Class a bjt amplifiers this worksheet and all related files. The object is to solve for the smallsignal voltage gain, input resistance, and output resistance. A common collector amplifier is one of three basic singlestage bipolar junction transistor bjt amplifier configurations. A common collector amplifier has the 1 collector at ac ground 2 emitter at ac ground 3 base at ac ground 4 no element at ac ground well i thought it was 2 but i was wrong. Fields of application for the common collector circuit. The equations derived in this article are symbolic, as is the derivation of any other formula in this website.
A typical transistor have three terminal base, collector emitter. Dividing the circuit into two different types of blocks, it is reasonable to investigate the duties. Because you now know vce and ic, you can use the same procedure from the. Common emitter amplifiers are also used in radio frequency transceiver circuits. The current gain of a commoncollector amplifier is equal to. The commoncollector amplifier can be thought of as a current amplifier. Applications it is useful as an impedance matching device since its input impedance is much higher than its output impedance. The analogous fet circuit is the common source amplifier, and the analogous tube circuit is the common cathode amplifier.
Introduction to electronics iv power supplies, power conservation, and efficiency 11. The sr amplifier circuit is shown to the right based on figure 6. As we discussed in our previous article, there are three transistor configurations that are used commonly for signal amplification i. The circuit is also referred to as the groundedcollector ampli fier. The circuit can be explained by viewing the transistor as being under the control of negative feedback. Permission is granted to copy, distribute andor modify this document under the terms of the gnu free documentation license, version 1. Transistor emitter follower, common collector amplifier. When the commonemitter amplifier is cascaded to a commoncollector amplifier, the cc amplifier can be thought of as an impedance transformer. In practical configurations its load resistor is in. Dc solution a replace the capacitors with open circuits. Heres a simple 100 watt amplifier circuit where the output power devices can be seen configured in an source follower design which is an mosfet equivalent of a bjt emitter follower.
In your circuit the emitter can only go up to slightly less than 9v, because rc is then dropping 1v so the transistor is saturated approaching zero. The output resistance of this amplifier is the resistance seen by the next stage, as looking to the emitter resistor r e, as in figure 1 in a previous article, derive the transfer function of the common collector amplifier with thevenins theorem, i used thevenins theorem to demonstrate, step by step, how to derive the smallsignal transfer. Common collector means that the collector is a common point for both input and output signals ie. 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. This means that the emitter follower circuit provides an ideal buffer stage, and as a result it is used in many circuits where there is a need not to load a circuit like an oscillator or. Emitter follower common collector transistor amplifier basics. Common emitter configuration commonly used in lownoise amplifiers. Common emitter amplifier working principle and its. However, the output is taken at the emitter terminal of the bjt. In other words, if you are shown a common collector amplifier circuit, this video will help you to figure out, via analyis. The effects of current loading of amplifier stages on each other in general is a source of much of my confusion. Emitter follower or common collector amplifier circuit this tutorial will help you to build and simulate a more complex circuit. 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.
Simulation of circuit performance with multisim and comparison with measured values. Cc amplifiers are used for impedance matching applications further reading 1. Common collector amplifier calculator small signal analysis this calculator computes the diffusion resistance rp, small signal output resistance r0 and output gain av for a common collector amplifier, i. The circuit is also referred to as the groundedcollector amplifier.
The commoncollector circuit is suited as a driver stage for connecting with a low impedance load. In a bjt configuration when the emitter terminal is used as the output, the network is called an emitterfollower. In electronics, a commonemitter amplifier is one of three basic singlestage bipolarjunctiontransistor bjt amplifier topologies, typically used as the voltage amplifier in this circuit the base terminal of the transistor serves as the input, the collector is the output, and the emitter is common to both for example, it may be tied to ground reference or a power supply rail, hence its. As there is no collector load resistance, the transistors collector terminal is connected directly to the dc supply rail, so v c v cc 12 volts. Common collector amplifier basic electronics tutorials. The voltage gain of the amplifier is less than but close to unity. The common collector circuit is suited as a driver stage for connecting with a low impedance load. There are additionally three capacitors but they do not play a role in the basic transistor amplifier design which mainly involves setting dc voltages. Common collector amplifier calculator small signal analysis. It is called a common emitter amplifier since the emitter is common to both the input circuti and the output circuit. Emitter follower circuit has a prominent place in feedback amplifiers. This file is licensed under the creative commons attributionshare alike 3.
Different configurations of transistors common base. The calculations for gain, lower cutoff frequency and higher cutoff frequency are as follows. 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. Help with simulating common collector amplifier in pspice.
