Digital Logic Design Course

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Introduction to Digital Logic Design

Digital Logic is an important concept for digital systems at a hardware level. Most computers that we have today can be considered as digital systems. Digital systems perform tasks within the hardware by taking in inputs and creating outputs with circuits. Circuits from digital systems only have two states, which are on and off. We do not care what exact voltage they have since we want them to perform operations based on only those two states. For an example, let us say that we have a combination of what parts of the circuit are off and on. We get certain outputs for that combination. Now, let us say that we have a different combination of states for the same circuit. The outputs may be different. Outputs really depends on the circuit configuration and system inputs. To summarize this, systems perform certain tasks that are determined by what parts of the circuit are on and what parts are off.

Reality of Off and On States

The off and on states are not perfect in the real world. Voltages in digital circuits are not truly zero when they are off since they still have little voltages going on. Instead of saying off and on states, we can say low and high states respectively. Furthermore, binary numbers 0 and 1 represent the low and high states respectively. Those discrete values that represent those states are used to perform operations in systems symbolically. That will be useful for digital circuit analysis and design, and you will see why.

For an example, let us say that we are using a 5-volt source that connects to a circuit. When we turn off the circuit, the voltage would be around 0.5 volts instead of 0. We need to set a range for voltage so the 0.5 volts can be qualified as the low state. Instead representing zero as the low state, we can use a range from 0 – 1 volt to represent the low state. When the circuit is turned on, the voltage is not truly 5 volts either. It can be around 4.5 volts. We also need to set a range for the high state. The range that represents high state can be from 4 to 5 volts. Remember that the binary number 0 represents the low state while the binary number 1 represents the high state. This example shows that this is a good reason to use binary numbers.

Types of Digital Circuits

There are two types of digital circuits, which are combinational and sequential. Combinational circuits depend on present inputs to the digital systems and can use them to create outputs. The sequential circuits depend on past and present inputs.  They can do what combinational circuits do and can also store inputs for future use. Thus, they are like memories in our computers. In future lessons, we will go over more about the combinational circuit first and then sequential circuit afterwards in details.


After taking this Digital Logical Design course, you will have a strong foundation of analyzing and designing digital systems. Digital logic is an important concept to follow in order to analyze and design digital computers and electronics successfully. When you are ready to follow this course, proceed to the next lesson that will cover number systems.

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