App-Notes » Simple Diode in Logic Gates (OR, AND): Uses & Benefits

Simple Diode in Logic Gates (OR, AND): Uses & Benefits

diode logic gates

Introduction : Logic gates are the building blocks of digital electronics. Diodes can be used to implement simple logic gates such as OR and AND in low power digital or TTL level circuits. This application note explains how simple diodes implement OR and AND logic, illustrating their working principles and the benefits they bring chiefly simplicity, speed, and low cost.

Diode OR Gate Circuit Working

Diode OR logic gate

The figure-1 depicts simple OR gate using diodes. The circuit connections are self explanatory.

  • As shown, when any one or all inputs are HIGH, corresponding diodes will become forward biased which drive current to output port and voltage is available.
  • When all the inputs are low (0V), all diodes are reverse biased and output is pulled to ground through pull-down resistor.

Diode AND Gate Circuit Working

Diode AND logic gate

The figure-2 depicts AND gate design using diodes. The circuit connections are self explanatory.

  • As shown, if any input is LOW (i.e. 0V), the corresponding diode becomes forward biased. This conducts current from supply through the pull-up resistor to ground through Low input. Hence output is pulled to LOW.
  • When all inputs are HIGH, all diodes are reverse biased. This allows output to be pulled to HIGH state through pull-up resistor.

Advantages of Diodes in Logic circuits

Following are benefits of diodes in logic circuits.

  1. Logic gates are simple to build using only diodes and resistors.

  2. Implementation of basic logic gates with diodes are cheaper than more complex ICs.

  3. In non-switching static conditions, diode based logic circuits draw less current and hence are useful for battery powered systems.

  4. Diode logic gates (OR & AND) functions in passive manner. This is good for simple logic where inversion and amplification is not required.

  5. Diodes can switch between conducting and non-conducting quickly under certain conditions, which is useful for signal level changes.

  6. They offer good reliability and are less prone to mechanical failure.

  7. They have minimal component footprint and hence take up little board space.Moreover it will simplify routing and layout.

Conclusion: OR and AND gates built with diodes offer minimal component count, fast switching and clear functionality.