Four-terminal method

The transistor can be considered as a four-terminal network where the relation between current and voltage is represented by two functions. Any of these magnitudes I _1, I _2, V ₁ ,V ₂ (Fig. 4.6) can be chosen as independent variable ones. Current and voltage consist of comparatively high constant components (V₌,I₌) and low variable components in linear circuits. Variable components we consider as the low current and voltage increments ( D I, D V), and they are basic ones.

The magnitudes which relate the low voltage and current increments to each other are called transistor differential parameters.

The real values of current and voltage conforming to the magnitudes I ₁ ,I ₂ ,V ₁ ,V ₂ depend on a transistor connection diagram.

Fig 4.6. Equivalent four-terminal network

If two of these magnitudes are considered to be independent ones, then two others will be found from a certain equation with the so-called characteristic parameters.

There are 6 systems of equations in the four-terminal network theory. These systems connect independent and dependent variable components with each other. Each of the systems is defined by chosen two independent magnitudes. There are three systems of parameters – h, y, z.