Bipolar Junction Transistor BJT

The emitter and collector are basically the same, although, generally the emitter is more heavily doped than the collector in order to make the depletion zone between the emitter and base thinner than the depletion zone between the base and the collector. Also, the base-collector junction cross section is often made larger than the emitter jimction since it is usually required to carry more current. 

There are four basic modes of transistor operation  

Active mode emitter forward biased, collector reverse biased 

Saturated mode both emitter and collector forward biased 

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As Figure 10 shows, the n—p—n bipolar junction transistor (BJT) may be regarded as two back-to-back p—n junctions separated by a thin base region (26,32,33). If external voltages are applied so that the base-emitter (BE) junction is forward biased and the base-coUector (BC) junction is reverse biased, electrons injected into the base from the emitter can travel to the base-coUector junction within their lifetime. If the time for minority carrier electrons to... 

Field-effect transistors (FETs) have dominated the semiconductor industry, largely displacing the earlier bipolar junction transistor (BJT) because of its negligible gate current and convenience in the design of integrated circuits. Figure 29 sketches how an FET works. 

Many semiconductor manufacturers have data sheets and PSpice models available online for easy access by engineers. In this section we will show how to obtain those models so that we can use them in a simulation. The types of models we will show can be split into two types. The first type of models are primitives that use only a. model statement. Examples of these are diodes, bipolar junction transistors (BJT), and MOSFETs. The second type of models we will download are subcircuit models such as op-amps, IGBT s, Darlington transistors, and MOSFET subcircuit models. 

When an np rectifier is connected, through a shared p region, to a pn rectifier, we have a npn junction "triode" transistor, or bipolar junction transistor (BJT). This transistor can amplify signals, just as does the vacuum-tube triode, but by a totally different mechanism. 

Both bipolar junction transistors (BJTs) and field-effect transistors (FETs) are charge-control devices [15]. The functions of the emitter, base, and collector electrodes of the BJT are replaced by the source, drain, and gate... 

The bipolar junction transistor (BJT) consists of three layers doped n-p-n or p-n-p that constitute the emitter, base and collector, respectively. This structure can be considered as two back-to-back p-n junctions. Under normal operation, the emitter-base junction is forward biased to inject minority carriers into the base region. For example, the n type emitter injects electrons into a p type base. The electrons in the base, now minority carriers, diffuse through the base layer. The base-collector junction is reverse biased and its electric field sweeps the carriers diffusing through the base into the collector. The BJT operates by transport of minority carriers, but both electrons and holes contribute to the overall current. 

Elements having three, four, or more than four terminals can also appear in practical electrical networks. The discrete component bipolar junction transistor (BJT), which is schematically portrayed in Fig. 2.2(a), is an example of a three-terminal element, where the three terminals at issue are the collector, the base, and the emitter. On the other hand, the monolithic metal- oxide-semiconductor field-effect transistor (MOSFET) depicted in Fig. 2.2(b) has four terminals the drain, the gate, the source, and the bulk substrate. 

A basic diagram of the bipolar junction transistor (BJT) is shown in Fig. 7.5. Whereas the diode has one PN junction, the BJT has two PN junctions. The three regions of the BJT are the emitter, base, and collector. The middle, or base region, is very thin, generally less than 1 /um wide. This middle electrode, or base, can be considered to be the control electrode that controls the current flow through the... 

A bipolar junction transistor (BJT) can be thought of as back-to-back n-p or p-n diodes to form an npn or pnp configuration as shown in Figure 22.1. 

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