Analysis and improvement of a high performance digital speaker system

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Although a substantial quantity of music data is stored as digital information, as in the case of CDs and MDs, an analog drive is still the main component of a loudspeaker. If the speaker can be driven digitally, it becomes possible to perform all processes from the input to the output digitally. As a result, the analog power amplifier and some other components become unnecessary and a small, light, and high-quality speaker can be achieved. In this research, we propose a digital-driven piezoelectric speaker employing multi-bit delta-sigma modulation.●Estimation of a piezoelectric speakerFrequency response : A piezoelectric speaker shows flat frequency response except low frequency band under 200kHz. Among two or more elements, the characteristics variation over 10% is observed.Distortion: Since a piezoelectric device has nonlinear characteristics, the device generates distortion which is an issue to realize a thin speaker. In the experiment of harmonic-distortion characteristics, the c … More omparatively high distortion rate of 32% (3rd distortion) is measured. When piezoelectric device is driven by an analog circuit, the method to reduce the influence of distortion is required.●A high performance digital direct drive loudspeakerStudy of a noise shaping dynamic element matching method (NSDEM) : Improving NSDEM for the digital speaker, the performance was confirmed by simulations. The logical circuit was designed, and the logic circuits were implemented by using a FPGA device. From evaluation of this FPGA, the scale of the circuit of proposed NSDEM is 20% smaller than conventional one.●Overall evaluation of the proposed digital direct drive loudspeakerEvaluation of the overall characteristic of the proposed speaker system using a FPGA and high speed driver circuit : The characteristics inputting a sinusoidal wave were evaluated. As a result, when the sub-loudspeaker has been arranged to the plane board, the variation of the sub-loudspeaker and arrangement make the characteristics of the sub-loudspeaker itself cause variation. The influence was reduced by the effect of NSDEM and it was confirmed by experiment. The distortion of 2% or less was realized. Less