The hybrid transistor model with two port network is discussed here.

1. Hybrid Transistor Model
WITH TWO PORT NETWORK
Prepared by:
Muhammad Ridwanul Hoque

2. Two Port Network
• A pair of terminals through which a
current may enter or leave a network is
known as a port.
• Two terminal devices or elements (such as
resistors, capacitors, and inductors)
results in one – port network.
• A two – port network is an electrical
network with two separate ports for
input and output.
• It has two terminal pairs acting as
access points. The current entering
one terminal of a pair leaves the
other terminal in the pair.

3. Why to Study Two Port Network
 Such networks are useful in communication, control
system, power systems and electronics.
 Knowing the parameters of a two – port network
enables us to treat it as a “black box” when
embedded within a larger network.

4. z-parameters/ Impedance Parameters
Here, I1 & I2 are independent
variables.A two-port network driven by voltage source
V1 = z11 I1 + z12 I2
V2 = z21 I1 + z22 I2

5. Where,
Z11 = open – circuit input impedance.
Z12 = open – circuit transfer impedance from
port 1 to port 2.
Z21 = open – circuit transfer impedance from
port 2 to port 1.
Z22 = open – circuit output impedance.
Fig: Determination of the z
parameters:
(a) finding z11 and z21 ,
(b) finding z12 and z22

6. Fig: General Equivalent Circuit of z-parameters

7. An ideal transformer has no z parameters.
The defining equations for the two-port
network are:
V1 = (1/n)V2
I1 = −nI2

8. y-parameters/
Admittance Parameters
Fig; Determination of the y parameters:
(a) finding y11 and y21, (b) finding y12
and y22.

9. I1 = y11 V1 + y12 V2
I2 = y21 V1 + y22 V2
Fig: General Equivalent Circuit
y11 = Short-circuit input admittance
y12 = Short-circuit transfer
admittance from port 2 to port 1
y21 = Short-circuit transfer
admittance from port 1 to port 2
y22 = Short-circuit output admittance

10. h-parameters/ Hybrid Parameters
A linear circuit is one in which
resistances, inductances &
capacitances remain fixed when
voltage across them changes.
Every linear circuit having input and
output terminals can be analysed by
4 parameters (one in ohm, one in
mho and two dimensionless)called
hybrid or h-parameters.

11. Matrix Form :
Here, I1 & V2 are independent
variables.

12. When V2=0 When I1=0
Where,
h11 =short– circuit input impedance.
h12 = open – circuit reverse voltage gain.
h21 = short – circuit forward current gain.
h22 = open – circuit output admittance.

13. The h-parameter equivalent
network of a two port network
V1 = h11 I1 + h12 V2
I2 = h21 I1 + h22 V2

14. 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.
 This circuit is called hybrid equivalent because its input
portion is a Thevenin equivalent, or voltage generator
with series resistance, while output side is Norton
equivalent, or current generator with shunt resistance.
Thus it is a mixture or a hybrid.

15. What will be the case if v1 & I2 are taken as
independent variables?

16. Transistor Hybrid Model

17. Table below shows the h-parameter
nomenclature of a transistor :
First letter i, r, f or o indicates the nature of parameter. The second letters
b, e and c respectively indicate CB, CE and CC arrangement.

18. Common-emitter configuration: (a) graphical symbol; (b)
hybrid equivalent circuit.

19. Common-base configuration: (a) graphical symbol; (b)
hybrid equivalent circuit.

20. Fig: Effect of removing h re and h oe from the hybird
equivalent circuit.
Fig: Approximate hybrid equivalent model.

21. 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.

22. Limitations of h Parameters
 It is very difficult to get the exact values of h parameters for a particular
transistor. It is because these parameters are subject to considerable
variation—unit to unit variation, variation due to change in temperature
and variation due to change in operating point. In predicting an
amplifier performance, care must be taken to use h parameter values
that are correct for the operating point being considered.
 The h-parameter approach gives correct answers for small ac signals
only. It is because a transistor behaves as a linear device for small signals
only.

23. THANK YOU