Digital-electronics 简明教程
OR Gate in Digital Electronics
在数字电子技术中， OR Gate 是一个基本逻辑门，具有两个或多个输入线和一个输出线。它执行布尔加法函数。
In digital electronics, an OR Gate is a basic logic gate having two or more input lines and one output line. It performs the Boolean addition function.
在本章中，我们将讲解或门理论。在此，我们将涵盖或门的定义、逻辑符号、布尔表达式、真值表、操作和电路。
In this chapter, we will explain the theory of the OR gate. Here, we will cover the definition of OR gate, its logic symbol, Boolean expression, truth table, operation, and circuits.
因此，让我们从或门的基本定义开始。
So, let’s get started with the basic definition of OR gate.
What is an OR Gate?
或门是一种用于执行逻辑加法操作的逻辑门。它可以有两个或更多个输入和一个输出。
An OR gate is a type of logic gate used to perform logical addition. It can have two or more inputs and one output.
仅当或门的全部输入都为低或逻辑 0 时，它的输出才为低或逻辑 0。对于输入的其余组合，或门的输出为高或逻辑 1。
The output of the OR gate is low or logic 0 only when all its inputs are low or logic 0. For rest input combinations, the output of the OR gate is high or logic 1.
图中显示了两输入或门和三输入或门的逻辑符号。
The logic symbols for a two-input and a three-input OR gate are shown in the following figure.
其中， A, B 和 C 是输入线， Y 是输出线。
Here, A, B, and C are the input lines and Y is the output line.
Truth Table of OR Gate
真值表是显示不同输入组合和输出之间关系的表格。
The truth table is a table that shows the relationship between different input combinations and output.
以下是双输入 OR 门的真值表 -
The following is the truth table for a two-input OR gate −
Input |
Output |
A |
B |
Y |
0 |
0 |
0 |
0 |
1 |
1 |
1 |
0 |
1 |
1 |
1 |
下表显示了三输入 OR 门的真值表 -
The following table shows the truth table for a three-input OR gate −
Input |
Output |
A |
B |
C |
Y |
0 |
0 |
0 |
0 |
0 |
0 |
1 |
1 |
0 |
1 |
0 |
1 |
0 |
1 |
1 |
1 |
1 |
0 |
0 |
1 |
1 |
0 |
1 |
1 |
1 |
1 |
0 |
1 |
1 |
1 |
1 |
1 |
从这两个真值表中，我们可以观察到，仅当 OR 门的所有输入均为逻辑 0 或低时，OR 门的输出才为逻辑 0 或低。否则，OR 门的输出将为高或逻辑 1。
From these two truth tables, we can observe that the output of the OR gate is logic 0 or low, only when all the inputs to the OR gate are logic 0 or low. Otherwise, the output of the OR gate is high or logic 1.
Boolean Expression of OR Gate
布尔表达式是一种逻辑函数，描述了 OR 门的输入和输出之间的数学关系。
The Boolean expression is a logical function that describes the mathematical relationship between inputs and output of the OR gate.
双输入 OR 门的布尔表达式如下 -
The Boolean expression of a two-input OR gate is given below −
Y = A + B
其中， A 和 B 是输入变量， Y 是输出变量。此表达式可译为“Y 等于 A 或 B”。此处，符号“+”代表“或”运算。
Here, A and B are input variables and Y is the output variable. This expression is read as "Y is equal to A OR B". Here, the "+" sign represents the OR operation.
类似地，三输入 OR 门的布尔表达式如下 -
Similarly, the Boolean expression of a three-input OR gate is given below −
Y = A + B + C
其中， A, B 和 C 是输入， Y 是输出。
Here, A, B, and C are the inputs and Y is the output.
同样，我们可以将此表达式扩展至任意数量的输入变量。
In the same way, we can extend this expression to any number of input variables.
Working of OR Gate
以下对不同输入组合的双输入 OR 门操作进行了描述 -
The operation of a two input OR gate for different input combinations is described below −
-
If A = 0 and B = 0, the output of the OR gate is Y = 0.
