Difference between class a amplifier and class b amplifier. Benha university faculty of engineering at shoubra l. Class ab and class c power amplifiers tutorialspoint. Its efficiency is about 75% because the active device is biased beyond cutoff. Class c class c amplifiers conduct less than 50% of the input signal and the distortion at the output is high, but high efficiencies up to 90% are possible. It is commonly used in rf circuits where a resonant circuit must be placed at the output in order to keep the sine wave going during the nonconducting portion of the input. Know all about classc power amplifier circuit and tutorial. The output amplitude is a nonlinear function of the input, so class c amplifiers are not used for.
The output of a class c amplifier is biased for operation at less than 180 of the cycle and will operate only with a tuned resonant circuit, which provides a full cycle of operation for the tuned or resonant frequency. We are now going to look at pushpull class b and class ab amplifiers, which are comprised of devices with conduction angles less than 360 degrees. Class a, class b and class c amplifier introduction for. The reduced conduction angle progresses the efficiency to a great expand, but roots a lot of distortion. Understanding amplifier operating classes electronic. Somewhat like a class g or h amp, the class b amp sustains the output most of the time, but the class c amp cuts in on high signal peaks. Let us now try to combine these two to get a new circuit which would have all the ad. Stage efficiency p lmax p s x 100 % where p s is dc input power. Both the price and quality of these amplifiers result from the operation of their output stages in. The output amplitude is a nonlinear function of the input, so class c amplifiers. The efficiency of class c amplifier is much more than the a, b, and ab. If the collector current flows for less than halfcycle of the input signal, it is called class c power amplifier. This page provides comparison between amplifier classes viz.
The class c amplifier design has the greatest efficiency but the poorest linearity of the classes of amplifiers mentioned here. The class b amplifier circuit above uses complimentary transistors for each half of the waveform and while class b amplifiers have a much high gain than the class a types, one of the main disadvantages of class b type pushpull amplifiers is that they suffer from an effect known commonly as crossover distortion. Pushpull class b and class ab amplifiers analog devices. This white paper covers power dissipation calculations for class b amplifiers. Power amplifier circuits output stages are classified as a, b, ab and c for analog designsand. Class ef amplifiers university of california, berkeley. May 14, 2006 class a has less crossover distortion than a b class amplifier, but in reality because most designs are ab anyway the difference is minimal.
Collector current waveforms for transistors operating in a class a, b class b, c class c amplifier stages. In transconductance amplifiers the current through the active device is known a priori, and so the voltage waveform is simply the voltage resulting from that known current forced through the known load impedance. The following is extracted from an article class a exposed and explained written in 2005 by mesa founder, randall smith. As a consequence, class b amplifiers are substantially more efficient than their class a counterparts, with a theoretical maximum of 78. We have seen here a number of classification of amplifiers ranging from linear power amplifiers to nonlinear switching amplifiers, and have seen how an amplifier class differs along the amplifiers load line. Explain what this means, contrasting it against the class a and class b operations common in audiofrequency amplifier circuits. The classes are based on the proportion of each input cycle conduction angle during which an amplifying device passes current.
The biasing of the transistor in class b operation is in such a way that at zero signal condition, there will be no collector current. The most commonly constructed amplifier classes are those that are used as audio amplifiers, mainly class a, b, ab and c and to keep things simple, it is these. Classes of amplifiers university of north carolina at charlotte. A short video explaining the differences between class a, b and ab amplifiers. The operation of class b power amplifier in terms of a. Class c bjt amplifiers worksheet discrete semiconductor. In the previous amplifiers, we have discussed the class a, b and ab are the linear amplifiers. Class c power amplifier is a type of amplifier where the active element transistor conduct for less than one half cycle of the input signal. Complementary symmetry class b and class ab power amplifiers. Amplifier classa operation in this classa, amplifier operates in active region at all the times2. A singletransistor class c amplifier 50 watts output for 30m cw. We will be investigating each of the classifications in the remainder of this section of.
Introduction amplifier types class a class b class ab class c. Learn about the different power amplifier classes such as class a amplifier, class b amplifier, class ab amplifier, class c amplifier, class d. Wes hayward and jeff damm publish stable hexfet rf power amplifiersshowing examples of singledevice cw amplifiers. Amplifier classes class a,class b,class ab,class c. Class ab home theater receivers audiogon discussion forum. Build a class a amplifier audio feb, 1977 by nelson pass in spite of their high cost and low efficiency, class a power amplifiers have recently been receiving more attention from audiophiles who demand uncompromising accuracy. Your author notes that complementary symmetry amplifiers may also be used in class c operation, especially for highefficiency, highpower radio frequency rf amplifier applications.
A tuned circuit or filter is a necessary part of the classc amplifier. However, it provides higher power output and hence collector efficiency. Class c power amplifier circuit diagram and theory. The main role of class a bias is to keep amplifier free from distortion by keeping signal waveform out of the nonlinear region which exists between 0v and 0. Class b amplifier power dissipation calculations abstract an amplifier takes dc input power, pin, and turns it into signal power, pout, in the speaker. What are the different types of audio amplifier classes. Class b power amplifier if the collector current flows during the half cycle of the signal only, the power amplifier is known as class b amplifier. Class a amplifiers have a collector current waveform with. As you can see, the operating point q is located at collector cut off voltage.
