Almost daily, engineers come across terms like digital circuits, especially while studying Boolean operations. Often engineers ignore such terms, maybe because they’re intimidated by the complexity of a vast topic like this. Well, ignorance is bliss but not always and in this situation it’s surely not. Nevertheless, it’s never too late to start.
This article promises to impart the basic knowledge related to digital circuits, right starting from what it is to the different uses it serves.
Digital electronics operate on digital signals and a digital circuit is an integral component of digital electronics. It is used in various electronic devices for different purposes. The main purpose of this circuit is the transmission of power to the different components of the circuit. It can perform different types of Boolean operations. Such circuits are used to make logic gates and transistors. These circuits consume relatively less power as compared to analog circuits.
First thing first: What is a digital circuit?
A digital circuit is a type of circuit that operates on different logic gates. The logic gates are used to differentiate between various power signals. It can be used to transmit the power signal to the different parts of the electronic device through various gates. This will help to create an output signal which is directly proportional to the energy level of the input signals. Most of these circuits consist of analog components. They have a more complex design as compared to that of analog circuits.
Furthermore, the input to any digital circuit is in the binary form “0’s” and “1’s”. The output obtained on processing raw digital data is of a precise value. These circuits can be represented in 2 ways either in a combinational way or a sequential way. Digital circuits use transistors to create logic gates in order to perform Boolean logic.
Examples of digital circuit:
The following are the examples of digital circuits:
• Mobile phones
• Calculators, etc.
Basic Components of Digital Circuit
Whilst studying digital circuit, it’s really very important to learn about the basic components of digital circuits. All those components are discussed below:
1. Diodes: Diodes are used to allow the flow of current in a particular direction only. Diodes are made up of semiconductor materials.
2. Transistor: Transistor is basically a semiconductor device that has three terminals. It can be used as an amplifier or a switching device.
3. Resistor: A resistor is a passive component that is used to oppose the flow of current in a circuit. Resistors follow Ohm’s law. Resistors are of two types: Fixed resistors and variable resistors.
• In a fixed resistor, we are not able to alter the value of resistance.
• In a variable resistor, the value of resistance can be changed as per our requirement.
4. Capacitor: A capacitor consists of two conducting plates between which there is an insulator. Capacitors are mainly used to store electrical energy in an electric field.
5. Inductors: Inductors are used to store electric energy in a magnetic field. It is also used to resist changes in current.
6. Battery: Battery is another important component of an electronic circuit which is used as a source of power. A battery converts chemical energy into electrical energy.
7. Logic Gates: Logic gates are the most basic components of a digital circuit. They have two or more inputs and they produce one output. Logic gates are basically of three types:
• Basic gates: In this type of gates, we can represent the Boolean functions either in the sum of products form or in the product of sums form. The basic logic gates are AND, OR and NOT gates.
• Universal gates: These are the logic gates using which all other gates can be constructed. NAND and NOR are the two universal gates.
• Special gates: EX-OR and EX-NOR are the two special gates as they are the two special cases of OR and NOR gates.
8. Switch: A switch is another component of an electric that is capable of regulating the flow of electric current through the circuit.
More about Logic Gates:
As already discussed, logic gates are an electronic component that is implemented using a Boolean function. Gates are usually implemented using diodes, transistors, and relays. There are different types of logical gates they are, AND, OR, NOT, NANAD, NOR, XOR. Among which AND, OR, NOT are basic gates and NAND and NOR are the universal gate. For example, AND gate representation has 2 inputs and one output.
The 2 Different Types of Digital Circuits:
1. Combinational Logic Circuit
The combinatorial logic circuit is made up of logic gates whose output is determined by the present input only. The output does not depend on the previous outputs of the circuit. Basically,it is a combination of various logic gates like AND, OR, NOT. This type of circuit is widely used in the electronic industries for various purposes. The circuits are designed by combining the different logic gates. Two types of combinatorial circuits are encoder and decoder. Other examples include half adder, full adder, and multiplexer.
2. Sequential Logic Circuit
The sequential logic circuit is one such circuit in which the output of the circuit not only depends on the present input but also on the past outputs. Sequential circuits have the ability to store the past output in various memory devices. They are designed using finite state machines. Different kinds of sequential logic circuits are counters and flip flops. Sequential circuits are again of three types: clock-driven circuits, event-driven circuits, and pulse-driven circuits.
Basics of Digital Circuits
Digital circuit design was first started up with a design of relays, later vacuum tubes, TTL Transistor-Transistor Logic, Emitter coupled logic, and CMOS logic. These designs use a large number of logical gates like AND, OR, NOT, etc integrated on a single IC. The input and output of digital data are represented in the logical truth table and timing diagram.
Digital data is represented in a logical format, that is in “0” and “1” format. Where logic 0 represents that the signal is low or “GND” and logic1 represents the signal is high or connected to “VCC” supply as shown below:
Logical Truth Table
A logical truth table is a mathematical representation of the performance of digital signal when passed through the digital circuit. The table consists of 3 columns they are the clock column, input column, and the output column. For example, NOT gate logic table is represented as follows:
Digital signal behavior is represented in time domain format, for example, if we consider NOT logic gate truth table the timing diagram is represented as follows when the clock is high, the input is low then the output goes high. Similarly, when the input is high then the output goes low.
Digital Circuit Design
Digital circuits can be designed using the various components which are generally used in the circuit. Here, we have shown a simple circuit consisting of a few important components. The following circuit has a diode, a resistor, an inductor, a capacitor, and a power supply.
The following circuit is that of a full-adder which can be used to add the bits of the circuit. The circuit performs Boolean operations on the input bits to produce the result. The circuit consists of two XOR gates, two AND gates, and an OR gate.
Summing up, it can be designed in the following ways:
• Using sequential system representation and combinational system representation
• Using the mathematical methods by reducing logical redundancy algorithms like K-Map, Boolean Algebra, QM algorithm, binary decision diagrams, etc.
• Using data flow machines which consist of registers and buses or wire. Data is communicated among various components using buses and registers. These machines are designed using hardware description languages like VHDL or Verilog.
• A computer is a general-purpose register transfer logic machine designed by using a microprogram and microsequencer processor.
Advantages of Digital Circuits
• A digital circuit can be used to rectify noise and produce correct signals.
• As digital circuits are made up of basic logic gates, they are not very expensive.
• Digital circuits can be used for precise representation of the circuit
• Switching time is much faster as compared to that of analog circuits.
Disadvantages of Digital Circuits
• Digital circuits consume more energy as compared to any other circuits.
• Digital circuits require a power supply.
Applications of Digital Circuits
• It’s an integral part of electronic devices.
• It can be used for designing the display of your watch or a countdown timer.
• We use digital circuits in complex processes like Rocket Science and Quantum Computing.
• Digital circuits are also used in traffic lights and automatic glass doors in offices and restaurants.
So, in this article, as promised, we have covered all the basics of digital circuits. We have summed up the basic components and the various advantages and disadvantages of digital circuits. We have also included different examples of digital circuits.