Q. What is the difference between field effect transistor and the bipolar junction transistor?
The important points of the comparison between the field effect transistor ands the bipolar junction transistor are:
Field effect transistor(FET)
1. It is a unipolar device.i.e,current in the device is carried by either holes or electrons.
2. Like the vacuum tube, it is a voltage controlled device i.e., voltage at the gate terminal controls the amount of the current flowing through the device.
3. Its input resistance is very high and is of the order of several mega ohms.
4. It has a negative temperature coefficient at very high current levels. it means that the current decreases as the temperature increases
5. It does not suffer from minority carrier storage effects and has higher switching speeds and cut off frequencies.
6. It is less noisy and is more suitable as an input amplifier for the low level signals.
7. it is much simpler to fabricate.
Bipolar junction transistor(BJT)
1. It is a bi polar device i.e, current in the device is carried by both the electrons and the holes.
2. It is a current controlled device i.e, the base current controls the amount of the collector current.
3. Its input resistance is very low and is of the order of few kilo ohms.
4. It has a positive temperature at the very high current level. It means that the collector current increases with the increase in the temperature.
5. It suffers from minority carrier storage effects and has lower switching speeds and cut off frequencies.
6. it is more noisy.
7. it is comparatively very difficult to fabricate.