Even though CAD tools are used to create combinational logic circuits in practice, it is important that a digital designer should learn how to generate a logic circuit from a specification. Understanding this process allows the designer to better use the CAD tools, and, if need be, to design critical logic sub-circuits by hand.
The design procedure for combinational logic circuits starts with the problem specification and comprises the following steps:
Design a circuit that has a 3-bit binary input and a single output (Z) specified as follows:
From the truth table, we use one of the following 2 methods to obtain the simplified boolean expression
Draw a logic diagram that represents the simplified Boolean expression. Verify the design by analysing or simulating the circuit.
Design a BCD to 7 segment decoder circuit for segment e that has a 4-bit binary input and a single output (7e) specified by the truth table
Obtained from the BCD to 7 segment decoder truth table. Note that 7e is obtained from column e.
From the truth table, we use one of the following 2 methods to obtain the simplified boolean expression
Draw a logic diagram that represents the simplified Boolean expression. Verify the design by analysing or simulating the circuit.
A bank wants to install an alarm system with 3 movement sensors.
To prevent false alarms produced by a single sensor activation, the alarm will be triggered only when at least two sensors activate simultaneously.
Design a circuit that has a 3-bit binary input and a single output that
Given two input bits A and B, produce three outputs X, Y, and Z so that