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

By fully exploiting the enhanced stability characteristics of multibit quantization, stable higher-order ΔΣ 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 ΔΣ modulator topology to realize FIR NTFs of arbitrary orders. Its key features include: reduced sensitivity to integrator nonlinearities, improved robustness to ΔΣ modulator coefficient variations, and decreased circuit complexity. Its performance is validated through simulations and compared to traditional ΔΣ modulator structures. This paper further discusses how the design of the signal transfer function (the signal path within the ΔΣ 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.