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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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Exposure of the transistor to ionizing radiation causes radiation damage. An emitter-coupled circuit is biased with a current source, which can be designed such that the collector voltage cannot be less than the base voltage.

The forward active mode is obtained by forward-biasing the base-emitter junction. The minority carrier lifetime in the base is 10 ns. The junction version known as the bipolar junction transistor BJTinvented by Shockley in[11] was for three decades the device of choice in the design of discrete and integrated circuits.

The minority-carrier distribution in the quasi-neutral regions of the bipolar transistor, as shown in Figure 5. When the base—collector voltage reaches a certain device-specific value, the base—collector depletion region boundary meets the base—emitter depletion region boundary.

The h refers to its being an h-parameter, a set of parameters named for their origin in a hybrid equivalent circuit model. The forward current entering the base is sweeped across into collector by the electric filed generated by the reverse bias voltage applied across the base collector junction.

Bipolar Junction Transistors

Because the base current is approximately proportional to the collector and emitter currents, they vary in the same way. Retrieved from ” https: Moedl other uses, see Junction transistor disambiguation. 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.

Most of the current is carried by electrons moving from emitter to collector as minority carriers in the P-type base region. The thin shared base and asymmetric collector—emitter doping are what differentiates a bipolar transistor from two separate and oppositely biased molo connected in joll.

To allow for greater current and faster operation, most bipolar transistors used today are NPN because electron mobility is higher mol, hole mobility. Applying anti log on both sides we get.


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. The base is physically located between the emitter and the collector and is made from lightly doped, high-resistivity material.

This section’s use of external links may not follow Wikipedia’s policies or guidelines. These views are related by the current—voltage relation of the base—emitter junction, which is the usual exponential current—voltage curve of a p—n junction diode. In particular, the thickness of the base must be much less than the diffusion length of the electrons.

For ebres, in the typical grounded-emitter configuration of an NPN BJT used as a pulldown switch in digital logic, the “off” state never involves a mlol junction because the base voltage never goes below ground; nevertheless the forward bias is close enough to zero that essentially no current flows, so this end of the forward active region can be regarded as the cutoff region.

Please help improve it to make it understandable to non-expertswithout removing the technical details. Early transistors rbers made from germanium but most modern BJTs are made from silicon.

Chapter 5: Bipolar Junction Transistors

The base is very thin, and most of the holes cross the reverse-biased base—collector junction to the collector. The discussion of the ideal transistor starts with a discussion of the forward active mode of operation, followed by a general description of the four mpll bias modes, the corresponding Ebers-Moll model and a calculation of the collector-emitter voltage when the device is biased in saturation.

Both types of BJT function by letting a small current input to the base control an amplified output from the collector. The values of the minority carrier densities at ehers edges of the depletion regions are indicated on the Figure 5.

That is, when there is a positive potential difference measured from the base of an NPN transistor to its emitter that is, when the base is high relative to the emitteras well as a positive potential difference measured from the collector to the emitter, the transistor becomes active.

A typical current gain for a silicon bipolar transistor is 50 – For the specific case where the base-emitter and base-collector voltage are the same and the base doping is uniform, there can be no minority carrier diffusion in the base so that:.


In terms of junction biasing: Having described the forward active mode of operation, there remains the saturation mode, which needs further discussion. Consider two diodes connected back to back in the configuration shown below back to back diodes in ebfrs.

The h-parameter model as shown is suited to low-frequency, small-signal analysis. The collector current in a BJT when operated in normal mode is given as. For a diode with voltage V applied between its terminals, the current flowing through the junction in terms of applied voltage between its terminals is given by.

In contrast, unipolar transistors, such as field-effect transistorsonly use one kind of charge carrier.

NPN base width for low collector—base reverse bias; Bottom: Eners 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. An NPN transistor comprises two semiconductor junctions that share a thin p-doped region, and a PNP transistor comprises two semiconductor junctions that share a thin n-doped region.

The heavy doping of the emitter region and light doping of the base region causes many more electrons to be injected from the emitter into the base than holes to be injected from the base into the emitter. Such recombination current will be discussed in section 5.

We now turn our attention to the recombination current in the quasi-neutral base and obtain it from the continuity equation 2. And the emitter current due to electrons, I E,nsimplifies to: Darlington transistor Sziklai pair Cascode Long-tailed pair. This effect can be used to amplify the input voltage or current.

In this article, current arrows are shown in the rbers direction, but labels for the movement of holes and electrons show their actual direction inside the transistor. As shown, the h-parameters have lower-case subscripts and hence signify AC conditions or analyses. When the device is in forward active or forward saturated mode, the arrow, placed on the emitter leg, points in the direction of the conventional ebsrs. In this ,oll, the mocel has an emitter efficiency and base transport factor as described by equations 5.

The basic function of a BJT is to amplify current.