Delta-sigma modulator topologies for high-speed high-resolution A/D converters

Abstract

By fully exploiting the enhanced stability characteristics of multibit quantization, stable higher-order /spl Delta//spl Sigma/ modulators with finite-impulse-response (FIR) noise-transfer-functions (NTF) can be designed to achieve high signal-to-quantization-noise ratios at low oversampling ratios (OSR). This paper proposes a multibit /spl Delta//spl Sigma/ modulator topology to realize FIR NTFs of arbitrary orders. Its key features include: reduced sensitivity to integrator nonlinearities, improved robustness to /spl Delta//spl Sigma/ modulator coefficient variations, and decreased circuit complexity. Its performance is validated through simulations and compared to traditional /spl Delta//spl Sigma/ modulator structures. This paper further discusses how the design of the signal transfer function (the signal path within the /spl Delta//spl Sigma/ modulator) can significantly reduce the harmonic distortion due to opamp nonidealities in the modulator's loop filter and can help reduce the power dissipation, especially for high-speed high-resolution analog-to-digital converters (ADC) designed in low-voltage fine-line technologies.