Circuits to Expressions

Very similar to the way we figure out Truth Table from Circuit, we deduce Expressions as well. The basic methods like finding intermediate outputs and naming them accordingly etc are common in both the methods.

Following are the important rules to be followed for deducing Expressions from circuits. See the following:

• Identify all those connections in the circuit where output of some gate is going as input to some other gate. In all these connections mark intermediate output like F₁, F₂, F₃,.... F_n. Meanwhile ignore all the fresh inputs and final output.
• Based on the specific gates, deduce the expressions for intermediate outputs and keep on doing that till expressions of all intermediate outputs are not generated.
• Now the expression of final output is easy to generate based on all the expressions of intermediate outputs.

See the following example:

Here, F₁ is AND of A and B, hence it becomes: (A . B).
Similarly F₂ is NOT of A, hence it becomes: A'.
Now since F₃ is OR of F₁ and F₂, the final output becomes: (A . B) + A'.