NEGATIVE RESISTANCE Is there a negative resistor?

Is there a negative resistor? Yes and No. There is no standalone component as a negative resistor. The “negative resistance” effect is a paradox that exists! It means that a voltage drop could paradoxically boost circuit current, instead of decreasing it.

Historical devices, such as gas discharge lamps, exhibit the strange physics of negative resistance. Some engineers suggest using the term “negristor” to describe devices that exhibit negative resistance.

Is there a negative resistor?

The negative resistance effect has been verified in both real devices and simulated circuits. The negative resistance effect is a local nonlinear behavior that occurs when increasing the voltage causes a decrease in the circuit current. The opposite is also true. Decreasing the voltage causes the circuit current to increase.

Simply put, voltage and current must follow an inverse relationship for negative resistance to exist. The traditional physics of voltage and current relationships is quite friendly. According to Ohm’s law, voltages and currents remain directly proportional. In practical terms, it means that if the voltage in a circuit increases, the current also increases.

Ohmic devices follow a linear slope. When discussing negative resistance, the common resistance becomes "positive resistance". In broader terms, positive resistance is known as static resistance.

According to Ohm’s law,

V = IR

The simple equation represents the proportional relationship between voltage and current. It’s where this gets tricky. In practical applications, the slope is not always linear. It keeps on changing instantaneously. To calculate instantaneous values, we must differentiate the static resistance equation with respect to the current.

The value dv/di is known as differential resistance. In ohmic devices, positive differential resistance suggests that the slope is increasing. The positive slope indicates normal resistance operation.

In non-linear devices, the slope is not straight. It can bend at some point in time and then, perhaps, follow Ohm's law later. The concept of negative resistance appears briefly when the slope of dv/di is negative. It’s a relatively small region of operation.

The answer to the question of is there a negative resistor lies in the equation, which proves that negative resistance is a part of positive/normal resistance. It’s just an unstable region of the I-V characteristics where the slope is negative.

RESISTOR CALCULATION

How to calculate voltage drop across a resistor?

Negative resistance applications

Is there a negative resistor? Negative resistance exists due to device physics, but can also be engineered.

High-frequency devices: Many semiconductor devices, such as Gunn diodes, tunnel diodes, thyratron tubes, magnetron tubes, IMPATT and TRIPATT RF diodes, exhibit negative resistance.

These devices “naturally” exhibit negative slopes in I-V curves. They function with the help of an external power supply, hence they’re called passive negative differential resistance devices.

Oscillations: Negative resistance-based devices are applicable in LC tanks, RF oscillators, signal generators, and various microwave devices. Such devices cancel losses and sustain oscillations.

Active filters: Frequency-dependent negative resistors (FDNR) can replace inductors and capacitors in filter circuits by offering greater phase shift and faster roll-off. FDNRs can help design compact filters using less bulky op-amps.

Amplification: Negative resistance can enhance and amplify small signals. A subreddit thread on negative resistance reports that negative resistance can provide gain.

Thyristor operations: Active negative resistance devices are manufactured to create the negative resistance effect. Examples include various thyristors.

The left graph shows voltage-controlled devices. It resembles the shape of the alphabet “N”, hence it’s known as N-type. The right graph shows current controlled devices.

The right graph is shaped like the alphabet “S”, hence known as S-type. Such characteristics are visible in oscillators and active filters.

BASIC KNOWLEDGE

The current “speed breaker”

Conclusion

Is there a negative resistor by clear definition? Negative resistance is not a device but refers to the point in the I-V characteristic curve where the slope is negative. It’s a brief period observed in many high-frequency semiconductor devices.

Normal resistor operation: Push more voltage — Get more current. Power is dissipated as heat.

Negative resistance operation( Negristor): Push more voltage — Current fights back. Such devices produce or source the power. They can also be made to consume more power overall.

Negative differential resistance can give rise to numerous applications, such as oscillation, amplification, and compact filter design.

References

• https://www.sciencedirect.com/topics/chemistry/negative-resistance

• https://www.reddit.com/r/AskElectronics/comments/kbl3j4/what_actually_is_negative_resistance/

• https://electronics.stackexchange.com/questions/86612/what-is-negative-resistance

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