output of class b amplifier

It is a two-port electronic circuit that uses electric power from a power supply to increase the amplitude of a signal applied to its input terminals. According to their specifications, Amplifiers are assigned different letter or alphabets which represent their classes. Because of the way they work, Class B amplifiers are also known as "push-pull" amplifiers. You have likely come across these terms before at some point, but you may not have given much thought to the impact of this basic structure on an amplifier's sound or operation. amplifiers misbehave and why they sound different Sources of distortion in class D amplifiers PWM, sigma-delta, and direct digital class D amplifiers. Abstract Switch mode operation of a GaN HEMT device is explored to determine the performance and limitations of this technology for P-Band Pulsed waveforms. In its classic form itconsists of two input terminals, one of which inverts the phase of the signal, the other preserves the phase, and an output terminal. Amplifiers can be specified according to their input and output properties. The figure-1 depicts class A amplifier bias characteristics. We present the first design of a wide bandwidth class-S power amplifier for ultrasonic devices. Chapter 15 Thermal compensation and thermal dynamics. Maximum efficiency = [pi/4] x 100% = 78.5%. The gain may be specified as "output voltage/input voltage". A power amplifier operates in class-A mode when its power transistors are on for the entire period of the input signal. The power rating of the amplifier you select should be based on the RMS rating of the speakers in your vehicle. Class-AB Audio Power Amplifier Circuit. In fact, we could easily create a three-way mix of operating classes, say Class-A, Class-AB, and Class-B, or Class-AB, Class-B, and Class-C. The emitters are shorted and the collectors are given the VCC supply through the primary of the output transformer Tr2. Most High Fidelity Amplifiers operate in Class AB. Unlike classes A, B, and AB, class D amps operate by switching on and off the current to their transistors very quickly. The output stage I 6. This is shown in fig.1 . Power supplies and PSRR 9. On this basis, they are classified as : (i) class A power amplifier (ii) class B power amplifier (iii) class C power amplifier. It is clear that a.c. output voltage has a peak value of VCE and a.c. output current has a peak value of IC(sat) . 'Push-Pull' Class A Amplifier The Class A transformer-coupled amplifier is limited in power output capability indirectly because of the quiescent collector current; this current flows through the transformer primary winding and adds a DC magnetic bias to the transformer core magnetic flux. Figure 7: Class H audio amps reduce dissipation across the output devices connected to that supply. Transformer-Coupled Class A Amplifiers. Class A amplifiers amplify over the whole of the input cycle such that the output signal is an exact scaled-up replica of the input with no clipping. Conventional approach A definition of a class B amplifier could be. You can typically manufacture a Class B amplifier for less money since you can use lower quality output devices since they aren't responsible for the full load of work in amplifying the audio signal. The transistor in a class A amplifier conducts for the full 360 of the cycle. BJTs generally require Class B power amplifiers to drive loads, such as loudspeakers. That makes Class-A the most linear of all amplifier types, where linearity means simply how closely the output signal of the amplifier resembles the input signal. The powers at various frequencies throughout the range are compared to a particular reference frequency, (the mid band frequency). On paper that probably sounds unusable, but in reality, it's quite different. Each of the amplifier types described above has one or more special electrical character that makes them well suited for one specific application and that's why we can find so many types of amplifiers. for my two penn'orth a Class B amplifier with a small bias to minimise crossover distortion, you might say optimally biased, is Class AB as it will operate in class A at very low output levels. The small signal stages 5. The operation and output characteristics of each of the circuit configurations differs from one another. For power amplifiers, optimal loads are often different than the conjugate match of the output impedance. class c amplifiers, which have conduction angles of less than 180 degrees, are the most efficient of the classical amplifier configurations, with efficiency approaching 100% as conduction angle approaches 0 degrees. In this configuration, the output transistor(s) always has current flowing through it, even if it has no audio signal (the output transistors never 'turn off'). Image courtesy of sound.westhost.com. The Q-point is set at the middle of the load line so that the AC signal can swing a full cycle. Introduction and general survey 2. That leaves distortion as the great unsolved power amplier problem; in particular, crossover distortion in a Class-B output stage is still very much with us, caused by a small wobble in the output stage gain. However, Class C amplifiers have a region of zero idle current which is more than 50% of the total supply voltage. This is the sound heard when one of the output devices goes open circuit in an audio amp! The main role of class-A bias is to keep amplifier free from distortion by keeping signal waveform out of the non-linear region which exists between 0V and 0.6V. This class of amplifier is the main focus of this appli-cation note. Compensation, slew-rate, and stability 8. Compensation, slew-rate, and stability 8. Harmonic output of Class-E amplifiers is similar to that of Class-B amplifiers. The general principles of power amplifiers 4. Other classes There are several other amplifier classes, although they are mainly variations of the previous classes. 