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Communications II (Laboratory)

Design Project No. 1

Analog Pulse Modulator Circuit


Rationale: The use of coded pulses for the transmission of analog-information bearing signals represents a basic ingredient in the application of digital communication.


Learning Objectives:

To be able to design and construct analog pulse modulation circuits.

To demonstrate the similarities and differences in the operation of PAM, PDM and PPM circuits.


Design Requirement: Design a functional pulse modulator circuit where one of the three parameters (amplitude, width and position) is varied in accordance with the message signal.

Results should be output-oriented, not process-oriented.



Pulse modulation includes many different methods of converting information into pulse form for transferring pulses from a source to a destination. The three common methods of analog pulse modulation are as follows:

Pulse Width Modulation (PWM) - Oftentimes called pulse length modulation (PLM) or pulse duration modulation (PDM). The pulse width (active portion of the duty cycle) is proportional to the amplitude of the analog signal.

Pulse Position Modulation (PPM) – The position of a constant-width pulse within a prescribed time slot is varied in accordance to the to amplitude of the analog signal.

Pulse Amplitude Modulation (PAM) – The amplitude of a constant-position pulse is varied according to the amplitude of the analog signal.

see illustrations




Class division: 5 students/group.

All groups are required to submit 3 different pulse modulator circuits: PAM, PPM and PWM. Circuits may be referred from existing design circuits or may be uniquely designed by the group. All circuits should have prior approval before the start of construction. ICs or discrete components maybe used depending on the group’s discretion.

Circuits must be presented in breadboard. Circuits in PCBs will not be accepted.

A written report must be submitted during the presentation of the circuits.


Documentation Format

Title Page

Letter of Transmittal

Bill of Materials

Discussion (modulation concepts and circuit operation)

Sample Output

Annexes (photocopy of references, approval sheet)

Leaders Assessment (to be placed on a paper, sealed on an envelope)



PAM circuit (due 3 weeks after project discussion)

PDM circuit (due a week after the submission of PAM)

PPM circuit (due a week after the submission of PDM)


Queries / Consultation

Students may seek consultation during the scheduled laboratory hours.

Questions may be electronically mailed at or