Class c amplifier design july 29, 2012 3 outline explanation of class c operation for an rf amplifier design procedure for 50w, 30m amplifier with v dd 24v and input power p in of 5w. 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. Amplifiers introduction amplifiers are used extensively in electronic circuits to make an electronic signal bigger. Power amplifiers designed to amplify pulse width modulatedpwm digital signals come under d, e, f etc. A class b rf linear amplifier will generate still more. 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. Class b stage the efficiency of a power amplifier may be increased using the following fig. As you can see, the operating point q is located at collector cut off voltage.
This video covers complementary configuration circuits using a single power supply to achieve class ab and class b operation. Class a amplifiers are the most common type of amplifier topology as they use just one output switching. The efficiency of classc can approach 85 %, which is much better than either the classb or the classa amplifier. Power amplifiers purpose of a power amplifier generate high output power efficient conversion of dc power to rf power linear amplification generally pas will be common source cascode inductor is a choke to provide d apacitor is a ac coupling path to output james buckwalter 2. For lowpower, this high voltage implies higher losses in. An amplifier takes dc input power, pin, and turns it into signal power, pout, in the speaker.
Class b amplifier and the classb transistor amplifier. Multiple choice questions and answers on transistor audio power amplifiers. However, it provides higher power output and hence collector efficiency. Amplifier will work with lower v dd and p in providing lower output power.
The operation of class b power amplifier in terms of a. For class c operation of the amplifier, some reverse bias is given to the base i. A singletransistor class c amplifier 50 watts output for. 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. That means the conduction angle is 180 for a class b amplifier. 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. The class ab amplifiers are using commonly in the audio power amplifiers. The image of the conduction angle derives from amplifying a sinusoidal signal. Class c amplifier class c amplifier operates for less than half of the input cycle. Classes a, b, and ab detailed descriptions in class a, biasing a single. Briefly said, unlike the class a, b, ab and c modes, most of the switching amplifiers with the exception of class d rely on selecting special times for changing the conduction state of the transistor. Class e amplifiers use lc tank circuits, like class c amplifiers, but in a class e amplifier, the active device becomes a switch. A class ab power amplifier is, as the name suggests, a mix of class a and class b power amplifiers. Coates 2007 2017 the voltage amplifiers described in amplifiers.
Linear wband hbt class a, ab power amplifier 100 ghz pa simulations 10 mm hbt emitter finger tsc 250nm inp hbt cell within larger pa. Compared to the gain for classa amplifier the power gain of classb is. Class ab amplifier radio frequencies rf class c amplifier vhf, uhf and shf. 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. 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. 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 types of amplifier classes we will look at here in more detail. Class g and class h are quests for improved efficiency over the classic classab amplifier.
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. Power dissipation for low signal levels higher than class b. Less than one half cycle means the conduction angle is less than 180 and its typical value is 80 to 120. The class ab is the combination of class a and class b amplifier. Penguat daya kelas b class b power amplifier penguat kelas b ini diciptakan untuk mengatasi masalah efisiensi dan pemanasan yang berlebihan pada penguat kelas a. Class c power amplifier circuit diagram and theory. For low power, this high voltage implies higher losses in. Compare class a amplifier, class b amplifier and class c. 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%. The reduced conduction angle progresses the efficiency to a great expand, but roots a lot of distortion. Classes g and h are like class ab amplifiers, but with multiple power rails. Using this approximation we see that a class ab amplifier acts much like a class b amplifier. Amplifier classes and the classification of amplifiers. The class of an amplifier is selected to meet the overall requirements.
Class c amplifier the class c amplifier design has the greatest efficiency but the poorest linearity of the classes of amplifiers mentioned here. There are very many more amplifier operational classes available to the designer these days. Class a, class b, class ab and class c amplifier scary. Multiple choice questions and answers on transistor audio. In class c power amplifier, the operating point is so adjusted that the collector current flows for less than half cycle of the input signal. Oct 14, 2017 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%. When the collector current flows for less than half cycle of the input signal, the power amplifier is known as class c power amplifier.
