Combinatorial logic circuits are built from a combination of different logic gates with a set of input and a logic network without memory that operates on the inputs to produce the outputs.
Comparator: Comparators are combinatorial logic circuits that are used to check whether a binary value is greater than, less than or equal to another binary value. A comparator is shown in figure 1.
Figure 1: A comparator
Flip-flop: Flip flops are sequential logic circuits that permit the storage of information on it and has two outputs (Q and Q’) that are complement of each other i.e. when the state of Q is HIGH, then that of Q’ is LOW.
Seven-segment display: The seven segment diaplays are used to output a single decimal digit driven by a binary coded decimal nibble. It is a combinatorial logic circuit as the set of combinatorial logic turns off or on each segment of the display to create the digit that is displayed. They are used in digital meter displays.
Latch: A latch being a sequential logic circuit is the most fundamental type of flip-flop circuit and is constructed using either NAND or NOR gates.
CPU: The CPU is a combination of sequential and combinatorial logic circuits controlling the operations of a computer through the execution of instructions.
Adder (Full / Half): Adders are combinatorial logic circuits that are used to carry out arithmetic addition operations. There are half adders and full adders. Half adders are 1-bit adders that do binary addition using a combination of XOR and AND gates. The full adder can add 3 bits at a time using three inputs and are made up of 2 half adders and one OR gate. Adders are used in the ALU of computers.
Finite State Machine: A finite state machine is used to implement algorithms in hardware consisting of a set of registers, a state vector and logic that advances the state for each clock cycle based on the current state and the external input.
Multiplexer: Multiplexers are combinatorial logic circuits that allows for the picking of only one of n-inputs at a point in time to be directed to an output.
Counters: A counter is a sequential logic circuit that has an input line known as the clock and multiple output lines. A counter possesses memory since it has to remember its past state and can be synchronous or asynchronous.
Subtractor: Subtractors are also combinatorial logic circuits like adders carrying out arithmetic subtraction operations. The half subtractor can carry out just operations on just 2 bits at a time while the full subtractor can handle more than 2 bits at a time.
De-multiplexer: Demultiplexers are the reverse of multiplexers as they allow only one of n outputs to be chosen from a single input.
Analog-to-Digital Converter (ADC): Analog to digital converters convert analog signals to digital signals through the process of sampling of the analog signal at regular intervals and quantization.
Bus: The bus is the electrical connection between the components in a circuit for the transmission of electrical signals between the components.
Clock: Clocks are logic circuits producing timing signals for sequential logic circuits and usually consists of an astable circuit that produces pulses that are constant in frequency, have the correct logic levels and fast rising and falling edges to the pulses.
Digital-to-Analog Converter (DAC): Digital to analog converters convert digital signals to analog signals using demultiplexers.
Register: Registers are sequential logic circuits made up of groups of flip-flops and are used for data storage.
WORKS CITED
1. Kuphaldt, T.R. (2005). Lessons In Electric Circuits, Volume I - DC. PDF. Retrieved from http://www.ibiblio.org/obp
2. Theraja, B.L. and Theraja, A.K. (2007). A Textbook of Electrical Technology. S. Chand and Company Ltd., New Delhi, ISBN 81-219-2441-3.
