Junction Capacitance in Diode Explained


The capacitance effect forms in a PN Junction Diode under Reverse Bias condition is called Junction Capacitance. As this capacitance effect forms in the junction position, it's known as Junction Capacitance. Junction Capacitance is also known as Depletion Capacitance or Transition Capacitance.


When Junction Capacitance form?


As I told before, when a PN junction diode is connected in reverse bias condition, Junction Capacitance forms.


Why Junction Capacitance forms in a Diode?


When a PN Junction Diode is connected in reverse bias, no current flowing through it. In that time, both the P and N regions act as electrodes and the depletion region between them acts as a dielectric medium. So there is a situation creates to store electrical charge. This situation is termed as Junction Capacitance.

How Junction Capacitance is formed?


A diode is connected in reverse bias condition means the positive terminal of the battery is connected to the N-type region and the negative terminal of the battery is connected to the P-type region. 

junction capacitance in diode


So holes in the P-type region are attracted by the negative terminal and moves away from the junction. On the other hand, the electrons in the N-type region attract by the positive terminal and moves away from the junction. 

As a result, the width of the depletion region will increase and it acts as a dielectric medium. At the same time, electrical charges start to accumulate in the P and N-type regions. So there is an electrical charge storing capability creates.

The equation of junction capacitance is,

Here, Cj is junction capacitance, w is the width of the depletion region.



Effect of Junction Capacitance


The effect of junction capacitance will be clearly noticed when the diode is connected in high-frequency circuits. The following effects will occur,

1. The diode will provide very little gain.
2. Propagation Delay will be more.
3. It will produce more heat.
4. It will give a very low-speed performance.
5. Dynamic Power Consumption in the circuit will be more.


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Junction Capacitance in Diode Explained Junction Capacitance in Diode Explained Reviewed by Author on 12/17/2019 Rating: 5
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