With respect to the figure to the right a modified version of figure 6. Buffer amplifiers are used to buffer heavy loads from signal sources. The collector is connected tied to a dc power supply. Emitter follower, common collector transistor configuration. Emitter follower and darlington amplifier are the most common examples for feedback amplifiers. A closer look at the common emitter amplifier and emitter. For most practical applications we can ignore r o because it is very often much larger than r l. The common emitter transistor amplifier circuit is one of the mainstay circuits for use within electronic design.
Whats good about it is its high input impedance, which has the effect of not loading, i. Because the transistor has a diode in it from the base to the emitter, the transistor has an internal voltage drop. The emitter follower or common collector circuit provides an ideal buffer amplifier and it is easy to design the circuit. Emitter follower circuit common collector configuration video lecture from bipolar junction transistor chapter of analog electronics subject for electronics engineering students. Class a npn emitterfollower amplifier analog devices wiki. The emitter follower or common collector transistor configuration is widely used in many applications. Here we cover topics common collector configuration of the transistor circuits, characteristics, applications, disadvantage, why it is called emitter follower circuit. Emitter follower article about emitter follower by the.
It is a mirror image, so to speak, of the input voltage. Emitter follower common collector amplifier ee105spring2008 lecture10,slide1prof. Bjt circuits by dennis l feucht one of the more troubling aspects of analog circuit design is amplifiers that oscillate when they are not supposed to. Usually targeted at audio applications, these circuit blocks find homes in all types of designs. An emitterfollower circuit with voltagedivider bias is shown in figure 625. A closer look at the common emitter amplifier and emitter follower. What are the advantages and uses of an emitter follower. A noninverting amplifier maintains the phase of the input signal waveforms. 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 other circuit, but provide a lower impedance to the following stages. A circuit that uses a commoncollector transistor amplifier stage with unity voltage gain, large input resistance r i, and small output resistance r o see illustration. This is also called the common drain cd and is analogous to the common collector a. Dynamic output resistance r o dynamic output resistance is defined as the ratio of change in output voltage or emitter voltage v ec to the corresponding change in output current or emitter current i e, with the input current or base current i b kept at constant. Analysis of the white emitterfollower amplifier trace.
In the early days of high speed circuits, simple emitter followers were often used as high speed buffers. A typical transistor have three terminal base, collector emitter. Ecen 326 lab 1 design of a commonemitter bjt ampli. Common collector configuration of transistor detailed. The emitter follower aka the common collector amplifier dc analysis for the emitter follower is similar to the common emitter amplifier that we have been with. Analysis of emitter follower core impact of source resistance impact of early effect emitter follower with biasing reading. In this configuration, the input current is base current ib and output current is emitter current ic. As we discussed in our previous article, there are three transistor configurations that are used commonly for signal amplification i. Therefore, the voltage at the output is the same as the. Common collector amplifier or emitter follower circuit. The emitter follower amplifier, often used in amplifier output stages, is known as a class a amplifier. The emitter follower or common collector circuit configuration acts as a buffer, presenting a high impedance to the circuit that is driving it. In this project, we will show how to build an emitter follower circuit. A classa amplifier like yours wastes a huge amount of power by getting hot.
Emitter follower circuit common collector configuration. The commoncollector amplifier also known as the groundedcollector amplifier, emitter follower, or voltage follower can be used in a wide variety of digital and analog amplifier and constantcurrent generator applications. The emitter follower transistor amplifier characteristics enable the circuit to be used as a buffer amplifier. To an ac signal this looks like the emitter is connected to ground. Common collector amplifier basic electronics tutorials. Transistor emitter follower, common collector amplifier. Ac equivalent circuit of amplifier circuit with commoncollector transistor. 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 as in figure below. The emitter follower amplifier presents a high input resistance to signals applied to its base and provides a low resistance effective voltage source at its output. In this circuit the base terminal of the transistor serves as the input, the emitter.
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. For both npn and pnp circuits, it can be seen that for the emitter follower, common collector amplifier. Emitter follower and other transistor configurations. Unlike the common emitter amplifier, the output voltage of the common collector amplifier is in phase with the input. An emitter follower circuit is a transistor circuit in which the voltage at the emitter follows the input voltage. This article deals with another type of bipolar transistor architecture used to amplify signals that is commonly known as common collector amplifier cca. The reason for this can be seen from the fact that as the input voltage rises, so the current increases through the base circuit. Wu,uc berkeley emitter follower core ee105spring2008 lecture10,slide3prof. In its behavior, the emitter follower is analogous and very similar to the source follower in metaloxidesemiconductor mos circuits. In this circuit a zener diode is placed at the base of the transistor to clamp the voltage at the base to vz of the zener.
