Linear amplifier classes of operation

RF power amplifier PA is the last stage which handles maximum amount of power in a transmit chain. In order to deliver large amount of power to load or antenna, it has to handle large signal swings which introduces distortion in the power output due to non-linear characteristics of the transistors. The amount of the distortion a PA can tolerate depends on the modulating signal wireless standard or modulation technique to be amplified. Ofcourse, apart from these, there are lot other parameters to influence the architecture selection. Following are important metrics often used to guage the performance of a power amplifier.

We are searching data for your request:

Linear amplifier classes of operation

Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

Content:

• The Classes and Classification of Amplifiers With Their Applications
• RF Power Amplifier
• Doretta Smith
• Electronic devices: POWER AMPLIFIERS [part 1]
• What You Need To Know About Amplifier Classes
• 4.3: Switching Amplifiers, Classes D, E, and F
• Go to School on RF Power Amplifier Classes
• Linear amplifier
• Amplifier Classes

WATCH RELATED VIDEO: Classification of Amplifier - (Class A, Class B, Class AB and Class C)

The Classes and Classification of Amplifiers With Their Applications

Amplifiers are commonly classified depending on the structure of the output stage. The classification consists of an alphabetical arrangement A, B, AB and C that relates to the historical emergence of the amplifiers. During this article, we will give a brief presentation of each amplifier class. Each class denotes the quality of the amplification according mainly to two criteria : the efficiency and the conduction angle.

P out is the power at the output, delivered to a load whereas P abs is the power absorbed by the amplifier. The conducting angle is a measure of how much of the input signal is used to realize the amplification. We will clarify this further on. There is a reason, before presenting the different classes of amplifiers, that we speak briefly about the biasing. Indeed, if there is truly something to remember about this tutorial is that the class of an amplifier is fully determined by the biasing applied to the transistor.

The quiescent point is very important because its position in the output characteristic dictates the conducting angle value and therefore the class of the amplifier. The set of values I C0 ,V C0 can be adjusted with the values of the biasing resistances and emitter resistance.

Indeed, the collector current I C0 is given by :. We can clarify two parameters in Equation 2 : 0. Note that in the following of this tutorial, we will always consider bipolar transistors, but everything we say applies also to other types of transistors such as MOSFETs.

Moreover, as a matter of simplification, we use the Common Emitter Amplifier as the configuration under study, the output signals shown in the figures will therefore be inverted. To achieve this feature, the quiescent point of a Class A amplifier is chosen to be in the middle of the load line such as shown in Figure 2 :. These formulas along with Equation 2 and Equation 3 enable to choose proper values for the biasing resistances to get a class A amplifier. The maximal efficiency is therefore :.

This low efficiency highlights the fact that class A amplifiers use power even when no AC input signals are applied. Class B amplifiers have been developed as an answer to the low efficiency of class A amplifiers. To achieve a class B amplification, one needs to bias the circuit accordingly with Figure 3 :.

It is pretty obvious that a faithful amplification can not be achieved with a class B amplifier. The NPN transistor takes care of amplifying the positive signal of the input and the PNP amplifies the negative signal.

The combination results in an addition of the two independent amplifications that reproduce the shape of the input signal. The consequence is a distortion of the signal around the 0 V point of the output signal, well known by audiophiles. As the name refers to, class AB amplifier behaves as a combination of class A and class B amplifiers. It has been developed in order to overcome the low efficiency of the class A and the distortion of the class B.

The operating point given by the bias circuit is located between a class A quiescent point and the cutoff point :. At the opposite, when the operating point approaches the quiescent point in the middle of the load line, the amplifier behaves more as a class A than a class B : the output is more faithfully reproduced but the efficiency decreases.

Since class AB amplifiers offer a good compromise between the advantages of linearity of class A and the good efficiency of class B, they are commonly used today in many applications. They are usually found in a push-pull configuration, such as presented in Figure 4 and they even eliminate the crossover distortion during the addition of the two amplified outputs from the NPN and PNP transistors.

The last most common class of amplifiers is the class C. The operating point of class C is beyond the cutoff point, aligned with the load line but in the region of negative biasing currents :. This circuit can indeed convert the output pulses into complete sine waves. For this reason, class C amplifiers are used in high frequency applications.

The biggest advantage of a class C amplifier is its efficiency that is above We have seen during this introduction to amplifier classes that for a given configuration MOSFET, Common Emitter … , the biasing circuit influences heavily the behavior of an amplifier. The way that the amplifiers are biased can be categorized into four main classes :. Later, after the development of these technologies, other classes of amplifiers have been developed to answer specific problems, mostly for high-frequency applications.

We can mention for example :. In the next tutorials, we will give much more detail about each of the most common classes : A, B and AB. Amplifier Classes Boris Poupet bpoupet hotmail. Introduction Amplifiers are commonly classified depending on the structure of the output stage. Note on the biasing There is a reason, before presenting the different classes of amplifiers, that we speak briefly about the biasing. The diagram presented in Figure 1 should be by now familiar : fig 1 : Voltage divider network.

