Theory of common collector amplifier

A common collector amplifier also known as an emitter follower is one of three basic single-stage 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 a power supply rail , hence its name. The analogous field-effect transistor circuit is the common drain amplifier and the analogous tube circuit is the cathode follower. It is called the common-collector 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. It should be apparent that the load resistor in the common-collector amplifier circuit receives both the base and collector currents, being placed in series with the emitter.

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• Common Collector Amplifier Circuit and Its Applications
• The Common-Collector Amplifier Input and Output Resistance – The Proof
• Transistor Common Collector
• Transistor Amplifier: Theory, Working, Circuit Diagram
• 7.4: Common Collector Amplifier
• Bipolar Transistor Cookbook — Part 2
• Common Collector Amplifier Electrical Engineering (EE) Notes | EduRev
• BJT Common Emitter Amplifier with emitter degeneration

WATCH RELATED VIDEO: BJT- Emitter Follower (Common Collector Amplifier) Explained with Solved Example

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In this configuration, the base terminal of the transistor serves as the input, the emitter terminal is the output and the collector terminal is common for both input and output. Hence, it is named as common collector configuration. The input is applied between the base and collector while the output is taken from the emitter and collector. In common collector configuration, the collector terminal is grounded so the common collector configuration is also known as grounded collector configuration.

Sometimes common collector configuration is also referred to as emitter follower, voltage follower, common collector amplifier, CC amplifier, or CC configuration. This configuration is mostly used as a voltage buffer.

The input supply voltage between base and collector is denoted by V BC while the output voltage between emitter and collector is denoted by V EC. In this configuration, input current or base current is denoted by I B and output current or emitter current is denoted by I E.

The common collector amplifier has high input impedance and low output impedance. It has low voltage gain and high current gain. The power gain of the common collector amplifier is medium. To fully describe the behavior of a transistor with CC configuration, we need two set of characteristics - input characteristics and output characteristics. Input characteristics. The input characteristics describe the relationship between input current or base current I B and input voltage or base-collector voltage V BC.

First, draw a vertical line and a horizontal line. The vertical line represents y-axis and horizontal line represents x-ax. The input current or base current I B is taken along y-axis vertical line and the input voltage or base-collector voltage V BC is taken along x-axis horizontal line.

To determine the input characteristics, the output voltage V EC is kept constant at 3V and the input voltage V BC is increased from zero volts to different voltage levels.

Next, the output voltage V EC is increased from 3V to different voltage level, say for example 5V and then kept constant at 5V. This process is repeated for higher fixed values of output voltage V EC. Output characteristics. The output characteristics describe the relationship between output current or emitter current I E and output voltage or emitter-collector voltage V EC.

The vertical line represents y-axis and horizontal line represents x-axis. The output current or emitter current I E is taken along y-axis vertical line and the output voltage or emitter-collector voltage V EC is taken along x-axis horizontal line. To determine the output characteristics, the input current I B is kept constant at zero micro amperes and the output voltage V EC is increased from zero volts to different voltage levels.

This region is known as the active region of a transisto r. This process is repeated for higher fixed values of input current I B I. In common collector configuration, if the input current or base current is zero then the output current or emitter current is also zero. As a result, no current flows through the transistor. So the transistor will be in the cutoff region. If the base current is slightly increased then the output current or emitter current also increases.

So the transistor falls into the active region. If the base current is heavily increased then the current flowing through the transistor also heavily increases. As a result, the transistor falls into the saturation region. Transistor parameters. Dynamic input resistance r i. Dynamic input resistance is defined as the ratio of change in input voltage or base voltage V BC to the corresponding change in input current or base current I B , with the output voltage or emitter voltage V EC kept at constant.

The input resistance of common collector amplifier is high. 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.

The output resistance of common collector amplifier is low. The current amplification factor is defined as the ratio of change in output current or emitter current I E to the change in input current or base current I B. Bipolar Junction Transistor. Common Collector Configuration In this configuration, the base terminal of the transistor serves as the input, the emitter terminal is the output and the collector terminal is common for both input and output.

The current gain of a common collector amplifier is high. Input characteristics The input characteristics describe the relationship between input current or base current I B and input voltage or base-collector voltage V BC. The vertical line represents y-axis and horizontal line represents x-ax The input current or base current I B is taken along y-axis vertical line and the input voltage or base-collector voltage V BC is taken along x-axis horizontal line.

