The theoretical maximum efficiency of a class a power amplifier is 50 %. This result shows that the best possible efficiency of a seriesfed. Maximum collector efficiency of seriesfed class a amplifier. The class ab circuit, over most of its input signal range, operates as if the q n or q p transistor is conducting and the q p or q n transistor is cut off. From the above circuit it is clear that the base of the transistor q1 is not biased and the negative half cycle of the input waveform is missing in the output. The class ab pushpull output circuit is slightly less efficient than class b because it uses a small. Power amplifier circuits output stages are classified as a, b, ab and c for analog designsand class d and e for switching designs. In this topology, each of the pair of complementary active elements is biased slightly into the active region, and so there is some overlap between the two at the turnonturnoff center point, figure 3. The theoretical maximum efficiency of a class a amplifier is 50% but in practice the figure would be nearer 25%.
The maximum theoretical efficiency of a class c amplifier is around 90%. The maximum theoretical efficiency of a classc amplifier is around 90%. Class ab amplifiers as might be expected a class ab amplifier falls between class a and class b. During the untuned mode, the tuner section is omitted from the amplifier configuration. Power amplifier circuits output stages are classified as a, b, ab and c for. Class b power amplifier, electronic circuits and diagrams.
From the below figure, we can observe that the qpoint is placed exactly at the centre of the ac load line and the transistor conducts for every point in the input waveform. We have already seen in our previous article about class b power amplifier that a pushpull circuit uses two transistors working in class b operation for class b operation, the q point is. Classes of power amplifiers class a, b, ab, c, d amplifiers. Mar 21, 2012 class ab sacrifices some of that efficiency for lower distortion. The maximum theoretical efficiency of a class a amplifier. A classf power amplifier pa improves efficiency and poweroutput capability over that of class a by using selected harmonics to shape its drainvoltage and draincurrent waveforms. Class ab and class c power amplifiers tutorialspoint. Conventionally, current entering the channel at d is designated by i d. Design and construction of class ab audio amplifier.
In linear amplifiers such as class ab, significant amounts of power are lost due to biasing elements and the linear operation of the output transistors. Where there are extra tuned circuits for regaining. We remember from the transistor tutorial that it takes a baseemitter voltage of. Why is the efficiency of a class b amplifier greater than a. Maximum efficiency and output of classf power amplifiers article in ieee transactions on microwave theory and techniques mtt496. Pdf on the design and efficiency of class a, b, ab, g, and.
Although the maximum theoretical efficiency of a class b amplifier is 78. A complimentary amplifier, or pushpull amplifier uses opposite polarity pnp and npn transistors that operate class b yet still provide the full waveform. The image of the conduction angle derives from amplifying a sinusoidal signal. Amplifier classes including class a, class b, class ab, class c and the like are.
Since in real life as opposed to advertising brochures there are always losses, this figure can only be approached no amplifier will equal or exceed the maximum theoretical efficiency. The total power of the three power amplifiers should some up to a total of 100w each driving a resistive load of 8 ohms. Multicarrier signals create large power variations that reduce the amplifier efficiency and requires the use of expensive amplifiers with large. The class a amplifier has great fidelity, it stays true to the original signal. How can i determince ps in the equation efficiency pload pssupply 100% thansk.
This is the theoretical maximum efficiency of a class b pushpull amplifier, assuming no losses. Fundamentals of class d amplifiers maxim integrated. For assessing the maximum collector circuit efficiency, we use idealized collector characteristic curves i. Power amplifier classes are, in electronics, letter symbols applied to different power amplifier. The efficiency is calculated for series fed and transformer coupled. As class a has the problem of low efficiency and class b has distortion problem, this class ab is emerged to eliminate these two problems, by utilizing the advantages of both the classes.
This part discusses the conversion efficiency of class a amplifier. Class a amplifiers purely linear, with the devices always on have a theoretical maximum efficiency of 50% and some versions have efficiencies below 20%. Efficiency for a class d output stage is attributed to the region of operation for its transistors. The schematic of a single ended class b amplifier and input, output waveforms are shown in the figure below. It turns out that the efficiency of the amplifier increases with increasing output, reaching a theoretical peak of 78% just before clipping. Source s, through which the carriers enter the channel. Compared to the dl case, the design of ul sumimo is constrained by the terminal power amplifier efficiency and hardware cost. Maximum collector circuit efficiency of class a amplifier. Mar 03, 2017 where v ce and i ce represents the rms value of the signals. In order to compensate these problems, the pushpull configuration is introduced in class b amplifier. The main use for class a bias is in low power audio and radio frequency voltage amplifiers, where the amount of power wasted is less significant than the amplifier. Modern class d amplifiers include all of the advantages of class ab amplifiers i. Each device turned on or became active half of the cycle, and due to this the efficiency gets improved, comparing to 25 30 % efficiency of class a amplifier, it provides more than 60% efficiency theoretically. Mar 03, 2017 maximum efficiency for class b power amplifier.