For most purposes, thats close enough to what goes on in class ab amplifiers, the difference being that well ignore. This white paper covers power dissipation calculations for class b amplifiers. Class c operation, especially for highefficiency, highpower radio frequency rf amplifier applications. The efficiency of class c can approach 85 %, which is much better than either the class b or the class a amplifier. The output amplitude is a nonlinear function of the input, so class c amplifiers are not used for linear amplification. 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. For highoutput power, a highvoltage power supply is needed. Its efficiency is about 75% because the active device is biased beyond cutoff. 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.
Class g and class h are quests for improved efficiency over the classic class ab amplifier. Power amplifiers designed to amplify analog signals come under a, b, ab or c category. As we said above, the class ab amplifier is a combination of classes a and b in that for small power outputs the amplifier operates as a class a amplifier but changes to a class b amplifier for larger current outputs. For the class b amplifier then and the power from the above power supply proportional to v cc. Modern silicon technology has opened up many more doors, but despite this, the basic three amplifier classes of class, class b, and class c, with the derivative class ab which is a cross between class a and b are still the most widely used. Amplifiers are given a classification according to the way in which they are biassed and they operate. Class b amplifier is a type of power amplifier where the active device transistor conducts only for one half cycle of the input signal. In addition to reading the questions and answers on my site, i would suggest you to check the following, on amazon, as well. Mar 07, 2018 the maximum collector efficiency of class c power amplifier is nearly 100%. Transistor audio power amplifiers questions and answers pdf free download mcqs interview objective type questions for eee ece electronics engineer students. The circuit requires various switching components like mosfets which has low on resistance. Power conversion efficiency similar to class b disadvantages. The maximum collector efficiency of class c power amplifier is nearly 100%.
Understanding amplifier operating classes electronic. Power amplifier circuits output stages are classified as a, b, ab and c for analog designsand class d and e for switching designs. Like the class b amplifier, it also uses 2 conducting elements transistors, but they both run at the same time. To have this kind of operation, q point must be located at cutoff. Class ab and class c power amplifiers tutorialspoint. Class d amplifier is the highest power efficient amplifier class in the a, b, ab, and c and d segment. This illustrative build guide has been written to aid anyone in building diyaudio s diyab. Types of amplifiers and their circuits with working. 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 circuit waveform of this amplifier is shown in given figure below. In class b amplifier, the negative halfcycle of the signal is cut off and hence severe distortion occurs. Know all about classc power amplifier circuit and tutorial. It has smaller heat dissipation, so small heatsink is needed. Aug 20, 2016 this video covers complementary configuration circuits using a single power supply to achieve class ab and class b operation. Class c amplifier linearity of the class c amplifier is the poorest of the classes of amplifiers. This is similar to class b but a tuned circuit brings only the intended frequency out of the device. B and class ab, which means that more output power can be obtained from class c operation.
Mar 16, 2019 multiple choice questions and answers on transistor audio power amplifiers. Complementary symmetry class b and class ab power amplifiers the circuit for a typical pushpull power amplifier is shown to the right figure 8. Class c amplifier linearity of the classc amplifier is the poorest of the classes of amplifiers. 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. Class ab output stage class ab amplifier operation. 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. The classes and classification of amplifiers and its. From the diagram the two transistors have the small amount of voltage which is 5 to 10% of the quiescent current and the bias the transistor just above the cutoff point. It is a widely used topology in digital audio players or controlling the motors as well. Oct 06, 2015 the operation of class b power amplifier in terms of a. May 24, 2015 a short video explaining the differences between class a, b and ab amplifiers.
Power amplifier circuit, classes and its characteristics. The classes are based on the proportion of each input cycle conduction angle during which an amplifying device passes current. A short video explaining the differences between class a, b and ab amplifiers. Dec 11, 2018 class d amplifier is the highest power efficient amplifier class in the a, b, ab, and c and d segment. The most commonly used power amplifiers are the ones that are used in audio amplifier circuits and they come under classes a, b, ab or c. As the power losses are very small in the high q resonant circuit, narrow pulse will compensate all the losses in the class c power amplifier. When the collector current flows for less than half cycle of the input signal, the power amplifier is. They are generally used in radio frequency rf applications, including circuits. Class b amplifiers are greatly preferred over class a designs for highpower applications such as audio power amplifiers and pa systems.