class-D Audio Power Amplifier Research Articles

High-Fidelity and High-Efficiency Digital Class-D Audio Power Amplifier

This study presents a high-fidelity and high-efficiency digital class-D audio power amplifier (CDA), which consists of digital and analog modules. To realize a compatible digital input, a fully digital audio digital-to-analog converter (DAC) is implemented on MATLAB and Xilinx System Generator, which consists of a 16x interpolation filter, a fourth-order four-bit quantized delta-sigma (ΔΣ) modulator, and a uniform-sampling pulse width modulator. 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 0.128 W and uses 7100 LUTs, which achieves 11.2% of the resource utilization rate. The analog module is fabricated in a 0.18 µm BCD technology. The postlayout simulation results show that the CDA delivers an output power of 1 W with 93.3% efficiency to a 4 Ω speaker and achieves 0.0138% of the total harmonic distortion (THD) with a transient noise for a 1 kHz input sinusoidal test tone and 3.6 V supply. The output power reaches up to 2.73 W for 1% THD (with transient noise). The proposed amplifier occupies an active area of 1 mm2.

A Multiphase Class-D Automotive Audio Amplifier With Integrated Low-Latency ADCs for Digitized Feedback After the Output Filter

A $5 \times 80$ W class-D audio power amplifier for automotive applications is presented. The amplifier is implemented in a 140-nm bipolar CMOS DMOS SOI. Configurable digital-loop filters can compensate for a range of LC output filters and their high loop gain (>50 dB between 20 Hz and 20 kHz) suppresses non-idealities of the output filter and enables low-cost output filter components. Key elements are the integrated low-latency $\Delta \Sigma$ analog to digital converters (ADCs) which digitize the output signals directly at the speaker load, after the output filter. The ADCs use filtering finite impulse response digital to analog converters in their feedback path to create an input–output transfer with a negative group delay at low frequencies. The ADCs have 116-dBA DR and −108 dB total harmonic distortion (THD). The bridge-tied load amplifier supports multiphase pulse-width modulation for lower electromagnetic interference. It operates with supplies from 6 to 25 V and with loads down to $1\Omega$ and achieves 19- $\mu \text{V}$ idle noise (Awtd) and 0.004% THD + N.

A $2 \times 70$ W Monolithic Five-Level Class-D Audio Power Amplifier in 180 nm BCD

A 2 × 70 W from 24 V into 4 Ω class-D audio power amplifier in 30/40 V 180 nm bipolar CMOS DMOS is presented. The device employs a flying capacitor (FC) three-level half bridge topology to reduce switching frequency and filter/load power losses in near-idle operation. This is combined with a fourth-order analog feedback system for shaping noise introduced by the digital FC voltage control loop. A power-efficient gate drive scheme suitable for power converters with multiple floating switching devices is also presented, including a compact fast low-power dV/dt robust high-voltage level shifter circuit. Power-efficient operation from idle to full-power operation is demonstrated along with a very high audio performance of 0.003% THD + N at 10 W/1 kHz into 4 Ω.

Design of a Sawtooth Generator Applied for Class-D Audio Power Amplifier

A systematic introduction to principles and advantages of the class-D audio amplifier based on pulse width modulation (PWM) are presented in this paper. The traditional sawtooth generator needs voltage-regulator tube to server as a core component. Against to such a disadvantage a simple way based on the charging and discharging capacitance is proposed to achieve sawtooth generator. The circuit design is based on SIMC 0.18um process. Spectre simulation results show that the sawtooth generator's performance is good. And it suits for the design of class-D audio power amplifier chip.

Modelling and analysis of a high-performance Class D audio amplifier using unipolar pulse-width-modulation

A high-performance class D audio amplifier using unipolar pulse-width-modulation (PWM) with double-sided natural sampling is presented in this article. In order to comprehend and design the system properly, the class D audio amplifier is modelled and analysed. A wide range triangle-wave signal with good linearity and magnitude proportional to supply voltage is embedded in the proposed class D audio amplifier for maximum output power, high power supply rejection ratio (PSRR) and low total harmonic distortion (THD). Design results based on CSMC 0.5-µm 5-V complementary metal–oxide–semiconductor process demonstrate that the proposed class D audio amplifier can operate with supply voltage in the range 2.4–5.5 V and supports 2.8 W output power from a 5.5 V supply; the maximum efficiency is above 95%, the PSRR is −82 dB, the signal-to-noise ratio (SNR) is 97 dB and the total harmonic distortion plus noise (THD+N) is less than 0.1% between 20 and 20 kHz with output power 0.4 W; the quiescent current without load is 1.8 mA, and the shutdown current is 0.01 µA. The active area of the class-D audio power amplifier is 1.5 mm × 1.5 mm.

