Definition
Negative resistance is an electrical phenomenon in which an increase in voltage across a device leads to a decrease in electric current through it, or conversely, a decrease in voltage causes an increase in current. In terms of the device’s I‑V (current‑voltage) characteristic, a region of negative slope (dI/dV < 0) indicates negative differential resistance, while a true negative resistance implies that the device delivers power to the external circuit rather than dissipating it.
Overview
Negative resistance is observed in certain active electronic components and circuits, such as tunnel diodes, Gunn diodes, IMPATT diodes, and some types of gas‑discharge tubes. It is exploited to create oscillators, amplifiers, and switching circuits. The effect arises from internal physical mechanisms—quantum tunneling in tunnel diodes, transferred electron effects in Gunn diodes, or avalanche breakdown in IMPATT devices—that cause the current to decrease as the applied voltage rises within a specific operating region.
Two distinct concepts are commonly distinguished:
- Negative differential resistance (NDR): the local slope of the I‑V curve is negative (dI/dV < 0), but the overall resistance, defined as V/I, remains positive. Most semiconductor devices that exhibit “negative resistance” fall into this category.
- Absolute negative resistance (ANR): the resistance defined by V/I itself becomes negative (V and I have opposite signs). ANR is less common and typically requires external feedback or energy‑supply mechanisms.
Etymology/Origin
The term combines “negative,” indicating a sign opposite to the usual direction of voltage‑current relationship, with “resistance,” the property measured in ohms that quantifies opposition to electric current. The concept was first documented in the early 20th century with the discovery of tunnel diode behavior by Leo Esaki in 1958, although earlier observations of anomalous I‑V characteristics in vacuum tubes predate this.
Characteristics
| Feature | Description |
|---|---|
| I‑V Curve | Exhibits a region where current decreases with increasing voltage, forming a peak‑valley shape (e.g., tunnel diode). |
| Stability | Circuits containing negative‑resistance elements can become unstable, leading to spontaneous oscillations unless suitably damped or biased. |
| Power Flow | In the negative‑resistance region, the device can supply power to the external circuit (P = VI can be negative, indicating power delivery). |
| Frequency Performance | Devices such as Gunn diodes operate at microwave frequencies (GHz range) due to fast carrier dynamics. |
| Temperature Dependence | The extent and location of the negative‑resistance region are temperature‑sensitive; cooling often widens the NDR region in tunnel diodes. |
| Implementation | Realized through semiconductor heterostructures, gas discharge configurations, or active circuit designs employing op‑amps or transistors to emulate negative resistance. |
Related Topics
- Tunnel diode – A semiconductor diode exhibiting pronounced negative differential resistance due to quantum tunneling.
- Gunn diode (Gunn effect) – A solid‑state device that shows negative differential resistance via transferred electron mechanism in certain III‑V compounds.
- IMPATT diode – Avalanche‑triggered diode used in high‑frequency oscillators, displaying negative resistance at microwave frequencies.
- Oscillator circuits – Many practical oscillators (e.g., the Colpitts, Hartley, and ring oscillators) employ negative‑resistance elements to sustain sinusoidal or relaxation oscillations.
- Negative impedance converter (NIC) – An active circuit that presents an effective negative resistance to a load, often used in filter design and antenna tuning.
- Stability analysis – Techniques such as Nyquist and Bode plots are applied to assess the impact of negative resistance on system stability.
Negative resistance remains a foundational principle in high‑speed and high‑frequency electronics, enabling the generation and control of electromagnetic signals across a broad spectrum of applications.