Digital-electronics 简明教程

Digital Electronics - Families

logic family 定义为一组具有诸如逻辑电平、电压电平、开关速度、功耗、抗噪性等技术参数的相似特性的电子电路设计。逻辑门电路在数字电子领域扮演着重要的角色，可以实施各种逻辑函数和运算。

A logic family is defined as a set of electronic circuit designs that have similar characteristics in terms of technical parameters such as logic levels, voltage levels, switching speed, power consumption, noise immunity, etc. The logic families play an important role in the field of digital electronics and allows to implement various logic functions and operations.

根据制造技术，可以将逻辑门电路划分为以下两类：

Depending on the fabrication technology, the logic families can be classified into the following two types −

Unipolar Logic Family
Bipolar Logic Family

一种逻辑门电路以单极型电子设备（如 MOSFET）为其主要元件，称为单极型逻辑门电路。一些单极型逻辑门电路的示例包括 PMOS、NMOS 和 CMOS。

A logic family that utilizes unipolar electronic devices like MOSFETs as their main element is known as a unipolar logic family. Some examples of unipolar logic families include PMOS, NMOS, and CMOS.

另一方面，双极型逻辑门电路是采用双极型电子设备（如晶体管和二极管）的逻辑门电路。双极型逻辑门电路可进一步划分为以下类型 −

On the other hand, a bipolar logic family is one that utilizes bipolar electronic devices such as transistors and diodes. The bipolar logic families can be further classified into the following types −

Resistor-Transistor Logic (RTL)
Diode Transistor Logic (DTL)
Transistor-Transistor Logic (TTL)

现在，我们详细讨论一下每一类逻辑门电路。

Let us now discuss about each of these logic families in detail.

Resistor-Transistor Logic (RTL)

顾名思义，这种逻辑门电路以电阻和晶体管为其主要元件。在 RTL 门电路中，晶体管根据施加在其上的输入电压在截止或饱和区域工作。RTL 门电路是最早用于数字电子设计领域的逻辑门电路之一。

As the name implies, this logic family utilizes resistors and transistors as their key elements. In the RTL family, the transistors operate in the cut-off or saturation regions depending on the input voltage applied to them. The RTL family was one of the earliest logic families used in the field of digital electronic design.

简而言之，在 RTL 门电路中，逻辑电路仅使用电阻和晶体管设计。

In short, in the RTL family, the logic circuits are designed using resistors and transistors only.

例如，双输入电阻晶体管逻辑 NOR 门的电路如下图所示。此处，A 和 B 是输入，Y 是门的输出。

For example, the circuit of a two-input resistor-transistor logic NOR gate is shown in the following figure. Here, A and B are the inputs and Y is the output of the gate.

该 RTL NOR 门针对不同输入组合的操作在以下表格中突出显示 −

The operation of this RTL NOR gate for different input combinations is highlighted in the following table −

Input A	Input B	Transistor T1	Transistor T2	Output Y
0	0	Off	Off	1
0	1	Off	On	0
1	0	On	Off	0
1	1	On	On	0

同样，我们也可以实现其他类型的逻辑门。

Similarly, we can also implement other types of logic gates as well.

Advantages of RTL Family

电阻晶体管逻辑门电路具有一些主要优势：

The following are some key advantages of resistor-transistor logic family −

Electronic circuits designed using RTL logic family are simple in design, as they consist of a minimum number of resistors and transistors.
Circuits manufactured in RTL family are less expensive. These circuits consume less amount of power than circuits implemented in other logic families.

Disadvantages of RTL Family

以下是电阻晶体管逻辑族的几个主要缺点 −

The following are some major drawbacks of resistor-transistor logic families −

RTL circuits have low noise margin. This limitation makes them susceptible to noise and interference.
These circuits have poor fan-out.
RTL circuits are slower in operation due to high propagation delay.
RTL family is not suitable for designing complex circuits due to some practical limitations in terms of design scalability and performance.

Applications of RTL Family

电阻晶体管逻辑 (RTL) 族在数字电子领域中有一些有限的应用。以下是 RTL 族的几个常见应用 −

Resistor-Transistor Logic (RTL) family finds some limited applications in the field of digital electronics. Some common applications of RTL family are listed below −

RTL family is cost-effective and easy to understand and design. For this reason, it is widely used for educational purposes in labs and classrooms to demonstrate digital electronic concepts to students.
RTL family is also used to design circuits for low-frequency control applications. Due to simplicity and ease of implementation, RTL family can be used for prototyping and experimental purposes.

Diode Transistor Logic (DTL)

在二极管晶体管逻辑 (DTL) 族中，二极管和晶体管是用于实现数字逻辑功能的关键元素。

In diode-transistor logic (DTL) family, the diodes and transistors are the key elements combinedly used to implement digital logic functions.

以下示例电路演示了 DTL 族中的电子电路设计。

The following example circuit demonstrates the electronic circuit design in DTL family.

这是一个双输入 NAND 门。其中，A 和 B 是 NAND 门的输入，Y 是该门的输出。

It is a two-input NAND gate. Where, A and B are inputs of the NAND gate and Y is the output of the gate.

