The Audio Amplifier Theoretrical Economics Essay

First of wholly, the aim of audio amplifiers are to reproduce audio signals at end product province, at desired volume and power degrees with a low deformation without altering the originality of the input signal. A good amplifier must get a really good frequence response over human hearable frequence scope, which is about 20 Hz to 20 kilohertzs.Power capablenesss for amplifiers are widely depending on the type of applications. Earphones merely deliver mili-watts of end product power and at the average clip Television or Personal computer sound produces few Wattss of power.

Other than that, place stereos and automotive sound deliver 10 of Watts to the user. Amplifier produces up to 100s Wattss at the powerful place and commercial sound system such as theatres or auditorium.Besides, an sound amplifier usage transistors in additive manner in order to make an end product electromotive force produce a reproduction transcript of the input electromotive force. This execution causes the forward electromotive force addition remains high at the value of 40 dubnium. If the forward addition is included in the feedback cringle, the overall cringle addition will in remain high. Therefore, high cringle addition can better public presentation stamp downing deformation caused by nonlinearities in the forward way by using feedback in the amplifier. Other than that, high cringle addition can besides cut down power supply noise by increasing the power-supply rejection ( PSR ) .

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1 Types of Amplifier

In Class A amplifier, there is ever bias current flowing in the end product devices. Therefore, the end product devices are continuously carry oning for the full rhythm. The advantage of this topology are least deformation and most additive among other additive amplifier. The con of this amplifier is the low efficiency at approximately 20 % . The design is typically non complementary with a high and low side end product device.

Figure 2.1: Class A amplifierIn the Class B amplifiers topology, two transistors have been used. Both transistors are switched on at the same time where as each transistor is turned on half of the clip. Therefore, when one of them operates during the positive rhythm of the input, the other is operate at the negative rhythm.The input signal plays the indispensable function in the amplifier. Without the being of input signal, both transistors are turned off.

Therefore, no power appears at the end product province. Efficiency of category B is better than category A. The operation to turn on the transistors draw some clip, there is a minute where no power appears at the end product. The part where no power appears is called as crossing over part which introduces a high sum of deformation.

This amplifier which is showed at the Figure 1.2 has high efficiency, but hapless truth is the chief drawback.Figure 2.2: Class B amplifierIn Class AB amplifiers, there are non much different comparison to category B amplifiers. The lone difference is the debut of two rectifying tubes that improved the public presentation of the amplifier and the same clip extinguish the crossing over part by leting both transistors to be turned on at the same clip. The efficiency which about 50 % can be achieved.However, the efficiency is non every bit high as category B because both transistors are turned on at the same time, but truth of the amplifier has mostly improved. Therefore, Class AB topology is chiefly used in audio power amplifier.

Figure 2.3: Class AB amplifierClass D amplifier is called as shift or PWM amplifier. The chief difference of this amplifier is the switches of the amplifier are either to the full on or to the full off at one clip. Therefore, the power loses in the end product devices can be significantly reduced.

Efficiencies of 90-95 % are possible to accomplish in existent. The audio signal is used to modulate a PWM bearer signal which drives the end product devices, with the last phase being a low base on balls filter to take the high frequence PWM bearer frequence.

2.2 Topology Comparison

Classes A, B and AB are categorized into additive amplifiers. In a additive amplifier the signals ever remain in the parallel sphere, and the end product transistors act as additive regulators to modulate the end product electromotive force. On the other manus, Class D amplifier converts analog signal into digital signal, and after go throughing the filter at the end product province, parallel signal has been reproduced.

2.21 Linear and Class D amplifier

Amplifier & A ; acirc ; ˆ™s efficiency is the major difference between additive and Class D amplifier.

Normally, additive amplifier is inherently really additive in footings of its public presentation and besides really inefficient at approximately 50 % typically for a Class AB amplifier. On the other manus, Class D amplifier is able to make 90 % efficiency in practical designs.Figure 2.4: Efficiency of Linear Amplifier Figure 2.

5: Efficiency of Class DIn the additive amplifiers, coach electromotive force fluctuations will non act upon the addition, which causes the changeless addition can be obtained. On the other manus, Class D amplifier & A ; acirc ; ˆ™s addition is relative to the coach electromotive force. Therefore, Class D amplifier has the power supply rejection ratio ( PSRR ) value of 0dB.

At the average clip, a additive amplifier merely has a really good PSRR value. Class D amplifiers frequently use feedback to counterbalance for the coach electromotive force fluctuations.Other than that, the energy flow is ever from supply to the burden for the additive amplifier and full-bridge Class D amplifier. On the other manus, half-bridge Class D amplifier nevertheless is different, as the energy flow can be bi-directional, which leads to the & A ; acirc ; ˆ?Bus pumping & A ; acirc ; ˆA? phenomena, which causes the coach capacitances to be charged up by the energy flow from the burden back to the supply. This occurs chiefly at the low sound frequences.

In the term of power losingss in the power switches, additive amplifiers have a batch of differences compared to Class D amplifier. First, the losingss in a additive Class AB amplifier will be discussed. The losingss can be defined as in the equation at Figure 2.

6 where as the power loss is non related to the end product device parametric quantities.Figure 2.6: Power loss of line drive amplifier equationNext, the power losingss in Class D amplifier will be discussed. The entire power loss in the end product devices for a Class D amplifier can be defined as in the equation at Figure 2.7.Figure 2.