Development of a class-D audio amplifier with switch-mode rectifier front-end and its waveform control

This study presents the development of a switch-mode class-D audio power amplifier and its robust waveform control. First, a pulse-width modulated inverter is designed and implemented to have successful high-frequency switching operation. Then a robust two degree-of-freedom control scheme is proposed to let the inverter-fed loudspeaker possess close and robust voltage arbitrary waveform tracking characteristics within wide audio frequency range. The waveform tracking performance of the developed inverter is evaluated under resistor load and loudspeaker load with the commands of varying-frequency sinewave, random signal and actual music signals. Finally, a front-end flyback switch-mode rectifier (SMR) is developed and employed to establish well-regulated and boostable DC-link voltage for the followed inverter. Significant improved inverter output waveform tracking performance can be obtained. Meanwhile, good line drawn power quality is achieved. Some experimental results are provided to demonstrate the performance of the whole SMR-fed switch-mode audio system.

A Low-Power High-PSRR Clock-Free Current-Controlled Class-D Audio Amplifier

A low power, high PSRR, clock-free, current-controlled class-D audio power amplifier is presented. The proposed audio amplifier utilizes integral sliding mode control (ISMC) to ensure robust operation and to minimize the steady-state error. This architecture has two feedback loops: an outer voltage loop that minimizes the voltage error between the input and output audio signals, and an inner current loop that measures the inductor current to track the input signal accurately. The proposed amplifier achieves up to 82 dB of power supply rejection ratio (PSRR), more than 90 dB of signal-to-noise (SNR) ratio over the entire audio band, and total harmonic distortion plus noise (THD+N) as low as 0.02%. A power-supply-induced intermodulation distortion (PS-IMD) of approximately - 90 dBc was measured for an input voltage signal of 2 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> at 1 kHz and a sinusoidal power-supply ripple of 300 mV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> at 217 Hz superimposed on the DC level. The IC prototype's controller consumes 30% less power than those of recently published works. The audio amplifier operates with a 2.7-V single voltage supply and delivers a maximum output power of 410 mW with 84% peak efficiency (η) into an 8 Ω speaker. It was fabricated using 0.5 μm CMOS standard technology, and occupies a total active area of 1.65 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Carrier Distortion in Hysteretic Self-Oscillating Class-D Audio Power Amplifiers: Analysis and Optimization

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> An important distortion mechanism in hysteretic self-oscillating (SO) class-D (switch mode) power amplifiers-–carrier distortion-–is analyzed and an optimization method is proposed. This mechanism is an issue in any power amplifier application where a high degree of proportionality between input and output is required, such as in audio power amplifiers or xDSL drivers. From an average-mode point of view, carrier distortion is shown to be caused by nonlinear variation of the hysteretic comparator input average voltage with the output average voltage. This easily causes total harmonic distortion figures in excess of 0.1–0.2%, inadequate for high-quality audio applications. Carrier distortion is shown to be minimized when the feedback system is designed to provide a triangular carrier (sliding) signal at the input of a hysteretic comparator. The proposed optimization method is experimentally proven in an audio power amplifier leading to THD figures that are comparable to the state of the art. Experimental hardware is a hysteretic SO bandpass current-mode-controlled single-ended audio power amplifier capable of 45 W into <formula formulatype="inline"><tex Notation="TeX">$\hbox{8}\;\Omega$</tex></formula> or 80 W into <formula formulatype="inline"><tex Notation="TeX"> $\hbox{4}\;\Omega$</tex></formula> from a <formula formulatype="inline"><tex Notation="TeX">$\pm\hbox{34}$</tex></formula> V supply with less than 0.03% THD from 100 Hz to 6.7 kHz. Carrier distortion is shown to account for this limitation in THD performance. </para>

A high efficiency PWM CMOS class-D audio power amplifier

Based on the difference close-loop feedback technique and the difference pre-amp, a high efficiency PWM CMOS class-D audio power amplifier is proposed. A rail-to-rail PWM comparator with window function has been embedded in the class-D audio power amplifier. Design results based on the CSMC 0.5 μm CMOS process show that the max efficiency is 90%, the PSRR is −75 dB, the power supply voltage range is 2.5–5.5 V, the THD+N in 1 kHz input frequency is less than 0.20%, the quiescent current in no load is 2.8 mA, and the shutdown current is 0.5 μA. The active area of the class-D audio power amplifier is about 1.47 × 1.52 mm2. With the good performance, the class-D audio power amplifier can be applied to several audio power systems.

