Basically, there are two types of signals, i.e., analog signals and digital signals.
从基本上来看，信号分为两种类型，即模拟信号和数字信号。

• Analog signals模拟信号

Analog signal is a continuous time-varying signal that has an infinite amount of samples in it. These analog signals are further divided into composite and simple analog signals. Sinusoidal waves being simple analog signals and all the others, composite signals, are made from the combination of multiple variants of simple sinusoidal waves.

模拟信号是一个连续的时变信号，它含有无限数量的采样。这些模拟信号又进一步分为复合模拟信号和简单模拟信号。正弦波是简单的模拟信号，其他的都是合成信号，是由简单正弦波的多种变体组合而成的。

• Digital signals数字信号

Digital signals also carry data just like analog signals, but in the case of digital signals, these values are discrete. It represents data in the form of a discrete sequence of values and is defined by interval or the bit rate. The digital signals thus contain a set of numbers that depict the samples of a continuous variable.

数字信号也像模拟信号一样携带数据，但在数字信号的情况下，这些值是离散的。它以离散值序列的形式表示数据，并由区间或比特率定义。因此，数字信号包含一组描述连续变量样本的数字。

The picture above represents the same signal in both analog and digital form. Note that the edges in the digital signal represent the point at which the sample was taken.

上图分别以模拟和数字形式表示相同的信号。请注意，数字信号中的边缘代表采样点。

注：

在数字电路中，无源晶振输出为正弦波信号，经由整形电路整形为方波后，供给下级电路。有源晶振一般输出为方波为主，可直接供给下级电路使用。