Audio Power Amplifier Research Articles

Audio power amplifier IC and audio system provided with the same

An audio power amplifier IC, which can suppress audio quality deterioration due to reference clock frequency, and an audio system provided with the audio power amplifier IC. The audio power amplifier IC is provided with a clock generating circuit (10) for generating an internal clock; a clock terminal (CLK) for performing internal clock output or external clock input; a clock selecting circuit (11) which selects either the internal clock or the external clock as the reference clock (BCLK); a first audio signal input terminal (IN1) to which a first audio signal (Lin) is inputted; and a first digital power amplifier circuit (51) which outputs a pulse synchronized with the reference clock (BCLK) by performing pulse modulation to the first audio signal (Lin) based on the reference clock (BCLK).

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.

System and method for minimizing DC offset in outputs of audio power amplifiers

An amplifier system receives an input signal and generating therefrom an amplified output signal. The amplifier system is recited as comprising an input stage and an amplifier stage. The input stage is configured to receive the input signal and provide a level-shifted signal that has an average signal level that is shifted in regards a level shift value. The amplifier stage is configured to receive the level-shifted input signal from the input stage and generate therefrom the amplified output signal. The level shift value being selected to minimize a DC offset in the amplified output signal at least when the amplifier system is initially powered on. Since the amplified output signal has a minimal or zero DC offset, the amplifier system avoids generation of undesirable noises when it is initially powered on.

Randomized Carrier PWM With Exponential Frequency Mapping

Pulsewidth modulation (PWM) and sigma-delta modulation (SDM) have been used in several high linearity, high accuracy power delivery applications such as dc-dc power converters, audio, and radio frequency power amplifiers and data converters. While PWM can generate high linearity signals with high efficiency, it suffers from discrete tonal output spectrums. SDM, on the other hand, can generate high linearity output spectrums with shaped quantization noise spectrums and lower efficiencies due to oversampling requirements. In this paper we present a particular class of carrier frequency modulated PWM (CFMPWM), which spreads the tonal content of regular PWM uniformly in frequency and reduces the baseband noise with respect to SDM by up to 15 dB. The new modulation scheme preserves the high efficiency properties of PWM. An approximate method to estimate the spectrum of CFMPWM signals with both deterministic and random modulation is also presented. Simulation results and experimental data are reported to analyze the spectral spreading properties of the proposed CFMPWM scheme

Narrow Pulse Elimination PWM for Multilevel Digital Audio Power Amplifiers Using Two Cascaded H-Bridges as a Nine-Level Converter

This paper presents a methodology to reduce total harmonic distortion (THD) in digital audio power amplifiers, using two new approaches: 1) a multilevel converter made of two cascaded full-bridges, with suitable power supplies to operate as a nine-level hybrid type converter and 2) a new pulsewidth modulation (PWM) technique called narrow pulse elimination (NPE) PWM. The proposed nine-level converter uses only eight MOSFETs. Unlike conventional PWM, the NPE PWM does not generate excessively narrow pulses, so that power semiconductors nonideal delays and switching times are still negligible. Therefore, the nine-level output voltage THD, mostly introduced in the power stage, is strongly reduced. With the NPE technique, the resolution of the generated PWM is no longer limited by the switching speed of the output switches, but only by the frequency of digital processing circuit. Simulation and experimental results from a laboratory prototype are presented in order to show the effectiveness of the proposed approaches

Sonic Broadcast Unit for Bird Control in Vineyards

Many wine grape growers experience bird damage in their vineyards. The potential economic loss provides considerable incentive for growers to invest in successful control strategies. Broadcast alarm and distress calls have gained recent interest because technological advancements have made these sounds easier and less expensive to reproduce. The objectives of this research were to develop a broadcast unit for use in vineyards with multiple bird species and to test the performance of the unit under commercial conditions. A digital audio circuit was designed with a 4-MiB flash memory, 8-bit resolution, and a 7.5-W audio power amplifier. The circuit had a bandwidth of 10 kHz, was light activated, and a microcontroller was used to control circuit operation. The interval between broadcasts was varied throughout the day, and a different call was selected at each broadcast event to maximize the amount of time before habituation occurred.

Output coupling capacitor free audio power amplifier dynamically configured for speakers and headphones with excellent click and pop performance

First and second channel bridge amplifiers are dynamically configured to drive either speakers or headphones. The first channel bridge amplifier includes a first amplifier driving one end of a first speaker through a mechanical switch in a headphone-jack, and a second amplifier driving another end of the first speaker. The second channel bridge amplifier includes third and fourth amplifiers driving respective ends of a second speaker. An amplifier control circuit dynamically detects the insertion or removal of a plug in the jack and configures the amplifiers accordingly. When a plug is inserted into the jack, the mechanical switch disconnects the first speaker from the first amplifier, and the fourth amplifier is tri-stated disconnect the second speaker. The first and third amplifiers are configured to drive the first and second channels of the headphones, while the third amplifier drives the headphone common point (shield ring) as a virtual ground connection. The virtual ground connection permits the bridge amplifiers to drive either speakers or headphones without the use of output coupling capacitors. To suppress click and pop, the amplifier control circuit maintains certain amplifiers (depending on headphone or speaker mode) tri-stated until the input coupling capacitors have fully charged and an input signal is detected. In the headphone mode, the driving amplifiers are current limited, the output signal level is automatically attenuated, and the second amplifier is controlled to prevent a ground loop short circuit condition. When a ground short is detected, the second amplifier is tri-stated by the amplifier control circuit.

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.