The qpoint is the point at which a transistor operates without a signal, and it pretty much determines the amount o. This is because musics peak to mean amplitude ratio is quite high typically 3 to 1 so the full power supply voltage is only rarely needed. Bruno clerckx, claude oestges, in mimo wireless networks second edition, 20. This type of amplifier is not used in audio amplifiers because of the vast amounts of distortion. Experiments and harmonicbalance circuit simulations verify the theoretical equations which predict classeamplifier output power, maximum frequency of operation, and dc. Thus, the maximum collector efficiency of a class a seriesfed amplifier is 25%. This question already includes the reason why is it so, and if you understand the qpoint, then you will understand why it is so. Drain d, through which the carriers leave the channel. An ideal classb amplifier has a theoretical maximum efficiency of 78%.
In actual practice, the collector efficiency is far less than this value. As the name implies, class ab is a combination of class a and class b type of amplifiers. Class ab amplifier output stage combines the advantages of the class a amplifier and the. Class j rick campbell phd portland state university.
This means 75% of power drawn by the amplifier from the supply line is wasted. Concurrently, class ab have less power usage than class a, inexpensive, and can be lighter, cooler and smaller. Classa efficiency vs rf power construct efficiency in terms of minimum device output voltage and d. There is distortion in that the transistors each have threshold voltages to overcome, which can be reduced by bias circuit on the. The maximum power output available from a power transistor is. Snider, a theoretical analysis and experimental confirmation of. The theoretical maximum efficiency of a class a power amplifier is 50%. In practical scenario, with capacitive coupling and inductive loads loud speakers, the efficiency can come down as low as 25 %. Using a less linear amplifier will be more power efficient, but distorts the signal reducing your snr and link margin.
The theoretical efficiency for a class a amplifier is 50%. Class b amplifier and the classb transistor amplifier. Class ab sacrifices some of that efficiency for lower distortion. Maximum 80% efficiency can be achieved in radio frequency related operations class c amplifier uses less than 180degree conduction angle.
An amplifier may be biased at a dc level above the zerobasecurrent level of class b and. Efficiency of a class ab amplifier how can i calculate the efficiency of a class ab amplifier circuit. The maximum theoretical efficiency of a class a amplifier is. Theoretical maximum efficiency of this amplifier class is roughly around 78. How can i determince ps in the equation efficiency. To design three class ab power amplifiers with feedbackpair complimentary symmetry output driven by an active 3way crossover network and a preamplifier.
What are amplifier classes and their power efficiencies. Class a power amplifier class a if the collector current flows at all times during the full cycle of the signal, the power amplifier is known as class a amplifier. From equation 12 we find that conversion efficiency for series fed class a amplifier approaches its maximum value of 25 % when v min approaches zero. Nov 19, 2015 substituting 1617 into 1616, we find the maximum possible efficiency of the seriesfed. The class ab amplifier circuit is a compromise between the class a and the class b configurations. The output power they produce is theoretically 50%, but practically only about 25 to 30%. Amplifier classes and the classification of amplifiers. Amplifier classes and efficiency electronics assignment. Most audio system design engineers are well aware of the powerefficiency advantages of class d amplifiers over linear audioamplifier classes such as class a, b, and ab. The above expression shows that in class a amplifier, maximum 50% of the dc power supplied can be converted into ac power output.
Pdf on the design and efficiency of class a, b, ab, g, and h audio. The classes are based on the proportion of each input cycle conduction angle during which an amplifying device passes current. In a power amplifier, this not only wastes power and limits operation with batteries, but increases operating costs and requires higherrated output devices. An input signal waveform will cause the transistors to operate as normal in their active region thereby eliminating any crossover distortion present in. Classf output network designs have been reported in the. Class a power amplifier circuit theory design circuit. Maximum efficiency for class b power amplifier electronics post. The term class d is sometimes misunderstood as meaning a digital amplifier. Substituting 1617 into 1616, we find the maximum possible efficiency of the seriesfed. Experiments and harmonicbalance circuit simulations verify the theoretical equations which predict class e amplifier output power, maximum frequency of operation, and dcrf conversion efficiency. Amplifier classes and efficiency electronics assignment help. How can i calculate the efficiency of a class ab amplifier circuit. It may be noted that maximum power is dissipated in the transistor in the zero signal. The limitations due to the efficiency of class a power amplifiers.
