Download Electronics

Electronics
- lectures for Mechanical Engineering
part 3
Dr. Bogusław Boratyński
Faculty of Microsystems Electronics and Photonics,
Wroclaw University of Technology,
2013
From the course syllabus
Basic literature & figure sources:
G. Rizzoni, Fundamentals of Electrical Engineering, McGraw-Hill
R.F. Pierret, Semiconductor Device Fundamentals, Addison-Wesley Publ.,
B.G. Streetman, Solid State Electronic Devices, Prentice-Hall,
D. Bell, Fundamentals of Electric Circuits, Oxford Univ. Press,
T. Mouthaan, Semiconductor Devices Explained, John Willey&Sons
Additional literature:
W. Marciniak, Przyrządy półprzewodnikowe i układy scalone, WNT,
A. Świt, J. Pułtorak, Przyrządy półprzewodnikowe, WNT,
B.G. Streetman, Przyrządy półprzewodnikowe, WNT
Semiconductor devices
Chapter 3 Electronic devices.
3.2 Bipolar transistors and applications: Amplifiers, Switches.
Transistor symbols and structure.
The amplifier and the switch.
Operation principle and biasing.
DC I-V characteristics for CE and CB configurations
Bias - operating point. The load line.
Small signal models and parameters.
Transistor amplifier circuit and analysis.
Transistor switch.
Bipolar transistor symbols and construction
Three regions, three terminals (leads)
Two p-n junctions
E – the most highly doped region (p+ or n+)
B – the thinnest region
Source: G. Rizzoni, Fundamentals of Electrical
Engineering, McGraw-Hill
The p-n diode and n-p-n transistor
A bipolar transistor – two back to back connected
p-n junctions
A p-n diode + another p-n junction…
N- type region
(donor dopants)
npn transistor in monolithic
integrated circuit design
C - collector terminal
in a discrete transistor
Source: R.F. Pierret, Semiconductor Device Fundamentals, Addison-Wesley Publishing Comp.
The amplifier circuit principles and the gain.
Transistor - two-port device
 - internal transistor gain
E - common terminal (input & output)
CE - Common Emmiter circuit
Independent source
+
Amplifier gain
VS2
IS1
Input
signal
Output
signal
Load
Equvalent transistor model
US symbols
Dependent (controlled) sources
European symbols
V
+
I
VCVS1
CCCS2
-
 - internal transistor voltage gain
 - internal transistor current gain
Source: R.F. Pierret, Semiconductor Device Fundamentals, Addison-Wesley Publishing Comp.
Transistor as a switch or a driver
Transistor - current or voltage activated switch
OFF
example: LED driver
ON
High –low
voltage
signal
Source: R.F. Pierret, Semiconductor Device Fundamentals,
Addison-Wesley Publishing Comp.
ON- OFF
state
Source: G . Rizzoni, Fundamentals of Electrical
Engineering, McGraw-Hill
Junction bias – operation modes
n-p-n
p-n-p
VCE
Active operation (Amplifier)
junction bias:
E-B forward , C-B reverse
Saturation (switch ON)
junction bias:
E-B forward , C-B forward
Cut-off (switch OFF)
junction bias:
E-B reverse , C-B reverse
Active operation
constant current gain
for signal amplification
Current relations:
IC + IE + IB =0
small IB, large IC  IE
Current gain:
Common Base
current gain
Common Emmiter
current gain
Source: G . Rizzoni, Fundamentals of Electrical
Engineering, McGraw-Hill
Junction bias – operation modes
Active operation
junction bias:
E-B forward , B-C reverse
p-n-p
Hole diffusion current (electrons in npn)
through the Base width (WB)
from Emitter to Collector
responsible for the gain
1
  0.995
electrons
IC  IE
holes
Recombination in the Base
loss of carriers, gain decrease
Flow of electrons and holes under proper junction bias for active operation.
Terminal currents
Carrier currents
Drift & Diffusion currents
circuit analysis
device analysis
physical phenomena
Source: G . Rizzoni, Fundamentals of Electrical
Engineering, McGraw-Hill
Transistor active bias – terminal bias
p-n-p
Active operation
junction bias:
E-B forward , C-B reverse
n-p-n
CB configuration gain:
CE configuration gain:
IC + IE + IB =0
1
 = /(1-)
  0.995
 = 0.995/(1-0.995)
= 0.995/0.005  200
»1
p-n-p
n-p-n
The CE transistor I-V characteristics
The output current-voltage dependence of the bipolar transistor
in Common Emitter configuration: IC–UCE for IB = const.
IB =const. – the base current is a parameter
of the family of I-V characteristics
In the active region of transistor operation
the gain  is almost constant.
IB= 0
P=U I or I=P/U
Max. dissipated power hiperbole
IC =  IB
In the saturation
region
this is not true.
In cut-off region
IC = ICE0 for IB = 0
Bipolar transistor - limits of dc bias
Voltage and current limits of a bipolar transistor operation:
- Voltage limit - CB junction breakdown, base region punch-through
- Current limit - rated current - thermal effects
- Power limit - dissipated power P = IU - thermal effects
Q-point
Common emitter – output voltage breakdown BVCBO
Common base – output voltage breakdown BVCEO
BVCBO >> BVCEO
typically: 50V – 100V (800V)
Source: B.C.Streetman Solid State Electronic Devices, Prentice Hall.
Transistor parameters - datasheet
Case and pins
Pad layout on PCB
Symbols
semiconductor:
A… - Ge
B… - Si
C… - GaAs, GaN
BC… - Si, low freq., low power
Transistor type:
BC – low. freq., low power
BD - low freq., power
BF – radio freq., low power
BL - radio freq., power
BS – switching
BU – high voltage
US code: 2Nxxxx
Transistor parameters - datasheet
Parametry dopuszczalne (elektryczne i cieplne)
important:
for common base.
for common emmiter
Transistor parameters - datasheet
BD… - low freq., power Si transistor
with radiator attached
Finding transistor operating point
Recall a DC circuit with a diode (nonlinear element)
The load line in a diode circuit
Finding the operating point - Qpoint
from KVL:
VT= RT iD + vD
and the load line equation is:
iD = -(1/ RT) vD + VT /RT
Operating point is;
iD = 21mA , vD = 1.0 V
Source: G. Rizzoni, Fundamentals of Electrical Engineering,
McGraw-Hill
The CE transistor I-V characteristics and Q-point
Basic amplifier circuit
The output current-voltage dependence of the bipolar transistor
in Common Emitter configuration: IC–UCE for IB = const. + the load line
UCC = RL IC + UCE
(from KVL)
IC = + UCE /RL – UCC /RL
UCC /RL
_
+
IC II
I
Q-point
=U
=UBE
BE
UCC
Q-point: IC = 48mA, UCE =4V, IB = 0.3mA
(quiescent point, operating point, DC bias point)
IB
=UCE
The CE transistor I-V characteristics
The input current-voltage dependence of the bipolar transistor
in Common Emitter configuration: UBE - IB for UCE = const. (parameter)
Input voltage
signal vBE
Input current
signal iB
The p-n junction (EB jn.)
forward I-V characteristic
The CE transistor I-V characteristics and ac signals
The output current-voltage characteristics and ac signal amplification
iC , iB , vCE – ac signals
iB
iC
Output current
ac signal iC =  iB
Output voltage
ac signal vCE
Source: G. Rizzoni, Fundamentals of Electrical Engineering, McGraw-Hill
The CE transistor I-V characteristics
The transfer (current-current) dependence of the bipolar transistor
in Common Emitter configuration: IC–IB for UCE = const. (parameter)
The slope denotes
the current gain 
The Gummel plot (current gain )
Source: R.F. Pierret, Semiconductor Device Fundamentals, Addison-Wesley Publishing Comp.
The output characteristics
Comparision of common emitter (CE) and common base (CB) output
characteristics of the bipolar transistor
from the previous
considerations:
if  » 1
IE  IC
IE - VBE
IE - VBE
VCE
VCB
VCE
VCE = VCB + VBE
(KVL)
The dc (large signal) model of a bipolar transistor
The current-voltage characteristics are derived based on
the Ebers-Moll equivalent model of a bipolar transistor
p
n
p
F
Active bias current
denotes
current gain at
active transistor
bias
R denotes
current gain at
reverse transistor
bias:
E-B jn. reverse
C-B jn. forward
R « F
Source: R.F. Pierret, Semiconductor Device Fundamentals, Addison-Wesley Publishing Comp.
The ac small signal model of a bipolar transistor
Small signal equivalent model [ hij ] - hybrid parameters
It is valid for low frequencies, f 100kHz (no capacitances included)
h11e 
h21e
For Common Emitter [ hije ]:
ac small signals:
I1 = iB = ΔIB
U1 = uBE = ΔUBE
I2 = iC = ΔIC
U2 = uCE =ΔUCE
dU BE U BE

