Bipolar Junction Transistor Common Base Configuration

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Unbiased NPN transistor Unbiased PNP transistor Bipolar Junction TransistorCommon Base ConfigurationIn this configuration emitter is The base emitter junction JE is.
the input terminal collector is the always forward biased and collector output terminal and base terminal is base junction JC is always reverseconnected as a common terminal for biased both input and output Let us consider NPN transistor.
It is also known as grounded in common base configuration base configuration Bipolar Junction TransistorCommon Base ConfigurationThe NPN transistor is formed when a single.
p type semiconductor layer is sandwichedbetween two n type semiconductor layers Base emitter junction JE is forward biased bythe supply voltage VBE while the collector basejunction JC is reverse biased by the supply.
voltage VCB Due to the forward bias voltage VBE the free electronics majority carriers inthe emitter region experience a repulsive force Similarly holes majority carriers in the base region experience a repulsive Bipolar Junction Transistor.
Common Base ConfigurationAs a result free electrons start flowing from emitter to base similarlyholes start flowing from base to emitter Thus free electrons which are flowingfrom emitter to base and holes which are flowing from base to emitterconducts electric current .
The free electrons which are flowing from emitter to base will combinewith the holes in the base region similarly the holes which are flowing frombase to emitter will combine with the electrons in the emitter region From the below figure it is seen that the width of the base region is verythin Therefore only a small percentage of free electrons from emitter region.
will combine with the holes in the base region and the remaining large numberof free electrons cross the base region and enters into the collector region Bipolar Junction TransistorCommon Base ConfigurationA large number of free electrons which entered into the collector.
region will experience an attractive force from the positive terminal of thebattery Therefore the free electrons in the collector region will flowtowards the positive terminal of the battery Thus electric current isproduced in the collector region Bipolar Junction Transistor.
Common Base ConfigurationThe electric current produced at the collector region is primarily due tothe free electrons from the emitter region similarly the electric currentproduced at the base region is also primarily due to the free electrons fromemitter region .
Therefore the emitter current is greater than the base current andcollector current The emitter current is the sum of base current andcollector current IE I B I CThe output collector current is less than the input emitter current so.
the current gain of this amplifier is actually less than 1 The base emitter junction JE at input side acts as a forward biaseddiode So the common base amplifier has a low input impedance lowopposition to incoming current Bipolar Junction Transistor.
Common Base ConfigurationThe collector base junction JC at output side acts somewhat likea reverse biased diode So the common base amplifier has high outputimpedance The common base amplifier provides a low input impedance and high.
output impedance Transistors with low input impedance and high output impedanceprovide a high voltage gain Even though the voltage gain is high the current gain is very low andthe overall power gain of the common base amplifier is low as compared to.
the other transistor amplifier configurations The common base amplifier is mainly used as a voltage amplifier orcurrent buffer This type of transistor arrangement is not very common and is not aswidely used as the other two transistor configurations .
Bipolar Junction TransistorCommon Base Configuration WorkingTo fully describe the behaviour of a transistor with CB configuration weneed two set of characteristics they areInput characteristics Output characteristics .
Input characteristicsThe input characteristics describe the relationship between input current IE and the input voltage VBE To determine the input characteristics the output voltage VCB collector base voltage .
is kept constant at zero volts and the input voltageVBE is increased from zero volts to different voltagelevels For each voltage level of the input voltage VBE the input current IE is recorded Bipolar Junction Transistor.
Common Base Configuration Working Input characteristicsNext the output voltage VCB is increased from zero volts to a certainvoltage level 8 volts and kept constant at 8 volts While increasing the outputvoltage VCB the input voltage VBE is kept constant at zero volts After wekept the output voltage VCB constant at 8 volts the input voltage VBE is.
increased from zero volts to different voltage levels For each voltage level ofthe input voltage VBE the input current IE is recordedA curve is then drawn between input current IE and input voltage VBE atconstant output voltage VCB 8 volts This is repeated for higher fixed values of the output voltage VCB .
When output voltage VCB is at zero volts and emitter base junction JE isforward biased by the input voltage VBE the emitter base junction acts like anormal p n junction diode So the input characteristics are same as the forwardcharacteristics of a normal pn junction diode Bipolar Junction Transistor.
Common Base Configuration Working Input characteristicsWhen the output voltage VCB is increased from zero volts to a certainvoltage level 8 volts the emitter current flow will be increased which inturn reduces the depletion region width at emitter base junction As aresult the cut in voltage will be reduced Therefore the curves shifted.
towards the left side for higher values of output voltage VCB Bipolar Junction TransistorCommon Base Configuration Working Output characteristicsThe output characteristics describe the relationship between outputcurrent IC and the output voltage VCB .
To determine the output characteristics the input current or emittercurrent IE is kept constant at zero mA and the output voltage VCB is increasedfrom zero volts to different voltage levels For each voltage level of the outputvoltage VCB the output current IC is recorded A curve is then drawn between output current IC and output voltage.
