User:Kid222r/Neutralization (electronics)

Neutralization is the act of reducing or cancelling unwanted impedances (usually by adding other impedances) in order to improve the operation of an electronic circuit. Neutralization is used in applications at RF, where devices like transistors and vacuum tubes exhibit inherent (stray) reactances between their terminals that affect signal coupling. When implemented as lumped impedances, neutralization may only be effective at one frequency (or over a small range of frequencies), although certain circuit designs lend themselves well to wideband neutralization.

Miller Effect Neutralization Example
Consider an NPN transistor circuit configured as an AC, common-emitter amplifier. The transistor has an inherent capacitance between its collector and base, the magnitude of which depends on the type of transistor, bias conditions, proximity of the leads, etc. Due to the Miller effect, the reactance of the capacitor will be magnified by a factor related to the gain of the transistor. This may cause an unacceptable degree of impedance mismatch, and the amplifier will exhibit a strong low-pass characteristic.

The collector-base capacitance will effectively be cancelled if placed in parallel with an equal & opposite reactance. In this case, an inductor may be used.