18-8. ecd output amplifiers chapter 11 output stages and power amplifiers introduction 11.7 power bjts 911 11.1 classification of output stages 11.2 class output. Ips is the DC power supply current taken by the amplifier output stage. In order to combine these two outputs, an NPN and a PNP transistor are placed in a so called push-pull configuration (Figure 4) that we will see in detail in the next section. The original designs of Futterman were all class B. An amplifier can saturate and clip the output if the input signal becomes too large for the amplifier to reproduce. Figure 7. A new (and disturbing) trend is for many amplifier manufacturers (and especially Class-D ICs) to rate the output power at 10% distortion. CLASS 'A': Many class A amplifiers use the same transistor(s) to reproduce both the top and bottom halves of the audio waveform. Class-A power amplifiers 10. They have some kind of gain, or multiplication factor relating the magnitude of the output signal to the input signal. 1. When the transistor is used as an amplifier, the amplifier circuit created is one of five classes of amplifier (Table 8.13). Typical output power rating of a power amplifier will be 1W or higher. These represents the class for nearly all linear power amplifiers. In addition to the class of operation, the overall efficiency of a Power Amplifier is affected by factors such as dielectric and conductor losses. In small-signal amplifiers, the main factors are usually amplification linearity and magnitude of gain. Abstract 2 Introduction 4 Classes of Amplifiers 4 Design Process 6 Choosing and Biasing the Transistor 8 Stability 10 Wide Band Matching 13 Final Circuit Design 22 Amplifier Power Output 26 Nonlinearity of Device 28 Final Remarks 29 Appendix 31 Reference 32. Many Class-AB amplifiers are far better than the vast majority of Class-A amps, despite being far more efficient and lacking the gravitas of being called 'Class-A'. Class C amplifiers are similar to Class B in that the output stage has zero idle bias current. On the other hand, in class A amplifier using parallel operation of two transistor to get the same output power of 50 watts, assuming maximum conversion efficiency of 50%, dc power requirement is watts. The discussion of amplifiers in the previous sections apply to class A operation. A class-B amplifier conducts 180 degrees, in other words it only amplifies one of the signal's half waves. practical amplifier always consists of a num-ber of stages that amplify a weak signal until sufficient power is available to operate a loud-speaker or other output device. The output stage of a Class-B transformer-coupled amplifier is shown in Fig. The input of class B amplifiers is large, due to which the output is also very large. In addition to the timing considerations discussed previously. Historically, amplifier class designations were related to the biasing of amplifier devicesthat is, over how many degrees of each input-signal swing they conducted. For Class A amplifier operation the switching transistors Q-point is located near to the centre of the output characteristic load line of the transistor and within the linear region. The amplifier is incorporated with a speaker as the output. This is the signal of unloaded amplifier versus loaded amplifier (5V per division): What is wrong here stays a mystery for me but maybe you can figure it out. They are very inefficient; a theoretical maximum of 50% is obtainable with inductive output coupling and only 25% with capacitive coupling, unless deliberate use of nonlinearities is made (such as in square-law output stages). The function of a practical power amplifier is to amplify a weak signal until sufficient power is achieved to operate a loudspeaker or output device. In simple words, these amplifiers amplify only half of the input cycle. Harmonic output of Class-E amplifiers is similar to that of Class-B amplifiers. Introduction and general survey 2. a) Operation of Class-A and Class-B amplifiers When the bias current of a transistor is adjusted to make the average collector current half of its maximum, the transistor operates in the active linear range, and distor tion-free output is available as long as the input signal level is moderate. When an amplifier is biased such that it always operates in the linear region where the output signal is an amplified replica of the input signal, it is a class A amplifier; conduction over the full 360 of the cycle. Note that the supply is connected to the center-tap of the transformer primary, and that Q2 and Q3 have grounded emitters. Another important characteristic of Class B amplifiers is the absence of DC bias on the base branch of the transistor. Harmonic output of Class-E amplifiers is similar to that of Class-B amplifiers. This white paper covers power dissipation calculations for Class B amplifiers. While this makes them the most efficient, it also produces the most distortion. The very clever bit of the amplifier he describes is that Blomley split the incoming signal into top and bottom halves before applying the separate signals to the output