W audio amplifier
Class D amplifiers, first proposed in , have become increasingly popular in recent years. What are Class D amplifiers? How do they compare with other kinds of amplifiers? Why is Class D of interest for audio?
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Content:
- W Audio EPX 800 Amplifier
- 1 Watt Audio Amplifier Kit
- Ahuja 500 W Audio Amplifier
- W-Audio DA300 Amplifier
- 10-Watt Audio Amplifier Using LM1875
- The Champ 0.5 Watt Audio Amplifier Kit
- Class D Audio Amplifiers: What, Why, and How
- High-Fidelity and High-Efficiency Digital Class-D Audio Power Amplifier
- How Much Amplifier Power Do I Need?
W Audio EPX 800 Amplifier
This study presents a high-fidelity and high-efficiency digital class-D audio power amplifier CDA , which consists of digital and analog modules. The CDA utilizes the closed-loop negative feedback and loop-filtering technologies to minimize distortion. The audio DAC, which is based on a field-programmable gate array, consumes 0. The analog module is fabricated in a 0.
The output power reaches up to 2. Following the rapid development in artificial intelligence Internet of Things, smart speaker and TWS headset based on class-D audio power amplifiers CDAs have become the most popular portable audio products. Simultaneously, with the continuous development in digital-storage technology, audio signals have mainly become digital audio signals.
The traditional CDAs usually introduce a digital-to-analog converter DAC to convert the digital audio signals into analog audio signals and then perform power amplification. This solution not only increases the complexity of the system and is not conducive to transplantation but also requires a high-precision DAC.
In addition, intrinsic quantization noise is introduced to reduce the system performance. Figure 1 shows the new CDA structure proposed in the s for compatibility with a digital audio interface [ 1 ], which has gradually become a research hotspot in recent years.
The modulation techniques of CDAs can be divided into uniform-sampling pulse width modulation UPWM [ 2 — 4 ], pulse-density modulation PDM [ 5 — 7 ], click modulation [ 8 , 9 ], and zero-position coding with separated baseband [ 10 , 11 ]. The CDAs comprise several main topologies. The open-loop architecture requires a precise carrier signal to achieve low distortion [ 12 ]. The closed-loop architecture does not require a similar precise carrier because the CDA loop gain suppresses the carrier distortion [ 13 ].
Moreover, some CDAs generally comprise a single-bit quantizer, but ensuring stability over all modulation indexes requires high controller power [ 14 , 15 ].
To overcome these drawbacks, we propose a CDA with a closed-loop negative feedback and loop-filtering technologies to improve the total harmonic distortion THD and suppress the noise introduced by the power supply.
This paper is organized as follows. Section 2 describes the design of the proposed architecture. The digital module is presented in Section 3. Section 4 shows the implementation of the analog module. The postlayout simulation results are provided in Section 5. Finally, the paper is concluded in section 6. Figure 2 shows the block diagram of the proposed class-D architecture, which mainly consists of a digital module called audio DAC and an analog module.
The analog module includes the closed-loop negative feedback, loop filter, and output-power stage. The output bitstream and sampled and held carrier signals are used to realize UPWM in the digital domain. The output UPWM signal drives the analog circuit. The loop filter, output-power stage, and closed-loop negative feedback are realized by the analog module.
The closed-loop negative feedback technology is used to effectively suppress the power-supply noise and system nonlinearity and to ensure high fidelity of the output audio signal.
The maximum swing of the audio output voltage can be doubled using the bridge-tied load configuration, which consequently quadruples the output power [ 17 ].
To realize sufficient SNR, the interpolation filter oversamples the input digital audio signal by interpolation and evenly distributes the quantization noise in the whole frequency domain of the signal. The conventional interpolation filter generally adopts half-band and comb filters [ 19 ]. Although the comb filter structure is relatively simple, its filtering ability is limited.
Thus, some compensation technologies should be employed to improve it. Figure 3 shows the block diagram of a 16x interpolation filter for the proposed CDA. Three half-band filters and an inverse sinc filter are cascaded to complete the 16x interpolation of the input digital audio signal.
In a high-performance audio DAC, the passband ripple usually ranges from 0. Therefore, in the interpolation process, the maximum allowable passband ripple of the interpolation filter must be 0. The SNR reaches up to However, if the power transistor is directly driven by the output bitstream signal of the single-bit quantizer, the frequency of the modulated switching signal [ 21 ] will be too high and will vary with the input signal, resulting in the reduction in the power efficiency.
