Mumbai University > Computer Engineering > Sem 3 > Electronic Circuits and Communication Fundamentals

Marks: 5 Marks

Year: May 2016

N-channel JFET

1. Device Features

• A small bar of extrinsic semiconductor material, n type is taken and at its two end, two ohmic contacts are made which are the drain and source terminals of FET
• Heavily doped electrodes of p type materials form p-n type junctions on each side of the bar.
• The thin region between the two p gates is called the channel.
• Since this channel is in the n-type bar, the FET is known as n-channel JFET.
• The electrons enter the channel through the terminal called source and leave through the terminal called drain.
• The terminals taken out from heavily doped electrodes of p type material are called gates.
• Usually, these electrodes are connected together and only one terminal is taken out, which is called gate.

2. Voltage-Current Characteristics

• The figure shows the V-I characteristics of a n-channel JFET.
• The curve represents relationship between the drain current I_D and drain to source voltage $V_{DS}$ for different values of $V_{GS}$.

P-channel JFET

1. Device Features

• The device could be made of p type bar with n type gates.
• The device characteristics of n type and p type JFET is similar, the only difference being that in n channel JFET the current is carried by electrons while in p-channel JFET, it is carried by holes.

2. Voltage-Current Characteristics

• In a p-channel JFET the source is positive with respect to the drain.
• Here the source is the source of holes which flow through the channel to the drain.
• The pinch-off is achieved by making the source to gate voltage, source to gate voltage negative there by reverse biasing the p-n junction diode formed by the channel and the gate.
• The figure shows the V_I characteristics of p channel JFET.