Class a amplifier efficiency calculation formula
In electronics , power amplifier classes are letter symbols applied to different power amplifier types. The class gives a broad indication of an amplifier 's characteristics and performance. The classes are related to the time period that the active amplifier device is passing current, expressed as a fraction of the period of a signal waveform applied to the input. A class A amplifier is conducting through all the period of the signal; Class B only for one-half the input period, class C for much less than half the input period.
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How to calculate RF power amplifier efficiency
In electronics, Amplifier is the most commonly used circuit device with huge application possibilities. In Audio related electronics pre-amplifier and power amplifiers are two different types of amplifier systems which are used for sound amplification related purposes. But, other than this application-specific purpose, there are huge differences in various types of amplifiers, mainly in Power Amplifiers.
So here we will explore different classes of amplifiers along with their advantages and disadvantages. Different type of power amplifiers gives different responses when passing current through them. According to their specifications, Amplifiers are assigned different letter or alphabets which represent their classes. Sometimes, improved version of traditional classes are assigned a letter to classify them as a different class of amplifier, like class G amplifier is a modified Amplifier class of Class B or Class AB amplifier.
Classes of the amplifier represent the input cycle proportion when the current is passed through amplifier. The input cycle is the conduction angle derives from the sinusoidal wave conduction in the amplifier input.
This conducting angle is highly proportional with the Amplifiers on time during a full cycle. If the amplifier is always ON during a cycle, the conduction angle will be degrees.
Below, we will demonstrate traditional Power amplifier classes ranging from Class A, B, AB and C, and also demonstrate Class D amplifier which is widely used in switching designs.
These classes are not only used in Power Amplifier but also used in Audio Amplifiers circuits. Class A amplifier is a high gain amplifier with high linearity. In case of Class A amplifier, the conduction angle is degree. As we stated above, a degree conduction angle means the amplifier device remains active for the entire time and use complete input signal. In the below image an ideal class A amplifier is shown. As we can see in the image, there is one active element, a transistor.
The bias of the transistor remains ON all of the time. Due to this never turn off feature, Class A amplifier provides better high frequency and feedback loop stability.
Other than these advantages, Class A amplifier is easy to construct with a single-device component and minimum parts count. Despite the advantages and high linearity, certainly, it has many limitations.
Due to continuous conducting nature, the class A amplifier introduce high power loss. Also, due to high linearity, Class A amplifier provides distortion and noises.
The power supply and the bias construction need careful component selection to avoid unwanted noise and to minimize the distortion. Because of high power loss in Class A amplifier, it emits heat and requires higher heat sink space. The Class B amplifier is a bit different from the Class A. It is created using two active devices which conduct half of the actual cycle , ie degrees of the cycle.
Two devices provide combined current drive for the load. In the above image, an Ideal Class B amplifier configuration has been shown. It consists two active devices which get biased one by one during the positive and negative half cycle of sinusoidal wave and thus the signal gets pushed or pulled to the amplified level from both positive and negative side and combine the result we get complete cycle across the output.
We can see each device input and output signal graph in the below image. The heat dissipation is minimized in this class providing a low heat sink space. But, this class also have limitation. A very profound limitation of this class is the crossover distortion.
As two devices provides each half of the sinusoidal waves which are combined and joined across the output, there is a mismatch cross over in the region, where two halves are combined. This is because when one device complete the half cycle, the other one needs to provide the same power almost at the same time when other one finish the job. It is difficult to fix this error in class A amplifier as during the active device the other device remains completely inactive.
The error provides a distortion in the output signal. Due to this limitation, it is a major fail for precision audio amplifier application.
An alternate approach to overcome the cross-over distortion, is to use the AB amplifier. Same as class B, it has the same configuration with two active devices which conducts during half of the cycles individually but each device biased differently so they do not get completely OFF during the unusable moment crossover moment. Each device does not leave the conduction immediately after completing the half of the sinusoidal waveform, instead they conduct a small amount of input on another half cycle.
Using this biasing technique, the crossover mismatch during the dead zone is dramatically reduced. But in this configuration, efficiency is reduced as the linearity of the devices is compromised. The efficiency remains more than the efficiency of typical Class A amplifier but it is less than the Class B amplifier system.
Also, the diodes need to be carefully chosen with the exact same rating and need to be placed as close as possible to the output device. In some circuit construction, designers tend to add small value resistor to provide stable quiescent current across the device to minimize the distortion across the output. Class C amplifier is tuned amplifier which works in two different operating modes, tuned or untuned.
Class C amplifier uses less than degree conduction angle. During the untuned mode, the tuner section is omitted from the amplifier configuration. In this operation, Class C amplifier also gives huge distortion across the output. When the circuit is exposed to a tuned load, the circuit clamps the output bias level with the average output voltage equal to the supply voltage.
