CP/PC364 Data Communications & Networks Laboratory

Pulse Amplitude Modulation

PRELAB

Overview

This week's laboratory investigates Pulse Amplitude Modulation (PAM). We will be using the 4066 chip to sample small pulses of a sine wave. The 4066 is an analog switch IC which will output whatever is on the input when the control is high. Since it is a CMOS chip the voltage levels are very important. We will use short pulses from a 2206 as our control and the frequency generator as the input.

Datasheet: XR2206 [Copyright 1972 EXAR Corporation. Datasheet June 1997]
Datasheet: MC14066B (4066) [Copyright Semiconductor Components Industries, LLC, 2000]

Objectives

  1. Understand pulse amplitude modulation by viewing the output of a sine wave at regular intervals.
  2. Examine how the frequency of the pulses affects the output waveform.

Setup

Setup the 2206 to create your control pulses as determined in step 1 of your prelab. View the output on the oscilloscope to ensure you get the correct waveform (frequency, amplitude and pulse width).

Setup the frequency generator as determined in step 3 of your prelab with f= 1Hz. View the waveform on the oscilloscope to ensure it is correct (frequency, amplitude & offset).

Exercise

  1. PAM

    Pulse Amplitude Modulation is a technique used to send a signal as a series of continuous pulses, called a pulse train. These pulses, or samples, that are being sent represent a small fraction of the original signal. The sampling rate of the original signal will determine the reliability of the signal and how accurately the original signal can be reconstructed at the receiving end.


    Connect the 2206 as determined in step 1 of your prelab for a 4 Hz pulse. Using the oscilloscope ensure you are getting the correct pulse output.
  2. Connect the 4066 as determined in your prelab, with the exception of the pulsed control input.
    • Tie the control input HIGH
    • Ensure your input wave and output wave are the same.
  3. Connect the output signal from the 2206 (pulses) to the control input. (You should see small spikes on the oscilloscope).
    • Print the input and output waveform and paste in your lab book.
    • How reliable would this signal be for recontrusting the analog signal at the receiving end?

    Demonstrate and explain your results to the lab instructor

  4. Increase the sampling rate by increasing the frequency of the pulses on the 2206 to 10 Hz (as determined in your prelab).
    • Print the input and output waveforms and paste in your lab notebook.
    • What are the advantages and disadvantages of increasing the frequency of the pulses?
    • Would this signal be more reliable? Why or why not?
  5. Repeat step 4 increasing the frequency to 20 Hz (as determined in your prelab).

    Demonstrate and explain your results to the lab instructor