Relation between the current gain of common base and common emitter amplifier .
β = α / 1 – α = I c / I e
The input and output signals are out of phase by π or 180 ° There is amplification in current , voltage and power of the given signal .
Light Emitting Diodes ( LED )
It is forward biased p-ri junction diode which emits light when recombination of electrons and holes takes place at the junction .
If the semiconducting material of p-ri junction is transparent to light , the light is emitting and the junction becomes a light source , i . e ., Light Emitting Diode ( LED ).
The colour of the light depends upon the types of material used in making the semiconductor diode .
( i ) Gallium – Arsenide ( Ga-As ) – Infrared radiation
( ii ) Gallium – phosphide ( GaP ) – Red or green light
( iii ) Gallium – Arsenide – phosphide ( GaAsP ) – Red or yellow light
Logic Gate
A digital circuit which allows a signal to pass through it , only when few logical relations are satisfied , is called a logic gate .
Truth Table