DLL-Based Pulse-Width Modulation Digital-to-Analog Converter for Continuous-Time Sigma Delta Modulators

Abstract

In this paper, the DLL-based pulse-width modulation (PWM) digital-to-analog converter (DAC) is proposed to convert the output of multi-bit quantizer to a single-bit pulse-width modulated signal in the modified continuous-time sigma-delta modulators (CT-SDMs) with improved signal transfer function (STF). The DLL-based PWM DAC is more robust to clock jitter and excess loop delay (ELD) effects than conventional multi-bit DAC and other PWM DAC with similar speed and power requirements of the integrators in CT-SDMs. Furthermore, the proposed PWM DAC is based on inherently linear single-bit DAC, so the dynamic-element matching (DEM) techniques, which increase the circuit complexity and power consumption to compensate the mismatch of unit elements in the multi-bit DAC, can be removed in CT-SDMs.