1. Analog Pulse Modulation: In these methods, one parameter of a pulse train is varied in a continuous manner according to the analog message signal.
• PAM: Amplitude is varied.
• PWM: Width (duration) is varied.
• PPM: Position in time is varied.
While the carrier is made of pulses, the information is still carried in an analog (continuous) format.
2. Digital Pulse Modulation:
Pulse Code Modulation (PCM) is fundamentally different. It involves three distinct steps:
• Sampling: Converting the continuous signal into discrete-time samples.
• Quantization: Mapping the continuous amplitude values of those samples into a finite set of discrete levels.
• Encoding: Representing each quantized level as a unique binary code (a sequence of '0's and '1's).