C
B
E
BJT – Bipolar Junction Transistor
Dua Type BJT Transistor:
npn
E
n
pnp
p
n
Cross Section
C
C
E
p
n
p
Cross Section
B
C
B
B
B
Symbol
Symbol
E
•
•
•
C
Collector doping is usually ~ 106
Base doping is slightly higher ~ 107 – 108
Emitter doping is much higher ~ 1015
E
Rumusan Dasar BJT
IE
-
E
IC
VCE +
IE
C
-
-
VBE
VBC
IB
+
+
E
+
VEC
+
VEB
IC
-
C
+
VCB
IB
-
-
B
B
npn
pnp
IE = IB + IC
IE = IB + IC
VCE = -VBC + VBE
VEC = VEB - VCB
DC  and DC 
 = Arus penguatan Common-emitter
 = Arus penguatan Common-base
 = IC
 = IC
IB
IE
Hubungan antara dua parameters tersebut adalah:
=

+1
=

1-
BJT Example
Konfigurasi Common-Base Transistor NPN
C
Diketahui : IB = 50  A , IC = 1 mA
Hitung
VCB
IC
+
_
IE ,  , and 
Penyelesaian:
IE = IB + IC = 0.05 mA + 1 mA = 1.05 mA
IB
B
:
 = IC / IB = 1 mA / 0.05 mA = 20
VBE
+
_
IE
E
 = IC / IE = 1 mA / 1.05 mA = 0.95238
 Juga dapat dicari dengan  dengan rumus
sebagai berikut.
=

= 20 = 0.95238
+1
21
Curve Transconductance BJT
Transistor Tipe NPN
Arus Collector :
IC =  IES eVBE/VT
IC
Transconductance:
(slope of the curve)
8 mA
gm =  IC /  VBE
6 mA
IES = Arus saturasi terbalik dari
B-E Junction.
4 mA
VT = kT/q = 26 mV (@ T=300K)
 = Coefisien emisi
2 mA
biasanya ~1
0.7 V
VBE
Modes of Operation
Active:
• Posisi terbaik pada daerah operasi
• Beroperasi sebagai penguat
Saturation: • Transistor berada sebagaimana pada posisi short
circuit.
Cutoff:
• Arus transistor nol
• Transistor yang edial sebagaimana posisi saklar terbuka
* Note: There is also a mode of operation
called inverse active, but it is rarely used.
TigaTypes dari Bias BJT
Bias transistor adalah kondisi tegangan dimana transistor
tersebut bisa melakukan operasi (kerja).
Bias Common-Base (CB) :
input
= VEB & IE
output = VCB & IC
Bias Common-Emitter (CE):
input
= VBE & IB
output = VCE & IC
Bias Common-Collector (CC): input
= VBC & IB
output = VEC & IE
Common-Base
Although the Common-Base configuration is not the most
common biasing type, it is often helpful in the understanding of
how the BJT works.
Emitter-Current Curves
Saturation Region
IC
Active
Region
IE
Cutoff
IE = 0
VCB
Common-Base
Circuit Diagram: NPN Transistor
C
VCE
IC
VCB
The Table Below lists assumptions
that can be made for the attributes
of the common-base biased circuit
in the different regions of
operation. Given for a Silicon NPN
transistor.
Region of
Operation
IC
Active
IB
Saturation
Max
Cutoff
~0
VCE
E
VBE
+
_
+
_
IB
B
VCB
VBE
=VBE+VCE ~0.7V
~0V
IE
VBE
VCB
 0V
C-B
Bias
E-B
Bias
Rev. Fwd.
~0.7V -0.7V<VCE<0 Fwd. Fwd.
=VBE+VCE  0V
 0V
Rev.
None
/Rev.
Common-Emitter
Circuit Diagram
VCE
IC
+
_
Collector-Current Curves
IC
VCC
IB
Active
Region
IB
Region of Description
Operation
Active
Arus basis yang kecil
mengontrol arus colektor
yang besar
Saturation VCE(sat) ~ 0.2V, VCE increases
with IC
Cutoff
Pada kondisi IB mendekati
0, edialnya, IC juga sama
dengan 0.
VCE
Saturation Region
Cutoff Region
IB = 0
Common-Collector
Emitter-Current Curves
The CommonCollector biasing
circuit is basically
equivalent to the
common-emitter
biased circuit except
instead of looking at
IC as a function of VCE
and IB we are looking
at IE.
Also, since  ~ 1, and
 = IC/IE that means
IC~IE
IE
Active
Region
IB
VCE
Saturation Region
Cutoff Region
IB = 0
Eber-Moll BJT Model
The Eber-Moll Model for BJTs is fairly complex, but it is
valid in all regions of BJT operation. The circuit diagram
below shows all the components of the Eber-Moll Model:
E
IE
IC
RIC
RIE
IF
IR
IB
B
C
Eber-Moll BJT Model
R = Common-base current gain (in forward active mode)
F = Common-base current gain (in inverse active mode)
IES = Reverse-Saturation Current of B-E Junction
ICS = Reverse-Saturation Current of B-C Junction
IC = FIF – IR
IB = IE - IC
IE = IF - RIR
IF = IES [exp(qVBE/kT) – 1]
IR = IC [exp(qVBC/kT) – 1]
 If IES & ICS are not given, they can be determined using various
BJT parameters.
Small Signal BJT Equivalent Circuit
The small-signal model can be used when the BJT is in the active region.
The small-signal active-region model for a CB circuit is shown below:
iB
iC
B
iB
r
r = ( + 1) * VT
IE
@  = 1 and T = 25C
r = ( + 1) * 0.026
IE
iE
E
Recall:
 = IC / IB
C
The Early Effect (Early Voltage)
IC
Note: Common-Emitter
Configuration
IB
-VA
VCE
Green = Ideal IC
Orange = Actual IC (IC’)
IC’ = IC
VCE + 1
VA
Early Effect Example
Given: The common-emitter circuit below with IB = 25A,
VCC = 15V,  = 100 and VA = 80.
Find:
a) The ideal collector current
b) The actual collector current
Circuit Diagram
IC
VCE
 = 100 = IC/IB
a)
VCC
+
_
IC = 100 * IB = 100 * (25x10-6 A)
IB
IC = 2.5 mA
b)
IC’ = IC
VCE + 1
VA
IC’ = 2.96 mA
= 2.5x10-3
15 + 1
80
= 2.96 mA
Breakdown Voltage
The maximum voltage that the BJT can withstand.
BVCEO =
The breakdown voltage for a common-emitter
biased circuit. This breakdown voltage usually
ranges from ~20-1000 Volts.
BVCBO =
The breakdown voltage for a common-base biased
circuit. This breakdown voltage is usually much
higher than BVCEO and has a minimum value of ~60
Volts.
Breakdown Voltage is Determined By:
•
•
The Base Width
Material Being Used
•
Doping Levels
•
Biasing Voltage
Sources
Dailey, Denton. Electronic Devices and Circuits, Discrete and Integrated.
Prentice Hall, New Jersey: 2001. (pp 84-153)
1
Figure 3.7, Transconductance curve for a typical npn transistor, pg 90.
Liou, J.J. and Yuan, J.S. Semiconductor Device Physics and Simulation.
Plenum Press, New York: 1998.
Neamen, Donald. Semiconductor Physics & Devices. Basic Principles.
McGraw-Hill, Boston: 1997. (pp 351-409)
Web Sites
http://www.infoplease.com/ce6/sci/A0861609.html