JFET & MOSFET, characteristics, biasing and small signal low frequency analysis of CD, CS configurations, FET as VVR, (6) Text Book: 1. IXAN0061 3 Figure 3: N-channel enhancement-mode Power MOSFET I-V Characteristics It has regions labeled as Ohmic, Current-Saturated and Cut-off. In the Cut-off region, the gate-source voltage (Vgs) is less than the gate-threshold voltage (Vgs(th)) and the device is an open-circuit or Off.

Threshold voltage, V_T, is the voltage required to fully deplete the doped channel layer:

Fet As Vvr Pdf

Two regions:

quadratic region where the depletion layer is less than the channel thickness d

saturated region where the depletion layer at the drain end equals the channel thickness d

The drain current become independent of the drain voltage and equals:

Fig.8.x Drain current versus Drain-Source voltage at a gate-source voltage of 0.2, 0.4, 0.6 0.8 and 1.0 Volt for a silicon JFET with built-in potential of 1 V. Channel parameters and device dimensions are listed in the table below.

Table 8.x JFET parameters

Fet As Vvr And Its Application

The transfer characteristic of a JFET is shown in the figure below and compared to a quadratic expression of the form

where is the average depletion layer width in the channel layer. The quadratic expression yields the same current at V_G = f_i for = 3d/8.

Fig.8.x Transfer characteristic of a JFET. Shown is the square root of the drain current of the JFET (solid line) and a quadratic fit with =3d/8.

Fet As Vvr In Vca

Fet As Vvr