The spectrum of periodic signals is a discrete spectrum, while the spectrum of non-periodic signals is a continuous spectrum.

Common periodic signals include: sinusoidal signals, pulse signals and their rectification, differentiation, integration, etc.

Signal classification

Common periodic signals include: sinusoidal signals signals, pulse signals and their rectification, differentiation, integration, etc. This type can be called a simple signal. Their characteristics are that there will be no more than two extreme points in a cycle and the periodic characteristics are obvious.

For this type of signal with clear periodic characteristics, the judgment of whether it is periodic or not is relatively simple, and the period measurement methods are also very mature and complete, such as: zero-crossing detection method, pulse shaping method, etc.

Expression

x (t) = x (t + kT), k = 1, 2...

In the formula, t represents time and T represents cycle.

Signal Division

A signal can be either analog or digital. If it is continuous time and continuous value, then it is an analog signal. If it's discrete time and discrete values, then it's a digital signal.

In addition to this distinction, signals can also be classified as periodic or aperiodic. A periodic signal is one that repeats itself over a certain period of time, whereas aperiodic signals do not repeat. Analog and digital signals can be either periodic or non-periodic.

Methods to distinguish between periodic signals and non-periodic signals:

1. The spectrum of periodic signals is discrete, while the spectrum of quasi-periodic signals is continuous.

2. Because periodic signals can be represented by a set of trigonometric functions that are multiples of integer frequencies, they are discrete frequency points in the frequency domain. When a quasi-periodic signal is subjected to Fourier transform, n tends to infinity, so it becomes continuous in the spectrum.