-: Tunnel Diode :-
A highly doped semiconductor device , which is used mainly for low voltage high frequency switching application, is known as Tunnel Diode.
It works on the principal of tunneling effect . It is also called as Esapi diode named after Leo Esapi.
Circuit Symbol-
-: Working Principle :-
The working of tunnel diode is discussed in following two steps -
1- In forward bias condition :- When a small forward bias is applied across the junction then under this condition the potential of P-side is higher than the potential of N-side . Since the electron in the conduction band on the N-side faces empty states in the valence band on the P-side , at same energy level.
The thin barrier across the junction would permit tunneling of electrons from N-side to P-side , with the consequent current flowing from the P-side to N-side . As the forward bias is increased , more such filled states on the N-side would come opposite to the empty states . With further increase in the forward bias , a specific condition would be reached when the maximum number of filled states in the conduction band on the N-side would face the maximum number of empty states in the valence band on the P-side. Then the tunneling current would reach a peak .
2- In Reverse Bias Condition :- When negative voltage is applied to the P-side with respect to N-side , then the P-side are directly opposite to the empty states on the N-side across a very narrow barrier . Thus the electrons form P-side would easily tunnel through this thin barrier by the process of 'Quantum Mechanical Tunneling'
and appear on the N-side .
Since , electrons travel from P-side to N-side , the actual direction of current is form N-side to P-side and is negative . As the amount of reverse bias is increased more number of filled states in the valence band of the P-side would appear opposite to the number of empty states and the reversed current would keep on increasing with reverse voltage .
V-I Characteristics of Tunnel Diode :-
The voltage current characteristics of tunnel diode is shown in following figure -
Advantages of Tunnel Diode :-
The advantages of tunnel diode is given as -
1- High speed of operation due to the fact that the tunneling takes places at the speed of light .
2- Low Cast
3- Low Noise
4- Environmental friendly
5- Low power dispute .
Disadvantages :-
The disadvantages of tunnel diode is given as -
1- Low output voltage swing
2- Because it is a two terminal device there is no isolation between input and output.
Applications :-
1- Tunnel Diode are used as very high speed switch .
2- Used as higher frequency microwave oscillator .
A highly doped semiconductor device , which is used mainly for low voltage high frequency switching application, is known as Tunnel Diode.
It works on the principal of tunneling effect . It is also called as Esapi diode named after Leo Esapi.
Circuit Symbol-
The working of tunnel diode is discussed in following two steps -
1- In forward bias condition :- When a small forward bias is applied across the junction then under this condition the potential of P-side is higher than the potential of N-side . Since the electron in the conduction band on the N-side faces empty states in the valence band on the P-side , at same energy level.
The thin barrier across the junction would permit tunneling of electrons from N-side to P-side , with the consequent current flowing from the P-side to N-side . As the forward bias is increased , more such filled states on the N-side would come opposite to the empty states . With further increase in the forward bias , a specific condition would be reached when the maximum number of filled states in the conduction band on the N-side would face the maximum number of empty states in the valence band on the P-side. Then the tunneling current would reach a peak .
2- In Reverse Bias Condition :- When negative voltage is applied to the P-side with respect to N-side , then the P-side are directly opposite to the empty states on the N-side across a very narrow barrier . Thus the electrons form P-side would easily tunnel through this thin barrier by the process of 'Quantum Mechanical Tunneling'
and appear on the N-side .
Since , electrons travel from P-side to N-side , the actual direction of current is form N-side to P-side and is negative . As the amount of reverse bias is increased more number of filled states in the valence band of the P-side would appear opposite to the number of empty states and the reversed current would keep on increasing with reverse voltage .
V-I Characteristics of Tunnel Diode :-
The voltage current characteristics of tunnel diode is shown in following figure -
The advantages of tunnel diode is given as -
1- High speed of operation due to the fact that the tunneling takes places at the speed of light .
2- Low Cast
3- Low Noise
4- Environmental friendly
5- Low power dispute .
Disadvantages :-
The disadvantages of tunnel diode is given as -
1- Low output voltage swing
2- Because it is a two terminal device there is no isolation between input and output.
Applications :-
1- Tunnel Diode are used as very high speed switch .
2- Used as higher frequency microwave oscillator .
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