how capacitance arises in diodes and how it effects diodes performance ? Is it that necessary to worry about the capacitance in diodes ? if so when ?
thanks in advance.

 

Any circuit or device has an inherent capacitance - matter of fact capacitance exists between any two conducting materials no matter what they are or how far apart they are, it's just negligible in most cases.

Diode capacitance affects switching time and in very high frequency circuits can affect how perfectly it rectifies.

There are also "diodes" (so to speak) that are named varactors, their capacitance varies according to the reverse bias you place across them. They're used in tuned circuits to replace manually variable capacitors.

I'm using a couple in an RF preamp design I'm going to assemble this weekend. The preamp module itself mounts out on the antenna mast; the power supply and control electronics mount down in the building. In addition to the coaxial cable that carries the RF signal I also have a CAT5 cable running up to the amp which supplies the main power as well as controllable voltages which allow me to vary the gain, input and output tuning from the ground.