Encoder:  An Encoder is a combinational circuit that has maximum of 2  input lines and ‘n’ output n lines; hence it encodes the information from 2  inputs into an n-bit code.  It will produce a binary code equivalent to the input, which is active High.

(4 to 2) line Encoder:  The 4 to 2 Encoder consists of four inputs D0 D1 D2 D3, and two outputs A and B.  (4 to 2) Encoder encodes the information from 4 inputs into a 2-bit code.

(8 to 3) line Encoder: The 8 to 3 Encoder or octal to Binary encoder consists of 8 inputs: D7 to D0 and 3 outputs A, B and C. Each input line corresponds to each octal digit and three outputs generate corresponding binary code.