It is also known as voltage follower and it is moderately used amplifier circuit because it has a. The commoncollector amplifier is used for coupling circuits with small driving capabilities with heavy loads. Lets try to first understand whats an emitter follower transistor and why its called a common collector transistor circuit whats an emitter follower transistor. Common collector amplifier or emitter follower circuit and. Build the circuit shown in figure 2, a simple common collector ampli. The voltage gain is approximately equal to 1 in practice, just a little bit less. Bipolar junction transistor circuits voltage and power. As defined above, the ac input is applied at c g and the ac output is taken at c d. What is the difference between a common base, a common. This is the second in a three series set on the different transistor configurations. I am actually considering using a common drain mosfet stage instead of a common collector stage directly after my ltp to minimize the loading of the rest of the overall amplifier on the differential amplifier.
The basic transistor amplifier circuit is indicated below. Commoncollector amplifier circuit all about circuits. To an ac signal this looks like the collector is connected to ground. Attached is a circuit diagram of a commoncollector amplifier. Common base bjt amplifier common collector bjt amplifier.
To build and test a similar circuit, go to experiment 6 in your lab manual laboratory. Yesterday, we used oct technique for the frequency response of commondrain and commongate ampli. Our next transistor configuration to study is a bit simpler in terms of gain calculations. The output resistance of the common collector amplifier in fact for all transistor amplifiers is somewhat.
Because of this behavior, the commoncollector amplifier circuit is also known as the voltagefollower or emitterfollower amplifier, because the emitter load. The best circuit is to use a complementary symmetry or a push pull type of amp. As you discovered, the input impedance rin of the ce amplifier is moderate to high. Emitter follower amplifier circuit everything in this circuit is the same as the one we used in the analysis of. The circuit has an output impedance that approximately equals the value of the input signal source impedance r s because the circuit shown in fig. The common collector circuit is a basic transistor amplifier with current gain. Emitter follower or common collector amplifier circuit. To work properly in an amplifier circuit a bipolar junction transistor bjt must be properly biased and operate in the active mode. C1 is input capacitor commonly known as coupling capacitors because of they couple input and. Describe and analyze the operation of commoncollector amplifiers. It is mostly used as a buffer due to its high input resistance, small output resistance and unity gain. It can take the high output impedance of the ce amplifier and transform it to a low output impedance capable of. A tutorial on how to do the ac analysis of a common collector amplifier.
Working and applications of common collector amplifier. Bjt common collector amplifier analog electronics course. Common collector emitter follower transistor amplifier basics. Oct 01, 2018 a very simple circuit designed for this transistor with a measured hfe value of 225 will be cutoff is the hfe is only 100 and will be saturated if the hfe is 300, then your circuit will not work. The output voltage on a commoncollector amplifier will be in phase with the input voltage, making the commoncollector a noninverting amplifier circuit. Calculate the maximum collector current ic flowing through the load resistor when the transistor is switched fully on saturation, assume vce 0. Here the output is taken at the emitter node and it is measured between it and ground. It has a high input impedance and a low output impedance. Emitter follower and darlington amplifier are the most common examples for feedback amplifiers.
The voltage gain for this circuit is less than unity but it has large current gain because the load resistor in this circuit receives both the collector and base currents. Feb, 2012 a tutorial on how to do the ac analysis of a common collector amplifier. Called the commoncollector configuration, its schematic diagram is shown in. An common emitter amplifier circuit has a load resistance, r l of 1. Emitter follower is a case of negative current feedback circuit. For this reason, the circuit is also known as an emitter follower because the emitter voltage follows the base voltage. 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. The input characteristics of a common collector configuration are quite different from the common base and common emitter configurations because the input voltage v bc is largely determined by v. It is also known as an emitter follower and is used as a voltage buffer. The emitter follower or common collector circuit is widely used in amplifier configuration of bipolar junction transistors bjts with gain of unity or less.
Linearity analysis of the common collector amplifier, or. This file is licensed under the creative commons attributionshare alike 4. Very simplified diagram of a single stage power amplifier. In practical configurations its load resistor is in series with its emitter terminal. This circuit is great for bringing a voltage up from a low to higher voltage but has very little current output. The commoncollector amplifier bipolar junction transistors. Jul 08, 2016 this is the second in a three series set on the different transistor configurations. The collector is connected tied to a dc power supply. Design the circuit shown in figures 1 and 2 by calculating the values of r 1, r 2, r 3 and r 4.
