of the experimental results from results expected from theoretical principles. Also try to reason why?
Conclusion:
List key achievements of this experiment.