transistors. The output devices continually turn on and off. The output stage II 7. Linear amplifier refers to a type of radio-frequency (RF) power amplifier, some of which have output power measured in kilowatts, and are used in amateur radio. In this type of amplifier, the switches are either fully on or fully off, significantly re-ducing the power losses in the output devices. Chapter 13 Class-D amplifiers. Remember that the DC load line indicates the minimum & maximum output voltage and current allowed by the DC power supply. Fig.1. This arrangement is known as push-pull circuit. While a Class A/B amplifier's efficiency improves as it approaches maximum output, Class D designs maintain a high efficiency rating over the majority of their operating range; as a result, real world efficiency tilts further in their favor. (If harmonic outputs must be well below the carrier power, only Class-A or push-pull Class-AB amplifiers can operate over a band wider than about 1.8:1 with only one fixed-tuned harmonic-suppression fil-ter.) Class B amplifier is a type of power amplifier where the active device (transistor) conducts only for a one-half cycle of the input signal. As far as I know, usual op-amps have always been said working in class B and have a small quiescent current. Devices operating in Class B are used in linear amplifiers, so called because the radio frequency output power is proportional to the square of the input excitation voltage. For class B operation, the maximum output power is delivered to the load when VL(p) = VCC: The corresponding peak ac current I(p) is then so that the maximum value of average current from the power supply is Using this current to calculate the maximum value of input power results in. The class gives a broad indication of an amplifier's characteristics and performance. 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. But, in the case of a single transistor, only half of the input signal is amplified. The input signal has to be a lot larger in order to drive the transistor appropriately. The output stage II 7. Power supplies and PSRR 9. To describe a change in output power over the whole frequency range of the amplifier, a response curve, plotted in decibels is used to show variations in output. In general, the class of an amplifier refers to the portion of the waveform being amplified for which an amplifier's transistors are "ON" or in their conduction state. Too low of idling, current moving the operation toward class B, will cause major distortion. In electronics, power amplifier classes are letter symbols applied to different power amplifier types. Class B operation has the following characteristics. But for amplifying signals at higher output-power levels, different amplifier configurations are needed. C4 blocks the DC voltage from the output of the amplifier and only lets the amplified AC microphone signal through. Unloaded amplifier behaves as expected, but loaded amplifier has great amount of distortion in between its output signal. An Inverting amplifier differs from the non-inverting amplifier due to much lower input impedance (equal to the value of R1). 'one in which the operating point of each output device is set at the lower extreme of its transfer characteristic. Finally, to be frank, I seriously looked for some good reason why the Dragon should NOT be in Class A. I couldn't find any. The crossover distortion is common at the output stage of class B and AB amplifiers. A combination of Class E and Inverse Class F amplifier operation is used to achieve high efficiency amplification. Class B Power Amplifiers, unlike Class A, work for only half of each input cycle, which means they have a conducting angle of 180 degrees. these, however, do not have good linearity. Class A is used for low to medium power output stages. The circuit of a push-pull class B power amplifier consists of two identical transistors T1 and T2 whose bases are connected to the secondary of the center-tapped input transformer Tr1. Thus, it produces a large amplification. 1. Amplifier Classes. 6 Functional blocks of an amplifier All power amplifiers have: 1.A Power supply 2.An input stage 3.An output stage. 1. An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the power of a signal (a time-varying voltage or current). The small signal stages 5. Therefore, a class-A amplifier is said to have a 3600 conduction angle. History, architecture and negative feedback 3. the standard symb A procedure for analyzing, designing, and assessing audio power amplifier output stages operating in classes A, B, AB, G, and H with reactive loads is presented. Different type of power amplifiers gives different responses when passing current through them. Class A. Operational Amplifier ( OPAMP ): The OPAMP: The op amp is one of the basic building blocks of linear design. Class D - This class of amplifier is a switching or PWM amplifier as mentioned above. The aim of a mixed class amplifier is to provide the high quality sound of Class-A operation with the greater efficiency and power output of Class-B operation. (If harmonic outputs must be well below the carrier power, only Class-A or push-pull Class-AB amplifiers can operate over a band wider than about 1.8:1 with only one fixed-tuned harmonic-suppression fil-ter.) When an amplifier is biased such that it always operates in the linear region where the output signal is an amplified replica of the input signal, it is a class A amplifier. See Figure 1, showing the time the output device conducts Class-D: Quasi-digital