Encoder

Encoder

Overview

An encoder is a combinational circuit that converts information from one format or code to another. In digital electronics, encoders take 2ⁿ input lines and produce an n-bit binary code as output. They are useful in reducing the number of signals in a system, such as converting multiple input signals into a compact, coded output.

Detailed Explanation

Operation Principle

For an n-to-2ⁿ encoder:
- Only one input is active at a time.
- The encoder outputs the binary equivalent of the active input’s number.

Example (4-to-2 encoder):
Inputs: D0, D1, D2, D3
Outputs: Y1, Y0

Logic:
Y1 = D2 + D3
Y0 = D1 + D3

Circuit Considerations

1. Priority Encoding: When more than one input is active, a priority scheme is used.
2. Active High vs. Active Low: Determines logic levels of valid signals.

Applications

- Keyboard encoding
- Address decoding in memory systems
- Data compression

Practice Problems

  1. Design a 8-to-3 encoder and list the Boolean expressions for each output.
  2. Describe a priority encoder for a 4-to-2 system when multiple inputs are active.
  3. Compare encoder designs under active high and active low conditions.

References

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