The primary function of a model is to predict the behaviour of a device in particular operating region. from Bell Laboratories in the early 1954. The Ebers-Moll model provides an alternative view or representation of the voltage-current equation model .
What is Ebers-Moll equation?
The Ebers-Moll equations are based on two exponential diodes plus two current-controlled current sources . The NPN Bipolar Transistor block provides the following enhancements to that model: Early voltage effect. Optional base, collector, and emitter resistances.
Why Ebers-Moll model is a large signal model?
The Ebers-Moll BJT Model is a good large-signal, steady-state model of the transistor and allows the state of conduction of the device to be easily determined for different modes of operation of the device . The different modes of operation are determined by the manner in which the junctions are biased.
What is VT in BJT transistor?
For BJT single stage amplifier we write gm=Ic/VT where VT is Thermal voltage whose value is 26mv .
What is meant by early effect?
The Early effect, named after its discoverer James M. Early, is the variation in the effective width of the base in a bipolar junction transistor (BJT) due to a variation in the applied base-to-collector voltage .
What are the biasing techniques used in BJT?
- Base Bias or Fixed Current Bias. ...
- Base Bias with Emitter Feedback. ...
- Base Bias with Collector Feedback. ...
- Base Bias with Collector And Emitter Feedbacks. ...
- Emitter Bias with Two Supplies. ...
- Voltage Divider Bias. ...
- Input Impedance. ...
- Output Impedance.
What is forward active mode?
Active mode is when the Base-Emitter junction is forward biased and the Base-Collector Junction is Reverse biased. For the npn this means that the Base has a higher potential than the Emitter and a lower potential than the collector.
What are gummel characteristics?
The Gummel Plot shows the logarithm of the base current as a function of the emitter-base voltage . From the slope of the base current characteristics, the ideality of the diode response can be determined. In addition, logarithm of the collector current as a function of the emitter-base voltage also will be plotted.
How does a multiple emitter transistor work?
Multiple-emitter transistors replace the diodes of diode–transistor logic (DTL) to make transistor–transistor logic (TTL) , and thereby allow reduction of switching time and power dissipation.
What is Ebers-Moll model of BJT?
The Ebers-Moll BJT Model is a good large-signal, steady-state model of the transistor and allows the state of conduction of the device to be easily determined for different modes of operation of the device. The different modes of operation are determined by the manner in which the junctions are biased.
Why is VBE 0.7 V?
The base emitter junction is a PN junction or you can consider that as a diode. And the voltage drop across a silicon diode when forward biased is ~0.7V. That is why most of the books write VBE=0.7V, for an NPN silicon transistor with forward biased emitter junction at room temperature.
Why VCE SAT is 0.2 V?
transistor vce voltage drop
It is because both the junctions in the transistor are forward biased at saturation . Under this condition, for npn transistor the emitter to base voltage is ~+0.7V and than between the base to collector ~0.5V (base p, collector n).
How is ICEO calculated?
Iceo = Icbo/(1-α) where Iceo is collector-emitter reversed current when Ib=0, Icbo is collector-base reversed current when Ie=0.
What are the effect of early effect?
The early effect is the variation in the width of the base in a bipolar transistor due to a variation in the applied base-to-collector voltage . For example a greater reverse bias across the collector- base junction increases the collector-base depletion width. If VCE increases VCB increases too.
What is the difference between BJT and FET?
| BJT FET | BJT gain is more FET gain is less | Its output impedance is high due to high gain Its output impedance is low due to low gain |
|---|
Why BJT is called current controlled device?
A BJT is a current controlled device because its output characteristics are determined by the input current . A FET is voltage controlled device because its output characteristics are determined by the Field which depends on Voltage applied.
