Audio Power Amplifier Research Articles

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.

The influence of program material on the nonlinear behavior of audio power amplifiers driving complex loads

Nonlinear distortion of an audio power amplifier is conventionally characterized by total harmonic distortion and other similar values, provided that it is excited by a sinusoidal signal and that it drives a resistive test load. In this paper, thoroughly selected segments of musical signals were fed to power amplifiers driving a complex load designed on a statistical basis. Output voltage and current waveforms, were digitized by means of a A/D acquisition system and projected in the V-I plane. The probability density function was computed and nonlinear operation of amplifiers was successfully traced in the same plane. The isolation of the nonlinear operation area and the evaluation of its associated probability value, provided a quantitative measure of amplifier nonlinear distortion, under music reproduction. It also became evident, that several other conclusions concerning design procedures of such devices, can easily be derived.

A high efficiency and wide bandwidth class D switching audio power amplifier with improved output stage and current mode control

The pulse width modulated class D power amplifier has the highest efficiency among the various class amplifiers. To obtain high efficiency and wide bandwidth at class D amplifier, there are two important points to be considered most carefully. They are the output driver and the feedback control scheme. Composite oscillation conditions of output driver are studied in detail and a new drive circuit is suggested in this paper. A detailed design procedure of the current mode control is also shown to improve the performances. The new-design class D amplifier provides wide full-power bandwidth and high efficiency with good stability.

Audio frequency power amplifiers with actively damped filter

An inverter for an audio amplifier. The inverter comprises a current damping feedback loop for actively damping oscillations caused by an output inductor within the inverter. A forward compensator is provided to compensate for the frequency response of the actively damped filter. The resulting inverter generates an output voltage that tracks an input voltage thereof with improved frequency response within the frequency range of interest.

A high-efficiency 4×20 W monolithic audio amplifier for automobile radios using a complementary D-MOS BCD technology

A monolithic quad audio power amplifier which reduces power dissipation by 45% with a music signal compared to a standard class-AB amplifier is described. A new two-stage operational amplifier, capable of providing high output current, is used for each one of eight power amplifiers. In a bridge configuration, a common-loop mode control is performed exploiting a sample-and-hold circuit. A multipower bipolar-CMOS-DMOS (BCD) technology is employed with a push-pull rail-to-rail output stage and a low-loss power switch. Experimental results are presented.

Audio power amplifier with reactance simulation

A preconditioned signal that is applied to the input of an audio power amplifier for providing a perceived control of reactance simulation (or the Damping Factor) of the amplifier. A low frequency fundamental resonance is combined with a slowly rising high frequency preemphasis to mimic or simulate an audible interaction with the impedance plot of the loudspeaker, without increasing the output impedance of the amplifier.

Differential-current derived feedback in error-correcting audio amplifier applications

A dominant distortion mechanism in audio power amplifiers results from nonlinearity in the voltage and current transfer functions within the power output stage. A technique is presented that uses a magnetic differential sensor to sense this distortion and to apply a supplementary error-correcting feedback path within the amplifier, in addition to overall negative feedback. Differential-current derived feedback is explored and the technique is shown to be applicable to both voltage and current transfer errors. Analysis reveals the system alignment for obtaining a distortion null and these results are confirmed using nonlinear transient analysis. Basic system topologies are presented using voltage transfer and transconductance gain cells as an aid to complete amplifier synthesis. Comparisons are made with feedforward-feedback error correction where the current-dumping amplifier is reconfigured using differential-current feedback. Generalisations are made to a multi-loop nest of amplifiers using individually aligned error correcting paths to achieve corresponding improvements in distortion reduction.

Audio power amplifier system with frequency selective damping factor controls

In a particular embodiment, an audio amplifier drives a load in the form of a sound producing loud speaker exhibiting a frequency variable impedance characteristic over a range of audio frequencies. Voltage and current feedback circuits respectively establish a minimum voltage feedback and a feedback characteristic representative of the load. A presence feedback circuit couples the voltage feedback circuit to ground for reducing feedback with increasing frequency above a selected level whereby the damping factor of the amplifier is reduced. A resonance feedback circuit coupled in parallel with the voltage feedback circuit reduces voltage feedback with decreasing frequencies below the selected level whereby the damping factor is accordingly reduced. The amplifier is responsive to the reduced damping factor for increasing power to the load for enhancing the sound produced by the loud speaker.

Continuous-Time Adaptive Control of Consumer Electronic Circuits

Abstract Adaptive systems have been exported to electronic applications, especially to telecommunications circuitry. The exported theory is mainly based on recursive or iterative methods. Continuous-time adaptive systems have been scarcely used for Electronic Design, especially for Consumer Electronics, a field with a primary industrial interest. At present, much theory has been developed and many problems related with the application of this theory have been studied: this makes possible to export their results to industrial consumer electronics field with full confidence. After a revision of the state-of-the-art, three well-known electronic circuits (audio power amplifiers) with different complexity are selected and analyzed in order to experiment applications of adaptive systems. Both Lyapunov and Hyperstability based theories (from reduced order models) are studied and an alternative to the classical electronic design is proposed. The performances of different adaptive structures are experimentally evaluated. Finally, some conclusions obtained either from physical implementation of the chosen adaptive systems or from the interpretation of experimental results are presented.

Audio frequency power amplifier with improved circuit topology

The present invention is an audio frequency power amplifier input circuit having improved vacuum tube circuit topology. The improved circuit includes a direct current feedback circuit within the input circuitry which stabilizes the operating point of a phase inverter. The feedback circuit maintains optimum operation of the circuit despite variations in tube characteristics or supply voltages. Another aspect of the improved circuit comprises a low impedance phase inverter which improves the drive capability of the phase inverter to push-pull power output vacuum-tube grids.

