A novel highly stable multiple-feedback oversampled lowpass Σ-Δ A/D converter configuration

The existing multiple-feedback Σ-Δ A/D converters usually feature, (a) complementary signal and noise transfer functions, and/or (b) unit-circle noise transfer function zeros. However, in corresponding switched-capacitor (SC) hardware implementations, such A/D converters may become prone to instability as a result of capacitor mismatches. This paper is concerned with the development of a novel multiple-feedback lowpass Σ-Δ A/D converter having, instead, magnitude-squared or magnitude complementary signal and noise transfer functions. The proposed A/D converter offers increased stability performance in the presence of capacitor mismatches in the SC hardware implementation. In addition, by ensuring that the noise transfer function zeros are located at DC, the SC hardware implementation embodies a significant improvement in both capacitance spread and total capacitance