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A DeltaSigma Modulator Using a Nonuniform Quantizer Adjusted for the Probability Density of Input Signals
Toru KITAYABU Mao HAGIWARA Hiroyasu ISHIKAWA Hiroshi SHIRAI
Publication
IEICE TRANSACTIONS on Communications
Vol.E95B
No.7
pp.22572265 Publication Date: 2012/07/01
Online ISSN: 17451345
DOI: 10.1587/transcom.E95.B.2257
Print ISSN: 09168516 Type of Manuscript: PAPER Category: Fundamental Theories for Communications Keyword: deltasigma modulator, nonuniform quantizer, quantization noise,
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Summary:
A novel deltasigma modulator that employs a nonuniform quantizer whose spacing is adjusted by reference to the statistical properties of the input signal is proposed. The proposed deltasigma modulator has less quantization noise compared to the one that uses a uniform quantizer with the same number of output values. With respect to the quantizer on its own, Lloyd proposed a nonuniform quantizer that is best for minimizing the average quantization noise power. The applicable condition of the method is that the statistical properties of the input signal, the probability density, are given. However, the procedure cannot be directly applied to the quantizer in the deltasigma modulator because it jeopardizes the modulator's stability. In this paper, a procedure is proposed that determine the spacing of the quantizer with avoiding instability. Simulation results show that the proposed method reduces quantization noise by up to 3.8 dB and 2.8 dB with the input signal having a PAPR of 16 dB and 12 dB, respectively, compared to the one employing a uniform quantizer. Two alternative types of probability density function (PDF) are used in the proposed method for the calculation of the output values. One is the PDF of the input signal to the deltasigma modulator and the other is an approximated PDF of the input signal to the quantizer inside the deltasigma modulator. Both approaches are evaluated to find that the latter gives lower quantization noise.

