Ete411 Lec15
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Transcript of Ete411 Lec15
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ETE444 :: Lec15
Dr. Mashiur Rahman
Copyright: Semiconductor Physics And Devices 3rd ed. - J. Neamen
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Forward-active mode
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Injection and collection of electrons
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E
c
i
i
α = Common-Base current gainβ = Common-Emitter gain
iE1= due to the flow of electrons injected into the base = ic
B
c
i
i
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Four operation mode of bipolar transistor
n
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Cuttoff mode
VCB> 0VBE < 0
Minority carrier distribution
B-E = reverse biased Mejority carrier electrons from the emitter will not injected into the bias
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Forward active mode
VCB> 0VBE > 0
Minority carrier distribution
The B-E junction becomes forward biased, an emitter current will be generated and the injection of electrons into the base results in a collector current
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Inverse active
VCB < 0VBE < 0
Minority carrier distribution
The B-E forward biased and C-B
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Saturation mode
VCB< 0VBE > 0
Minority carrier distribution
Both B-E and B-C junctions are forward biased and the collector current no longer controlled by the B-E voltage.
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Application
• Voltage amplifier by Bipolar Transistors
• Switching
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Voltage amplifier by Bipolar Transistors
Input sinusoidal signal voltage
Sinusoidal collector currents
Sinusoidal base currents
Sinusoidal voltage across the Rc resistor
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Switching
Circuit used for transistor switching
Delay time
Raise time Storage time
Fall time
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Switching :: Important parameter
• Current gain
– lower doping in the base region is used.
• Switching time
– The transistor can be doped with gold to introduce midgap recombination centers and thus reduce the switching time.
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