 Rinput
dI B
I B
dI C I C



dI B I B
h22e 
h12e 
Where a small signal means:
uBE = ΔUBE = UM sin ωt
amplitude UM  25mV
current gain
dI C
I C
1


dU CE U CE Routput
dU BE U BE

dU CE U CE
The ac small signal model of a bipolar transistor
Basic amplifier circuit
Small signal parameters – graphical analysis
Q-point
Q-point
h11e 
dU BE U BE

 Rinput
dI B
I B
h22e 
dI C
I C
1


dU CE U CE Routput
Small signal parameters from the datasheet
BC846 hij parameters BC846 ( CE configuration)
Temperature dependence of hFE =h21E = β
IC – bias current (Q-point)
The CE transistor amplifier small signal model
Circuit diagram of a Common
Emitter (CE) amplifier
Equivalent small signal model of the
CE amplifier for low frequencies (LF)
Transistor model
Procedure:
1. Transistor is substituted by its small
signal equivalent model.
2. Power supply, due to its large
internal capacitance, for ac signals
is shorted to the ground.
The CE transistor amplifier small signal model
Voltage gain of Common Emitter (CE)
amplifier :
Equivalent small signal model of
a CE amplifier for LF
U2
U1
U
I1  I b  1
h11e
AV 
U 2  h21e I b RL
AV 
h21e
RL
h11e
if
1 / h22e  RL
AV  
Routput
AV  
Routput
General case:
AV  h21
Routput
Rinput
since
for CE amplifier
»1
Rinput
Rinput
Routput  Rinput
for CB amplifier
1
then
Av >>1 in any case