PIN Diode - General Description

It is a junction photo diode. 

Basic principle :- The diode is operated under reverse biased condition. Under photo excitation , photons are absorbed mainly in depletion region and also in neutral region , particularly on top where light is incident. the absorbed photons create e-h pairs

They give rise to photo current , the magnitude of which depends on quantum efficiency.

so photo excitation is therefore detected as an increase in reverse biased current of a junction photo diode.

Large depletion layer may increase no.of e-h pairs generated but it consequently increases response time of diode degrading its high speed performance.

Pin diodes have no internal gain but can have very large band widths.

Since dark current in a reverse biased junction is very small , pin diode is more sensitive device than a photo conductor.

Difference between Impedance and Reactance

For all the circuits lumped elements in which time varying voltages / current exists , we find a relation in which the voltage is proportional to Current . The proportional quantity is in general a complex number and this is called Impedance.

It is a function of frequency of ‘w’ strictly speaking impedance is sum of its real and imaginary parts.

Z= R+ IX

Impedance is equivalent to a Resistance in series with pure imaginary Impedance - called a Reactance.

The voltage drop across the resistance is in phase with the current , while the voltage drop across the purely Reactive part is out of phase with the current.

The average energy loss in an impedance Z= R + iX depends only on real part of ‘Z’ and not on complex part.

There is no energy loss in Reactive part.