Design of Low Voltage Unsaturated Ring Oscillator for a Sigma Delta Time to Digital Converter

Abstract

This thesis investigates the phase noise of two different 2-stage cross-coupled pair unsaturated ring oscillators with no tail current source. One oscillator consists of top cross-coupled pair delay cells, and the other consists of top cross-coupled pair and bottom cross-coupled pair delay cells. Under a low supply voltage restriction, a phase noise model is developed and applied to both ring oscillators. Both top cross-coupled pair and top and bottom cross-coupled pair oscillators are fabricated with 0.13 um CMOS technology. Phase noise measurements of -92 dBc/Hz and -89 dBc/Hz ,respectively, at 1 MHz offset is obtained from the chip, which agree with theory and simulations. Top cross-coupled ring oscillator, with phase noise of -92 dBc/Hz at 1 MHz offset, is implemented in a second order sigma-delta time to digital converter. System level and transistor level functional simulation and timing jitter simulation are obtained.