Class a amplifier circuit operation and applications. Class b and bridgetied load amplifiers a pushpull amplifier can be built using amplifier ics, rather than discretes, as in the. At an output power of 1w, efficiency is 1%, and so on with the voltages and currents as described. This is twice the efficiency of a class a amplifier with a resistive load. This is part iv of the video series of power amplifiers. So the class ab amplifier is a good compromise between class a and class b in terms of efficiency and linearity, with conversion efficiencies reaching about 50% to 60%. Class a power amplifier output characteristics ac load line in practice, with the capacitive coupling and inductive loads loudspeakers, the efficiency can decrease as low as 25%. The applications of the class c amplifier mainly involve in radio frequency circuits like rf amplifier, rf oscillator, etc. Due to power loss in the primary of the transformer, the collector efficiency of class a amplifier is always less than 50%. With class a amplifier q point lies middle of the load line so that signal can swing over the maximum possible range without saturating or cut off the transistor. This very small diode biasing voltage causes both transistors to slightly conduct even when no input signal is present.
Electronics tutorial about the class ab amplifier circuit that is forward biased to. In practical scenario, with capacitive coupling and inductive loads loud speakers, the efficiency can come down as. The efficiency of a class c amplifier is d greater than classes a, b, or ab class c amplifiers are more efficient than either class a or pushpull class b and class ab floyd. Understanding amplifier operating classes electronic design. Conventionally, current entering the channel at s is designated by i s. Class f output network designs have been reported in the. Know all about classc power amplifier circuit and tutorial. While the resistive biasing of a class ab amplifier works in theory. In actual practice, however, in considerably smaller than this value of 25 %, typically value being only 15 %.
Maximum efficiency and output of classf power amplifiers. As might be expected a class ab amplifier falls between class a and class b. In other words, the conduction angle of a class ab amplifier is somewhere. Currently, there are a wide variety of class d amplifiers available, thus making them suitable for numerous applications. A maximum theoretical efficiency of 25% is obtainable using usual configurations, but 50% is the maximum for a transformer or inductively coupled configuration. Currents and voltages on the output of the classa amplifier. Highefficiency class d audio amplifiers extend battery life. An ideal class b amplifier has a theoretical maximum efficiency of 78%. The class ab efficiency maximum is 100% minus the biaspower, see for example d. Classf and inverse classf power amplifier loading networks. Understanding amplifier operating classes electronic.
Amplifier efficiency an overview sciencedirect topics. The main objective of this project was to design a 100w power amplifier with feedbackpair complementary symmetry output power transistors. To improve the full power efficiency of the previous class a amplifier by reducing the wasted power in the form of heat, it is possible to design the power amplifier circuit with two transistors in its output stage producing what is commonly termed as a class b amplifier also known as a pushpull amplifier configuration. Though the efficiency of class b power amplifier is higher than class a, as only one half cycle of the input is used, the distortion is high. For class b operation, the q point is located at cutoff on both d.
On the design and efficiency of class a, b, ab, g, and h audio power amplifier output stages. Maximum collector efficiency of transformer coupled class. Highefficiency class d audio amplifiers extend battery. Class c amplifier the class c amplifier design has the greatest efficiency but the poorest linearity of the classes of amplifiers mentioned here. The class ab pushpull output circuit is slightly less efficient than class b because it uses a small quiescent current flowing, to bias the transistors just above cut off as shown in fig.
In practical scenario, with capacitive coupling and inductive loads loud speakers, the efficiency can come down as low as 25%. With a classa amp, the efficiency falls with reduced power, until at zero output power, efficiency is 0%. The maximum efficiency of a class ab amplifier is d slightly less than a class b the maximum efficiency. Using this approximation we see that a class ab amplifier acts much like a class b amplifier. Efficiency of a class ab amplifier all about circuits. We have already seen in our previous article about class b power amplifier that a pushpull circuit uses two transistors working in class b operation. Optimization of class e power amplifier design above. The main features of a largesignal amplifier are the circuits power efficiency, the maximum amount of. The output stage of a class d amplifier, in contrast, delivers a maximum theoretical efficiency of 100% over its full dynamic range, and with sub1% thd. Theoretical maximum efficiency of class b power amplifier is 78.
Amplifier classes represent the amount of the output signal which varies within the. That says the amplifier actually runs cooler even though its putting out twice as much power. Maximum collector efficiency of transformer coupled class a power amplifier in class a amplifier, the load can be either connected directly in the collector or it can be transformer coupled. The class ab amplifier is a blend of class a and class b, and strives to offer a compromise in efficiency and performance. In other words, the maximum efficiency of the class a amplifier with transformer coupled resistive load is. Why class ab amplifier have high efficiency answers. That isnt to imply this is a good amplifier and better options dont exist. Amplifier linearity and power efficiency are inversely proportional.
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