Decoders: Turning Binary into One Active Line

Lesson notes

Key points

• A decoder is a combinational circuit with n inputs and up to two to the power n outputs, activating exactly one.
• In a two-to-four decoder, each output is one minterm, like D-zero equals A-bar B-bar.
• Because every minterm is available, a decoder plus an OR gate can implement any Boolean function.
• Real systems use decoders for memory address selection and for enabling one chip on a shared bus.

Definitions

Decoder

n-input circuit that activates exactly one of 2ⁿ outputs matching the binary input code

Takeaway: A decoder outputs every minterm, so it can build any function.

DecoderMintermsSum of mintermsAddress decoding