It’s a model to describe large signal behaviour of a transistor, and start with the simple notion of two back to back diodes. For example the diodes seen at the two . The Ebers-Moll model is an ideal model for a bipolar transistor, which can be used, in the forward active mode of. 1. 2 The Ebers-Moll Bipolar Junction Transistor Model. Introduction. The bipolar junction transistor can be considered essentially as two p- n junctions placed.

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Ebers Moll Model of a Bipolar Transistor – Electronics Area

Principles, Techniques and Applications. This is called conventional current. In addition, the collector-base area is typically larger than the emitter-base area, so that even fewer electrons make it from the collector into the emitter. They are the forward active mode of operation, the reverse active mode of operation, the saturation mode and the cut-off mode. The thermal runaway process associated with secondary breakdown, once triggered, occurs almost instantly and may catastrophically damage the transistor package.

When a transistor is used at higher frequencies, the fundamental limitation is the time it takes the carriers to diffuse across the base region The carrier densities vary linearly between the boundary values as expected when using the assumption that no significant recombination takes place in the quasi-neutral regions. Your email address will not be published. From Wikipedia, the free encyclopedia.

Consider two diodes connected back to back in the configuration shown below. Sometimes it is also called Giacoletto model because traansistor was introduced by L. The minority-carrier distribution in the quasi-neutral regions of the bipolar transistor, as shown in Figure 5.


The basic function of a BJT is to amplify current.

Ebers-moll model of transistor

While this boundary condition is mathematically equivalent to that of an ideal contact, there is an important difference.

Physics and Technology of Heterojunction Devices. Instead, they drift through the base-collector depletion region and end up as majority carriers in the collector region.

A combination of equations 5. The resulting reduction in minority carrier lifetime causes gradual loss of gain of the transistor. Early transistors were made from germanium but most modern BJTs are made ebes silicon.

The h-parameter model as shown is suited to low-frequency, small-signal mooll. These current sources depend on the current through each diode. In the reverse active mode, we reverse the function of the emitter and the collector.

Calculate the saturation voltage of a bipolar transistor biased with a base current of 1 mA and a collector current of 10 mA. Ebers—Moll model for a PNP transistor.

These equations are based on the transport model for a bipolar junction transistor. This ratio usually has a value close to unity; between 0. Because base—emitter voltage varies as the logarithm of the base—emitter and collector—emitter currents, a BJT can also be used to compute logarithms and anti-logarithms.

The Base to emitter voltage and base to collector voltage in terms of currents can be derived as follows. When the base—collector voltage reaches a certain device-specific value, the base—collector depletion region boundary meets the base—emitter depletion region boundary. Small changes in the voltage applied across the base—emitter terminals cause the current between the emitter and the collector to change significantly. This two-port network is particularly suited to BJTs as it lends itself easily to the analysis of circuit behaviour, and may be used to develop further accurate models.


The model can be quite accurate for low-frequency circuits and can easily be adapted for higher-frequency circuits with the addition of appropriate inter-electrode capacitances and other parasitic elements. The common-base current gain is approximately the gain of current from emitter to collector in the forward-active region.

The emitter current due to electrons and holes are obtained using the “short” diode expressions derived in section 4.

The Bipolar Transistor (Ebers Moll Model)

Transistod coming to important question of Why two back to back diodes cannot function as a transistor? The emitter is heavily doped, while the collector is lightly doped, allowing a large reverse bias voltage to be applied before the collector—base junction breaks down.

Such recombination current will be discussed in section 5.

An increase in the collector—base voltage, for example, causes a greater reverse bias across the collector—base junction, increasing the collector—base depletion region width, fransistor decreasing the width of the base. For high-frequency analyses the inter-electrode capacitances that are important at high frequencies must be added.