The N-channel JFET consists of a silicon bar of N-type semiconductor with two P type regions on both sides. JFET is a tri-terminal device whose terminals are called drain, source and gate.
The Outline of an n-channel JFET is described on picture (a), n-channel JFET symbol is shown on picture (b), p-channer JFET symbol is shown on picture (c).
JFET biasing requires that the pn junctions are reverse-biased. In order to have a current flowing throught the channel, on a n-channel JFET or NJFET.
The Drain voltage must be greater than the Source voltage. In addition, to have the p-n junction reversed biased, the gate must have a more negative voltage than the source. Both cases are shown in the picture.
The JFET electric characteristics curves are similar to the bipolar transistor curves. However, the JFET devices are controlled by a voltage, and bipolar transistors are controled by current.
JFET has 3 main parameters:
- ID (Current flowing from drain to source),
- VGS (Gate to Source voltage) and
- VDS (Drain to Source voltage).
There are four basic operation regions: cut off, triode or Ohmic and active or saturation. We will make a brief description of each of these regions for an NJFET. (See the image above)