ELEX Solid State Devices 2

• It is constructed with three doped semiconductor regions separated by two PN junctions. BJT
• BJT is constructed with Three doped semiconductor separated by Two PN junctions.
• BJT is a bipolar Current controlled.
• The term refers to the use of both Holes and Electrons as current carriers in the transistor structure.
• The three terminals of BJT are: Base, Collector, Emitter
• It is lightly doped and thin. Base
• It has less carrier. Base
• It is moderately doped. Collector
• It has more carrier than base. Collector
• It is heavily doped. Emitter
• It has higher carrier. Emitter
• This has the highest current among three terminals. Current Emitter
• The uses of BJT are: Amplifier, switch and impedance matching
• When the emitter cannot emit charged carriers resulting to no current flow from emitter to collector, then the transistor is at Cutoff.
• Cutoff occurs when the base to emitter is Reverse biased.
• The voltage across collector-emitter when at cutoff is Maximum.
• The resistance between collector-emitter at cutoff is Very high.
• The current when transistor is at cutoff is Zero.
• The transistor when cutoff is an Open circuit
• When the emitter emits maximum charged carriers resulting to maximum current flow from emitter to collector, the transistor is said to be at Saturation.
• The voltage across collector-emitter when the transistor is saturated is Minimum.
• The resistance between collector-emitter at saturation is Very low.
• Saturation occurs when base to emitter is in Forward bias.
• To achieve maximum current in saturation, the base to collector must be in Forward bias.
• This operation of transistor is in between of cutoff and saturation. Active
• The current flowing from emitter to collector in active region is Moderate only.
• The voltage and resistance across collector to emitter in active region is Moderate.
• Reverse + Forward = Cutoff
• Reverse + Reverse = Cutoff
• Forward + Forward = Saturation
• Forward + Reverse = Active
• The emitter is connected to the input voltage and the collector is connected to the output voltage. Common base
• The common base is mainly used for Impedance matching.
• The common base has Low input impedance.
• The common base has High output impedance.
• The common base has High voltage gain.
• The common base has Low current gain.
• Alpha is the amplification factor of common base.
• The base is connected in the input voltage and the collector is connected to the output voltage. Common emitter
• Common emitter is frequently used in Practical amplifier.