This document discusses amplifiers, specifically focusing on BJT (Bipolar Junction Transistor) and MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) small signal models used for analyzing common emitter, common base, and common collector configurations. It covers the hybrid parameter model for transistors, including advantages, various parameters, and their applications in circuit analysis. Additionally, it includes links to video resources and references for further study in electronic devices and circuits.

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

2. 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

3. 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

4. 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

5. 5
Two Port Network

6. 6
Two Port Network

7. 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

8. 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

9. 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

10. 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.

11. 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. 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. 13
Common emitter hybrid equivalent circuit

14. 14
Common base hybrid equivalent circuit

15. 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>

16. January 2004ENGI 242/ELEC 22216
HYBRID MODEL PI

17. January 2004ENGI 242/ELEC 22217
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

18. January 2004ENGI 242/ELEC 22218
HYBRID MODEL PI PARAMETERS
 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

19. January 2004ENGI 242/ELEC 22219
HYBRID MODEL PI PARAMETERS
 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

20. January 2004ENGI 242/ELEC 22220
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

21. January 2004ENGI 242/ELEC 22221
Hybrid Pi Relationships

22. January 2004ENGI 242/ELEC 22222
HYBRID MODEL PI MID BAND

23. January 2004ENGI 242/ELEC 22223
HYBRID MODEL PI HIGH FREQ.

24. January 2004ENGI 242/ELEC 22224
Common Emitter Amplifier

25. January 2004ENGI 242/ELEC 22225
Common Emitter Amplifier – DC Bias Model

26. January 2004ENGI 242/ELEC 22226
Common Emitter Amplifier - Complete Hybrid PI

27. January 2004ENGI 242/ELEC 22227
Mid Band Hybrid PI Common Emitter

28. January 2004ENGI 242/ELEC 22228
Equivalent Circuit to find ZO

29. January 2004ENGI 242/ELEC 22229
High Frequency Hybrid PI CE Amp

30. January 2004ENGI 242/ELEC 22230
Common Emitter Amplifier

31. January 2004ENGI 242/ELEC 22231
CE Amplifer Example output

32. January 2004ENGI 242/ELEC 22232
Common Emitter Amplifier

33. January 2004ENGI 242/ELEC 22233
CE Amplifer Example output

34. January 2004ENGI 242/ELEC 22234
Emitter Follower

35. January 2004ENGI 242/ELEC 22235
Emitter Follower

36. January 2004ENGI 242/ELEC 22236
Emitter Follower

37. January 2004ENGI 242/ELEC 22237
Emitter Follower

38. January 2004ENGI 242/ELEC 22238
Emitter Follower

39. January 2004ENGI 242/ELEC 22239
Common Base

40. January 2004ENGI 242/ELEC 22240
Common Base

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

42. 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

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

44. 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
44 Dr Gnanasekaran Thangavel 7/11/2018

45. Other presentations
http://www.slideshare.net/drgst/presentations
45 Dr Gnanasekaran Thangavel 7/11/2018

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