Spread -spectrum technique in sigma -delta modulators

The application of spread-spectrum techniques to sigma-delta (SigmaDelta) modulators as a method to reduce the effects of integrated circuit nonidealities is investigated in this work. The research primarily focuses on reducing the effects of DC offset, flicker noise, nonlinear amplifier DC gain, DAC and power supply noise, and substrate noise. The proposed design may prove beneficial in Power-over-Ethernet (IEEE 802.3) or other AC powered applications and vibration power-scavenging applications where the power supply and substrate noise may still exhibit strong spectral tones affecting the modulator's performance. In addition, the insensitivity of the proposed design to process variations and circuit nonidealities such as low frequency noise and DC offset makes it suitable for high-resolution ADC applications in more advanced CMOS technologies.;A step-by-step design methodology for transforming a conventional SigmaDelta modulator into a spread-spectrum SigmaDelta modulator is described. To illustrate this process, the design of a third-order 1-bit spread-spectrum SigmaDelta modulator is shown in detail. Additionally, the requirements for a particular spread-spectrum sequence are described with respect to the expected noise performance of the SigmaDelta modulator.;An experimental prototype third-order 1-bit fully-differential spread-spectrum SigmaDelta modulator is implemented using the TSMC 2-poly/4-metal 0.35mum CMOS process. The spread-spectrum sequence utilized for the measurements is a second-order blue noise sequence that was synthesized on an Altera FPGA. The prototype is clocked at 200kHz and digitizes a 500Hz bandwidth signal with 94dB of dynamic range. Additionally, the prototype achieves SNR and SNDR measurements of 85.2dB and 81.7dB, respectively.;The spread-spectrum technique in SigmaDelta modulation also is explored for bandpass SigmaDelta modulators. Specifically, a two-path bandpass SigmaDelta modulator utilizing a spread-spectrum capacitor randomization scheme within the resonator structure and a bandpass SigmaDelta modulator employing modulation with a band-stop spread-spectrum sequence are described. Both methods are shown to be effective at spreading in-band spectral interferers to make them appear as wideband noise.;We also apply spread-spectrum techniques to Nyquist rate analog-to-digital converters. A time-interleaved Nyquist-rate analog-to-digital converter employing spread-spectrum channel ADC selection is shown to effectively randomize the individual channel ADC mismatches such as gain, offset, and flicker noise, thereby improving the ADC's performance.