What is drain current of JFET?
For the case vGG=vGS=0, the drain current at pinch-off is called the drain-source saturation current, IDSS. Operation beyond the pinch-off point (vDS > vGS – VP for an n-channel device) defines the normal operating or saturation region of the JFET.
What is drain current?
It indicates the current conduction capability of the silicon chip; it can be used as a guide when comparing different devices. However, the rated maximum drain current should not be allowed to flow to the chip.
What is P-channel JFET?
In the case of p-channel JFET, the major portion made of the device is made of p-type into which embedded are the two small n-type regions. Thus it has an n-type gate terminal and p-type source and drain, causing the channel to be of p-type where the holes will be the majority charge carriers.
How to calculate the drain current I d of a JFET transistor?
The formula to calculate the drain current in the ohmic region is: The formula to calculate the drain current in the active region is: Note: V GS,off and I DSS are typically the knowns. You can get their values from looking them up in a data table or on the package they came in.
Why is the input impedance high in JFET?
Since the gate of JFET is reverse-biased, the input impedance is very high. This is one advantage of JFET over bipolar junction transistor. In JFET data sheet, the input impedance is given by gate reverse current IGSS for a given gate-source voltage VGS. Thus, input impedance can be expressed as
How is the JFET biased in normal operation?
4.1 Biasing the JFET In normal operation, the gate of JFET is always reverse-biased. Thus, an n-channel type, the gate is biased with negative voltage i.e. gate voltage is less than zero volt VG < 0, whilst for p-channel type, the gate is biased with positive voltage i.e. gate voltage is greater than zero voltage VG > 0.
What is the transconductance gain of a JFET?
This is called the transconductance gain (abbreviated as g. m) of the JFET and has units of conductance which is measured in Siemens. The gain value is very low (typically between 0.0001 and 0.02 –but remember that what matters is power gain and that is very high for a JFET) and is often expressed in mS.