Lecture 7: Transistors
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Lecture 7: Transistors
Largely replaced the vacuum tube
Heart of modern electronics
Three-terminal semiconductor device
Amplification and switching
Two basic forms (BJT and FET)
John Bardeen William Shockley Walter Brattain
1956 Nobel Prize in Physics
Silicon
oxide
Source DrainGate
goldgold
gold
MOSFET: Metal-Oxide-Semiconductor Field-Effect Transistor
n-doping n-doping
Source DrainGate
gold• • • • • ••
Source DrainGate
gold
Current flow
p pn
BJT: Bipolar Junction Transistor
Emitter
Base
Collector
p pn
BJT: Bipolar Junction Transistor
Emitter
Base
Collector
p pn
BJT: Bipolar Junction Transistor
E
B
C
Small base current controlsmuch larger collector current
p pn
E
BC
E
BC
n np
B
B
E
EC
C
Getting the dc voltages correct: BIAS
E
BC
n-p-n transistor
Forward bias
n
np
Collector
Base
Emitter
+
−
Getting the dc voltages correct: BIAS
E
BC
n-p-n transistor
Forward bias
n
np
Collector
Base
Emitter
Reverse bias
+
+
−
−
RC
RB VC
VB
Getting the dc voltages correct: BIAS
E
BC
n-p-n transistor
Forward bias
n
np
Collector
Base
Emitter
Reverse bias
+
+
−
−
RC
RB
The BJT Amplifier
VC
VB
AC small signal input
•
o
RC
RB
VOUT
VC
The BJT Amplifier
o
VIN
VOUT
VIN
= Gain
The Transistor as a Switch
- No base bias voltage- Input current turns transistor on and off
5 V
Transistor OFF Transistor ON
5 V
VOUT = 5 V VOUT = 0.2 VZero input
currentInput
current
Collectorcurrent
No collectorcurrent
Intuitive picture of the transistor switch:Current-controlled resistor
5 V
Transistor OFF Transistor ON
Zero inputcurrent
InputcurrentR ≈ ∞
5 V
R ≈ 0
The Transistor Switch: Boolean Logic Device
5 V
VOUT
IOUT
IIN
VIN
LOGIC 0: VOLTAGE < 0.4 V LOGIC 1: VOLTAGE > 3 V
VIN IIN IOUT VOUT
Logic 0
Logic 1
0 0 Logic 1
Logic 0µA mA
NOT Gate
The Transistor AND Gate
0
1
0 0
0 0
5 V
VOUT
V1
V2
10 0
1 1 1
VOUTV1 V2
VOUT
V1
V2
The Transistor OR Gate
0
1
0 0
0 1
5 V
VOUT
V1
V2
10 1
1 1 1
VOUTV1 V2
VOUT
V1
V2
5 V
The NOR Gate
0
1
0 1
0 0
10 0
1 1 0
VOUTV1 V2
The NOR Gate
0
1
0 1
0 0
10 0
1 1 0
VOUTV1 V2
VOUTV1
V2
5 V
5 V
The NOR Gate
0
1
0 1
0 0
10 0
1 1 0
VOUTV1 V2
VOUTV1
V2
5 V
The NOR Gate
0
1
0 1
0 0
10 0
1 1 0
VOUTV1 V2
VOUTV1
V2
5 V
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