EC8353 ELECTRONIC DEVICES AND CIRCUITS Unit 3

EC8353 ELECTRONIC DEVICES AND CIRCUITS
Unit 3
Dr Gnanasekaran Thangavel
Professor and Head
Electronics and Instrumentation
Engineering
R M K Engineering College

UNIT III AMPLIFIERS
BJT small signal model – Analysis of CE, CB, CC
amplifiers- Gain and frequency response – MOSFET
small signal model– Analysis of CS and Source follower
– Gain and frequency response- High frequency
analysis.
2 Dr Gnanasekaran Thangavel 7/11/2018
https://www.youtube.com/watch?v=jZ-pD8nVD6s
https://www.youtube.com/watch?v=Vd5cxAS-lpg
https://www.youtube.com/watch?v=3m2_p3SFWdQ

BJT small signal model
Definition
Small-signal modeling is a common analysis technique in
electronics engineering which is used to approximate the
behavior of electronic circuits containing nonlinear devices
with linear equations.
It is applicable to electronic circuits in which the AC signals,
the time-varying currents and voltages in the circuit, have a
small magnitude compared to the DC bias currents and
voltages.
A small-signal model is an AC equivalent circuit in which the
nonlinear circuit elements are replaced by linear elements
whose values are given by the first-order (linear)3 Dr Gnanasekaran Thangavel 7/11/2018
https://www.youtube.com/watch?v=NESchIntkR8

The hybrid parameter model for Transistor
 The transistor is two port device with one terminal being
common to both the input and the output
 The behavior of the two port network is analyzed using the
current and voltage parameters of the ports.
 Out of the four parameters two are considered
independent and the remaining two are dependent and
they are expressed in terms of the independent
parameters.
 Consider a generalized two port network

January 2004ENGI 242/ELEC 2227
Hybrid Equivalent Circuit for BJT
1 11 12 1
2 21 22 2
V h h I
=
I h h V

Hybrid Parameter Model
hi
hrVo
hohfIiVi
Ii
2
2'
Io
Vo
1
1'
11 12
21 22
i i o i i r o
o i o f i o o
V h I h V h I h V
I h I h V h I h V
   
   
Linear Two port DeviceVi
Ii Io
Vo

11 12
21 22
0 0
0 0
i i
o ii o
o o
o ii o
V V
h h
V II V
I I
h h
V II V
 
 
 
 
h-Parameters
h11 = hi = Input Resistance
h12 = hr = Reverse Transfer Voltage Ratio
h21 = hf = Forward Transfer Current Ratio
h22 = ho = Output Admittance

The dimensions of h – parameters
7/11/2018Dr Gnanasekaran Thangavel10
h11 - Ω
h22 – mhos
h12, h21 – dimension less.
As the dimensions are not alike, (i.e) they are hybrid in nature, and
these parameters are called as hybrid parameters.

Transistor Hybrid Model - Advantages
7/11/2018Dr Gnanasekaran Thangavel11
• Use of h – parameters to describe a transistor have the following
advantages:
• h – parameters are real numbers up to radio frequencies .
• They are easy to measure
• They can be determined from the transistor static characteristics curves.
• They are convenient to use in circuit analysis and design.
• Easily convert able from one configuration to other.
• Readily supplied by manufactories.

12
General h-Parameters for any Transistor Configuration
hi = input resistance
hr = reverse transfer voltage ratio (Vi/Vo)
hf = forward transfer current ratio (Io/Ii)
ho = output conductance

13
Common emitter hybrid equivalent circuit

14
Common base hybrid equivalent circuit

15
h-parameter Model for Common Emitter
Parameters from the spec sheet (x = lead based on circuit configuration):
h11 = hix
h12 = hrx
h21 = hfx
h22 = hox
hrx and hfx are dimensionless ratios
hix is an impedance <>
hox is an admittance <S>

HYBRID MODEL PI

HYBRID MODEL PI PARAMETERS
 Parasitic Resistances
 rb = rb’b = ohmic resistance – voltage drop in base region caused by
transverse flow of majority carriers, 50 ≤ rb ≤ 500
 rc = rce = collector emitter resistance – change in Ic due to change in
Vc, 20 ≤ rc ≤ 500
 rex = emitter lead resistance
 important if IC very large, 1 ≤ rex ≤ 3

 Parasitic Capacitances
 Cje0 = Base-emitter junction (depletion layer) capacitance, 0.1pF ≤
Cje0 ≤ 1pF
 C0 = Base-collector junction capacitance, 0.2pF ≤ C0 ≤ 1pF
 Ccs0 = Collector-substrate capacitance, 1pF ≤ Ccs0 ≤ 3pF
 Cje = 2Cje0 (typical)
 0 =.55V (typical)
 F = Forward transit time of minority carriers, average of lifetime of
holes and electrons, 0ps ≤ F ≤ 530ps

 r = rb’e = dynamic emitter resistance – magnitude varies to give
correct low frequency value of Vb’e for Ib
 r = rb’c = collector base resistance – accounts for change in
recombination component of Ib due to change in Vc which causes a
change in base storage
 c = Cb’e = dynamic emitter capacitance – due to Vb’e stored charge
 c = Cb’c = collector base transistion capacitance (CTC) plus Diffusion
capacitance (Cd) due to base width modulation
 gmV = gmVb’e = Ic – equivalent current generator

Hybrid Pi Relationships
C
m
T
T
C
m
C B
I
g =
V
k T
V = = 26mV @ 300 K
q
I
g =
26mV
(26mV) ( ) 26mV
r = =
I I



 = gm r
π
c m π
π
β v
i = = g v
r

Hybrid Pi Relationships

HYBRID MODEL PI MID BAND

HYBRID MODEL PI HIGH FREQ.

Common Emitter Amplifier

Common Emitter Amplifier – DC Bias Model

Common Emitter Amplifier - Complete Hybrid PI

Mid Band Hybrid PI Common Emitter

Equivalent Circuit to find ZO

High Frequency Hybrid PI CE Amp

CE Amplifer Example output

Emitter Follower

Common Base

Analysis of CE, CB, CC amplifiers
https://www.youtube.com/watch?v=QupXV7rcDIA

MOSFET small signal model
 Semiconductors
 Doping
• n-type material
• p-type material
 pn-Junctions
• forward, reverse, breakdown
• solar cells, LEDs, capacitance
https://www.youtube.com/watch?v=GQ-inadbdrg

Analysis of CS and Source follower
https://www.youtube.com/watch?v=IvoYMykaRWM
https://www.youtube.com/watch?v=4QBs3k4AZI8

References
1. David A. Bell ,”Electronic Devices and Circuits”, Prentice Hall of India,.
2. ux.brookdalecc.edu/fac/engtech/andy/engi242/powerpoint/doc/08_bjt_model.ppt
3. sietkece.com/wp-content/uploads/2016/08/EDC-PPT5.ppt
4. https://vturemedybalaji.files.wordpress.com/2016/02/electronic-circuits_unit-4.ppt

Other presentations
http://www.slideshare.net/drgst/presentations

46
Thank You
Questions and Comments?
Dr Gnanasekaran Thangavel 7/11/2018

EC8353 ELECTRONIC DEVICES AND CIRCUITS Unit 3

More Related Content

What's hot (20)

Similar to EC8353 ELECTRONIC DEVICES AND CIRCUITS Unit 3 (20)

More from RMK ENGINEERING COLLEGE, CHENNAI (20)

Recently uploaded (20)

EC8353 ELECTRONIC DEVICES AND CIRCUITS Unit 3

Editor's Notes