More tutorials in Amplifiers. Connect with. I allow to create an account. When you login first time using a Social Login button, we collect your account public profile information shared by Social Login provider, based on your privacy settings. We also get your email address to automatically create an account for you in our website.

Once your account is created, you'll be logged-in to this account. Disagree Agree. Notify of. I agree to the Privacy Policy.

The comment form collects your name, email and content to allow us keep track of the comments placed on the website. Please read and accept our website Terms and Privacy Policy to post a comment. Inline Feedbacks. Class A amplifiers Read More. Common Base Amplifier Read More.

RF Power Amplifier

The Class A amplifier uses a single switching transistor in the standard common emitter circuit configuration to produce an inverted output. In other words, a class B amplifier is biased to conduct over half the waveform. By using two transistors that conduct each half of a cycle, the complete signal is recovered. This results in very high levels of distortion, but also achieves very high efficiency levels. Class C amplifiers are more efficient than class A, class B or class AB, which means that more output power can be obtained from class C operation. The output amplitude is a nonlinear function of the input, so class C amplifiers are not used for linear amplification. They are generally used in radio frequency RF applications, such as oscillators that have a constant output amplitude, and modulators, where a high-frequency signal is controlled by a low-frequency signal.

Doretta Smith

Mar 26, Amplifiers , Engineering Resources. Power amplifiers PAs boost input signals using different amplification schemes depending upon application requirements and the nature of the signals to be boosted. Signals may be continuous wave CW or many forms of pulsed waveforms, with different pulse widths and duty cycles. Different signal types have different amplification needs in terms of output power, gain, efficiency, linearity, and other performance parameters. Ideally, a PA operates with high efficiency, so most of its applied power supply is used to boost the amplitude of an input signal, and high linearity, so output power is directly proportional to input power over most of the input power range. In reality, though, designers make tradeoffs between efficiency and linearity depending on the requirements of a given application. Lower efficiency results in power converted to heat in PA semiconductor junctions, which must be dissipated to avoid performance degradation and protect the amplifier and its active devices from overheating. At the same time, poor linearity means the amplifier will operate more in the non-linear region of its power curve, which can create distortion in the form of harmonics and intermodulation products.

Electronic devices: POWER AMPLIFIERS [part 1]

Amplifiers are electronic devices used in boosting the voltage of a weak audio signal to output a stronger signal that can drive speakers more effectively. Amplifiers are a must-have in any serious car or home audio system. While amplifiers are a great addition to a sound system, are they built the same? Basically, the key characteristics of an amplifier are power output, efficiency, signal gain, and linearity. Consequently, amplifier classes are used in differentiating different types of amps based on these characteristics.

What You Need To Know About Amplifier Classes

Home » Amplifier Classes from A to H. Engineers and audiophiles have one thing in common when it comes to amplifiers. They want a design that provides a strong balance between performance, efficiency, and cost. His article provides a comprehensive look at the characteristics, strengths, and weaknesses of different amplifier classes so you can select the best one for your application. The following article excerpts, in part, answer that question. This enables the output signal to swing.

4.3: Switching Amplifiers, Classes D, E, and F

There are already many articles on the Net that cover this topic, some quite well but often without enough information , some badly and some that are largely wrong. It's usually not the descriptions that are incorrect, but the comments about alleged sound quality. For example, some Class-A amplifiers are very good indeed, but others are terrible. It's not only the class of operation that makes an amplifier good, bad or indifferent, but how the circuit is designed and how much effort has gone into minimising problems. Many 'boutique' amplifier makers will make outlandish claims for their chosen topology, but advertising hype is not fact and should be ignored.

Go to School on RF Power Amplifier Classes

Click here to go to our main page on amplifiers. New for February ! The curves of a transistor are shown in the following two figures. First is a field effect transistor.

Linear amplifier

RELATED VIDEO: How to Design an RF Power Amplifier: Class A, AB and B

R F amplifiers are classified A, AB, B or C according to the phase-angle number of degrees of current flow during each degree RF cycle over which plate- or collector-current flows. Their efficiency in converting DC-source-power to RF-output-power is poor. DC source power that is not converted to radio frequency output power is dissipated as heat. However, in compensation, Class A amplifiers have greater input-to-output waveform linearity lower output-signal distortion than any other amplifier class. They are most commonly used in small-signal applications where linearity is more important than power efficiency, but also are sometimes used in large-signal applications where the need for extraordinarily high linearity outweighs cost and heat disadvantages associated with poor power efficiency.

Amplifier Classes

In earlier days, before the invention of electronic amplifiers , the coupled carbon microphones are used as crude amplifiers in telephone repeaters. The first electronic device that practically amplifies was the Audion vacuum tube, invented by the Lee De Forest in the year The term amplifier and amplification are from Latin word amplificare to expand or enlarge. The vacuum tube is the only simplifying device for 40 years and dominated electronics up to When the first BJT was in the market it has created another revolution in the electronics and it is a first portable electronic device like transistor radio developed in the year This article discusses the classes and classification of amplifiers.

Jump to: navigation , search. Even if there is no signal then there is a significant ldling power. Class B : has two large transistors in a push-pull setup. When output current is less than a few amps all the power output comes from the single chip circuitry, maximising the speed and linear properties of this design.