PAMPulse Amplitude

Modulation

Professor: Dr. Miguel Alonso Jr.

Outline

Description Bandwidth Requirements Signal Reconstruction Types of PAM LABVolt Module 2: PAM

Description

PAM is a type of pulse modulation A PAM signal consists of samples of the

analog signal, in which the amplitude of each pulse is proportional to the analog signal at that point

Pulses have a fixed width

Bandwidth Requirements

Sampling Rate of the PAM pulses should be twice that of the analog signal to be transmitted. Nyquist

But what about the bandwidth of the PAM signal itself?

Bandwidth of the PAM signal is roughly computed as

1KBT

Where BT is the transmission bandwidth τ is the pulse width K1 is a constant that depends on the spacing

between adjacent pulses, the level of acceptable adjacent pulse crosstalk, the sharpness of the cutoff rate, and other factors

Typical values range from 0.5 to 1

Example

An analog signal is sampled at a rate of 5kHz. The width of each sample is 40 us. Compute the approximate bandwidth for K1=0.5

and K1 = 1 What is the duty cycle of the sampling pulse? Answer: 12.5kHz and 25kHz

What is the bandwidth requirement for a K1 = 1 and a sampling width of 15us?

Signal Reconstruction

Reconstruction of the PAM occurs through the use of a low-pass filter

Types of PAM

Flat-top Natural PAM

LAB Volt Module

Labvolt Module 2: PAM Exercise 2-1 and 2-2