Encoder
An encoder is a device, circuit, or algorithm that converts information from one format or code to another, for purposes such as data compression, error correction, or motion feedback. In electromechanical systems, encoders provide feedback on position, velocity, or direction by converting mechanical motion into electrical signals, typically digital pulses, for use in control systems, robotics, and automation.[1][2] These devices are essential in applications requiring precise motion detection, such as motor control and industrial machinery, where they translate rotary or linear displacement into countable signals readable by microcontrollers or computers.[3] Encoders are broadly classified into two main types: incremental and absolute. Incremental encoders generate pulses relative to a starting position, allowing calculation of change in position or speed but requiring a reference point to determine absolute location; they often use quadrature encoding with two channels (A and B) phased 90 degrees apart to detect direction.[3][4] Absolute encoders, in contrast, output a unique code for each position without needing a reference, making them suitable for applications where power loss or system restarts cannot afford repositioning, such as elevators or CNC machines.[5] Technologies underlying encoders include optical, magnetic, and mechanical methods. Optical encoders employ a light source, photodetector, and patterned disk to produce signals, offering high resolution (up to thousands of pulses per revolution) and reliability in clean environments.[6] Magnetic encoders use hall-effect sensors and magnetic fields for robust performance in harsh conditions like dust or vibration, while mechanical encoders rely on contact switches for cost-effective but less durable solutions.[7] In digital electronics, encoders refer to combinational logic circuits that map multiple active inputs to a binary code output, serving as the inverse of decoders and facilitating efficient data representation in systems like keyboards or analog-to-digital converters.[8] Priority encoders, a key subtype, resolve conflicts from multiple simultaneous inputs by assigning precedence, commonly used in interrupt handling and fault detection.[9] In coding theory, encoders implement algorithms to add structured redundancy to data for error detection and correction, such as in block codes and convolutional codes. Beyond these, the term "encoder" extends to software and algorithms in fields like data compression and machine learning, where it transforms input data into a compact or feature-rich representation. For example, in machine learning, autoencoders compress data for dimensionality reduction and feature extraction.[10]Digital Logic Encoders
Binary Encoders
A binary encoder is a combinational logic circuit in digital electronics that converts 2^n binary input lines into n binary output lines, where only one input is active at a time, producing an output code corresponding to the position of the active input.[11] These circuits perform the inverse function of binary decoders, mapping a single active input signal to its binary representation on the outputs.[12] A standard example is the 8-to-3 line binary encoder, which has eight input lines labeled D0 through D7 and three output lines Y2, Y1, and Y0. The circuit activates the output binary code for the index of the single active input (e.g., if D5 is high and all others low, the output is 101). The full truth table is as follows:| Inputs | Outputs | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 | Y2 | Y1 | Y0 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 |
| 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 1 |
| 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 1 | 0 |
| 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 1 |
| 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | 0 |
| 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 1 |
| 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 0 |
| 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 |
| All other combinations (multiple 1s or all 0s) are invalid |
Priority Encoders
A priority encoder is a combinational digital logic circuit designed to convert multiple binary inputs into a single binary output code representing the highest-priority active input, thereby resolving conflicts when more than one input is asserted simultaneously.[11] The purpose of this circuit is to ensure reliable encoding in systems where multiple inputs may activate at once, prioritizing the input with the highest designated index (typically the most significant bit) while ignoring lower-priority ones.[15] This contrasts with basic binary encoders, which assume only a single input is active and produce invalid outputs otherwise.[11] A common example is the 8-to-3 priority encoder, which accepts eight inputs labeled I_0 through I_7 (with I_7 having the highest priority) and produces a 3-bit binary output A_2 A_1 A_0 corresponding to the index of the highest active input, along with a valid flag V that asserts high if any input is active.[11] For instance, if I_2 and I_5 are both active, the circuit selects I_5 (index 101 in binary), outputting A_2 = 1, A_1 = 0, A_0 = 1, and V = 1.[15] The behavior of an 8-to-3 priority encoder can be illustrated through key cases in its truth table, focusing on scenarios that demonstrate priority resolution and the valid output:| Active Inputs | A_2 A_1 A_0 | V | Description |
|---|---|---|---|
| None | 000 | 0 | No input active; outputs invalid |
| I_0 only | 000 | 1 | Lowest priority selected |
| I_0, I_1 | 001 | 1 | I_1 prioritized over I_0 |
| I_2, I_5 | 101 | 1 | I_5 prioritized over I_2 |
| I_3, I_7 | 111 | 1 | I_7 prioritized over I_3 |
| All inputs | 111 | 1 | Highest priority I_7 selected |