7: Power loss of Class D amplifier equationPsw are called as shift loses at the MOSFET.Besides, Pcond are the conductivity losingss and Pgd are the gate thrust losingss in the circuit. Three of these power losingss are given at the equation at Figure 2.8.Figure 2.8: Equations of exchanging losingss, conductivity losingss and gate thrust losingss.From the above equations, the end product losingss of Class D amplifiers are dependent on the parametric quantities of the device used.

Therefore, persist optimisation is indispensable in order to bring forth most effectual device, based on Qg, RDS ( on ) , Cqss, and Tf.

2.22 Half Bridge and Full Bridge


One-half Bridge

Full Bridge

Supply Voltage

0.5 ten 2 Channel1 Channel

Current evaluation




Gate Driver

1 Gate Driver/CH2 Gate Driver/CH

PWM Pattern

2 Degree3 DegreeTable 2.1: Comparison between Half Bridge and Full BridgeIn general, Class D amplifier contains of two topologies, half-bridge and full-bridge constellations.

Each topology has own advantages and failings. In term of execution, a half-bridge is simpler than full span. On the average clip, a full-bridge is better in audio public presentation due to the ability to extinguish the XT noise.The full-bridge topology is built by uniting two half-bridge amplifiers, and therefore, requires more constituents in the design. However, the differential end product construction of the span topology inherently can call off even the order of harmonic deformation constituents and DC beginnings, as in Class AB amplifiers. A full-bridge topology allows of the usage of a better PWM transition strategy, such as the three degree PWM which basically has fewer mistakes due to quantisation.On the other manus, the failing of half-bridge topology is that the power supply might endure from the energy being pumped back from the amplifier, ensuing in terrible coach electromotive force fluctuations when the amplifier outputs low frequence sound signals to the burden.

Therefore, the boot back energy to the power supply is a cardinal feature of Class D elaboration. On the other manus, complementary exchanging legs in the full-bridge tend to devour energy from the other side of the leg and it will forestall energy being pumped back towards the power supply.

2.3 Major Cause of Imperfection

When a Class D amplifier is in ideal province, efficiency towards 100 % can be achieved and remained the originality of the input signal without any noise or deformation.

In world, practical Class D amplifiers have imperfectnesss that generate deformations and noise. The imperfectnesss are caused by the deformed shift wave form being generated by the Class D phase.First, nonlinearity in the PWM signal from modulator to exchanging phase due to limited declaration and/or jitter in clocking have caused the deformation. Besides, the 2nd ground of imperfectness is the timing mistakes added by the gate drivers, such as dead-time, ton/toff, and tr/tf. Other than that, parasitic constituents that cause pealing on transient borders is one of the cause of imperfectness.

Furthermore, unwanted features in the shift devices, such as finite ON opposition, finite exchanging velocity or organic structure diode features will do the deformation at the wave form. Furthermore, power supply electromotive force fluctuations due to its finite end product electric resistance and reactive power fluxing through the DC coach is another ground of imperfectness. Non-linearity in the end product LPF has caused the imperfectness.Figure 2.9: Major Cause of ImperfectionFigure 2.10: Dead TimeSwitch overing clocking mistake in a gate signal is the primary cause of the nonlinearity. Therefore, the nonlinearity in a Class D phase is chiefly caused by dead clip in the gate driver. Besides, a 10s of nano-seconds of dead clip can easy bring forth more than 1 % of THD ( Total Harmonic Distortion ) .

Therefore, the chief concern is the accurate shift timing.There are three different parts in the operation manner of a Class D end product phase based on how the end product wave form follows the input timing. Therefore, the end product wave form follows different borders in high side and low side input signal when operating at different parts.

First of all, observation is focused on the first operating part where the end product current flows from the Class D phase to the burden when the sum of the current is larger than the inductance ripple current.The end product node is driven to the negative DC coach when at the blink of an eye of high side turn-off and at the same clip prior to low side turn-on. Low side turn-on causes the commuting current from the demodulation inductance. Therefore, the timing in the end product wave form will non affected by the dead-time inserted into the turn-on border of low side, and at the same clip ever follows the high side input timing. Furthermore, the dead-time inserted into the high side gate signal will do the PWM wave form to short and ensue somewhat lower electromotive force addition as expected from the input responsibility rhythm.Other than that, negative operation part will confront the same state of affairs like the positive operation part where the end product current flows from the burden to the Class D phase.

The inductance ripple current is lower than the sum of the current flow in the burden. Therefore, the dead-time inserted into the turn-on border of the high side will non act upon the timing in the end product wave form and ever follows the low side input timing.The dead-time inserted into the low side gate signal will do the PWM wave form to short. Between two operation manners, there is a part where the end product timing is independent towards the dead-time. When the end product current is smaller than the inductance rippling current, the end product timing follows the turn-off border of each input because, in this part, turn-on is made by ZVS ( Zero Voltage Switching ) operation.

Hence, there is no deformation in this in-between part.The sound input signal that feeds into the amplifier do the end product current to vary and changes the operation parts of Class D amplifier which each have a somewhat different addition. these three different addition parts in a rhythm of the audio signal will do end product wave form in deformation.


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