OVERVIEW

Baseband modulation techniques encode information directly as the amplitude, width, or position of a pulse. They do not utilize a sinusoidal carrier. Some of these modulation schemes are known by the acronyms PWM ( pulse width modulation), PPM ( pulse position modulation), and PAM ( pulse amplitude modulation). PWM is often used as the process control voltage for DC servomotors, and PPM is employed in optical data communication systems.

PAM was originally implemented as analog modulation, where the pulse amplitude is linearly related to the sampled analog signal. PAM is easily adapted to the binary transmission of information. PAM utilizes several types of signaling pulse waveforms with different transmission bandwidths, and simple and optimum receivers that can be conveniently designed and analyzed in SystemVue.

Binary digital data can be represented as either a symmetrical polar ( 3.3 V or 5 V) or asymmetrical unipolar PAM signal (for example, 0 and +3.3 V or 5 V). PAM signals can be a portion ? of the bit time T _b (a duty cycle of less than 100%), the entire bit time, or even extend beyond a single bit time without causing intersymbol interference (ISI). PAM is used to introduce the concept of the baseband bandwidth needed to transmit pseudonoise (PN) random data, and the reception of data with bit error in the presence of additive white Gaussian noise (AWGN).

Shaping of the PAM signal from the simple rectangular pulse improves the spectral efficiency...