Ete411 Lec15
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Transcript of Ete411 Lec15
ETE444 :: Lec15
Dr. Mashiur Rahman
Copyright: Semiconductor Physics And Devices 3rd ed. - J. Neamen
Forward-active mode
Injection and collection of electrons
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
Four operation mode of bipolar transistor
n
Cuttoff mode
VCB> 0VBE < 0
Minority carrier distribution
B-E = reverse biased Mejority carrier electrons from the emitter will not injected into the bias
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
Inverse active
VCB < 0VBE < 0
Minority carrier distribution
The B-E forward biased and C-B
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.
Application
• Voltage amplifier by Bipolar Transistors
• Switching
Voltage amplifier by Bipolar Transistors
Input sinusoidal signal voltage
Sinusoidal collector currents
Sinusoidal base currents
Sinusoidal voltage across the Rc resistor
Switching
Circuit used for transistor switching
Delay time
Raise time Storage time
Fall time
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.