A Single Chip 1 W CMOS Audio Power Amplifier with Pseudo Buffer Analog and Class D Switching Mixed Mode for Mobile Application

A single chip analog and class D switching mixed mode audio power amplifier using 0.35 μm CMOS process is presented in this paper. It has on-chip power MOSFET's and adopts a novel reverse recovery current free gate control that can reduce EMI noise and current stress of the power MOSFETs. It shows about 0.1% THD at 1 kHz and up to 87% efficiency at 4 Ω BTL at 3.3 V single power supply.

Hysteresis controller with constant switching frequency

Switch mode audio power amplifiers are showing up on market in still greater numbers because of advantages in form of high efficiency and low total system cost, especially for high power amplifiers. Several different modulator topologies have been made, ranging from standard PWM to various self-oscillating and digital modulators. Performance in terms of low distortion, noise and dynamic range differs significantly with the modulator topology used. Highest system performance is generally achieved with analog modulators made as a modulator loop including at least the power stage of the amplifier, because of benefits from continuous time operation and non-quantized resolution. This type of modulator uses no external carrier signal, and is called self-oscillating modulators. The work presented in this paper refers to switch mode audio power amplifier, but can be used within a wide range of DC-DC or DC-AC converters as well.

A multi-loop voltage feedback filterless class-D switching audio amplifier using unipolar pulse-width-modulation

Voltage feedback is frequently used in class-D switching audio power amplifiers. This paper discusses the design and implementation of a low-cost filterless class-D, unipolar pulse-width modulation switching audio amplifier having a multi-loop voltage feedback scheme. Classical frequency-compensation techniques are used to design and stabilize the three voltage feedback loops implemented in this application. This design method proves to be a cost-effective solution for designing high-fidelity (hi-fi) audio amplifiers. The cost is reduced because no output filter is used, the required switching frequency is half of the one needed if bipolar PWM was used, and no current sensor is needed for feedback purposes. The output impedance is extremely low due to the reduction of the successive voltage loops, making the amplifier less load dependent. Simulation results show that a total harmonic distortion (THD) of 0.005% can be achieved using this topology, as well as a flat frequency response, free of phase distortion in the audio band. Experimental results show the feasibility of this control scheme, since a THD of 0.05% was achieved with a laboratory prototyped amplifier. A comparison of the performance of this audio amplifier with that of some commercial class-D audio amplifiers, reveals that our design can seriously compete with some of the ICs leading the market at a lower cost.

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.

Analysis of the class AD audio amplifier including hysteresis effects

Combinations of analog and switching techniques have led to the development of audio power amplifiers capable of producing low distortion with high efficiency. The high efficiency is achieved with a combination of an inverter and an analog amplifier, where the inverter provides the power, and the analog amplifier acts as an active filter to correct distortion. In this paper, a full analysis of the system is presented using the hysteresis describing function approach to model the inverter. The set of equations obtained allows the description of the nonlinear behavior of the system, such as the limit cycle of the output voltage and its dependency on the hysteresis. The theoretical development also provides the relation between the switching frequency and the system parameters. The derived equations are verified and compared using PSpice simulations.

Portable and hand-held device for making humanly audible sounds responsive to the detecting of ultrasonic sounds

A portable and hand-held device for making humanly audible sounds responsive to the detecting of ultrasonic sounds. The device includes a hand-held housing and circuitry that is contained in the housing. The circuitry includes a microphone that receives the ultrasonic sound, a first low voltage audio power amplifier that strengthens the signal from the microphone, a second low voltage audio power amplifier that further strengthens the signal from the first low voltage audio power amplifier, a 7-stage ripple carry binary counter that lowers the frequency of the signal from the second low voltage audio power amplifier so as to be humanly audible, a third low voltage audio power amplifier that strengthens the signal from the 7-stage ripple carry binary counter, and a speaker that generates a humanly audible sound from the third low voltage audio power amplifier.

Controller for digital audio power amplifier with bit stream input

A new controller for a digital audio amplifier with bit stream input is proposed. The proposed controller has excellent features such as wide error correction range and no limitation on the modulation index. The controller is implemented in the half-bridge class-D amplifier and performance is verified through experiments.

Class D audio power amplifier with fine hysteresis control

A new simple and efficient control method for a class D audio power amplifier is presented. The new fine hysteresis control method can control the switching frequency freely and guarantees stability for any load condition without having any outside compensation circuit at all.

A reconfigurable audio power amplifier delivering 150 W to 1 Ω loudspeakers for in-car sound systems

A reconfigurable audio amplifier is proposed. It can be configured to operate as a standard dual-bridge, a high-efficiency dual-bridge, or a high-power mono-bridge amplifier. Moreover, all these configurations can be set in low-noise mode. Built-in diagnostics with an I/sup 2/C-bus interface completes the features. The device, realized in a 0.6 /spl mu/m technology, delivers to 1 /spl Omega/ up to 150 W in high-power mode, saves 50% of the dissipated power in the high-efficiency configuration, and has a 16 /spl mu/V RMS in-band output noise in the low-noise configuration.

The 2N3055: a case history

The 2N3055 power transistor was introduced by the Radio Corporation of America (RCA) in the early 1960s. It was one of the first silicon power transistors, offered unrivalled second breakdown immunity and found many applications particularly in audio power amplifiers and linear power supplies. Other companies tried to copy it with varying degrees of success: one company acknowledges it now by naming a power MOSFET after it. We trace its history, manufacture and eventual decline against pressure from competing technologies. Modern simulation tools have been used to investigate the operation of the device which illustrate its good, and not so good, features. We also relate its geometry to a SPICE model. Neither of these tools would have been available to the original developers. We propose that this transistor be given a place in the archives of history, ranked alongside other famous devices of the 20th century such as the 300B tube.

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.

Audio frequency power amplifiers with actively damped filter

Audio frequency power amplifiers with actively damped filter