The classes and classification of amplifiers and its applications. Amplifier classes including class a, class b, class ab, class c and the like are widely seen when dealing with amplifier specifications and their design. The limitations due to the efficiency of class a power amplifiers. Another pair of designs engineered with an eye towards improved efficiency, technically speaking neither class g nor class h amplifiers are officially recognized. The class c amplifier is a deeply biased hence the output current is zero for more than the onehalf of the input signal and the transistor idling at the cut off point. The class c power amplifier is one kind of amplifier where the transistor conduct for less than 180 onehalf cycle of the input signal and its typical value is 80 to 120. A parallel tuned circuit will ring or oscillate at its resonant frequency whenever it receives a dc pulse. This page compares class a amplifier vs class b amplifier and mentions difference between class a amplifier and class b amplifier. In class c power amplifier, the base is negatively biased, so that collector current does not flow just when the positive halfcycle of the signal starts. Class c amplifiers are more efficient than either class a or pushpull class b and class ab, which means that more output power can be obtained from class c operation. Jul 30, 2017 class a, class b and class c amplifier introduction for power amplifier electronics physics and spirituality. Some class ab amps are dirty as sin and perform poorly on am, much less ssb.
Its a traditional amplifier which works differently than the other amplifiers classes. Power amplifier circuits output stages are classified as a, b, ab and c for analog designsand class d and e for switching designs. Classes of power amplifier bias point amplifiers class a class b class c switching amplifier class e class f james buckwalter 22. Class c amplifier is tuned amplifier which works in two different operating modes, tuned or untuned. What is class a and how does it differ from class ab.
Class c amplifier class c amplifier operates for less than half of the input cycle. Class a, class b and class c amplifier introduction for power. In class f amplifiers, the waveforms are assumed to be composed entirely of loworder harmonic. In class b amplifier, the negative halfcycle of the signal is cut off and hence severe distortion occurs. The usual application for class c amplifiers is in rf transmitters operating at a single fixed carrier frequency, where the distortion is controlled by a tuned load on the amplifier. Class c amplifiers are biased so that conduction occurs for much less than 180o. You shouldnt actually have worry too much about the different types of amplifier classes, because modern amplifiers sound very similar.
These classes are defined as class a, class b, class ab and class c. Oct 14, 2017 classes of amplifiers the following is the presentation of our topic from subject amplifiers and oscillators classes of amplifiers. Amplifiers are given a classification according to the way in which they are biassed and they operate. Clamper bias of class c amplifier altair university. A tuned class b amplifier works with a single devices by sending half sinusoid current. Classes of power amplifiers class a, b, ab, c, d amplifiers. Class c amplifier the class c amplifier design has the greatest efficiency but the poorest linearity of the classes of amplifiers mentioned here. These amplifiers are usually employed in rf radiofrequency power amplification. Apart from the class a, b, and ab amplifier, there is another amplifier class c. The way in which an amplifier operates is defined by its class amplifier classes including a, b, ab, c, d and others are widely used. The primary purpose of this tuned circuit is to form the complete ac sine wave output.
Class c operation for completeness, we will briefly introduce the class c amplifier. We saw that class a amplifiers offer reasonable linearity, but have poor performance with respect to efficiency. Class ab power amplifiers are slightly inefficient than the class b configurations but far better in terms of distortion when compared to class a configurations. The class ab configuration is a compromise the efficiency of the class a and the linearity of the class b stage have been significantly although not perfectly improved. Class ab and class c power amplifiers the class a and class b amplifier so far discussed has got few limitations. Amplifier classes and the classification of amplifiers. Given the relatively high efficiency, class b was used in some professional sound reinforcement amplifiers as well as some home audio tube amps. Class b amplifier and the classb transistor amplifier. A common class of operation used in radiofrequency rf amplifier circuits is class c. When the collector current flows only during the positive half cycle of the input signal, the power amplifier is known as class b power amplifier class b operation. Power amplifier classes are, in electronics, letter symbols applied to different power amplifier. Class ab configuration is actually a tradeoff between class a and class b configurations where efficiency is slightly compromised for fidelity. Class a, class b and class c amplifier introduction for power amplifier electronics physics and spirituality.
Some class c amps are very clean and work extremely well on am. I dont think you will find a pure class b anywhere now in hifi its generally used in pa circuits and instrument amplifiers as well as for some transmitter circuits. The benefit of the doherty is increased efficiency. Class c has very good efficiency because whenever the. Doug demaw publishes go class b or c with power mosfetsshowing how inexpensive transistors can be used in rf power amplifiers qst, nov. Class c amplifiers are biased so that conduction occurs for much less than class c amplifiers are more efficient than either class a or pushpull class b and class ab, which means that more output power can be obtained from class c operation. This circuit will look very strange if you are accustomed to analyzing audio.
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