They are common emitter, common base and common collector configurations. Operating point collector current depends on two circuit parameters. Different configurations of transistors common base. A very common type of amplifier used in electronic circuits is the voltage buffer, sometimes called a voltage follower. Common collector amplifier has collector common to both input and output. Calculate the amplifier voltage gain for a fully bypassed emitter using eq. As the sinusoidal collector current increases, the. In practical configurations its load resistor is in series with its emitter terminal. Common collector bjt bipolar junction transistor amplifier. This schematic is our old friend the common emitter bjt amplifier with an inductor replacing the collector resistor. The circuit is also referred to as the groundedcollector ampli fier. In this design the bias voltage between emitter and collector should be 5v dc. It can take the high output impedance of the ce amplifier and transform it to a low output impedance capable of.
Mar 16, 2019 multiple choice questions and answers on transistor audio power amplifiers. Commoncollector amplifier design 3 in round numbers, a typical value for r br emax is in the to 25 range and a typical value for b is 100. The commoncollector amplifier input and output resistance. The base is connected to the previous stage, and often this may be directly connected as this can save on additional bias resistors which lower the input impedance and hence increase the loading to the previous stage. So the common base amplifier has high output impedance. Multiple choice questions and answers on transistor audio. Study aids, multisim, and lt spice files for this chapter are available. Its voltage gain is close to unity one and, therefore, any increment in the input voltage i. A common collector amplifier also known as an emitter follower is one of three basic singlestage bipolar junction transistor bjt amplifier topologies, typically used as a voltage buffer. Common collector amplifier or emitter follower circuit. Amplifier power we all know that the amplifiers power rating tells us how loud the amplifier will get. Find the bias point and the amplifier parameters of the circuit below. The emitter follower common collector amplifier assumptions.
Commoncollector configuration of a transistor youtube. Observe the output waveform on the scope to be sure that there is no distortion if there is, reduce the input signal or check th dc bias. Problems for amplifier section university of california. The three basic configurations of a bjt are a common emitter ce, b. Bjt amplifiers 6 chapter outline 61 amplifier operation 62 transistor ac models 63 the common emitter amplifier 64 the common collector amplifier 65 the common base amplifier 66 multistage amplifiers 67 the differential amplifier 68 troubleshooting device application chapter objectives describe amplifier operation discuss transistor models. Commoncollector configuration of a transistor topics covered. The common base format is probably most commonly used for rf applications, where its input impedance can be used for matching to the low source impedances often found in this arena.
The input to the ce is applied to the baseemitter circuit and the output is taken from the collectoremitter circuit, making the emitter the element common to both input and output. The common collector amplifier is a well known circuit see figure 1. Common collector amplifier basic electronics tutorials. Called the commoncollector configuration, its schematic diagram looks like this. Bjt amplifiers 6 chapter outline 61 amplifier operation 62 transistor ac models 63 the commonemitter amplifier 64 the commoncollector amplifier 65 the commonbase amplifier 66 multistage amplifiers 67 the differential amplifier 68 troubleshooting device application chapter objectives describe amplifier operation discuss transistor models. The amplifier is also defined with an opencircuit voltage gain avo.
Transistor amplifiers in commoncollector configuration can be designed with transistoramp 1. Commonbase amplifier it is called the commonbase configuration because dc power source aside, the signal source and the load share the base of the transistor as a common connection point shown in figure below. Our next transistor configuration to study is a bit simpler in terms of gain calculations. The circuit can be explained by viewing the transistor as being under the control of negative feedback. The commoncollector amplifier can be thought of as a current amplifier. At high collector voltage the collector current depends on the base current only. The commoncollector circuit is suited as a driver stage for connecting with a low impedance load. The voltage gain of each of these devices is unity a v 1. Effect of rerl on power gain of common collector amplifier 0. Commonemitter commonbase commoncollector input impedance z in moderate r r r1 2.
