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 . It can be shown that (see S.M. Sze, Physics of Semiconductor Devices), therefore . where. More Complete Ebers-Moll Model. Model includes configurational. Ideal transistor model. Forward active mode of operation General bias modes of a bipolar transistor The Ebers-Moll model Saturation.

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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, and decreasing the width of the base.

Ebers Moll Equations

This section’s use of external links may not follow Wikipedia’s policies or guidelines. The DC emitter and collector omll in active mode are well modeled by an approximation to the Ebers—Moll model:. For this the h oe and h re parameters are neglected that is, they are set to infinity and zero, respectively.

A small current leaving the base is omdel in the collector output. Transistor Manual 6th ed. The incidental low performance BJTs inherent in CMOS ICs, however, are often utilized as bandgap voltage referencesilicon bandgap temperature sensor and to handle electrostatic discharge.

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.

The electrons in the base are called minority carriers because the base is doped p-type, which makes holes the majority carrier in the base.


The two diodes represent the base-emitter and base-collector diodes. It is convenient to rewrite the emitter current due to electrons, I E,nas a function of the total excess minority charge in the base, D Q n,B.

Chapter 5: Bipolar Junction Transistors

Sedra and Kenneth C. This variation in base width often is called the Early effect after its discoverer James M.

However, current in many metal conductors is due to the flow of electrons which, because they carry a negative charge, move in the direction opposite to conventional current. This mode, transport factor can also be expressed in function of the diffusion length in the base:. Arrow according to schematic.

In contrast, unipolar transistors, such as field-effect transistorsonly use one kind of charge carrier. Small changes in the voltage applied across the base—emitter terminals cause the current between the emitter and the collector to change significantly.

In a PNP transistor, the emitter—base region is forward biased, so holes are injected into the base as minority carriers. If the emitter-base junction is reverse biased into avalanche or Zener mode and charge flows for a short period of time, the current gain of the BJT will be permanently degraded.

Ebers Moll Model

That drift component of transport mkll the normal diffusive transport, increasing the frequency response of the transistor by shortening the transit time across the base.

Therefore, the base-collector junction is also forward biased. The long minority-carrier lifetime and the long diffusion lengths in those materials justify the exclusion of recombination in the base or the depletion layer.


These regions are, respectively, p type, n type and p type in a PNP transistor, and n type, p type and n type in an NPN transistor. By design, most of the BJT collector current is due to the flow of charge carriers electrons or holes injected from a high-concentration emitter into the base where they are minority carriers that diffuse toward the collector, and so BJTs are classified as minority-carrier devices. Semiconductor Device Physics and Simulation.

The forward- and reverse-bias transport factors are obtained by measuring the current gain in the forward active and reverse active mode of operation. The emitter current therefore equals the excess minority carrier charge present in the base region, divided by the time this charge spends in the base.

Bipolar junction transistor

The minority-carrier distribution in the quasi-neutral regions of the bipolar transistor, as shown in Figure 5. The BJT remains a device that dbers in some applications, such as discrete circuit design, due to the ehers wide selection of BJT types available, and because of its high transconductance and output resistance compared to MOSFETs. The collector current in a BJT when operated in normal mode is given as.

The saturation voltage equals: Moll introduced their mathematical model of transistor currents: A bipolar junction transistor bipolar transistor or BJT is a type of transistor that uses both electron and hole charge carriers. This model of transistor is known as Ebers Moll model of transistor.