Pulse Amplitude Modulation (PAM)

Pulse Amplitude Modulation (PAM) is a type of modulation technique where the amplitude of a series of pulses is varied in accordance with the amplitude of an analog signal. PAM is commonly used to transmit analog signals over digital communication systems.

In PAM, a continuous-time analog signal is sampled at regular intervals to obtain a series of discrete-time samples. Each sample is then represented by a pulse whose amplitude is proportional to the amplitude of the sample.

Pulse Amplitude Modulation (PAM)

The basic block diagram of a PAM transmitter includes three main blocks: a sampler, a quantizer, and a pulse generator. The sampler samples the analog signal at regular intervals to produce a series of discrete-time samples. The quantizer rounds each sample to the nearest discrete amplitude level to reduce the number of possible amplitudes to a finite set. The pulse generator then generates pulses whose amplitudes correspond to the quantized samples.

The modulated signal can be expressed as:

s(t) = ∑ a_n p(t-nT)

where a_n is the amplitude of the nth sample, p(t) is the pulse shape, and T is the sampling interval.

PAM has several limitations, including poor noise immunity, limited dynamic range, and poor spectral efficiency. To address these limitations, other modulation techniques such as Pulse Code Modulation (PCM) and Delta Modulation (DM) have been developed. PCM is a type of PAM where the amplitude of each sample is quantized to a binary code, while DM is a type of PAM where the difference between consecutive samples is quantized to a binary code. These techniques improve noise immunity and dynamic range while maintaining the simplicity and effectiveness of PAM.