In common collector amplifier as the collector resistance is made to zero, the collector is at ac ground that is the reason for which the circuit is also called as grounded collector amplifier or this configuration has voltage gain close to unity and hence a change in base voltage appears as an equal change across the load at the emitter, hence the name emitter follower is given to. Emitter follower common collector transistor amplifier basics. How to design a transistor amplifier in common collector configuration. The common base amplifier configuration comes into its own at high frequencies where. Multiple choice questions and answers on transistor audio power amplifiers. In this circuit the base terminal of the transistor serves as the input, the emitter is the output, and the collector is common to both for example, it. The commoncollector amplifier is also known as an emitterfollower. How to design a transistor amplifier in commoncollector configuration. On the other hand, the collector base junction j c at output side acts somewhat like a reverse biased diode. The common emitter and common collector emitter follower configurations are far more widely used because their characteristics are generally more useful. Commonsource amplifier with a source resistor the bias circuit of the currentsource bias amplifier, shown in fig. In electronics, a common collector amplifier also known as an emitter follower is one of three basic singlestage bipolar junction transistor bjt amplifier topologies, typically used as a voltage buffer in this circuit the base terminal of the transistor serves as the input, the emitter is the output, and the collector is common to both for example, it may be tied to ground reference or. Describe and analyze the operation of commoncollector amplifiers. Common collector amplifier or emitter follower circuit and.
The commoncollector amplifier is used for coupling circuits with small driving capabilities with heavy loads. H1lin this circuit r c is at ac ground at both ends. The function of the circuit components in this figure is very similar to those in a triode vacuum tube commoncathode amplifier circuit. The output voltage on a commoncollector amplifier will be in phase with the input voltage, making the commoncollector a noninverting amplifier circuit. Common base amplifier it is called the common base configuration because dc power source aside, the signal source and the load share the base of the transistor as a common connection point shown in figure below. Aug 29, 2017 common collector bjt bipolar junction transistor amplifier. Output impedance z out moderate rc moderate rc low 1 2 s e 0 r r r r r 1. Common base transistor amplifier electronics notes.
Figure 1 is a plot of substituting these typical values into equation 4 and plotting the power gain versus r er l. When the commonemitter amplifier is cascaded to a commoncollector amplifier, the cc amplifier can be thought of as an impedance transformer. Theory in common collector amplifier, the external load is capacitorcoupled to the transistor emitter terminal. It turns out that for commoncollector amplifiers, the tmodel as opposed to the hybrid. In addition to reading the questions and answers on my site, i would suggest you to check the following, on amazon, as well. Using the tmodel, we find that the smallsignal circuit for amplifier a is. So the common base amplifier has a low input impedance low opposition to incoming current. A transistor amplifies current because the collector current is equal to the base current multiplied by. The commoncollector amplifier bipolar junction transistors. Called the commoncollector configuration, its schematic diagram is shown in figure below. The equations derived in this article are symbolic, as is the derivation of any other formula in this website. May 11, 2018 the common emitter amplifier that we saw last time is an inverting amplifier, in that as an increasing current on the base causes more collector current to flow it pulls the collector voltage down. Common base cb configuration or common base amplifier.
The common base amplifier is the least widely used of the three transistor amplifier configurations. The emitter follower transistor amplifier has a very straightforward circuit. A 200w at 8 ohm amplifier is designed to deliver 40v to an 8 ohm loudspeaker, resulting in 5a of current 40v divided by 8 ohms. In this schematic of a common gate amplifier, i have removed the source resistance r source and applied v in directly. The common collector amplifier is used for coupling circuits with small driving capabilities with heavy loads. However, even though it had an extremely high gain, its output impedance prevented it from properly amplifying a signal to drive a speaker.
Common collector amplifier design 3 in round numbers, a typical value for r br emax is in the to 25 range and a typical value for b is 100. Common source amplifier with a source resistor the bias circuit of the currentsource bias amplifier, shown in fig. It is called the commoncollector configuration because ignoring the power supply battery both the signal source and the load share the collector lead as a common connection point. Dc solution a replace the capacitors with open circuits. Common collector and common base 1 objective in the previous lab, we explored the properties of a common emitter ampli. It should be apparent that the load resistor in the commoncollector amplifier circuit receives both the base and collector. Of course, 40v times 5a yields the amplifier rating of 200w. Nevertheless the common base transistor amplifier finds applications where a low input impedance is required. It is mostly used as a buffer due to its high input resistance, small output resistance and unity gain. With respect to the figure to the right a modified version of figure 6.
