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Course Code: BEEE205L
Course Title: Electronic Devices and Circuits
Pre-requisite: BECE101L, BECE101P
Course Instructor: Dr. Aravind C K, Associate Professor Senior/SELECT
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Course Objectives
Familiarize with the semiconductor circuit
components of electronics
Describe the detailed study of discrete electronic
circuits with amplifiers as a demonstration vehicle.
Define the small-signal model extraction and analysis
of modern electronic circuits.
Dr. Aravind C K, Asso.Prof., SELECT 3
Module:2 BJT DC Analysis
BJT structure and characteristics, current gains, h-
parameters, load line, operating point analysis, DC
analysis and biasing circuits.
Dr. Aravind C K, Asso.Prof., SELECT 4
Module:3 BJT Amplifier
Small signal analysis of BJT amplifiers, calculation of
gain, input impedance, output impedance, Basic BJT
(common emitter, common collector and common
base) amplifiers, emitter degeneration.
Dr. Aravind C K, Asso.Prof., SELECT 5
Module:6 Frequency Response
Amplifier frequency response, system transfer
functions, frequency response of transistor amplifier
with circuit capacitors, high frequency response of the
MOSFET, high-frequency response of BJT.
Dr. Aravind C K, Asso.Prof., SELECT 6
12/09/2024
Dr. Aravind C K, Asso.Prof., SELECT 7
Hybrid Parameters
H-Parameters
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To predict the behaviour of a small-signal transistor amplifier, it is important
to know its operating characteristics e.g., input impedance, output
impedance, voltage gain
Every linear circuit having input and output terminals
can be analysed by four parameters (one measured in
ohm, one in mho and two dimensionless) called hybrid or
h Parameters
Dr. Aravind C K, Asso.Prof., SELECT 9
The equivalent circuit of a transistor can be dram using simple
approximation by retaining its essential features. These equivalent circuits
will aid in analyzing transistor circuits easily and rapidly.
Dr. Aravind C K, Asso.Prof., SELECT 10
Two port devices & Network Parameters:-
A transistor can be treated as a two port network.
The terminal behavior of any two-part network can be specified by the
terminal voltages V1 & V2 at parts 1 & 2 respectively and current i1 and
i2, entering parts 1 & 2, respectively.
Dr. Aravind C K, Asso.Prof., SELECT 11
Of these four variables V1, V2, i1 and i2, two can be selected as
independent variables and the remaining two can be expressed in terms
of these independent variables.
This leads to various two part parameters out of which the following
three are more important.
1. Z – Parameters (or) Impedance parameters
2. Y – Parameters (or) Admittance parameters
3. H – Parameters (or) Hybrid parameters.
Dr. Aravind C K, Asso.Prof., SELECT 12
Hybrid parameters (or) h – parameters:-
→ If the input current i1 and output Voltage V2 are takes as independent
variables, the input voltage V1 and output current i2 can be written as
v=h i+h v
1 11 1 12 2
i=h i+h v
2 21 1 22 2
Dr. Aravind C K, Asso.Prof., SELECT 13
Determination of h Parameters
If we short-circuit the output terminals - output voltage v2 = 0.
Putting v2 = 0 in equations
h11 is a ratio of voltage and current (i.e. v1/i1), it is an impedance and is
called * “input impedance with output shorted ”.
h21 is the ratio of output and input current (i.e., i2/i1), it will be
dimensionless and is called “current gain with output shorted ”.
Dr. Aravind C K, Asso.Prof., SELECT 14
Determination of h Parameters
other two h parameters (viz h12 and h22) can be found by making i1 = 0
h12 is a ratio of input and output voltages (i.e. v1/v2), it is dimensionless and is
“voltage feedback ratio with input terminals open”.
h22 is a ratio of output current and output voltage (i.e. i2/v2), it will be
admittance and is called “output admittance with input terminals open”. 15
Dr. Aravind C K, Asso.Prof., SELECT
Determination of h Parameters
The four hybrid parameters h11, h12, h21 and h22 are defined as follows.
h11 = [V1 / i1] with V2 = 0
= Input Impedance with output part short circuited.
h22 = [i2 / V2] with i1 = 0
= Output admittance with input part open circuited.
h12 = [V1 / V2] with i1 = 0
= reverse voltage transfer ratio with input part open circuited.
h21 = [i2 / i1] with V2 = 0
= Forward current gain with output part short circuited.
Dr. Aravind C K, Asso.Prof., SELECT 16
The dimensions of h – parameters are as follows:
h11 - Ω
h22 – mhos
h12, h21 – dimension less.
→ as the dimensions are not alike, (ie) they are hybrid in nature, and
these parameters are called as hybrid parameters.
I = 11 = input ; 0 = 22 = output ;
F = 21 = forward transfer ; r = 12 = Reverse transfer.
Dr. Aravind C K, Asso.Prof., SELECT 17
Notations used in transistor circuits:-
hie = h11e = Short circuit input impedance
h0e = h22e = Open circuit output admittance
hre = h12e = Open circuit reverse voltage transfer ratio
hfe = h21e = Short circuit forward current Gain.