此双输入 NAND 门的操作在以下真值表中进行了说明 −

The operation of this two-input NAND gate is explained in the following truth table −

Input A	Input B	Diode D1	Diode D2	Transistor T	Output Y
0	0	Forward biased	Forward biased	Off	1
0	1	Forward biased	Reverse biased	Off	1
1	0	Reverse biased	Forward biased	Off	1
1	1	Reverse biased	Reverse biased	On	0

我们还可以使用二极管晶体管逻辑族实现其他类型的逻辑电路。

We can also implement other types of logic circuits using the diode-transistor logic family.

Advantages of DTL Family

以下是二极管晶体管逻辑族的一些主要优点 −

The following are some key advantages of diode-transistor logic family −

DTL circuits are easy and simple to design and implement, as they consist of only diodes, transistors, and resistors.
DTL circuits are cost-effective as they use basic electronic components like diodes and transistors which are generally cheap.
DTL circuits have good noise immunity. Hence, these circuits are relatively less susceptible to noise and interference than some other types of logic families.
DTL circuits have high fan-out. The power dissipation in DTL circuits is comparatively low.

Limitations of DTL Family

除了上面提到的优势外，DTL 电路还有一些缺点，如下所列：

Apart from the advantages given above, the DTL circuits also have some disadvantages which are listed below −

DTL family circuits require higher amount of power as compared to other logic families.
DTL circuits consist of a greater number of elements than other types of logic families.
DTL circuits have a moderate speed of operation. This is due to high propagation delay.
DTL circuits are not suitable to design more complex digital circuits due to increased complexity and size of the circuit.

Applications of DTL Family

以下是二极管晶体管逻辑家族的一些常见应用：

The following are some common applications of diode-transistor logic family −

DTL family was popular in early digital computers and other digital systems.
These days, DTL circuits are mainly used for educational purposes to explain the implementation of digital logic designs to students.
DTL circuits are used to design custom electronic projects.

Transistor-Transistor Logic (TTL)

晶体管-晶体管逻辑 (TTL) 是数字电子领域中最流行的逻辑族之一。在这个逻辑族中，晶体管是关键功能器件，作为开关运行，以执行逻辑运算。

Transistor-Transistor Logic (TTL) is one of the most popular logic family in the field of digital electronics. In this logic family, the transistor is the key functional element which is operated as a switch to perform the logical operations.

让我们现在了解如何在 TTL 家族中设计逻辑电路。下图显示了一个二输入 NAND 门：

Let us now understand how we can design a logic circuit in TTL family. The following figure shows a two-input NAND gate −

此处，A 和 B 是输入端，Y 是输出端。电路的工作原理总结在以下表格中。

Here, A and B are the input terminals and Y is the output terminal. The operation of this circuit is summarized in the following table.

Input A	Input B	Emitter Junction of Transistor T1	Emitter Junction of Transistor T2	Transistor T2 and T3	Output Y
0	0	Forward biased	Forward biased	Off	1
0	1	Forward biased	Reverse biased	Off	1
1	0	Reverse biased	Forward biased	Off	1
1	1	Reverse biased	Reverse biased	On	0

以相同方式，我们还可以在晶体管-晶体管逻辑 (TTL) 家族中设计其他逻辑门。

In the same manner, we can also design other logic gates in the transistor-transistor logic (TTL) family.

Advantages of TTL Family

以下是 TTL 家族的一些关键优势：

Here are some of the key advantages of TTL family −

TTL circuits have high speeds of operation and hence well-suited to use in high-speed digital systems.
TTL circuits are standardized to make them compatible with a variety of digital circuits and systems.
TTL circuits have good noise immunity. Thus, they are suitable to use in noisy environments.

Disadvantages of TTL Family

尽管如此，TTL 电路还是有一些如上所列的优势。不过，它们也有一些缺点，如下所示 −

Although, TTL circuits have several advantages as listed above. But they also have some disadvantages which are given below −

TTL circuits consume more power than other types of logic families. This limitation makes the TTL circuits less energy efficient.
TTL circuits generate significant heat during operation and this is due to high power consumption. Thus, a proper heat management system is required.
TTL logic levels are relatively strict, requiring specific voltage levels for proper operation. This can sometimes lead to compatibility issues with other logic families.
TTL circuits have a significant propagation delay that limit their use in certain high-speed systems.

Applications of TTL Family

晶体管-晶体管逻辑 (TTL) 系列广泛用于数字电子领域的各种应用。TTL 系列的一些常见应用如下所示 −

Transistor-Transistor Logic (TTL) family are widely used in various applications in the field of digital electronics. Some of the common applications of TTL family are listed below −

TTL circuits are widely used in digital computers, memory units, CPUs, etc.
TTL circuits are also used in embedded systems for different purposes such as interfacing with sensors, processing data in real-time applications, and more.
In communication systems, TTL circuits are for signal conditioning, protocol handling, data processing, etc. TTL circuits are commonly used in a variety of testing and measuring instruments.

Conclusion

总之，逻辑系列是一组共享相同的技术参数（例如逻辑电平、电压电平、处理速度等）的数字电路。在本章中，我们解释了最常用的数字逻辑系列，即 RTL、DTL 和 TTL，以及它们的优势、劣势和应用。

In conclusion, a logic family is a set of digital circuits that share same technical parameters such as logic levels, voltage levels, processing speed, etc. In this chapter, we explained the most commonly used digital logic families viz. RTL, DTL, and TTL, along with their advantages, disadvantages, and applications.