One analog to digital conversion method is called pulse amplitude modulation or PAM. This technique takes an analog signal, samples it and generates a series of pulse based on the results of the sampling. The term sampling means measuring the amplitude of the signal at equal intervals. The method of sampling used in PAM is more useful to other areas of engineering than it is to data communication. However, PAM is the foundation of an important analog to digital conversion method Pulse Code Modulation or PCM. In PAM the original signal is sampled at equal intervals. PAM uses a technique called sample and hold technique. At a given moment, the signal level is read, and then held briefly. The sampled value occurs only instantaneously in the actual waveform, but is generalized over a still short but measurable period in the PAM result. PAM is not useful to data communications because even though it translates the original wave form to a series of pulses, these pulses are still of many amplitude (still an analog signal, not digital). To make them digital we must modify them by pulse code modulation. Pulse code modulation has some applications, but it is not used by itself in data communication. However, it is the first step in another every popular conversion method called pulse code modulation.