Dr. Aravind C K, Asso.Prof., SELECT 18
Find the h parameters of the circuit shown in Fig
To find h11 and h21, short - circuit the output terminals
To find h22 and h12, open - circuit the output terminals
Dr. Aravind C K, Asso.Prof., SELECT 19
h Parameter Equivalent Circuit
Dr. Aravind C K, Asso.Prof., SELECT 20
input portion is a Thevenin equivalent, or voltage generator with series
resistance,
Output side is Norton equivalent, or current generator with shunt resistance.
This circuit is called hybrid equivalent because its is a mixture or a hybrid.
The symbol ‘h’ is simply the abbreviation of the word hybrid
Dr. Aravind C K, Asso.Prof., SELECT 21
Performance of a Linear Circuit in h Parameters
Input impedance
Consider a linear circuit with a load resistance RL across its terminals as
shown in Figgure.
The input impedance Zin of this circuit is the ratio of input voltage to
input current
Dr. Aravind C K, Asso.Prof., SELECT 22
v1 = h11 i1 + h12 v2 in terms of h parameters.
Substituting the value of v1 in the above expression,
Dr. Aravind C K, Asso.Prof., SELECT 23
i2 = – v2/rL.
Dr. Aravind C K, Asso.Prof., SELECT 24
Dr. Aravind C K, Asso.Prof., SELECT 25
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Output impedance. In order to find the output impedance, remove the load
rL, set the signal voltage v1 to zero and connect a generator of voltage v2 at the
output terminals.
Then h parameter equivalent circuit becomes as
. By definition, the output impedance Zout =v2/i2
Dr. Aravind C K, Asso.Prof., SELECT 27
Dr. Aravind C K, Asso.Prof., SELECT 28
The h Parameters of a Transistor
Dr. Aravind C K, Asso.Prof., SELECT 29
Nomenclature for Transistor h Parameters
Dr. Aravind C K, Asso.Prof., SELECT 30
The Hybrid Model for Two-port Network:-
V1 = h11 i1 + h12 V2
I2 = h1 i1 + h22 V2
↓
V1 = h1 i1 + hr V2
I2 = hf i1 + h0 V2
The Hybrid Model for Two-port Network
Dr. Aravind C K, Asso.Prof., SELECT 31
Transistor Hybrid model:-
Use of h – parameters to describe a transistor has the following advantages.
1. h – Parameters are real numbers up to radio frequencies.
2. They are easy to measure
3. They can be determined from the transistor static characteristics
curves.
4. They are convenient to use in circuit analysis and design.
5. Easily convert able from one configuration to other.
Readily supplied by manufactories.
Dr. Aravind C K, Asso.Prof., SELECT 32
Nomenclature for Transistor h Parameters
Dr. Aravind C K, Asso.Prof., SELECT 33
Transistor Circuit Performance in h Parameters
General CE
Dr. Aravind C K, Asso.Prof., SELECT 34
Dr. Aravind C K, Asso.Prof., SELECT 35
AC equivalent
This can be obtained by replacing all the dc sources with their respective
internal impedances
Dr. Aravind C K, Asso.Prof., SELECT 36
Determination of h-parameters from
Transistor Characteristics
Dr. Aravind C K, Asso.Prof., SELECT 37
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Dr. Aravind C K, Asso.Prof., SELECT 40
Typical h-Parameter Values for a Transistor
Dr. Aravind C K, Asso.Prof., SELECT 41
Conversion Formulae for Hybrid
Parameters
Dr. Aravind C K, Asso.Prof., SELECT 42
SIMPLIFIED CE HYBRID MODEL
It is justified to make approximations and simplify the expressions for AI,
AV, AP, Ri and Ro.
In addition, a better understanding of the behaviour of the transistor
circuit can be obtained by using the simplified hybrid model.
Since CE configuration is more useful and general, it is taken for
consideration
Dr. Aravind C K, Asso.Prof., SELECT 43
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Dr. Aravind C K, Asso.Prof., SELECT 45
Under this condition the magnitude of voltage of generator in the emitter
circuit is
Dr. Aravind C K, Asso.Prof., SELECT 46
if the load resistance R is small it is possible to neglect the parameter hre and
L
hoe and obtain the approximate equivalent circuit as shown below
Dr. Aravind C K, Asso.Prof., SELECT 47
Generalised Approximate Model
Dr. Aravind C K, Asso.Prof., SELECT 48
A transistor used in CE arrangement has the following set of h parameters
when the d.c. operating point is VCE = 10 volts and IC = 1 mA : hie = 2000Ω ;
hoe =10-4mho; hre = 10-3; hfe = 50 Determine (i) input impedance (ii) current
gain and (iii) voltage gain. The a.c. load seen by the transistor is rL = 600 Ω.
Dr. Aravind C K, Asso.Prof., SELECT 49
Find the (i) input impedance and (ii) voltage gain for the circuit shown in
Fig
Dr. Aravind C K, Asso.Prof., SELECT 50
Dr. Aravind C K, Asso.Prof., SELECT 51
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Dr. Aravind C K, Asso.Prof., SELECT 53
Fig. shows the transistor amplifier in CE arrangement. The h parameters
of transistor are as under :
Dr. Aravind C K, Asso.Prof., SELECT 54
