In addition to the drain, gate and source, there is a substrate, or body, contact. This is analogous to the emitterresistor configuration of the bjt. Bjt sparameter measurement and analysis using utmost. Development of the large signal model of a bjt ebers moll model input. Bjt is constructed with three doped semiconductor regions separated by two pn junctions that are called emitter, base and collector. As shown, the hparameters have lowercase subscripts and hence signify ac conditions or analyses. Bjt and notation conventions to get where we want to be as follows. This set of characteristics obeys the same exponential relationship as the diode, has the same turn on voltage 0. The presentation of the material in this chapter parallels but does not rely on that for the mosfet in chapter 4. Only transistor type determines model selection, since all transistors.
Real shows finite slope due to base width modulation dependent on the applied v. Thus, only four of these 6 parameters are independent. This lab will look at obtaining important device parameters from a bjt. The model parameter subs facilitates the modeling of both vertical and lateral geometrics. Model selection to select a bjt device, use a bjt element and model statement. Bjt4 bipolar junction transistors wsubstrate terminals. For commonemitter mode the various symbols take on the specific values as. The pspice model contains parameters for uhf npn and pnp transistors. A bjt is not the same as two diodes connected backtoback although it does have two pn junctions. Small signal equivalent circuits and parameters for the bjt r model when the ac portion of the input is small around the q point ndc nab npn pnp 3. The extraction of bjt dc and capacitance parameters is relatively straight forward and easy to perform using sophisticated parameter extraction software such as utmost.
The bjt element parameters specify the connectivity of the bjt, normalized. Bjt model, this effect can be modeled in two exclusi ve ways, either by using the distributed base model 5 as shown in fig. Sometimes it is also called giacoletto model because it was introduced by l. For instance, a transistor used in cb arrangement may have. In order to read some of these files, you must have adobe reader installed on your computer.
The hybridpi model is a popular circuit model used for analyzing the small signal behavior of bipolar junction and field effect transistors. In this course, we are mostly interested in the wtoport voltagegain ampli er model shown below. Two slightly different versions of what is known as the t model of the bjt. Generally, for practical applications, the substrate is connected to the source terminal. One type of bipolar junction transistor bjt consists of two nregions separated by a p region npn transistor and the other type consists of two p regions separated by an n regionpnp. Describe the r parameter transistor model determine r9e using a formula compare ac beta and dc beta list and define the h parameters r parameters the r parameters that are commonly used for bjts are given in table 61. Metaloxide semiconductor fieldeffect transistor mosfet the metaloxide semiconductor fieldeffect transistor mosfet is actually a fourterminal device. These semiconductor materials can either be a p type positive with an excess of holes, or a n type negative with an excess of.
The hparameters can often be found on the transistor datasheets. Here we will describe the system characteristics of the bjt. A bjt looks like 2 diodes placed back to back if we apply a voltage to only two of the three terminals, letting the third terminal. Narrowband test circuit component designations and values 520 mhz. Real iv is limited by breakdown of the base collector junction. The values of i2 and i3 are dramatically di erent than the ones obtained earlier. These are the four basic parameters for a bjt in common emitter. The term x in the model represents a different bjt lead depending on the topology used. For the ce topology, an approximate hparameter model is commonly used which further simpli. It is a semiconductor device and it comes in two general types. Bipolar transistors two port representation of the bipolar.
Bjt ac characteristics introduction when designing a circuit, it is important to know the properties of the devices that you will be using. Logic gate can turn loads on bjt in saturation or off bjt in cutoff i. However, most of the time in our studies, the majority of these parameters will be set to their default values a very good thing. Bjt circuit configurations, bjt design, base resistance and emitter current crowding in bjts, punchthrough breakdown in bjts, gummelpoon bjt equivalent circuit accounting for the leakage currents. Refer to the following documents, software and tools to aid your design process. An npn transistor has an n type emitter, a p type base and an n type collector while a pnp transistor. Ac analysis defining the important parameters of any system. These models explicitly show the emitter resistance re rather than the base resistance r. There are two types of bjt, the so called npn and pnp transistors, dependig obviously on.
Two relationships among these four parameters i b,v be,i c and v ce represent the iv characteristics of the bjt. Hybrid parameters also known as h parameters are known as hybrid parameters as they use z parameters, y parameters, voltage ratio, and current ratios to represent the relationship between voltage and current in a twoport network. Bipolar junction transi stors bjts i ntroduction in this chapter, we study the other major threeterminal device. Bjt and its differnet parameters linkedin slideshare. Bjt transistor modeling 4 a model is a combination of circuit elements, properly chosen, that best approximates the actual behavior of a semiconductor device under specific operating conditions. The addition of the emitter resistor to the dc bias of the bjt provides improved stability, that is, the dc bias currents and voltages remain closer to where they were set by the circuit when outside conditions, such as temperature, and transistor beta, change. Bjt amplifier circuits pdf 23p this note covers the following topics. However, if the bjt devices in question are going to be used in high frequency circuit applications then the spice parameters associated with the bjt small.
Bjt smallsignal analysispurpose of ssac analysis purpose of ssac analysis the purpose of smallsignal ac ssac analysis to determine the three parameters of an ampli er input resistance, output resistance and gain. In the source resistor sr configuration, the ac input is applied at c g, the ac output is taken at c d and c s is omitted. The circuit in a is a voltagecontrolled current source representation and that in b is a currentcontrolled current source representation. Gold signifies that the tolerance is 5%, so the real resistance could lie anywhere between 4,465. Click on the tab below to simply browse between the. Bjt characteristics theory the transistor is a two junction, three terminal semiconductor device which has three regions namely the emitter region, the base region, and the collector region. Use allparams with a dataaccesscomponent to specify file based parameters. The hparameters of a transistor will give you a good idea of how to use it effectively in a circuit, and whether it is appropriate for a particular circuit. Bipolar junction transistors, bjt in active mode, a simple bjt circuit, ebersmoll model for a pnp transistor, ebersmoll model, ic vce characteristics. Bipolar junction transistors bjt general configuration and definitions the transistor is the main building block element of electronics. Recommended software programs are sorted by os platform windows, macos, linux, ios, android etc. The forward biased junction in the bjt follows the same curve as we saw for the forward biased diode. Junction field effect transistor jfet the single channel junction fieldeffect transistor jfet is probably the simplest transistor available.
The middle section base is narrow and one of the other two regions emitter is heavily doped. An example of the 40 parameters used in pspice for a generic bjt is illustrated in table 4. Note the distinction between cs the configuration and c s the capacitor dont let this confuse you. The table below lists the four hparameters for the bjt in common base and common collector emitter.
You can download a free copy of this program from the adobe website. In practise, only a few hparameters are commonly used. The model can be quite accurate for lowfrequency circuits and can easily be adapted for higher frequency circuits with the addition of appropriate inter. We can likewise define a smallsignal emitter resistance.
Hybrid parameters also known as h parameters are known as hybrid parameters as they use z parameters, y parameters, voltage ratio, and current ratios to represent the relationship between voltage and current in a two port network h parameters are useful in describing the inputoutput characteristics of circuits where it is hard to measure z or y parameters such as a transistor. For bicmos devices, use the high current beta degradation parameters, ikf and ikr, to modify high injection effects. Typical values are h re 1 x104, h oe typical value 20us, h ie typically 1k to 20k and h fe can be 50 750. The 2n4400 bipolar junction transmitter is utilized to verify theoretical material presented in the lecture course analog and semiconductor devices through the use of laboratory measurement equipment and calculations.
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