Research On The Design And Optimization Techniques Of High-Performance Audio Delta-Sigma Data Converters

Featuring high conversion precision and low hardware overhead, delta-sigma data converters are appropriate for portable medical devices and high performance audio signal processing. However, there are still many technical problems remain to be discussed, especially for that the rapid development of modern CMOS technology and digital electronics makes a trend that the supply voltage of the electronic system is consistently lowering. This trend restricts the dynamic range of the analog signal, and therefore makes the design of high precision data converters even more difficult.In addition, the long battery life is always of key importance to the portable equipment to enhance its core-competitiveness, which makes low-power design facing more challenges.According to the key requirements of some major applications, this dissertation deeply studied the design techniques of high-precision audio delta-sigma data converters, especially their power and chip area optimization. The major contents and innovation include:1. Aiming at the demands on low-voltage ultra-low power and miniaturization of the audio delta-sigma ADC applying to implantable biomedical devices such as cochlear implants, an improved design process of delta-sigma modulator was summarized based on theoretical calculations, modeling and simulation combining with the in-depth analysis of non-ideality factors in design. Based on it, the circuit specifications satisfying the requirements were finally determined. Switched op-amps and the op-amp shared techniques were used to achieve low-power integrators, and an improved multi-bit quantizer based on high-density capacitor array was employed to optimize the chip area. A novel two-step adding scheme was proposed to realize the internal signals summation and avoid the attenuation of the signal swing caused by charge sharing between two or more capacitors, and therefore the design specifications of multi-bit quantizer were simplified. The split-and-bidirectional-shift data weighted averaging (DWA) technique was proposed to eliminate the mismatch errors caused in the feedback DAC without introducing signal-dependent tones. The prototype ADC has been implemented in a standard0.18-μm process and measured to have92.2-dB peak SNR and94.6-dB dynamic range with20-kHz signal bandwidth. The power consumption is164-μW of the ADC at0.9V supply voltage, and58-μW of the modulator, which translates to a figure-of-merit (FoM) of42-fJ/step.2. According to the demands on audio signal processing of high performance portable devices, the research on low power and area-efficiency optimization of high precision audio-band delta-sigma DAC was carried out. An improved common subexpression elimination method, which decreased the hardware overhead and logical depth was proposed to implement the coefficients of the interpolator. The split-and-bidirectional-shift DWA technique was applied in full-digital form to eliminate the mismatch errors of conversion units in the reconstruction filter. A hybrid FIR/IIR based direct charge transfer (DCT) DAC was employed to build the reconstruction stage, combined with an on-chip smooth filter to improve the system performance. Experimental and test results showed that the peak SNR and the dynamic range of the prototype delta-sigma DAC are102.2-dB and103.6-dB respectively, and the power consumption is3.54-mW under a voltage supply of1.5-V. it has been proven that a favorable balance between the converting precision and the power consumption is achieved.