amplification. Disadvantage of class-A amplifiers. Then he was easily able to design the output transistors to work only in their linear region (above a collector current of ~15mA). The output stage I 6. Large-signal or power amplifiers, on the other hand, primarily provide sufficient power to an output load to drive a speaker or other power device, typically a few watts to tens of watts. Let's try to understand each class of amplifier one by one starting from class A. Therefore, constant output voltages need to be produced across the wide bandwidths of a power amplifier. Typically two class-B amplifiers are run in a parallel configuration where each amplifier handles its own corresponding half wave. Wide bandwidth ultrasonic devices are a necessity in high-resolution ultrasonic systems. Transformer T2 couples load resistor RL, to the collector circuits of transistors Q2 and Q3. Amplifier classes are the identity of amplifier's performance and characteristics. Transformer Coupled Class B Amplifier Circuit. The Class A amplifier uses a single switching transistor in the standard common emitter circuit. This characteristic prevents distortion of amplitude-modulated or frequency-modulated signals passing through the amplifier. The Class C Amplifier design has the greatest efficiency but the poorest linearity of the classes of amplifiers mentioned here. The output stage generally employ class B amplifiers in push-pull arrangement. Conversely, output transistors of Class B amps only pass electrical current when audio signals are present. This allows the amp to operate with an optimized Class AB efficiency, regardless of output power level. Class AB power amplifier When there is no input signal, transistors in class AB amplifiers must be biased slightly above cut-off to eliminate crossover distortion. This search for a "reason" was partly because of the now unusual result; Two separate amplifiers, from the same company, both being in Class A at the same time. This meant that the available power depended highly upon the impedance of the speakers. History, architecture and negative feedback 3. Chapter 2 Power amplifier architecture and negative feedback. For example, Class G and Class H amplifiers are marked by variation of the supply rails (in discrete steps or in a continuous fashion, respectively) following the input signal. Class-A power amplifiers 10. (If harmonic outputs must be well below the carrier power, only Class-A or push-pull Class-AB amplifiers can operate over a band wider than about 1.8:1 with only one fixed-tuned harmonic-suppression fil-ter.) In contrast, a Class-B amplifier is designed so that only one of the output stages is allowed to be on at a time. This complete power of 100 watts must be dissipated in the two transistors are zero signal. When an amplifier has a value of PP = 2lCQrC, exceeding the value of PP results in cutoff clipping. The classes are related to the time period that the active amplifier device is passing current. In a word: extremely. device on-resistance plays a major role in the efficiency performance of a Class-E amplifier. Class H amps are generally more complex than other audio amplifier designs. The class B power amplifier's efficiency is higher as compared to class A because, in class B, there is no DC base bias current because its quiescent current (IQ) is zero so that the DC power is very small. Amplifier 1: EF-VAS, CFP Output Stage, Miller Compensation. In theory, a class A amp can achieve 50% efficiency with inductive output coupling or 25% with capacitive coupling. Related to output current capability is the specification of minimum stable or safe output impedance that an amplifier can drive. Amplifier Design Examples. A push-pull amplifier, on the other hand, amplifies the signal as two mirror images and combines them at the output. Due to the excessive global feedback they acted as Voltage output sources, just like solid state amplifiers and op-amps. Chapter 14 FET output stages. To differentiate the characteristics and behavior of different power amplifier circuits, Power Amplifier Classes are used in which, letter symbols are assigned to identify the method of operation. However, the circuit will experience nonlinear distortion before the amplifier peak-to-peak output reaches the value of PP. The output voltage from the DAC is applied through an op-amp based signal conditioning circuit, and this provides the input to a class B amplifier. Chapter 3 The general principles of power amplifiers. This allows the transistor to conduct for the complete 360 o so the output signal varies over the full cycle of the input signal. In Class B amplifier, the positive and negative halves of the signal are dealt with by different parts of the circuit. There are a number of criteria to consider when specifying the transistor used in the output stage. The study considers steady-state sinusoidal analysis for BJT, IGBT, and MOSFET technologies. For example, a Class-G amplifier improves upon the efficiency of a Class-AB design by using multiple rails at different voltages to amplify the input voltage more efficiently. Class B single ended RF Power amplifiers (single output device) also operate slightly above cutoff to eliminate distortion caused by non linearities. Hence in a push pull design, for any symmetrical input signal, each output device conducts only one half of the output. While we could measure it with a meter, the purpose of this white paper is to show how.

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