-
If A = 0 and B = 1, the output of the OR gate is Y = 1.
-
If A = 1 and B = 0, the output of the OR gate is Y = 1.
-
If A = 1 and B = 1, the output of the OR gate is Y = 1.
这个理论解释说，当应用于 OR 门的两个输入都为低电平或逻辑 0 时，OR 门的输出也为低电平或逻辑 0，否则为高电平或逻辑 1。
This theory explains that when both inputs applied to an OR gate are low or logic 0, the output of the OR gate is also low or logic 0, otherwise it is high or logic 1.
同样，以下对三输入 OR 门的工作原理进行了说明 -
Similarly, the working of a three-input OR gate is described below −
-
If A = 0, B = 0, and C = 0, the output of the OR gate is Y = 0.
-
If A = 0, B = 0, and C = 1, the output of the OR gate is Y = 1.
-
If A = 0, B = 1, and C = 0, the output of the OR gate is Y = 1.
-
If A = 0, B = 1, and C = 1, the output of the OR gate is Y = 1.
-
If A = 1, B = 0, and C = 0, the output of the OR gate is Y = 1.
-
If A = 1, B = 0, and C = 1, the output of the OR gate is Y = 1.
-
If A = 1, B = 1, and C = 0, the output of the OR gate is Y = 1.
-
If A = 1, B = 1, and C = 1, the output of the OR gate is Y = 1.
这个理论还解释说，只有当所有三个输入都为低电平或逻辑 0 时，OR 门的输出才为低电平或逻辑 0。
This theory also explains that the output of an OR gate is low or logic 0, only when all the three inputs are low or logic 0.
OR Gate using Transistors
我们可以使用晶体管实现 OR 门逻辑电路。以下图示说明了使用 BJT 晶体管实现二输入 OR 门。
We can implement the OR gate logic circuit using transistors. The implementation of a two-input OR gate using BJT transistors is shown in the following figure.
该 OR 门电路也称为晶体管-晶体管逻辑 (TTL) OR 门。
This OR gate circuit is also referred to as transistor-transistor logic (TTL) OR gate.
Working of Transistor OR Gate
上述晶体管 OR 门电路的操作如下 -
The operation of the above shown transistor OR gate circuit is explained below −
When both inputs A and B are low ，即 A 和 B 都连接到低电压 (0 V)，晶体管 Q1 和 Q2 保持关闭并充当开路开关。结果是输出线将直接连接到地电位。这使得电路输出为低电平或逻辑 0。
When both inputs A and B are low, i.e., both A and B are connected to a low voltage (0 V), the transistors Q1 and Q2 remain off and act as open switches. The result is that the output line will directly connect to the ground potential. This makes the output of the circuit low or logic 0.
If the input A is low and the input B is high 时，晶体管 Q1 将关闭，并且晶体管 Q2 将开启并充当闭合开关。因此，电源电压 VCC 将通过晶体管 Q2 连接到输出线路。因此，电路的输出为高电平或逻辑 1。
If the input A is low and the input B is high, the transistor Q1 will be off, and the transistor Q2 will turn on and acts as a closed switch. Thus, the supply voltage VCC will connect to the output line through the transistor Q2. Consequently, the output of the circuit is high or logic 1.
If the input A is high and the input B is low 时，晶体管 Q1 将导通，而晶体管 Q2 将充当开路开关。因此，输出线将通过晶体管 Q1 连接到电源 VCC。因此，电路的输出为高电平或逻辑 1。
If the input A is high and the input B is low, the transistor Q1 will conduct, while the transistor Q2 will act as open switch. Thus, the output line will connect to the power supply VCC through the transistor Q1. Consequently, the output of the circuit is high or logic 1.
When both inputs A and B are high 时，晶体管 Q1 和 Q2 都将导通并充当闭合开关。输出线将通过两个晶体管连接到电源 VCC，这会使得电路的输出为高电平或逻辑 1。
When both inputs A and B are high, both transistor Q1 and Q2 will conduct and act as the closed switches. The output line will connect to the power supply VCC through both transistors, this makes the output of the circuit high or logic 1.
