On the use of passive circuits to implement LC-based band-pass CT ΣΔ modulators

This paper discusses the use of passive circuits for the implementation of band-pass continuous-time ΣΔ modulators intended for digitizing radio-frequency signals in wireless communication systems. Several alternative loop filters, considering either a fully passive or an hybrid active/passive circuit realization of the embedded resonators, are applied to the high-level design of fourth-order single-loop band-pass ΣΔ modulators with current-mode feedback digital-to-analog converter. The resulted modulator topologies are synthesized considering a widely programmable notch frequency, and compared in terms of their sensitivity to main circuit error mechanisms, including finite output swing, quality factor of inductors, and technology process variations. Time-domain simulations validate the presented approach, showing the feasibility of using fully passive and hybrid active/passive resonators to implement band-pass continuous-time ΣΔ analog-to-digital converters.