- Research Article
Distortion-Free 1-Bit PWM Coding for Digital Audio Signals
EURASIP Journal on Advances in Signal Processingvolume 2007, Article number: 094386 (2007)
Although uniformly sampled pulse width modulation (UPWM) represents a very efficient digital audio coding scheme for digital-to-analog conversion and full-digital amplification, it suffers from strong harmonic distortions, as opposed to benign non-harmonic artifacts present in analog PWM (naturally sampled PWM, NPWM). Complete elimination of these distortions usually requires excessive oversampling of the source PCM audio signal, which results to impractical realizations of digital PWM systems. In this paper, a description of digital PWM distortion generation mechanism is given and a novel principle for their minimization is proposed, based on a process having some similarity to the dithering principle employed in multibit signal quantization. This conditioning signal is termed "jither" and it can be applied either in the PCM amplitude or the PWM time domain. It is shown that the proposed method achieves significant decrement of the harmonic distortions, rendering digital PWM performance equivalent to that of source PCM audio, for mild oversampling (e.g.,) resulting to typical PWM clock rates of 90 MHz.
Nishio A, Ichimura G, Inazawa Y, Horikawa N, Suzuki T: Direct stream digital audio system. Proceedings of the 100th Convention of Audio Engineering Society (AES '96), May 1996, Copenhagen, Denmark preprint 4163
Verbakel J, van de Kerkhof L, Maeda M, Inazawa Y: Super audio CD format. Proceedings of the 104th Convention of Audio Engineering Society (AES '98), May 1998, Amsterdam, The Netherlands preprint 4705
Goldberg JM, Sandler MB: Pseudo-natural pulse width modulation for high accuracy digital-to-analogue conversion. Electronics Letters 1991,27(16):1491-1492. 10.1049/el:19910933
Nielsen K: A review and comparison of pulse width modulation (PWM) methods for analog and digital input switching power amplifiers. Proceedings of the 102nd Convention of Audio Engineering Society (AES '97), March 1997, Munich, Germany preprint 4446
Nielsen K: Linearity and efficiency performance of switching audio power amplifier output stages—a fundamental analysis. Proceedings of the 105th Convention of Audio Engineering Society (AES '98), September 1998, San Francisco, Calif, USA preprint 4838
Hawksford MJ: Modulation and system techniques in PWM and SDM switching amplifiers. Journal of the Audio Engineering Society 2006,54(3):107-139.
Esslinger R, Gruhler G, Stewart RW: Digital power amplification based on pulse-width modulation and sigma-delta loops. A comparison of current solutions. Proceedings of the Institute of Radio Electronics, Czech and Slovak Radio Engineering Society (RADIOELEKTRONIKA '99), April 1999, Brno, Czech Republic
Magrath AJ, Sandler MB: Digital power amplification using sigma-delta modulation and bit flipping. Journal of the Audio Engineering Society 1997,45(6):476-487.
Hawksford MJ: SDM versus PWM power digital-to-analogue converters (PDAC) in high-resolution digital audio applications. Proceedings of the 118th Convention of Audio Engineering Society (AES '05), May 2005, Barcelona, Spain preprint 6471
Bowes SR: New sinusoidal pulsewidth-modulated invertor. IEE Proceedings 1975,122(11):1279-1285.
Hawksford MJ: Linearization of multilevel, multiwidth digital PWM with applications in digital-to-analog conversion. Journal of the Audio Engineering Society 1995,43(10):787-798.
Jung J-W, Hawksford MJ: An oversampled digital PWM linearization technique for digital-to-analog conversion. IEEE Transactions on Circuits and Systems 2004,51(9):1781-1789. 10.1109/TCSI.2004.834487
Nielsen K: High-fidelity PWM-based amplifier concept for active loudspeaker systems with very low energy consumption. Journal of the Audio Engineering Society 1997,45(7-8):554-570.
Black HS: Modulation Theory. Van Nostrand, Princeton, NJ, USA; 1953.
Mellor PH, Leigh SP, Cheetham BMG: Reduction of spectral distortion in class D amplifiers by an enhanced pulse width modulation sampling process. IEE Proceedings—Part G: Circuits, Devices and Systems 1991,138(4):441-448. 10.1049/ip-g-2.1991.0076
Bowes SR, Lai Y-S: Relationship between space-vector modulation and regular-sampled PWM. IEEE Transactions on Industrial Electronics 1997,44(5):670-679. 10.1109/41.633469
Bowes SR, Bird BM: Novel approach to the analysis and synthesis of modulation processes in power converters. IEE Proceedings 1975,122(5):507-513.
Floros A, Mourjopoulos J: Analytic derivation of audio PWM signals and spectra. Journal of the Audio Engineering Society 1998,46(7):621-633.
Lipshitz S, Wannamaker R, Vanderkooy J: Quantization and dither: a theoretical survey. Journal of the Audio Engineering Society 1992,40(5):355-375.
Gray RM: Quantization noise spectra. IEEE Transactions on Information Theory 1990,36(6):1220-1244. 10.1109/18.59924
Blesser BA: Digitization of audio: a comprehensive examination of theory, implementation, and current practice. Journal of the Audio Engineering Society 1978,26(10):739-771.
Floros A, Mourjopoulos J: A study of the distortions and audibility of PCM to PWM mapping. Proceedings of the 104th Convention of Audio Engineering Society (AES '98), May 1998, Amsterdam, The Netherlands preprint 4669
Floros A, Mourjopoulos J, Tsoukalas DE: Jither: the effects of jitter and dither for 1-bit audio PWM signals. Proceedings of the 106th Convention of Audio Engineering Society (AES '99), May 1999, Munich, Germany preprint 4656
Craven P: Toward the 24-bit DAC: novel noise-shaping topologies incorporating correction for the nonlinearity in a PWM output stage. Journal of the Audio Engineering Society 1993,41(5):291-313.
Floros A, Mourjopoulos J: On the nature of digital audio PWM distortions. Proceedings of the 108th Convention of Audio Engineering Society (AES '00), February 2000, Porte Maillot, Paris, France preprint 5123