Output characteristics The output characteristics describe the relationship between output current or emitter current I E and output voltage or emitter-collector voltage V EC. Transistor parameters Dynamic input resistance r i Dynamic input resistance is defined as the ratio of change in input voltage or base voltage V BC to the corresponding change in input current or base current I B , with the output voltage or emitter voltage V EC kept at constant. 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.

Common Collector Amplifier Circuit and Its Applications

Skip to Main Content. A not-for-profit organization, IEEE is the world's largest technical professional organization dedicated to advancing technology for the benefit of humanity. Use of this web site signifies your agreement to the terms and conditions. This paper introduces a new design topology for HBT DA's which incorporates attenuation compensation on both the input and output transmission lines. The resulting gain-bandwidth product is 84 GHz. Attenuation compensation of the input transmission line is realized using HBT active impedance transformations.

The Common-Collector Amplifier Input and Output Resistance – The Proof

Our first article gave an introductory outline of bipolar transistor principles, characteristics, and basic circuit configurations. This time we'll concentrate on practical ways of using bipolar transistors in useful common-collector voltage follower circuit applications. The common-collector amplifier also known as the grounded-collector amplifier, emitter follower, or voltage follower can be used in a wide variety of digital and analog amplifier and constant-current generator applications. Figure 1 shows a simple npn common-collector digital amplifier in which the input is either low at zero volts or high at a V peak value not greater than the supply rail value. When the input is low, Q1 is cut off and the output is at zero volts. When the input is high, Q1 is driven on and current I L flows in R L , thus generating an output voltage across RL — intrinsic negative feedback makes this output voltage take up a value one base-emitter junction volt-drop about mV below the input V peak value. Common-collector digital amplifier basic details. If this buffer circuit is fed with a fast input pulse, its output may have a deteriorated falling edge, as shown in Figure 2.

Transistor Common Collector

Darlington Pair amplifier circuit is a connection of two transistors which acts as a single unit with overall current gain equal to the multiplication of the individual current gains of the transistors. Darlington pair transistor amplifier circuit is very popular in electronics. Clearly, it is an Amplifier circuit. In this article, we are going to discuss the theory and the applications of Darlington pair amplifier.

Transistor Amplifier: Theory, Working, Circuit Diagram

I am new into electronics, and I dont get it how we find input and output impedance of Common-Collector Amplifier. I mean, I dont know what we are looking at when we are trying to find input and output impedance. First I want to tell you that I put Rc resistor here just to know where he goes in input and output impedance. When we replace transistor with his re-model,how can I then find input and output impedance here? What I am looking at?

7.4: Common Collector Amplifier

This article deals with another type of bipolar transistor architecture used to amplify signals that is commonly known as Common Collector Amplifier CCA. The CCA can also sometimes be called emitter-follower amplifier and we will understand why later in this article. The first figure below is a simplified electric diagram with no particular biasing circuit presenting the CCA configuration :. We see in Figure 2 an equivalent circuit of the CCA configuration of Figure 1 considering the transistor such as described above. It is easy to understand that in the configuration presented in Figure 1 , the voltage gain is approximately equal to 1. To provide better stability, the base of the bipolar transistor is biased with a voltage divider network such as shown in the following figure.

Bipolar Transistor Cookbook — Part 2

In this article I will show a method to deduce the input and output resistance of the common collector amplifier. The common-collector amplifier is a well known circuit see Figure 1. It is mostly used as a buffer due to its high input resistance, small output resistance and unity gain.

Common Collector Amplifier Electrical Engineering (EE) Notes | EduRev

RELATED VIDEO: Common Collector and Common Base Amplifiers

Granted publication date : Effective date of abandoning : The utility model discloses a push-pull type radio-frequency power amplifier with improved linearity, which comprises an input matching network connected with the input end of the power amplifier, an output matching network connected with the output end of the power amplifier and a power amplification circuit connected between the input matching network and the output matching network. The power amplification circuit comprises a primary amplification circuit connected with the input matching network and a secondary amplification circuit connected with the primary amplification circuit and the output matching network, the second amplification circuit adopts a NPN-NPN push-pull amplification circuit which comprises a second common-collector amplifying tube and a second common-emitter amplifying tube, and a secondary harmonic series resonant network and a base-frequency parallel resonant network are arranged between the input end of the second amplification circuit and the ground.

BJT Common Emitter Amplifier with emitter degeneration

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In this transistor tutorial, we will learn about Different Configurations of Transistors. Since a Bipolar Junction Transistor is a 3-terminal device, there are three different configurations of Transistors possible with BJTs. Understanding these different configurations of transistors will help you in better implementation of your application. We know that generally the transistor has three terminals — emitter E , base B and collector.