Negative Resistance Oscillator (tube based)

Resistance (positive) is marked by an increase in current with voltage increase. Negative resistance is also possible where you get a decrease in current with voltage increase. You typically need some kind of active device such as a transistor to get negative resistance.

The differential pair amplifier is a good way to obtain negative resistance since one side of the pair can sense an increase in voltage and decrease the current flowing in the other side.

Typical use cases for negative resistance are:

• Oscillators: Negative resistance is used in many types of oscillators to generate AC signals. For example, tunnel diodes and Gunn diodes are both negative resistance devices that are commonly used in microwave oscillators.

• Amplifiers: Negative resistance can also be used to amplify signals. For example, a negative resistance amplifier (NRA) can be used to amplify a weak signal to a much higher level.

• Switching circuits: Negative resistance can also be used to create bistable circuits, which have two stable states. These circuits can be used to store information or to create switches that are very fast and efficient.

The following is another view point of the differential pair for oscillator circuits