VCB at constant input current IE 0 mA When the emitter current or input current IE is equal to 0 mA thetransistor operates in the cut off region Next the input current IE is increased from 0 mA to 1 mA by adjustingthe input voltage VBE and the input current IE is kept constant at 1 mA While.
increasing the input current IE the output voltage VCB is kept constant Bipolar Junction TransistorCommon Base Configuration Working Output characteristicsAfter we kept the input current IE constant at 1 mA the output voltage VCB is increased from zero volts to different voltage levels For each voltage.
level of the output voltage VCB the output current IC is recorded A curve is then drawn between output current IC and output voltageVCB at constant input current IE 1 mA This region is known as the activeregion of a transistor This is repeated for higher fixed values of input current IE I e 2 mA 3.
mA 4 mA From the characteristics we can see that for a constantinput current IE when the outputvoltage VCB is increased the outputcurrent IC remains constant .
Bipolar Junction TransistorCommon Base Configuration Working Output characteristicsAt saturation region both emitter base junction J E and collector base junction JC areforward biased From the above graph we can see that a sudden increase in the collectorcurrent when the output voltage VCB makes the collector base junction JC forward biased .
Early effectDue to forward bias the base emitter junction JE acts as a forward biased diodeand due to reverse bias the collector base junction JC acts as a reverse biasedTherefore the width of the depletion region at the base emitter junction J E is verysmall whereas the width of the depletion region at the collector base junction J Cis.
very large If the output voltage VCB applied to the collector base junction JC is furtherincreased the depletion region width further increases The base region is lightlydoped as compared to the collector region So the depletion region penetratesmore into the base region and less into the collector region As a result the width.
of the base region decreases This dependency of base width on the output voltage VCB is known as an early effect Bipolar Junction TransistorCommon Base Configuration Transistor parametersDynamic input resistance ri .
Dynamic input resistance is defined as the ratio of change in input voltage oremitter voltage VBE to the corresponding change in input current or emittercurrent IE with the output voltage or collector voltage VCB kept at constant The input resistance of common base amplifier is very low Dynamic output resistance ro .
Dynamic output resistance is defined as the ratio of change in output voltage orcollector voltage VCB to the corresponding change in output current or collectorcurrent IC with the input current or emitter current IE kept at constant The output resistance of common base amplifier is very high Bipolar Junction Transistor.
Common Base Configuration Transistor parametersCurrent gain The current gain of a transistor in CB configuration is defined as the ratio ofoutput current or collector current IC to the input current or emitter current IE The current gain of a transistor in CB configuration is less than unity The.
typical current gain of a common base amplifier is 0 98 Bipolar Junction TransistorCommon Emitter ConfigurationIn common emitter configuration base is the input terminal collector isthe output terminal and emitter is the common terminal for both input and.
output That means the base terminal and common emitter terminal are knownas input terminals whereas collector terminal and common emitter terminalare known as output terminals In common emitter configuration the emitter terminal is grounded so.
the common emitter configurationis also known as grounded emitterconfiguration The common emitter CE configuration is the most widelyused transistor configuration .
The common emitter CE amplifiersare used when large current gain is needed Bipolar Junction TransistorCommon Emitter ConfigurationThe input signal is applied between the base and emitter terminals while.
the output signal is taken between the collector and emitter terminals Thus the emitter terminal of a transistor is common for both input and output andhence it is named as common emitter configuration The supply voltage current between base and emitter is denoted by V BE IB while the supply voltage current between collector and emitter is.
denoted by VCE IC The common emitter amplifier has medium input and output impedance Bipolar Junction TransistorCommon Emitter Configuration WorkingTo fully describe the behaviour of a transistor with CE configuration we need.
two set of characteristics they areInput characteristics Output characteristics Input characteristicsThe input characteristics describe the relationship between input current orbase current IB and input voltage or base emitter voltage VBE .
To determine the input characteristics the output voltage VCE is kept constantat zero volts and the input voltage VBE is increased from zero volts to differentvoltage levels For each voltage level of input voltage V BE thecorresponding input current IB is recorded A curve is then drawn between input current IB and input voltage VBE at.
constant output voltage VCE 0 volts Next the output voltage VCE is increased from zero volts to certain voltagelevel 10 volts and the output voltage VCE is kept constant at 10 volts Bipolar Junction TransistorCommon Emitter Configuration Input characteristics.
While increasing the output voltage VCE the input voltage VBE is kept constantat zero volts After we kept the output voltage V CE constant at 10 volts the inputvoltage VBE is increased from zero volts to different voltage levels For each voltagelevel of input voltage VBE the corresponding input current IB is recorded A curve is then drawn between input current IB and input voltage VBE at constant.
output voltage VCE 10 volts This process is repeated for higher fixedvalues of output voltage VCE When output voltage VCE is at zero volts andemitter base junction is forward biased by input.
voltage VBE the emitter base junction acts likea normal p n junction diode So the input characteristics of the CEconfiguration is same as the characteristicsof a normal pn junction diode .
Bipolar Junction TransistorCommon Emitter Configuration Input characteristicsIn common emitter CE configuration the input current IB is very small asBipolar Junction TransistorCommon Base Configuration. The collector-base junction J C. at output side acts somewhat like a reverse biased diode.. So the common base amplifier has high output impedance. The common base amplifier provides a low input impedance and high output impedance.

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