Common collector emitter follower transistor amplifier basics. An emitter follower, or common collector, configuration usually has either a current source or resistor supplying current into the emitter. The emitter follower has a high input impedance and low output impedance, which is almost equal to the emitter resistance. I can get a common emitter circuit to amplify the voltage from an lc resonant circuit, enough to drive headphones and pick up radio. C, which induces an ac collectoremitter voltage as shown in the. The term buffer was generally accepted to mean a unitygain, openloop amplifier. You will focus on the preamplifier in this chapter and then on the power amplifier in chapter 7. The circuit is therefore a commoncollector circuit for ac. The voltage divider at left is a poor voltage source because it is so strongly affected by the value of the load resistor.
Common emitter connection, common base connection, and common collector. How to connect common emitter with emitter follower to. R1 sits between the transistor base and the sine input, and r2 sits between the transistor emitter and ground. The cca can also sometimes be called emitter follower amplifier. It is therefore widely used as both the input and output stages for a multistage voltage amplification circuit. Common collector amplifier has collector common to both input and output. The same voltage divider with the transistor buffer at right will supply power to keep the voltage constant over its range of operation. The class a amplifier consists of a transistor thats always on. So the conclusion is that emitter voltage is always nearly equal to base voltage hence it called emitter follower. Common collector amplifier or emitter follower circuit and. The ac collectoremitter voltage, or output voltage, in general, will be larger than the sinusoidal input signal, so that the circuit has produced signal ampli.
What i want to do now is create an emitter follower, which. The commoncollector amplifier is also known as an emitter follower. If the input of the current follower is driven by the relatively high output impedance of a transconductance amplifier such as the common emitter or source amplifier from earlier then the output impedance for the combined amplifier can be very high. Vcc is 15v, and the input at the base is a 5v 60hz sine wave with a 0v dc offset. Emitter follower circuit has a prominent place in feedback amplifiers. Single transistor amplifier stages mit opencourseware. One of the application in which i have personally used emitter follower circuit is a discrete voltage regulator.
In this lab, we investigate a typical bjt output stage or driver stage, the common collector or emitter follower amplifier. Pdf common base, emitter, collector bowo hadiamatrejo. Tanya verma thanks for a2a, common means something present in two or more situations. H2lthe base bias can be represented by its theveninequivalent hr b r b1 eer b2 l emitter follower. In its behavior, the emitter follower is analogous and very similar to the source follower in. Bjt emitter follower voltage amplifiervoltage amplifier with r l, r o should be as small as possible what if a given amplifier configuration does not have small rwhat if a given amplifier configuration does not have small r o for example ce. Ac equivalent circuit of emitterfollower configuration.
This video discusses how to correctly bias a transistor emitter follower circuit. It considers input impedance, output impedance and correct choice for voltagedivider resistors. Emitter follower applications hyperphysics concepts. Darlington emitterfollower circuit all about circuits. The base voltage is achieved using a voltage divider as before, and the base voltage is found as. Below is the spice model for a simple emitter follower circuit. Notice, the effective output impedance of the emitter follower is a factor smaller than the circuit on the left. Engineers commonly respond to spurious oscillations with empirical efforts. The single stage common emitter amplifier circuit shown above uses what is commonly called voltage divider biasing. Emitter follower common collector transistor amplifier.
Emitter follower is a case of negative current feedback circuit. C b r in i supply i 1 q 1 r e i b 1kr b r c kr b v cc v e v c c c c e r g r l v out v in figure 1. Therefore, the voltage at the output is the same as the voltage at the input. How to build an emitter follower circuit learning about electronics. With the capacitors open circuit, this circuit is the same as our good biasing circuit of page 79 with rc 0. It considers input impedance, output impedance and correct. The input resistance of common collector amplifier is high. These are the mostly used ones with a number of applications. To design, build, and test an emitter follower amplifier using a 2n3904 npn transistor, with an input resistance of at least 1 k. To an ac signal this looks like the collector is connected to ground. The common emitter circuit configuration is used as a basic switch for logic circuits, as an analogue amplifier and in many other applications.
The commoncollector amplifier workforce libretexts. Lab 8 common collector or emitter f ollower amplifier prelab objective. The current gain of a commoncollector amplifier is equal to. The bias point currents and voltages can be found using procedure of pages 7881. Aug 24, 2019 that becomes possible due to the many emitter follower stages involved within an amplifier circuit. An emitter follower can serve as a buffer for a voltage source.