Therefore, the quantizer in the CDAs is usually considered to be multibit quantizers. However, the quantizer bits should not be very high because the system clock will be too fast to increase the system power consumption, and implementing the system becomes difficult.
However, a higher number of quantizer bits or a higher modulator order is required for a low oversampling rate. A higher oversampling rate can greatly reduce the requirements of the modulator and quantizer. In addition to the increase in the system frequency and power consumption, the output pulse signal frequency also exponentially increases.
Therefore, in this study, the oversampling rate is set to 16, the order of modulator is set to 4, and the number of bits of the quantizer is set to 4.
The hardware platform uses Artix-7 MIA development board. The development board integrates a wealth of hardware resources to meet the digital design requirements of audio digital-to-analog converters.
The UPWM modulator is a direct modulator that converts the digital signal into a switching signal. The loop filter can reduce the harmonic distortion of the feedback loop using the noise-shaping technology. The frequency-response curve of the Butterworth filter is relatively flat in the passband without fluctuations and gradually decreases to zero in the stopband.
Hence, a Butterworth loop filter is designed in this study. Therefore, the open-loop transfer function of the system can be expressed as where. In the audio band, the noise-suppression effect of the Butterworth loop filter increases with the order, but the increasing trend gradually slows down. By considering the effect of the loop filter on the in-band noise suppression and the complexity of the circuit design, the order is considered as a second order. In this study, the loop filter of the proposed CDA adopts a second-order integrator architecture, as shown in Figure 9.
It consists of two cascaded Miller integrators. Figure 10 shows that the OTA is a two-stage amplifier with a Miller compensation. The transfer function of the two-stage operational amplifier is expressed as where V id is the input differential signal, A DC is the open-loop gain of the amplifier, and p z , p 1 , p 2 , and p 3 are the zero point, main pole, second pole, and third pole, respectively.
The comparator compares the output of the first- and second-stage integrators to generate a PWM waveform to drive the power transistor. Figure 11 shows the circuit of the rail-to-rail differential comparator, which consists of a preamplifier and a single-stage open-loop comparator.
To ensure that the comparator has sufficient accuracy, the preamplifier employs a folded cascade structure to achieve a high DC gain. Moreover, to achieve a wide swing input range, the input stage of the operational amplifier employs a rail-to-rail input structure using NMOS and PMOS in parallel to reduce the distortion.
Figure 11 shows that M 5— M 9 are current-mirror structures, which provide the bias current required for normal operation of the circuit. The load is composed of M 10— M 15, R 1, and R 2. In addition, R 1 and R 2 form a common-mode feedback circuit. The single-stage open-loop comparator consists of a single-stage OTA and two-stage buffers.
M 16— M 19 are composed of a simple OTA to realize the function of converting the differential output to a single output.
The two-stage buffer plays an isolation role and improves the driving ability of the circuit. The power transistor of CDAs can be considered as equivalent to a switch. In reality, the power transistor is not an ideal switch when it turns on, and the influence of the on-resistance should be considered.
When current flows through the on-resistance, it generates heat loss, which is called conduction loss. On the other hand, when the PWM signal drives the power transistor to turn it on or off, the gate capacitance is charged and discharged, resulting in a switching loss. Figure 12 shows the equivalent diagram of the power transistor [ 26 ].
G, S, D, and B represent the gate, source, drain, and substrate of the power transistor, respectively. R on is the equivalent on-resistance. Therefore, conduction loss P con of the power transistor can be expressed as where I rms is the effective value of the current that flows through the power transistor. P con is proportional to L and inversely proportional to W. Total gate capacitance C G of the power transistor can be expressed as where x d is the transverse diffusion length.
P sw is proportional to W and L. Moreover, Figure 13 shows the gate-driving circuit. It consists of a nonoverlap configuration and an inverter-chain driving circuit to reduce the short-circuit current and parasitic gate capacitance of the power transistor [ 27 ].
There are two major types of architecture for closed-loop negative feedback. The first one is the single-loop and the second is the multiloop. A major drawback of the multiloop architecture is that precise matching of the analog and digital signal processing paths is required to avoid large errors caused by integrator gain coefficient variations [ 28 ].
