Digital-electronics 简明教程
Logic Levels and Pulse Waveforms
digital system 是一种利用二进制数制工作的电子系统。换言之，数字系统是一种二态电子系统，用于表示两个二进制数 0 和 1，其中 0 表示系统中低或“关”状态，1 表示高或“开”状态。
A digital system is a type of electronic system that utilizes the binary number system to work. In other words, a digital system is a two-state electronic system used to represent two binary digits 0 and 1, where 0 represents the low or "off" state and 1 represents the high or "on" state of the system.
在数字电子领域中，不同的电压等级用于表示数字信号中的两个二进制值，即 0 和 1。这些电压等级被称为 logic levels 。
In the field of digital electronics, different voltage levels are used to represent the two binary values, i.e., 0 and 1 in a digital signal. These voltage levels are known as logic levels.
在本章中，我们将学习逻辑电平和脉冲波形的概念。
In this chapter, we will learn the concept of logic levels and pulse waveforms.
What is a Logic Level?
在数字电子中，表示特定二进制值 0 或 1 的电压电平称为 logic level 。在此，二进制值 0 表示低电压电平，而二进制值 1 表示高电压电平。
In digital electronics, a voltage level that represents a specific binary value either 0 or 1 is called a logic level. Here, the binary value 0 represents the low voltage level while the binary value 1 represents the high value level.
因此，逻辑电平可分为以下两类：
Hence, the logic levels can be classified into the following two types −
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High Logic Level
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Low Logic Level
让我们详细讨论这两种逻辑电平。
Let’s discuss these two logic levels in detail.
High Logic Level
对于数字系统，该系统能够处理而不损坏的最大电压电平接近的电压电平称为 high logic level 。
In the case of a digital system, the voltage level closer to the maximum voltage level that the system can handle without getting damaged is called high logic level.
高逻辑电平由二进制数字“1”表示。高逻辑电平的电压电平取决于用于设计系统的技术标准。通常，介于 2 V 和 5 V 之间的电压值表示高逻辑电平或 1。
The high logic level is represented by the binary digit "1". The voltage level for a high logic level depends on the technological standard used to design the system. Typically, the voltage value between 2 V and 5 V represents the high logic level or 1.
Low Logic Level
在数字系统中， low logic level 被定义为系统将保持 OFF 状态的最大电压电平。
In a digital system, the low logic level is defined as the maximum voltage level for which the system will remain in the OFF state.
低逻辑电平由二进制数字“0”表示。与高逻辑电平类似，低逻辑电平的电压电平取决于用于设计系统的技术标准。在实际应用中，介于 0 V 和 0.8 V 之间的电压值表示低逻辑电平或逻辑 0。
The low logic level is represented by the binary digit "0". Similar to the high logic level, the voltage level for a low logic level depends on the technology standard used to design the system. In actual practice, the voltage value between 0 V and 0.8 V represents the low logic level or logic 0.
在大多数实际数字系统中，接地电压用于表示低逻辑电平。
In most practical digital system, the ground voltage is used to represent the low logic level.
Note - 介于 0.8 V 和 2 V 之间的电压范围称为不确定逻辑范围。如果数字信号介于 0.8 和 2 V 之间，则系统的响应不可预测。
Note − The voltage range between the voltage values 0.8 V and 2 V is known as the indeterminate logic range. If a digital signal lies between the value 0.8 and 2 V, the response of the system is not predictable.
What is a Pulse?
pulse 是一种电子信号类型，可以突然在两个可能状态（即高状态和低状态）之间切换。
A pulse is a type of an electronic signal that can change suddenly between two possible states i.e., high state and low state.
pulse waveform 用于表示脉冲转换的图形。 脉冲对于数字系统、通信系统及许多其他电子设备和电路的运行非常重要。
The graph used to represent the transition of a pulse is called the pulse waveform. Pulses are very important in the operation of digital systems, communication systems, and many other electronics devices and circuits.
根据开关特性，脉冲可分为以下两类：-
Depending on the switching characteristics, the pulses can be classified into the following two types −
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Positive Pulse − When a signal normally goes from low logic level to the high logic level and then returns to its normal low logic level, then it is called a positive pulse.
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Negative Pulse − When a signal normally goes from high logic level to the low logic level and then returns to its normal high logic level, then it is known as a negative pulse.
正脉冲和负脉冲的脉冲波形如图所示。
The pulse waveforms for positive and negative pulses are depicted in the following figure.
脉冲有两个边缘，即 leading edge 和 trailing edge 。
A pulse has two edges namely, a leading edge and a trailing edge.
对于正脉冲，从低逻辑电平变为高逻辑电平的边缘称为前沿，从高逻辑电平变为低逻辑电平的边缘称为后沿。
In the case of a positive pulse, the edge going from low logic level to high logic level is called the leading edge, and the edge going from high logic level to low logic level is called the trailing edge.
对于负脉冲，从高逻辑电平变为低逻辑电平的边缘称为前沿，而从低逻辑电平变为高逻辑电平的边缘称为后沿。
In the case of a negative pulse, the edge going from high logic level to low logic level is called the leading edge, whereas the edge going from low logic level to high logic level is called the trailing edge.
上图所示的正脉冲和负脉冲波形是理想脉冲波形，因为它们的上升沿和下降沿瞬时变化，即在零时间内。但在实际应用中，脉冲的边缘不会瞬时地从低逻辑电平变为高逻辑电平，或从高逻辑电平变为低逻辑电平。
The positive and negative pulse waveforms shown in the above figure are ideal pulse waveforms, because their leading and trailing edges change instantaneously i.e., in zero time. But in actual practice, the edges of pulses do not change instantaneously from low logic level to high logic level or from high logic level to low logic level.
用有限时间从低逻辑电平变为高逻辑电平，反之亦然的脉冲波形称为 non-ideal pulse waveforms 。
The pulse waveforms that take a finite time to change from low logic level to high logic level and vice-versa are known as non-ideal pulse waveforms.
对于非理想脉冲波形，脉冲从低逻辑电平变为高逻辑电平所用的时间称为 rise time 。 脉冲从高逻辑电平变为低逻辑电平所用的时间称为 fall time 。
In the case of a non-ideal pulse waveform, the time taken by the pulse to go from low logic level to high logic level is called the rise time. The time taken by the pulse to go from the high logic level to the low logic level is called the fall time.
Types of Pulse Waveforms
用于数字系统的脉冲波形主要分为以下两类：-
The pulse waveforms used in digital systems are mainly classified into the following two types −
Conclusion
总而言之，“逻辑电平”是数字系统中用于表示系统状态的概念。 数字系统中有两个可能的逻辑电平，即高逻辑电平和低逻辑电平。 高逻辑电平用二进制 1 表示，而低逻辑电平用二进制 0 表示。
In conclusion, "logic level" is a concept used in digital systems to represent the state of the system. There are two possible logic levels in the case of digital systems namely, high logic level and low logic level. The high logic level is represented by the binary 1 while the low logic level is represented by the binary 0.
数字信号或脉冲的图形表示称为“脉冲波形”。 脉冲波形用于表示数字信号的脉冲转换或脉冲或数字系统的状态。 在本章中，我们讨论了逻辑电平和脉冲波形的概念。 在下一章中，我们将了解“数字系统的组件”。
The graphical representation of a digital signal or a pulse is termed as the "pulse waveform". Pulse waveforms are used to represent the transition of a pulse or digital signal or the states of a digital system. In this chapter, we have discussed the concept of logic levels and pulse waveforms. In the next chapter, we will learn about "components of a digital system".