Effect of rerl on power gain of commoncollector amplifier 0. The characteristics of this circuit include high input impedance and a high voltage gain. The common collector amplifier our next transistor configuration to study is a bit simpler for gain calculations. Thus the collector terminal is common to both the input and output circuits. Ece 255, bjt basic configurations purdue engineering. The generic commonemitter amplifier circuit of section d2 is reproduced to the left below and the small signal circuit using the high frequency bjt model is. The circuit is also referred to as the grounded collector ampli fier. To build and test a similar circuit, go to experiment 6 in your lab manual laboratory. The important feature of common collector amplifier is that, its input resistance is very large and output resistance is small compared to other configurations. C1 and c3 are the input and output coupling capacitors.
The common collector circuit is suited as a driver stage for connecting with a low impedance load. Lets start our discussion on common emitter amplifier ce amp, rather from the first bjt lab, in which we discussed about base voltage and collector voltage in the operating region. Figure 1a gives the basic circuit of a common collector amplifier, popularly called emitter follower. Common collector configuration of a transistor topics covered. The voltage gain of the amplifier is less than but close to unity. The object is to solve for the smallsignal voltage gain, input resistance, and output resistance. The common emitter amplifier that we saw last time is an inverting amplifier, in that as an increasing current on the base causes more collector current to flow it pulls the collector voltage down. The common collector transistor circuit configuration gains its name from the fact that the collector circuit is common to both input and output circuits, the base being associated with only the input, then the emitter with the output only. Common collector emitter follower transistor amplifier basics. Design the circuit shown in figures 1 and 2 by calculating the values of r 1, r 2, r 3 and r 4. The common collector amplifier can be thought of as a current amplifier. This report attempts to characterize the common emitter amplifier circuit by explaining the theoretical basis and simulating the circuit in the. It has a emitterdegeneration bias with a voltage divider.
The voltage gain is approximately equal to 1 in practice, just a little bit less. The current gain of a commoncollector amplifier is equal to. The bjt transistors have mainly three types of configurations. Common collector amplifier or the emitter follower.
High frequency response of the ce and er amplifier the generic commonemitter amplifier circuit of section d2 is reproduced to the left below and the small signal circuit using the high frequency bjt model is given below right based on figures 10. One advantage of this is that the input is at zero dc volts such that the signal can be connected directly without interfering with the bias. In the previous lab, you designed a commonemitter ce amplifier. As we discussed in our previous article, there are three transistor configurations that are used commonly for signal amplification i. This type of configuration is called common collector, cc because the collector terminal is effectively. Theory this experiment will discuss the common collector. The common collector amplifier is another type of bipolar junction transistor, bjt configuration where the input signal is applied to the base terminal and the output signal taken from the emitter terminal. Transistor emitter follower, common collector amplifier. A common collector amplifier also known as an emitter follower is one of three basic singlestage bipolar junction transistor bjt amplifier topologies, typically used as a voltage buffer in this circuit the base terminal of the transistor serves as the input, the emitter is the output, and the collector is common to both for example, it may be tied to.
If you make a cc output amplifier, it should be very low output impedance, not to match the load. Designing a commoncollector amplifier school of engineering. The input to the ce is applied to the baseemitter circuit and the output is taken from the collector emitter circuit, making the emitter the element common to both. A transistor be junction has a low resistance due to forward bias and the bc junction has a high resistance due to reverse bias. For that we set the quiescent point need to be set with the circuitry external to the transistor, the values of resistors rc and rb, and the dc voltage sources, vcc and vbb, have chosen accordingly. When the common emitter amplifier is cascaded to a common collector amplifier, the cc amplifier can be thought of as an impedance transformer. Input between emitter and base, output between collector and base. Transistor amplifiers in common collector configuration can be designed with transistoramp 1. Among all these three configurations common emitter configuration is mostly used type. However, even though it had an extremely high gain, its output impedance prevented it from properly amplifying a. What im trying to do here folks is maintain consistency in the notation when we use v in it is applied directly to the amplifier.
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