So, in case of any kind of guidance related to these amplifiers you can check out this chart and if you do not know about these amplifiers and are confused between the selections, then this chart will help you anyway. Its a traditional amplifier which works differently than the other amplifiers classes. In order to bias a transistor for class c operation, it is necessary to. As you can see, the operating point q is located at collector cut off voltage. Comparison chart for class ab amplifier vs class d here, i am going to present a comparison chart between these two amplifiers, class ab and class d. This video covers complementary configuration circuits using a single power supply to achieve class ab and class b operation. Class a amplifier circuit operation and applications. Amplifier design is very straightforward corresponds to what many designers do without knowing it. Benha university faculty of engineering at shoubra l.
Apart from the class a, b, and ab amplifier, there is another amplifier class c. An amplifier where the load is coupled to the output of the transistor using a transformer is called a direct coupled amplifier using transformer coupling technique, the efficiency of an amplifier can be enhanced to a great extent. Class ab as its name indicates, class ab amplifiers are midway between class a and class b. All the smallsignal amplifiers have been designed so that output voltage can vary in response to both positive and negative inputs. You shouldnt actually have worry too much about the different types of amplifier classes, because modern amplifiers sound very similar. Another pair of designs engineered with an eye towards improved efficiency, technically speaking neither class g nor class h amplifiers are officially recognized.
The theoretical efficiency in class b operation is about 78. There are different classes of amplifiers starting from a, b, c, ab, d, e, f, t etc. Class a, class b, class ab and class c amplifier scary voice. An amplifier may be biased at a dc level above the zerobasecurrent level of class b and above onehalf the supply voltage level of class a. In class b amplifier, the negative halfcycle of the signal is cut off and hence severe distortion occurs.
Out of those classes most commonly used audio amplifiers classes. If you slightly change the transistors biasing, it will enable a small current to continuously flow. Pdf on jan 1, 2011, bill slade and others published amplifier alphabet soup. Class c amplifier is tuned amplifier which works in two different operating modes, tuned or untuned. Difference between class a amplifier and class b amplifier. Amplifier classes and the classification of amplifiers.
However, some of these designs are now rendered obsolescent by changes in the availability. Part i, class a,ab, b and c find, read and cite all the research you need on. The classes are based on the proportion of each input cycle conduction angle during which an amplifying device passes current. 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. Amplifier classes including class a, class b, class ab, class c and the like are. 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. R f amplifiers are classified a, ab, b or c according to the phaseangle number of degrees of current flow during each 360degree rf cycle over which plate or collectorcurrent flows class a amplifiers class a amplifiers operate over a relatively small portion of a tubes. Push pull amplifier circuit diagram class a, class b and.
One way to realize a practical class b amplifier is to use a pair of active devices transistors arranged in pushpull mode where one transistor conducts one half. But average resistance is the same for class a i max 2. Its efficiency is about 75% because the active device is biased beyond cutoff. 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. This page compares class a amplifier vs class b amplifier and mentions difference between class a amplifier and class b amplifier. However, it provides higher power output and hence collector efficiency. The harmonic matching is provided by the device output capacitance only external matching is only done for the fundamental for many traditional transistors, cds provides a short to all harmonics class ab, b, etc. The aboveshown circuit is a directly coupled class a amplifier. The class c amplifier is used in the applications like rf oscillators, rf amplifier, fm transmitters, booster amplifiers, high frequency repeaters and tuned amplifiers. Most audio power amplifiers use class a circuitry except in the drive and output stages, where they use class b or ab operating modes to achieve high efficiency.
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 class b configuration employs 2 transistors, each of which conducts for exactly half of the signal cycle. The efficiency of class c amplifier is much more than the a, b, and ab. The efficiency of class c can approach 85 %, which is much better than either the class b or the class a amplifier. Complementary symmetry class b and class ab power amplifiers the circuit for a typical pushpull power amplifier is shown to the right figure 8. The limitations due to the efficiency of class a power amplifiers. This page provides comparison between amplifier classes viz. A tuned circuit or filter is a necessary part of the classc amplifier.
