Gain medium Incoherent Light Coherent Light ECE 663 Transistor/switch/amplifier – a 3 terminal...
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Transcript of Gain medium Incoherent Light Coherent Light ECE 663 Transistor/switch/amplifier – a 3 terminal...
Gain medium
Incoherent Light
Coherent Light
ECE 663
Transistor/switch/amplifier – a 3 terminal device
Source
Drain
Gate
Valve
ArteryVein
Emitter Collector
Base
Ion Channel
Dam Laser Heart
Axonal conductionMOSFETBJT
All of these share a feature with…
• Output current can toggle between large and small (Switching Digital logic; create 0s and 1s)
• Small change in ‘valve’ (3rd terminal) creates Large change in output between 1st and 2nd terminal (Amplification Analog applications; Turn 0.5 50)
Aim of this chapter
• How can we get ‘Gain’?
• What is the structure of the device to get gain?
• What is the equation for gain?
• How can we use this equation to maximize gain?
• How can we model this device as a circuit element?
• What are its AC characteristics and speed?
Recall p-n junction
P N
W
Vappl > 0
-+
N P
W
Vappl < 0
-+
Forward bias, + on P, - on N (Shrink W, Vbi)
Allow holes to jump over barrier into N region as minority carriers
Reverse bias, + on N, - on P (Expand W, Vbi)
Remove holes and electrons awayfrom depletion region
I
V
I
V
So if we combine these by fusing their terminals…
P N
W
Vappl > 0
-+
N P
W
Vappl < 0
-+
Holes from P region (“Emitter”) of 1st PN junction driven by FB of 1st PN junction into central N region (“Base”)
Driven by RB of 2nd PN junction from Base into P region of2nd junction (“Collector”)
• 1st region FB, 2nd RB
• If we want to worry about holes alone, need P+ on 1st region
• For holes to be removed by collector, base region must be thin
Bipolar Junction Transistors: Basics
+
- +
-
IE IBIC
IE = IB + IC ………(KCL)
VEC = VEB + VBC ……… (KVL)
+
- +
-
IE IBIC
ECE 663
Bipolar Junction Transistors: Basics
VEB, VBC > 0 VEC >> 0IE, IC > 0 IB > 0
VEB >-VBC > 0 VEC > 0 but smallIE > -IC > 0 IB > 0
VEB < 0, VBC > 0 VEC > 0IE < 0, IC > 0 IB > 0 but small
ECE 663
Bipolar Junction Transistors: Basics
Bias Mode E-B Junction C-B Junction
Saturation Forward Forward
Active Forward Reverse
Inverted Reverse Forward
Cutoff Reverse Reverse
ECE 663
PNP Transistor Active Bias Mode
Most holesdiffuse tocollector
Large injectionof Holes
Collector Fields drive holesfar away where they can’t return thermionically
Few recombinein the base
VEB > 0 VCB > 0
ECE 663
PNP transistor amplifier action
IN (small)
OUT (large)
Clearly this works in common emitterconfiguration
ECE 663
Emitter Injection Efficiency - PNP
EnEp
Ep
E
Ep
II
I
I
I
10
ECIEp
ICp
IEn ICn
IB
IE IC
Can we make the emittersee holes alone?
ECE 663
Base Transport Factor
ECIEp
ICp
IEn ICn
IB
IE IC
Ep
CpT I
I
10 T Can all injected holesmake it to the collector?
ECE 663
Common Base DC current gain - PNP
Common Base – Active Bias mode:
IC = DCIE + ICB0
ICp = TIEp = TIE
IC = TIE + ICn
DC = T
ECE 663
Common Emitter DC current gain - PNP
Common Emitter – Active Bias mode:
IE = DCIB + ICE0
DC = DC /(1-DC)
IE
IB
IC
IC = DCIE + ICB0
= DC(IC + IB) + ICB0
IC = DCIB + ICB0
1-DC
GAIN !!
ECE 663
Common Emitter DC current gain - PNP
T
Tdc
1
Thin base will make T 1Highly doped P region will make 1