The tuned operation is called as clamper. During this operation, the signal gets its proper shape and the center frequency became less distorted. The conduction angle is not a factor in such case as the direct input signal is changed with a variable pulse width. In this Class D amplifier system, the linear gain is not accepted as they work just like a typical switch which have only two operations, ON or OFF.
Before processing the input signal, the analog signal is converted into a pulse stream by various modulation techniques and then it is applied to the amplifier system. As the pulses duration is related with the analog signal it is again reconstructed using low pass filter across the output. It has smaller heat dissipation, so small heatsink is needed. It is a widely used topology in digital audio players or controlling the motors as well.
But we should keep in mind that It is not a Digital converter. Although, for higher frequency, Class D amplifier is not a perfect choice as it has bandwidth limitations in few cases depending on the low pass filter and converter module capabilities. Class E amplifier is a highly efficient power amplifier which uses switching topologies and works in radio frequencies. A single pole switching element and the tuned reactive network is the main component to use with the class E amplifier.
Class F is high impedance amplifier in respect of the harmonics. It can be driven using square wave or sine wave. For the sinusoidal wave input, this amplifier can be tuned using an inductor and can be used to increase the gain. Class G use rail switching to decrease the power consumption and to improve efficiency performance.
And Class H is the further improved version of Class G. Additional classes are special purpose amplifier. In some cases, the letters are provided by the manufacturer for signifying their proprietary design. Great analysis. Get Our Weekly Newsletter! Helena St. Related Content. Parameters to be Considered for an Efficient Design.
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Confusion calculating Amplifier efficiency
We have already discussed, the classes and classifications of power amplifiers in our earlier articles. The power amplifier circuits are used to deliver high power to drive the loads likes loudspeakers. The power amplifiers are classified based on their mode of operation that is the portion of the input cycle during which the collector current is expected to flow. On this basis, the power amplifiers are classified as given below. In this article, we will discuss Class A Amplifier in detail. Generally, the power amplifiers large signal are used in the output stages of an audio amplifier system to drive a loudspeaker load.
Analyse A Meter
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Class B power amplifier
High efficiency RF power amplifiers are increasingly employed in modern mobile communication systems to reduce battery size and power supply consumption. To do this task, a suitable load network is to be synthesized in order to present the proper harmonic impedances at the output of the RF power transistor. In this paper, a new load network for class F power amplifiers has been introduced and derived analytically. The benefits of this topology include simplicity of design, controllable bandwidth, and harmonic tuning and impedance transformation at the same time.
Primary analog circuit: 5-2 series fed class a power amplifier
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RF Power Amplification 101: Amplifier Classes
Facebook Twitter. Series fed Class-A Amplifier: The simple fixed-bias circuit connection shown in the figure below can be used to discuss the main features of a series fed class A amplifier. The only differences between this circuit and the small-signal version considered previously are that the signals handled by the large-signal circuit are in the range of volts and the transistor used is a power transistor that is capable of operating in the range of a few to tens of watts. As will be shown in this section, this circuit is not the best to use as a large-signal amplifier because of its poor power efficiency. The beta of a power transistor is generally less than , the overall amplifier circuit using power transistors that are capable of handling large power or current while not providing much voltage gain. The dc bias set by V cc and R B fixes the dc base-bias current at. To appreciate the importance of the dc bias on the operation of the power amplifier, consider the collector characteristic shown in the figure. An AC load line is drawn using the values of V cc and R c.
Maximum Efficiency for Class B Power Amplifier
Class A Circuit — Instead of capacitor coupling, a Transformer Coupled Class A Amplifier may be used to ac couple amplifier stages while providing dc isolation between stages. The resistance of the transformer windings is normally very small, so that there is no effect on the transistor bias conditions. Figure shows a load resistance R L transformer-coupled to a transistor collector.
Back to the catalog. The series fed type is to transfer the load R L In this section, we mainly analyze the series fed class a power amplifier. The simplest circuit form is shown in the following figure:. The DC analysis of series fed class a power amplifier is relatively simple, and the calculation formula of DC parameters is as follows:.
Class B amplifier is a type of power amplifier where the active device transistor conducts only for one half cycle of the input signal. Since the active device is switched off for half the input cycle, the active device dissipates less power and hence the efficiency is improved. Theoretical maximum efficiency of Class B power amplifier is The schematic of a single ended Class B amplifier and input , output waveforms are shown in the figure below. One way to realize a practical Class B amplifier is to use a pair of active devices transistors arranged in push-pull mode where one transistor conducts one half cycle and the other transistor conducts the other half cycle. The output from both transistors are then combined together to get a scaled replica of the input.
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