Decoders

Decoders are devices or circuits that convert encoded information into a form suitable for use. In digital electronics, a decoder is typically a combinational circuit that takes n input signals and activates one of up to 2^n outputs. When an enable input is used, the circuit asserts the selected output only if enable is true, otherwise all outputs stay inactive. Common examples include 2-to-4, 3-to-8 decoders, and specialized forms such as BCD-to-seven-segment decoders.

Decoders serve various roles: address decoding in memory and microprocessors to select a particular location; display drivers that convert binary data to a human-readable form; and instruction decoders within CPUs that translate opcodes into control signals. The outputs are often one-hot, with exactly one line active for a given input pattern.

Beyond digital logic, the term decoder also refers to devices that reconstruct original data from encoded media or communications signals. This includes audio and video codecs, where compressed bitstreams are decoded to usable data, and error-correcting decoders such as Reed-Solomon, LDPC, or Huffman-based decoders used in CDs, DVDs, QR codes, and network protocols. Decoders are the inverse of encoders; some circuits function as decoders by implementing a demultiplexer with gating, while others are dedicated blocks optimized for specific codes. Design considerations include speed, fan-out, power consumption, and integration in integrated circuits or microprocessors.