• The figure shows the
capacitance v/s applied voltage across the diode.
• Shunt capacitive effects that
can be ignored at very lower frequencies since Xc=1/2πfc
is very large (open circuit)
• However this can not be
neglected in very high frequencies since it introduces a low
reactance (shorting) path.
• Two types of capacitive effects
to be considered in FB and RB condition.
• In RB region transition or
depletion region capacitance CT in FB diffusion
capacitance CD or storage
capacitance.
• W.k.t C=εA/d.
• ε is the permittivity of
dielectric between tow plates of area A separated by distance d.
• In RB, depletion region which
is free of carriers that behaves essentially like an
insulator between the layers of
opposite charges. This depletion region width increase
with increase in RB potential.
• Since d is increasing,
capacitance effect is more in FB.
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