kynnysjännitys

Kynnysjännitys, a Finnish term, translates to "threshold voltage" in English and is a fundamental concept in electronics, particularly in the study of semiconductors and transistors. It refers to the minimum voltage that must be applied to a gate terminal of a field-effect transistor (FET) to initiate a conducting channel between the source and drain terminals. Before this voltage is reached, the transistor effectively acts as an open switch, preventing current flow.

For n-channel enhancement-mode MOSFETs, the kynnysjännitys is positive. Applying a positive voltage to the gate attracts minority carriers (electrons in this case) to the interface between the gate and the semiconductor, forming an n-type channel. If the gate voltage is below the kynnysjännitys, these electrons are not sufficiently concentrated to create a conductive path. Conversely, for p-channel enhancement-mode MOSFETs, the kynnysjännitys is negative, and a negative gate voltage is required to attract holes and form a p-type channel.

Depletion-mode transistors also exhibit a kynnysjännitys, but their behavior differs. Depletion-mode n-channel MOSFETs have a negative kynnysjännitys, meaning they are normally "on" and conducting even with zero gate voltage. A negative gate voltage is then needed to deplete the existing channel and turn the transistor off. The value of the kynnysjännitys is a critical parameter that influences a transistor's switching speed, power consumption, and overall performance in electronic circuits. It is determined by factors such as the semiconductor material, the doping concentrations, and the physical dimensions of the transistor.