Although the circuit above shows an enhancement nmos, these configurations are valid for all jfets and mosfets discussed. This circui t does not provide any voltage gain, but it combines high input impedance with low output impedance, which translates into a. This darlington emitter follower circuit attenuates the output current rather than increasing it. The common collector junction transistor amplifier is commonly called an emitter follower. 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. An emitter follower circuit, also known as a commoncollector amplifier, is the quintessential negative feedback device. This handy amplifier doesnt offer much in the way of voltage gain it has none, but it provides buffering or isolation for sensitive amplifiers and muscle to output circuits for driving loads like headphones or coaxial cables. It has a emitterdegeneration bias with a voltage divider.
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. At the beginning of this chapter, we saw how transistors could be used as switches, operating in either their saturation or cutoff modes. Common base bjt amplifier common collector bjt amplifier. Common collector emitter follower amplifier in the emitter follower, the output voltage is taken between emitter and ground. Common collector ampli er emitter follower r e r 2 v cc v i v o r 1 c c dc analysis. Common emitter amplifier common base amplifier common collector amplifier common base amplifier circuit emitter follower with an impedance lifter amplifier bjt amplifier sensor amplifier swamped amplifier audio amplifier 2a3 audio amplifier amplifier mcq pdf download amplifier design dc coupling amplifier amplifier repair power. Lecture 10 emitter follower common collector amplifier. The voltage gain of an emitter follower is just a little less than one since the emitter voltage is constrained at the diode drop of about 0. Therefore, the emitter voltage is equal to the base. That becomes possible due to the many emitter follower stages involved within an amplifier circuit.
In electronics, a common collector amplifier is one of three basic singlestage bipolar junction transistor bjt amplifier topologies, typically used as a voltage buffer. Transistor common emitter amplifier electronics notes. A classab amplifier like an lm386 is much more efficient and works very well. This is a common collector amplifier emitter follower. The datasheet for the lm386 amplifier shows that its output at clipping with a 9v supply is 450mw into 8 ohms with low distortion. With the availability of matching pnp transistors, a simple emitter follower can be improved, as shown in figure 21a. The output voltage on a commoncollector amplifier will be in phase with the input voltage, making the commoncollector a noninverting amplifier circuit. These characteristics make the emitter follower amplifier well suited for use as a voltage buffer amplifier. The emitter follower common collector amplifier assumptions. 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 output follows or tracks any voltage changes to the base input signal, except that it remains. Common emitter amplifier common base amplifier common collector amplifier common base amplifier circuit emitter follower with an impedance lifter amplifier bjt amplifier sensor amplifier swamped amplifier audio amplifier 2a3 audio amplifier amplifier mcq pdf download amplifier design dc coupling amplifier amplifier repair.
As we see in the previous article, there is basically three type of transistors connections. Im still plugging away trying to understand the theory and practice of transistors as amplifiers. The emitter follower or common collector circuit configuration provides a high input impedance and a low output impedance. Wu,uc berkeley analysis of emitter follower core impact of source resistance impact of early effect emitter follower with biasing reading. In this type of circuits, base emitter voltage is constant and value of this voltage is 0. Transistors amplifiers common emitter amplifier simplified l whats common ground in a common emitter amp.
This month we start off by looking at practical digital amplifier. There is usually no collector load resistor, with the collector connected directly to the supply. Emitter follower article about emitter follower by the free. An emitter follower also known as a common collector amplifier is one of three basic singlestage bipolar junction transistor bjt amplifier topologies, typically used as a voltage buffer. The emitter is connected tied to ground usually by a capacitor. An emitter follower is a type of noninverting amplifier, indicating that the signal at the emitter of a transistor is following that is, matching with unity gain but perhaps an offset the input signal.
Bjt amplifiers 6 chapter outline 61 amplifier operation 62 transistor ac models 63 the common emitter 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. H1lin this circuit r c is at ac ground at both ends. Coates 2007 2012 power amplifiers introduction to power amplifiers power amplifiers amplifier circuits form the basis of most electronic systems, many of which need to produce high power to drive some output device. Npn common collector amplifiers hyperphysics concepts. Find the bias point and the amplifier parameters of the circuit below. 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. What is the difference between a common base, a common. The voltage gain of the emitter follower is less than one, but it has reasonably high current gain. Its function is not voltage gain but current or power gain and impedance matching. 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. Jul 02, 2015 this video discusses how to correctly bias a transistor emitter follower circuit. The voltage gain of this amplifier is nearly one the output follows the input hence the name. This month we start off by looking at practical digital amplifier circuits. Common collector or emitter f ollower amplifier prelab.