Field effect transistors (FETs) are mainly composed of junction field effect transistors (JFETs) and insulated gate field effect transistors (MOS transistors). The field effect transistor is mainly composed of a majority of carriers, also known as unipolar transistors. Field effect transistor (FET) is a kind of semiconductor device which controls the output circuit current by controlling the electric field effect of the input circuit.
The following is a JFET buffer (common drain amplifier), useful in everyday use because it has a very high input impedance compared to transistors.
VGS is called gate to source interleave voltage or cut-off voltage, which is shown by VGS (off). The case of N channel JFET is VGS (off). Value with negative symbols, measure the actual JFET corresponding ID = 0 VGS because it is very difficult, in the use of small signal JFET amplifier, will reach ID = 0.1-10muA VGS There are more cases defined as VGS (off).