A microcomputer-controlled system for measuring reactivity in small animals

A microcomputer-controlled system has been designed for measuring reactivity in small laboratory animals. This system uses a microcomputer to trigger an acoustic signal, which is fed to a loudspeaker through an audio power amplifier. An animal’s acoustic startle response is recorded using a moving-coil loudspeaker as a movement transducer. The transducer output is coupled to a peak-hold circuit that records the maximum voltage generated by the animal’s response. After conversion to digital form, the data for each stimulus presentation are stored and then printed when all trials have been completed.

Feedforward compensation of the amplifier output stage for improved stability with capacitive loads

It is pointed out that the stability margin of an audio power amplifier is reduced by a pole in the loop-gain transfer function caused by shunt capacitance in the loudspeaker load. The problem is most severe in amplifiers with output stages that have a high output impedance before feedback. Because MOSFET devices can have an output impedance that is much higher than BJT (bipolar junction transistor) devices, amplifiers with MOSFET output stages are particularly susceptible to load-induced oscillations. A feedforward frequency compensation technique is described that bypasses the pole in the output stage caused by the load capacitance for improved stability of the amplifier.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Average Efficiency of Class-G Power Amplifiers

Class-G operation is an inexpensive and yet effective means of increasing the efficiency of audio power amplifiers (PAs) and amplitude modulators. A class-G PA consists of two or more parallel-connected class-B PAs with different supply voltages. Low-voltage segments of the signal are amplified by the low-voltage component of the amplifier, thus reducing power dissipation and increasing efficiency. The average efficiency of a class-G PA depends upon both the supply-voltage transition point and the amplitude distribution of the signal. Average efficiencies are computed for a number of signals that occur in AF amplification, full- carrier amplitude modulation, and envelope modulation of a linear RF PA. For typical peak-to-average ratios, an ideal, two-voltage class-G PA has average efficiencies in the range of 60 to 70 percent, in contrast to the 35 to 40 percent of an analogous class-B PA.

A High-Efficiency Audio Power Amplifier Using a Self-Oscillating Switching Regulator

A new high-efficiency audio power amplifier has been developed. This amplifier consists of a conventional power amplifier and a self-oscillating switching power supply which is arranged to vary the power supply output voltage according to the input signal voltage. The new amplifier achieves a higher efficiency than the conventional amplifier, by making the collector voltage of the emitter-follower-transistor follow the waveform of the output signal. Applying this idea to class A amplifiers, a one-third power dissipation can be achieved compared with the conventional class A amplifier. A power MOSFET is used as a switcher. The switching frequency is from 150 kHz to 300 kHz. The new amplifier shows sufficient favorable characteristics. Switching noise is suppressed to a low noise level, which has no influence on the AM tuner or other audio equipment. By stabilizing the single-ended push-pull (SEPP) output transistors, the amplifier can reproduce high quality tone. The present idea is also applicable to dass B power amplifiers and may be suitable for PA or car audio power amplifiers.

Audio de-emphasis circuit

First Page

Ultrasonic fluid leak detector

A device for detecting ultrasonic noise, particularly such noise as generated by fluid leaks, includes a directional ultrasonic microphone, amplifiers and ultrasonic filters, an envelope detector, an audio preamplifier and filter, a level control, a meter, an audio power amplifier and speaker, and a phase shift feedback network connected from the output of the power amplifier to an input thereof. A switch is operable in a first setting to connect the power amplifier to the level control to convey the audio frequency amplitude envelope of the detected ultrasonic noise through the speaker or in a second setting to connect the power amplifier to the feedback network. A level detector is operatively connected to the level control and provides a control signal which is conducted to the feedback network. When the control signal exceeds a selected level, the feedback loop circuit is completed, whereby the power amplifier oscillates audibly through the speaker and gives audible indication of an ultrasonic noise. The components are enclosed in a pistol shaped housing for substantially single handed aiming and operation.

Highest Efficiency and Super Quality Audio Amplifier using MOS Power FETS in Class G Operation

A Class G audio power amplifier has achieved a rated continuous output power of 200 watts and peak power of 400 watts. This power amplifier produced no more than 0.01 per cent total harmonic distortion at 20 kHz and 200 watts by using Power MOS FETs in its output stage.

New Power Supply for Audio Power Amplifiers

A switch-mode power supply was developped to meet requirement for reduction in size and weight for high power amplifiers.

A new result in negative‐feedback theory, and its application to audio power amplifiers

AbstractA nest of differentiating loops is described by means of which a very large amount of negative feedback can be applied to a specified stage in an amplifier (normally the output stage) with progresively less being applied to other stages. The effects of nonlinearity (other than hard limiting) in the specified stage can be virtually eliminated. The structure enables Bode's limit for loop‐gain roll‐off to be exceeded for the specified stage; both the frequency up to which loop gain is maintained constant and the frequency at which loop gain falls through unity are free design variables. As a result, practical difficulties associated with excess phase shift in low‐frequency power transistors are minimized. The structure does not increase the susceptibility to transient overload and the resulting intermodulation. A practical amplifier using output transistors with fT∼2 MHz has an output‐stage loop gain of 25,000 (88 dB) at 20 kHz and 0.002 per cent harmonic distortion.

Fault Protection of Monolithic Audio Power Amplifiers in Severe Environments

Monolithic power operational amplifiers used in automotive AM-FM stereo receivers require protective mechanisms to assure performance in severe environments. Such protective mechanisms were developed and incorporated in an audio module after the identification of five major fault categories. The module, containing two operational amplifiers to meet radio power requirements, has seven reference comparators along with the necessary output control circuitry on a single silicon die. The comparators not only sense excess voltage on the power source, current, and temperature extremes but output load faults as well. A discussion of the environment, fault categories, control requirements, and fault detection means used to obtain the objectives follows.