The document discusses transistor hybrid parameters (h-parameters) and their use in analyzing transistor circuits. It defines the four h-parameters - h11, h12, h21, h22 - for a two-port network. It describes how h-parameters are defined for common emitter, base, and collector configurations. The hybrid model allows representing a transistor as a dependent current source and voltage-controlled dependent voltage/current sources. The parameters help analyze small signal amplifiers by obtaining their current gain, input resistance, voltage gain, and output resistance.

2. Prepared By:
Himal Desai 140120109008
Abhishek Choksi 140120109005
Harsh Dedakiya 140120109012

3. H – Parameter model :-
→ 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.
Two port devices & Network Parameters:-
→ A transistor can be treated as a two part network. The terminal
behaviour 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, as shown in figure.

4. → 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.
 Z – Parameters (or) Impedance parameters
 Y – Parameters (or) Admittance parameters
 H – Parameters (or) Hybrid parameters.

5. Why is the name hybrid parameters
• The four parameters associated with this model are input
impedance, current gain and output conductance. Since
their units are completely different from each other, this
set of parameters is called as hybrid parameters.

6. 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
V1 = h11 i1 + h12 V2
i2 = h21 i1 + h22 V2
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.

7. 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.
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.

8. The Hybrid Model :-
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

9. Transistor Hybrid model:- Consider the simple CE configuration of Fig. For this
configuration the four variables are as follows :
1- Input current Ii = Ib 3 - Output current Io = Ic
2- Input voltage Vi = Vbe 4 – Output voltage Vo = Vce
CE Transistor Circuit

10. • By applying KCL at the collector node ,
• Expressions for h-parameters for CE configuration can be
obtained from above equ. By letting Vce or Ib equal to 0
• h- parameters for CE configuration are : if we consider Vce =
0 ,
 hie = Vbe / Ib
 hfe = Ic / Ib
 Now if we consider Ib = 0 ,
 hre = Vbe / Vce
 h0e = Ic / Vce

11. • Hence we can neglect hre and h0e while drawing the h-
parameter equivalent circuit. Such an equivalent circuit is
called as the approximate hybrid equivalent circuit which is
shown iv above fig.
• Note that the dependent voltage source Vce has been
replaced by a short circuit.
• And h0e has been replaced by an open circuit.

12. h-Parameter Model for CC Configuration
• h- parameters for CE configuration are : if we consider Vec =
0 ,
 hie = Vbe / Ib
 hfe = Ie / Ib
 Now if we consider Ib = 0 ,
 hre = Vbe / Vec
 h0e = Ice / Vec

13. • If these parameters are specified for a particular
configuration, then suffixes e,b or c are also included, e.g.
hfe ,h ib are h parameters of common emitter and common
collector amplifiers
• Using two equations the generalized model of the amplifier
can be drawn as shown in fig.

14. Various Forms
Common
Emitter (e)
Common
Base (b)
Common
Collector (c)
hi (ohms) VB/IB VE/IB VB/IB
hr (unitless) VB/VC VE/VC VB/VE
hf (unitless) IC/IB IC/IE IE/IB
ho (watts) ICVC ICVC IEVE

15. Merits of Hybrid Model
• H parameters can be easily measured.
• They can be calculated from the static
characteristics of transistor.
• Manufacturers provide h parameters in their
data sheets.
• H parameters can be used easily and
conveniently in circuit analysis and design.

16. Demerits of the h-parameters
• The hybrid parameters suffer from a major
disadvantage that they are defined only for a
particular set of operating conditions.
• The paremeters of other equivalent circuit can
be determined for any region of operation
within the active region and are not limited by
the single set of parameters provided by the
specification sheet.

17. Small Signal Amplifier Analysis
• We represent the transistor amplifier circuit in
the form of a two port network as shown in
fig.
• This two port network represent the transistor
in any one of its three configurations
(CE,CB,CC).

18. Meaning of Analysis
• In the process of analysis, we obtain the
expressions for the following parameters of an
amplifier.
• 1 – Current gain
• 2 – Input resistance
• 3 – Voltage gain
• 4 – Output resiistance
• By comparing the values of these parameters
with the others, we can judge the performance of
the amplifier.

19. Steps to follow for analysis of a
Transistor Amplifier Circuit :
• Replace the DC voltage sources by a short
circuit.
• Replace each of the coupling capacitors and
bypass capacitors by a short circuit.
• Finally, replace the transistor by its hybrid
equivalent model or re model and proceed
with the analysis.