| Summary: | 碩士 === 國立臺灣大學 === 電信工程學研究所 === 94 === CD-AUDIO is a high-quality audio standard that supports 16-bit linear pulse-code modulation (PCM) with sampling rate 44.1 kHz. The growth of CD-AUDIO has increased the demands of audio digital-to-analog converters (DAC) that meet the low-cost needs of consumer applications, achieves the wide dynamic range and high linearity required for the professional studio and also low power demand for portable products.
Conventional multi-bit audio DAC’s use an R-2R resistor ladder to obtain a binary weighted range of current source equal to the number of bits to be converted. While properly adjusted, the DAC’s using the R-2R resistor ladder can function well but are extremely dependent on the tolerances of resistor networks and on matched and glitch-free electronic switches. Hence, the conventional DAC’s are typically rather expensive products.
The use of 1-bit Delta-Sigma (∆-Σ) modulator with the oversampling technique eliminates the resistor matching problem by trading digital complexity for desired insensitivity to analog non-idealities. However, in order to achieve the requirement of high resolution, the high order or high oversampling ratio 1-bit modulator will be needed. Although the achievable resolution does improve in ∆-Σ modulators employing a 1- bit quantizer, these improvements diminish rapidly due to the in-stability of high order modulator. In addition, because of the substantial out-of-band quantization noise power in delta-sigma modulators, the design of analog output filters for oversampled DACs can be quite difficult. One solution to the above problems is to use a multi-bit quantizer in the ∆-Σ modulators.
In this thesis, we have simulated and implemented a complete third-order multibit ∆-Σ modulation system for CD-AUDIO digital-to-analog converter. It consists of a 64X digital interpolation filter to bring the input sample rate up to the modulator rate, a multibit ∆-Σ modulator to reduce the word length by trading off the out-of-band noise, and dynamic element matching to dynamically swap the unit-element with mismatch problem caused by process variance.
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