All circuits fall into one of two well-known categories: In a combinational circuit, all circuit outputs are a strict combination of the current circuit inputs, whereas in a sequential circuit, some outputs may depend on past inputs (the sequence of inputs over time).
The category of combinational circuits is the simpler of the two. Practitioners use three major techniques for summarizing the behavior of such circuits.
- logic circuits
- Boolean expressions, which allow an algebraic representation of how the circuit works
- truth tables, which list all possible input combinations and the corresponding outputs