Semiconductor-part-IV : Semiconductor-part-IV 1.Junction transistors
2.Amplifier
3.Logic gates
4.Home work
Junction transistors : A junction transistor is made of a semiconductor in which a thin layer of one type of extrinsic semiconductor (p-type or n-type) is sandwiched between two thick layers of other type of extrinsic semiconductor. For example n-p-n transistor or p-n-p transistor. Junction transistors
Terminology used in transistors : Emitter-The left region of a transistor is known as emitter. It supplies majority charge carrier to the base region. Emitter region is heavily doped.
Collector-The right region of transistor is known as collector and it is doped slightly less than the emitter region. The collector collects the majority charge carriers. Moreover, the thickness of collector region is slightly more than the thickness of the emitter region. Terminology used in transistors
Cont… : Base- The middle region of a transistor is known as base. The base is very thin as compared to the emitter and collector regions and it is lightly doped.
The junction between emitter and base is called emitter-base junction while the junction between the collector and the base is called collector-base junction. The Emitter-base junction is always forward biased whereas the collector-base junction is reverse biased. Cont…
Action or working of transistors : Action of n-p-n transistor. Action or working of transistors p
Action or working of transistors : Action of p-n-p transistor. Action or working of transistors n
Basic transistor circuit configurations : 1.Common-base configuration-In this configuration, base terminal of transistor is common between the input and output circuits.
2. Common-emitter configuration-In this configuration, emitter terminal of transistor is common between the input and output circuits.
3.Common-collector configuration-In this configuration, collector terminal of transistor is common between the input and output circuits. Basic transistor circuit configurations
Common emitter transistor characteristic : Input characteristic-The variation of base current Ib (input)with base –emitter voltage(Veb) at constant collector-emitter voltage (Vce) is called input characteristic.
Rin =Vce/Ib (Vce=Constant)
Output characteristics-The variation of collector current Ic (output)with collector-emitter voltage(Vce) at constant base current(Ib) is called output characteristic.
Rout=Vce/Ic (Ib=constant) Common emitter transistor characteristic
Transistor as an Amplifier : A device which increases the amplitude of the input signal is called amplifier. Transistor as an Amplifier Amplifier Input signal Output signal
Common emitter Amplifier : In common emitter amplifier, input signal to be amplified is applied between base-emitter circuit and the output amplified signal is taken across the load resistance in the emitter-collector circuit. Emitter is made as a common terminal.
Ie=Ib+Ic
Vo=Vce-IcRL Common emitter Amplifier
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Transistor Gains in CE amplifiers : A.C Current Gain(ß)-It is defined as the ratio of the collector current(Ic) to the base current(Ib)
?=Ic/Ib
Ic>Ib .thereforeß>1.Its value lies between 15 and 50.
Resistance gain-It is defined as the ratio of the output resistance to the input resistance. Transistor Gains in CE amplifiers
Cont… : Resistance gain=Ro/Ri
Voltage gain-It is defined as the ratio of small change in the output voltage to the small change in the input voltage.
Av=Vo/Vi
Av=ß x resistance gain
Power gain-It is defined as the ratio of small change in the output power to the small change in the input power Cont…
Cont… : Power gain=Po/Pi
Power gain=ß² x resistance gain Cont…
Logic gates : Logic gates-The digital circuit that can be analyzed with the help of Boolean algebra is called logic gate or logic circuit. A logic gate has one or two inputs but only one output.
There are primarily three logic gates namely the OR gate, the AND gate and the NOT gate.
Truth Table-The operation of a logic gate or circuit can be represented in a table which contains all possible inputs and their corresponding outputs and is called the truth table. Logic gates
OR ,AND,NOT gates : OR gate has two inputs(A and B) and only one output(Y)
Y=A+B
AND gate has two inputs and only one output
Y=A.B
NOT has only one input and only one output
Y=A OR ,AND,NOT gates Y y
Truth table- AND gate : Truth table- AND gate
Truth Table-OR gate : Truth Table-OR gate
Truth Table NOT gate : Truth Table NOT gate
Home work question : 1.Identify a gate from the Boolean expression Y=A.B=A+B and arrive at its truth table.
2.Calculate the emitter current for ß=50 and base current 5µA. (0.25mA)
3.The base region of a transistor is lightly doped .Explain why?
4.Why is a transistor so called? Home work question