To reduce the noise and nonlinearity of the system, the proposed CDA adopts a second-order single-feedback loop structure [ 29 , 30 ]. Figure 14 b shows that the loop gain of the closed-loop system is calculated as. The transfer function of the closed-loop system is given by where. Owing to the closed-loop negative feedback technology, equation 13 indicates that the noise function of the closed-loop system exhibits high-pass characteristics. The noise-shaping technology can be realized by reasonably setting the loop gain of the system.
Equation 14 indicates that the THD of the closed-loop system also decreases with the increase in the loop gain, which greatly improves the system performance.
Equation 15 illustrates that the PSRR of the closed-loop system also becomes more negative as the loop gain increases, and the ability to suppress the power-supply noise becomes stronger. Because of the voltage negative feedback effect, the output impedance of the closed-loop system is reduced and is independent of the load.
During the stabilization of the output impedance, it reduces the voltage division by the output impedance; thus, more power can be obtained from the load, and the system efficiency is improved. The proposed CDA consists of digital and analog modules.
The digital module is implemented on the field-programmable gate array FPGA. Figure 15 shows the resource utilization and power-consumption distribution of the audio DAC. It consumes 0. The analog module of the proposed CDA is designed and fabricated in the 0.
1 Watt Audio Amplifier Kit
The LM can deliver 50watts of output power into an 8 ohm loudspeaker. LM has excellent signal to noise ratio and has wide supply voltage range. Other features of LM are output to ground short circuit protection, input mute function, and output over voltage protection, etc. Applications of LM are component stereo, compact stereo, surround systems, self powered speakers, etc. The 50 watt audio amplifier circuit shown below is designed based on the application diagram from the data sheet of LM Some modifications are made on the original circuit for improving the performance. The bipolar electrolytic capacitor C7 is the input DC decoupling capacitor.
Ahuja 500 W Audio Amplifier
It has been tested and is in full working order. The item is in good to average condition and has some marks to the top. The feet are also missing due to the item being previously rack mounted. It comes with the power lead and manual. This W-Audio DA Amplifier does not include original packaging but has been professionally packaged to ensure safe delivery to your door. The amps are incredibly well built for the price and sound fantastic. Audio Visual Commodity Ltd trading as whybuynew.
W-Audio DA300 Amplifier
Proposition 65 is a California law that applies to companies selling products in California. Proposition 65 requires warnings if a product contains any listed chemical present above very low levels. Proposition 65 is not a product safety law, but rather a "right-to-know" law. Businesses are required to provide warnings to comply with Proposition The list includes naturally occurring and man-made chemicals.
10-Watt Audio Amplifier Using LM1875
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The Champ 0.5 Watt Audio Amplifier Kit
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Class D Audio Amplifiers: What, Why, and How
It has been tested and is in full working order. The amp is mostly in very good condition but there is a small bend to one of the rear rack ears please see photos. It comes with the power lead and manual. This W-Audio DA Amplifier does not include original packaging but has been professionally packaged to ensure safe delivery to your door.
High-Fidelity and High-Efficiency Digital Class-D Audio Power Amplifier
A mode selector switch allows the PAG2 to deliver two channels of 20 watts each into 4 ohms, or a single, bridged channel of 40 watts at 8 ohms. This Class D amplifier is energy efficient and convection cooled. It can deliver stereo or mono output, and provides mixing for the balanced and unbalanced audio inputs, each with independent gain and mute control. In addition to the amplified speaker output, a line level audio output allows the incoming audio to be fed into an additional amplifier or audio system.
How Much Amplifier Power Do I Need?
Audio power is the electrical power transferred from an audio amplifier to a loudspeaker , measured in watts. The electrical power delivered to the loudspeaker, together with its efficiency , determines the sound power generated with the rest of the electrical power being converted to heat. Amplifiers are limited in the electrical energy they can output, while loudspeakers are limited in the electrical energy they can convert to sound energy without being damaged or distorting the audio signal. These limits, or power ratings , are important to consumers finding compatible products and comparing competitors. In audio electronics , there are several methods of measuring power output for such things as amplifiers and power handling capacity for such things as loudspeakers. As an amplifier's power output strongly influences its price, there is an incentive for manufacturers to exaggerate output power specs to increase sales.
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