BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4...
Transcript of BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4...
![Page 1: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/1.jpg)
B
C
E
BIASING OF BJTS
![Page 2: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/2.jpg)
The Bipolar Junction Transistor_ slide 3
BJT Relationships – Equations slide 4
DC and DC slides 5
BJT Example slide 6
BJT Transconductance Curve _slide 7
Modes of Operation_ slide 8
Three Types of BJT Biasing_ slide 9
Common Base_ _slide 10-11
Common Emitter_ _slide 12
Common Collector slide 13
Eber-Moll Model_ slides 14-15
Small Signal BJT Equivalent Circuit _slides 16
The Early Effect slide 17
Early Effect Example slide 18
Breakdown Voltage _slide 19
Sources slide 20
Table of Contents
![Page 3: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/3.jpg)
The BJT – Bipolar Junction Transistor Note: It will be very helpful to go through the Analog Electronics
Diodes Tutorial to get information on doping, n-type and p-type materials.
The Two Types of BJT Transistors:
npn pnp
B
C
B
C E n p n
Cross Section
E p n p
Cross Section
B
C
E
Schematic
Symbol
B
C
E
Schematic
Symbol
• Collector doping is usually ~ 106
•
•
Base doping is slightly higher ~ 107 – 108
Emitter doping is much higher ~ 1015
![Page 4: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/4.jpg)
BJT Relationships - Equations
B
C E
IE IC
IB
-
+
VBE VBC
+
-
- V + CE
B
C E
IE IC
I B -
+
VEB VCB
+
-
+ - VEC
npn
IE = IB + IC
VCE = -VBC + VBE
pnp
IE = IB + IC
VEC = VEB - VCB
Note: The equations seen above are for the
transistor, not the circuit.
![Page 5: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/5.jpg)
DC and DC
= Common-emitter current gain
= Common-base current gain
= IC = IC
IB IE
The relationships between the two parameters are:
= =
+ 1 1 -
Note: and are sometimes referred to as dc and dc
because the relationships being dealt with in the BJT
are DC.
![Page 6: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/6.jpg)
BJT Example
+ _
+ _
Find: IE , , and
Solution:
IE = IB + IC = 0.05 mA + 1 mA = 1.05 mA
= IC / IB = 1 mA / 0.05 mA = 20
= IC / IE = 1 mA / 1.05 mA = 0.95238
could also be calculated using the value of
with the formula from the previous slide.
= = 20 = 0.95238
+ 1 21
IC
IE
IB
V CB
VBE
E
Using Common-Base NPN Circuit Configuration
C Given: IB = 50 A , IC = 1 mA
B
![Page 7: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/7.jpg)
BJT Transconductance Curve
IC
2 mA
4 mA
6 mA
8 mA
0.7 V
Typical NPN Transistor 1
Collector Current:
IC = IES eVBE/ VT
Transconductance:
(slope of the curve)
gm = IC / VBE
IES = The reverse saturation current
of the B-E Junction.
VT = kT/q = 26 mV (@ T=300K)
= the emission coefficient and is
VBE usually ~1
![Page 8: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/8.jpg)
Modes of Operation
• Most important mode of operation
• Central to amplifier operation
• The region where current curves are practically flat
Active:
Saturation: • Barrier potential of the junctions cancel each other out
causing a virtual short
Cutoff: • Current reduced to zero
• Ideal transistor behaves like an open switch
* Note: There is also a mode of operation
called inverse active, but it is rarely used.
![Page 9: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/9.jpg)
Three Types of BJT Biasing
Biasing the transistor refers to applying voltage to get the
transistor to achieve certain operating conditions.
Common-Base Biasing (CB) : input = VEB & IE
output = VCB & IC
Common-Emitter Biasing (CE): input = VBE & IB
output = VCE & IC
Common-Collector Biasing (CC): input = VBC & IB
output = VEC & IE
![Page 10: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/10.jpg)
Common-Base S
atu
rati
on
Re
gio
n
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
IC
Active
Region
IE
Cutoff
IE = 0
VCB
![Page 11: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/11.jpg)
Common-Base
Circuit Diagram: NPN Transistor
+
_
+
_
I C I E
I B
V CB V BE
E C
B
VCE
VBE VCB
Region of Operation
I C V CE V BE V CB Bias C-B E-B
Bias
Active IB =VBE+VCE ~0.7V 0V Rev. Fwd.
Saturation Max ~0V ~0.7V -0.7V<VCE<0 Fwd. Fwd.
Cutoff ~0 =VBBEE+VCCEE 0V 0V Rev. None /Rev.
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.
![Page 12: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/12.jpg)
Common-Emitter Circuit Diagram
+ _ VCC
I C
VCE
IB
Collector-Current Curves
VCE
IC
Active
Region
IB
Saturation Region
Cutoff Region
B I = 0
Region of Operation
Description
Active Small base current controls a large collector current
Saturation V ~ 0.2V, V CE(sat) CE
increases with IC
Cutoff Achieved by reducing IB to 0, Ideally, IC will
also equal 0.
![Page 13: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/13.jpg)
Common-Collector
Emitter-Current Curves
V CE
IE
Active
Region
I B
Saturation Region
Cutoff Region
IB = 0
The Common-
Collector 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
![Page 14: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/14.jpg)
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 C
IR IF
IE IC
IB
B
RIE RIC
![Page 15: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/15.jpg)
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]
![Page 16: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/16.jpg)
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 r
iE
iC iB
B C
E
r = ( + 1) * VT
IE
@ = 1 and T = 25 C
r = ( + 1) * 0.026
IE
Recall:
= IC / IB
![Page 17: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/17.jpg)
The Early Effect (Early Voltage)
VCE
IC Note: Common-Emitter
Configuration
-VA
IB
Green = Ideal IC
Orange = Actual IC (IC’)
IC’ = IC VCE + 1
VA
![Page 18: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/18.jpg)
Early Effect Example
Given: The common-emitter circuit below with IB = 25A,
VCC = 15V, = 100 and VA = 80.
Find: a) The ideal collector current
b) The actual collector current
Circuit Diagram
+ _ V CC
IC
V CE
I B
= 100 = I /I C B
a)
C B I = 100 * I = 100 * (25x10-6 A)
IC = 2.5 mA
b) IC’ = IC VCE + 1 = 2.5x10-3 15 + 1 = 2.96 mA
VA 80
IC’ = 2.96 mA
![Page 19: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/19.jpg)
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
![Page 20: BIASING OF BJTS...The Bipolar Junction Transistor_ slide 3 BJT Relationships – Equations slide 4 DC and DC slides 5 BJT Example slide 6 BJT Transconductance Curve _slide 7 Modes](https://reader030.fdocuments.in/reader030/viewer/2022040103/5e4ea2bc9e01a4273b521bfc/html5/thumbnails/20.jpg)
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