A method is presented to convert 1-bit digital audio signals into an analogue signal with sufficient current and voltage to drive loudspeakers. For this goal a novel non-PWM class D power stage is constructed that performs this function with very low distortion and very high efficiency, without the use of feedback or other analogue processing. Results of the prototype development are detailed.
Convention Paper 5631

14:30 h
Z2 A Novel Approach to High-Speed Digital Pulse-Formers Based on Ring Oscillators for PWM and Class-D Applications – Martin Streitenberger¹, Helmut Bresch², Jens Kaszubiak², Thomas Schindler² - ¹University of Hannover, Hannover, Germany; ²Otto von Guericke University Magdeburg, Magdeburg, Germany

In this paper, a new concept for a high speed, high resolution digital pulse-former is presented. A digital pulse-former basically maps each input data word (sample) into a binary pulse of corresponding width. Such binary pulse-length modulated signals are incorporated in digital class-D amplifiers and PWM applications. In our approach a synchronous digital counter converting the “rough” part of the input sample is combined with a ring oscillator serving as “fine” counter. This hybrid configuration yields a drastically increased resolution while maintaining moderate clock rates. Results of a first discrete implementation of this concept are discussed.
Convention Paper 5632

15:00 h
Z3 Distortions by Switching Errors in Digital Power Amplifiers using Sigma-Delta Coded Signals – Rolf Esslinger¹, Gerhard Gruhler¹, Robert W. Stewart² - ¹University of Applied Sciences, Heilbronn, Germany; ²University of Strathclyde, Glasgow, UK

The development of a fully digital audio power amplifier based on PWM or Sigma Delta technologies still has many unsolved practical problems. The most problematic part of the amplifier system is the switching (class-D) power stage. It is extremely difficult to turn on or off the high power voltage impulses as required for a high performance signal quality (e.g. 16 bit CD quality).
In this paper the typical switching errors introduced by the power transistors, the power supply voltage and the load will be analyzed formally and with computer simulations. From the results it can be seen, that a degrading of the Signal-to-Noise quality by harmonic distortions and unwanted modulation products occur by the signal errors in the output stage.
Convention Paper 5633

15:30 h
Z4 Sigma-Delta Modulation in Digital Class-D Power Amplifiers: Methods for Reducing the Effective Pulse – Rolf Esslinger¹, Gerhard Gruhler¹, Robert W. Stewart² - ¹University of Applied Sciences, Heilbronn, Germany; ²University of Strathclyde, Glasgow, UK

To use one-bit Sigma-Delta Modulation (SDM) in digital class-D power amplifiers the effective pulse frequency has to be reduced. This paper contains a review about this problem. It will be shown, how the efficiency of the amplifier is degraded by too high pulse frequencies. Fundamental approaches to create high resolution pulse signals with lower pulse rates around 300 to 500 kHz will be shown. One of these is a controlled generation of the pulse-pattern, like it is done in the “Bit-Flipping”. Alternative approaches can be found, when the dependency of the generated pulse patterns by the loop filter structure is considered.
Convention Paper 5634

16:00 h
Z5 Modeling Nonlinearity of Air with Volterra Kernels for Use in a Parametric Array Loudspeaker – Kelvin Lee, Jun Yang, Woon Seng Gan, Meng-Hwa Er - Nanyang Technological University, Singapore

The use of a parametric array in air as a directional audio loudspeaker has been reported in previous literature and the self-demodulation phenomenon is well-understood to seriously distort the generated audible sound as a result of inter-modulation distortion. We propose to model the nonlinear interaction in air using a second-order Volterra kernel at the Rayleigh distance within which sound intensity and parametric conversion efficiency are assumed to be high. Results first obtained from Burgers’ equation-based numerical simulations and actual measurements are then used in the nonlinear system identification process.
Convention Paper 5635

16:30 h
Z6 Method to Enhance Low-Frequency Perception from a Parametric Array Loudspeaker – Furi Karnapi, Woon Seng Gan, Meng-Hwa Er - Nanyang Technological University, Singapore

Human auditory does not perceive sound of all frequencies with equal loudness. It is known that a low frequency signal needs to be produced with higher power level to have the same loudness as the middle frequency part. There are two ways to overcome this problem. There are either carried out by boosting the power of the low frequency part or utilizing psychoacoustics’ effect called the ‘missing fundamental’. Parametric array’s usage to generate highly directional audible signal has been reported since few decades ago. However the reproduced signal lacks low frequency content. One reason is the relatively low power level produced by the existing parametric array. Utilizing the non-linearity of air, it is proposed to psycho-acoustically enhance the low frequency perception of a parametric array loudspeaker.
Convention Paper 5636