Hybrid Transistor Model with Two Port Network
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This document discusses a two-port network model and the hybrid transistor model. It describes different two-port network parameter representations including z-parameters, y-parameters, and h-parameters. H-parameters are a mixture of impedance and admittance parameters, making them hybrid parameters. The document shows h-parameter equivalent circuits for common-emitter, common-base, and common-collector transistor configurations. While h-parameters can be easily measured and used for circuit analysis, their values can vary between transistors and with operating conditions.
Hybrid Transistor Model with Two Port Network
- 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?
- 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