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A “backward diode,” also known as an “AU diode” or “back diode,” is a type of semiconductor diode that exhibits a unique characteristic where its current-voltage \(I-V\) curve is opposite to that of a conventional diode. Here’s a detailed explanation:


  • Reverse I-V Curve: Unlike standard diodes, which conduct current when forward-biased and block current when reverse-biased, a backward diode conducts significant current in the reverse direction at a certain voltage threshold.
  • Breakdown Voltage: It typically has a low breakdown voltage in the reverse direction, allowing it to conduct efficiently when the reverse voltage exceeds this threshold.
  • Negative Resistance Region: The unique feature of a backward diode is its region of negative resistance in the reverse bias region of its I-V curve. This means that as the reverse voltage increases beyond the threshold, the current through the diode increases rather than decreases, which is opposite to the behavior of regular diodes.


  • Microwave and RF Circuits: Backward diodes are often used in microwave and RF circuits where their unique negative resistance characteristics can be exploited for oscillation and mixing applications.
  • Detector and Mixer Circuits: Due to their low forward voltage drop and high sensitivity to changes in voltage, backward diodes can be used as detectors and mixers in signal processing applications.
  • High-Frequency Switching: They are suitable for high-frequency switching applications where their fast switching times and unique I-V characteristics are advantageous.


  • Fast Switching Speeds: Backward diodes typically have very fast switching times, making them suitable for applications requiring rapid signal processing.
  • Sensitive Detection: Their sensitivity to small changes in voltage makes them ideal for low-power detection circuits.

Backward diodes, also known as AU diodes or back diodes, are semiconductor devices with a reversed I-V characteristic compared to standard diodes. They find applications in microwave circuits, RF signal processing, detectors, and mixers, where their unique negative resistance and fast switching properties are beneficial for specialized electronic functions.

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