High-Quality Single-Phase Power Conversion by Reconsidering the Magnetic Components in the Output Stage—Building a Better Half-Bridge

A novel half-bridge switching topology is presented which is based on using a split-wound series-connected coupled-winding inductor, interleaved switching, and zero-deadtime operation to achieve multilevel pulsewidth-modulation output with a reduced part count, reduced current ripple, and improved total harmonic distortion (THD) performance. This new topology is presented to highlight the design process for low-power high switching frequency designs requiring high performance, where circuit size and complexity are normally limiting factors. The design process demonstrated includes considering the current performance characteristics of the inverter and the design of the coupled-winding inductor. Design tradeoffs that are unique to this topology are explored that allow optimized designs for electrical performance, magnetic component size, or system losses. The benefit of the new topology is demonstrated using a case design for a class-D audio power amplifier, which shows a reduction in open-loop THD + N to as low as 0.29%.

Use of Sliding-Mode Modulation in Switch-Mode Power Amplification

This paper presents a recently developed feedback modulation scheme called sliding-mode modulation. Sliding-mode modulation, operating in sliding mode, simultaneously minimizes the accumulated quantization error and in-band modulation error while converting a continuous input signal into a coarsely quantized signal. With these minimization mechanisms, the modulator exhibits simple tractable behavior in the sliding mode and high in-band linearity in signal conversion. These two distinct properties make sliding-mode modulation an attractive substitute for other modulation schemes such as pulsewidth modulation and sigma-delta modulation. A simple method is presented for designing sliding-mode modulators. Moreover, a class-D audio power amplifier with three-level sliding-mode modulation is designed to demonstrate the practicality and superiority of this modulation technique.

Integrated overcurrent protection system for class-D audio power amplifiers

A fully integrated overcurrent protection system is presented suitable for application in integrated class-D audio power amplifiers. Accurate overcurrent detection is used based on parallel measurement of the voltage drop across the DMOS power transistors. A logic circuit enables continuous current limiting during overload situations. Actual short circuits can be distinguished from load impedance minima using a simple short-circuit discrimination method.

An integrated 200-w class-d audio amplifier

An integrated stereo class-D audio power amplifier realized in a silicon-on-insulator (SOI)-based BCD technology is presented. The amplifier is capable of delivering 2×100 W in two 4-/spl Omega/ loads at a supply voltage of 60 V. A second-order feedback loop is used to suppress supply ripple and pulse-shape errors in the switching power stage. The limiting factor in the performance of any class-D amplifiers is the quality of the switching power stage. A high-speed low-current levelshifter and a robust deadtime control arrangement are proposed that enable the realization of a robust high-quality switching power stage. Some practical issues with respect to robustness and electromagnetic compatibility are discussed.

Effect of dead time on harmonic distortion in class-Daudio power amplifiers

A model is described for predicting the harmonic levels introduced by the use of dead time in class-D, PWM-driven audio power output stages. The model demonstrates that the harmonic levels are a function of load impedance, modulation depth, dead time and switching frequency. In addition, measurements show that, for audio applications, dead time is the dominant cause of power stage nonlinearity.

A design of a 10-W single-chip class D audio amplifier with very high efficiency using CMOS technology

A one-chip integrated circuit (IC) of a 10-W class-D audio power amplifier with very high efficiency using CMOS technology is presented. A mixture of a class D output stage and a bridge tied load (BTL) is the main topology of the proposed amplifier. The new 10-W IC audio power amplifier operates at 12 V with the efficiency of more than 90% and the total harmonic distortion (THD) of 0.1%. The amplifier is implemented in a 4-/spl mu/m double-metal, single-poly CMOS technology that provides with relatively high voltage (12 V) MOSFETs.

Intelligent magnetic-amplifier-controlled soft-switching method for amplifiers and inverters

This paper proposes a simple efficient soft-switching method for switching power converters, inverters and amplifiers. Soft switching of a DC/AC H-bridge power converter is realized by paralleling two auxiliary switches and a magnetic amplifier with the load. The auxiliary switches are turned on at a predetermined time before the commutation of the main switches. The magnetic amplifier then automatically determines the necessary amount of redirection current to ensure soft switching of all switches under any load conditions. This method requires no expensive sensors or complex control circuitry. It is ideal for class-D audio power amplifiers, where the load current is widely changing. Further applications include DC/DC power converters, motor drivers, uninterruptible power supplies (UPS), communication and space power applications, where high efficiency, low electromagnetic interference (EMI) and small size are crucial.