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Experiment No. (2) : Pulse Amplitude Modulation

This experiment aims to simulate pulse amplitude modulation (PAM) using LabVIEW. The circuit samples a modulating signal like a sine wave using a square wave clock. This creates a PAM signal which is then reconstructed using a low-pass filter. The experiment studies over, Nyquist, and under sampling by varying the modulating frequency. In oversampling, the modulating signal is reconstructed perfectly from the filtered PAM signal. In Nyquist sampling, low frequencies of the modulating signal are reconstructed while higher frequencies are lost. In under-sampling, the reconstructed signal is distorted and the modulating signal cannot be recovered fully.

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94 views11 pages

Experiment No. (2) : Pulse Amplitude Modulation

This experiment aims to simulate pulse amplitude modulation (PAM) using LabVIEW. The circuit samples a modulating signal like a sine wave using a square wave clock. This creates a PAM signal which is then reconstructed using a low-pass filter. The experiment studies over, Nyquist, and under sampling by varying the modulating frequency. In oversampling, the modulating signal is reconstructed perfectly from the filtered PAM signal. In Nyquist sampling, low frequencies of the modulating signal are reconstructed while higher frequencies are lost. In under-sampling, the reconstructed signal is distorted and the modulating signal cannot be recovered fully.

Uploaded by

khaled lotees
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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EXPERIMENT No.

(2)

PULSE AMPLITUDE MODULATION

Objectives

The objective of this experiment is to simulate sampling circuit to:

a. Study the sampling theory and design the circuit of sampling and
reconstruction.

b. Study the different cases of sampling. Nyquist, Over and Under


Sampling.

Procedures

1- Draw the Circuit of sampling as shown in figure (1) Using LabView


Communication program.

Figure (1)

The circuit of Figure 1 may be implemented on LabView Communication


program with the following steps.

a. In Search bar you can write: Wave Generator, Multiply and PSD.
b. From Wave Generator you can select type of wave (sine wave and
square wave), and from Help bar we can know the function of each bin
as shown in figure (2).

Figure 2

C. From each block extracted in step b, choose indictor to display the


output of each one as in figure (3) for sine wave.

Figure (3)

d. Set the amplitude of the sine wave block to 5 volt, frequency to 20 Hz,
and For the square wave block let the amplitude is 5 volt, frequency 100
Hz and offset is 5 volt.

e. Let the sample rate for both sine and square waves the same and is
equal to 10000.

Create the circuit diagram of the sampling system shown in figure (4)
f.
on LabView communication Program.
Figure (4)

g- Draw the modulating signal waveform.


h- Draw the spectrum of modulating signal.

i- Draw the sampling signal waveform.

j- Draw the spectrum of sampling signal


k- Draw the PAM signal waveform.

l- Draw the spectrum of PAM signal

m- Vary the frequency of sine wave to be 50 Hz (half value of square


wave frequency) and then make it equal to 80 Hz and run the program
again. Draw the waveform and the spectrum of PAM signal for each
case. Comment on your results.
At fm = 50 Hz
At fm = 80 Hz

Comment:

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2. To reconstruct the original signal, we simply pass the sampled signal
through LPF as shown in figure (5).

Figure (5)

On Lab View Communication Program, you can construct the LPF and
connect it with the circuit shown in figure (4) above and record the
results.

a. In search bar you can write filter and select Low Pass Filter
Butterworth type (Figure 6). Set the cutoff frequency to 30Hz and the
filter order is 5.

Figure (6)

b. The reconstruct circuit is shown in figure (7).

Figure (7)
c. Run the program and record the results for the three cases of
sampling frequency.

At fm = 30 Hz (Over-Sampling):
d. Draw the filter output.

e. Draw the spectrum of filter output.


At fm = 50 Hz (Nyquist rate):
f. Draw the filter output.

g. Draw the spectrum of filter output.


At fm = 30 Hz (Under-Sampling):

h. Draw the filter output.

i. Draw the spectrum of filter output.

Comment

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