该理论说明，当电路的两个输入都连接到逻辑 0 或低电平时，输出为低电平或逻辑 0；否则，输出为高电平或逻辑 1。因此，此电路实现了或门功能。
This theory explains that when both inputs of the circuit are connected to logic 0 or low signal, the output is low or logic 0, otherwise the output is high or logic 1. Hence, this circuit implements the OR gate function.
我们可以在电路中添加更多晶体管来实现更高阶的或门。
We can add more transistors to the circuit to implement a higher order OR gate.
OR Gate using Switches
我们还可以使用电气开关、电池和灯泡来实现或逻辑运算。下图描绘了双输入或门的开关电路图。
We can also use electrical switches, a battery, and a lamp to implement the OR logic operation. The following figure depicts the switching circuit diagram of a two-input OR gate.
该电路的工作原理如下所述 −
The working of this circuit is explained below −
When both switches A and B are open 时，有电流流经的闭合路径。因此，灯泡将保持熄灭，这表示低电平或逻辑 0 输出。
When both switches A and B are open, there is closed path for the flow of current. Hence, the lamp will remain off which represents the low or logic 0 output.
If the switch A is open and the switch B is closed 时，有电流流经开关 B 的闭合路径。在这种情况下，灯泡将点亮并表示高电平或逻辑 1 输出。
If the switch A is open and the switch B is closed, there is a closed path for the current flow through the switch B. In this case, the lamp will glow and represents the high or logic 1 output.
If the switch A is closed and the switch B is open 时，将有电流流经开关 A 的闭合路径。在这种情况下，灯泡将点亮，这表示高电平或逻辑 1 输出。
If the switch A is closed and the switch B is open, there will be a closed path for the current to flow through the switch A. In this case, the lamp will glow that represents the high or logic 1 output.
If both switches A and B are closed 时，将有电流流经的闭合路径。这也将点亮灯泡并表示高电平或逻辑 1 输出。
If both switches A and B are closed, there will a closed path for the current to flow. This will also turn on the lamp and represents the high or logic 1 output.
这样，上面显示的开关电路就可以实现或门运算。我们可以在并联中添加更多开关来实现更高阶或门逻辑。
This way, the above shown switching circuit implements the OR gate operation. We can add more switches in parallel to implement a higher order OR gate logic.
OR Gate IC
在实践中，或门采用集成电路或 IC 的形式。最流行的或门 IC 是 IC 7432，它是一种四双输入或门 IC。它有四个双输入或门。
In practice, the OR gate is available in the form of integrated circuits or ICs. The most popular OR gate IC is IC 7432 which is a Quad 2-input OR gate IC. It has four two-input OR gates.
下图描绘了或门 IC 7432 的管脚和框图。
The following figure depicts the pin and block diagram of the OR gate IC 7432.
或门 IC 7432 有 14 个管脚，它是一种晶体管到晶体管逻辑 (TTL) 或门 IC。
The OR gate IC 7432 has 14 pins and it is a transistor-transistor logic (TTL) OR gate IC.
Conclusion
综上所述，或门是一种基本逻辑门，有两个或多个输入线和一个输出线。仅当所有输入为低电平时，它才会产生低电平或逻辑 0 输出；否则，它将产生高电平或逻辑 1 输出。
In conclusion, the OR gate is a basic logic gate having two or more input lines and one output line. It produces a low or logic 0 output only when all its inputs are low, otherwise it produces a high or logic 1 output.
在本章中，我们解释了或门的理论。在这里，我们仅介绍了两个和三个输入或门。但同样的理论和技术解释对于具有任意数量输入的或门是有效的。
In this chapter, we explained the theory of OR gate. Here, we covered only two and three-input OR gates. But the same theoretical and technical explanation is valid for OR gate with any number of inputs.