Amplifier classes class a,class b,class ab,class c. 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. The previous classes, a, b and ab are considered linear amplifiers, as the output signals amplitude and phase are linearly related to the input signals amplitude and phase. Class b only for onehalf the input period, class c for much less than half. The class a, b and ab amplifiers are called as linear amplifiers because the output signal amplitude and phase are linearly related to the input signal amplitude and phase. Anyway, class c amplifiers are more often used in rf power amplifier applications. 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. However, the class c amplifier is heavily biased so that the output current is zero.
Efficiency class b in comparison to class a amplifiers average current is less, power dissipation is less. However, as an audiophile, its an advantage when you can understand the different core principles of an amplifier. Amplifier classes of operation amplifier operation is distinctly different depending on the class of operation. Class a, class b, class ab and class c amplifier scary.
However, a single device operating in class b reproduces only half of the input. Power amplifier circuits output stages are classified as a, b, ab and c for analog designsand class d and e for switching designs. Class c power amplifier circuit diagram and theory. What are the different types of audio amplifier classes. This action is achieved by prebiasing the two transistors in the amplifiers output stage. 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. In class b and ab modes, the output stage operates in a pushpull configuration, where one set of output devices delivers positive voltage and current and another set. Class c amplifier the class c amplifier design has the greatest efficiency but the poorest linearity of the classes of amplifiers mentioned here.
Class c amplifier class c amplifier operates for less than half of the input cycle. Thus the class c amplifier model is implemented using theactivate tool. The classes a, b, ab and c refer to the way the amplifiers are biased. Class a amplifier design introduction to amplifier design basic design process. Class b operation general characteristics an amplifier operating in class b offers certain advantages over a class a design. Class ab and class c power amplifiers tutorialspoint. 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. Prominent among these is a higher output level and a more efficient use of energy under nosignal or quiescent conditions. The class c amplifier design has the greatest efficiency but the poorest linearity of the classes of amplifiers mentioned here. The efficiency of the a class b output stage is around 78% but the primarily disadvantage of this configuration is the transfer distorsion that. The class b amplifier is used in push pull arrangement in which one amplifier operates in positive half cycle and other amplifier operates in negative half cycle.
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. Amplifier classes class a, class b, class ab, class c. Amplifier class a operation in this class a, amplifier operates in active region at all the times2. Classes of power amplifier bias point amplifiers class a class b class c switching amplifier class e class f james buckwalter 22. Amplifiers are given a classification according to the way in which they are biassed and they operate. Define the various classes of power amplifiers and determine the maximum power efficiency of each class of amplifier. The maximum collector efficiency of class b power amplifier is 78.
Classesa, ab, b, and c amplifiers can be defined in terms of the conduction angle y as follows. Class c has very good efficiency because whenever the. Simple class a amplifier a 10w design giving subjectively better results than class b transistor amplifiers by j. Class c amplifier linearity of the class c amplifier is the poorest of the classes of amplifiers.
Class b amplifier is the actual pushpull amplifier. The operation of class b power amplifier in terms of a. During the past few years a number of excellent designs have been published for domestic audio amplifiers. A class a amplifier is conducting through all the period of the signal. Output characteristics of a single ended class b power amplifier is shown in the figure below. For a class c amplifier, there is collector current for. This module shows how to simply calculate the values needed to make a working amplifier that has correct class a bias as described in amplifier. Class b amplifiers were invented as a solution to the efficiency and heating.
Introduction amplifier types class a class b class ab class c. In the quiescent state, no current at all flows through the transistors. The main advantage of the class c amplifier is, it has a lowest physical size for a given power output. The image of the conduction angle derives from amplifying a sinusoidal signal. The diagram shows a waveform from a simple classc circuit without the tuned load. To have this kind of operation, q point must be located at cutoff. Have a look at the class b schematic shown in figure 2. When the collector current flows for less than half cycle of the input signal, the power amplifier is known as class c power amplifier.
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