In this circuit the base terminal of the transistor serves as the input, the collector is the output, and the emitter is common to both for example, it may be tied to ground reference or a power supply rail, hence its name. To obtain the base to ground resistance of the transistor. The object is to solve for the smallsignal voltage gain, input resistance, and output. Design of common collector class b rf power 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. Designing a commonemitter amplifier using bjt all about. Lets proceed immediately to a spice analysis of this amplifier circuit, and you. For both npn and pnp circuits, it can be seen that for the common base amplifier circuit, the input is applied to the emitter, and the output is taken from the collector. They are biasing resistors, they are used for the providing stable biasing to the amplifier circuit. There are additionally three capacitors but they do not play a role in the basic transistor amplifier design which. These are the mostly used ones with a number of applications. The common emitter amplifier circuit in the bipolar transistor tutorial, we saw that the most common circuit configuration for an npn transistor is that of the common emitter amplifier circuit and that a family of curves known commonly as the output characteristic curves, relate the transistors collector current ic, to the output or collector voltage vce, for different values of base.
The common collector amplifier is a well known circuit see figure 1. Fields of application for the commoncollector circuit. Input characteristics of common collector amplifier. If you replace the collector load with 10k, the voltage drop across 10k will be 16v. The commoncollector amplifier is also known as an emitterfollower. Apr 26, 2019 this common collector configuration is a non inverting amplifier circuit. Complete the table of output voltages for several given values of input voltage in this commoncollector amplifier circuit. This means the collector has nowhere to go in one direction. This article discusses the working of the common emitter amplifier circuit and its applications. Bjt smallsignal equivalent circuit 143 the common emitter amplifier 145. Robert boylstad, louis nashelsky, electronic devices and circuit theory, phi, 2008. The commoncollector circuit is a basic transistor amplifier with current gain. By reading the above information you have got an idea about this concept.
The base is grounded for the signal and for this reason the circuit may sometimes be called a grounded base circuit. Common collector amplifier calculator small signal. 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 and connected. Called the commoncollector configuration, its schematic diagram looks like this. The commoncollector amplifier is considered a voltagebuffer since the voltage gain is unity. The circuit is also referred to as the grounded collector ampli fier. As the amplifiers output signal is taken from across the emitter load this type of transistor configuration is also known as an emitter follower circuit as the emitter. Larger values will still work, but with reduced output voltage swing. Such a circuit is in fact the first stage of the 741 opamp. Designing a commoncollector amplifier school of engineering. A recently introduced early modeling of transistors is applied to the study of the common collector amplifier or emitter follower, an important type of electronic circuit typically employed as. A very simple circuit designed for this transistor with a measured hfe value of 225 will be cutoff is the hfe is only 100 and will be saturated if the hfe is 300, then your circuit will not work. It is also used for cascade amplifier circuit isolation.
Emitter follower the common collector amplifier circuit is shown on figure. The common collector amplifier is used for coupling circuits with small driving capabilities with heavy loads. Introduction to electronics xvi 1 i use the word supposedly because, in my view, the official rewards for textbook authoring fall far short of what is appropriate and what is achievable through an equivalent. In a true common collector circuit the value of rc is zero ohms. The common collector circuit configuration is more widely known as the emitter follower and it provides a high input impedance and a low output impedance. Attached is a circuit diagram of a common collector amplifier. The common collector s emitter followers dc and ac characteristics are discussed and then examined in a test. Common collector amplifier or emitter follower circuit. Common collector amplifier for spice common collector. Unlike the common emitter amplifier, the output voltage of the common collector amplifier is in phase with the input voltage.
The commoncollector amplifier input and output resistance. Jul 29, 2019 in common collector amplifier, input is applied to bc junction and output is taken from ec terminal, here collector terminal is common for both input and output. Tanya verma thanks for a2a, common means something present in two or more situations. Common collector amplifier is called as emitter follower as the phase of the output signal at emitter follows the phase of the input signal at base. The circuit you are looking for is called a common collector.
But the supply is only 12v, so the collector will use up all the 12v and pull the voltage down to 1v6 plus about 0v2 the minimum collectoremitter voltage when the transistor is fully turned on 1v8. 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. In common collector amplifier, input is applied to bc junction and output is taken from ec terminal, here collector terminal is common for both input and output. It is also known as voltage follower and it is moderately used amplifier circuit because it has a good current gain but the voltage gain is unity. This re resistor is placed in the emitter terminal of a transistor, and it. Commonemitter amplifiers are also used in radio frequency transceiver circuits. The common collectors emitter followers dc and ac characteristics are discussed and then examined in a. A common collector amplifier has the 1 collector at ac ground 2 emitter at ac ground 3 base at ac ground 4 no element at ac ground well i thought it was 2. The voltage signal applied at the input will be duplicated at the output. The commoncollector amplifier also widely know as the emitterfollower has its input applied between its base and collector and its output is taken across its emitter and collector.
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