Single OpAmp Higher-Order Filters in Sigma-Delta Modulators
Final Report Abstract
Efficient loopfilter design in Delta-Sigma Modulators are key for advanced state-of-the-art ADCs. The loopfilter determines not only the noise-shaping order and thus the ideal quantization-noise performance, but it also determines the thermal noise performance, the linearity performance and dominates the power consumption. Therefore, the intention of this work was to investigate the general advantage of realizing the loopfilter with a reduced number of operational amplifiers, i.e. single-opamp resonator (SOR) filters. During the conduction of this work, the focus was broadened to the investigation of power efficient, unconventional opamp architectures, such as inverter and ring-amplifier based operational amplifiers, both of which have become more prominent lately in delta-sigma modulators. Within the project, we could show in several theses as well as in a recently submitted publications, that the general statement found in literature, i.e. the sheer reduction of number of operational amplifiers in the loopfilter reducing power consumption, is not true. Dependent on the chose single- opamp resonator structure, the circuit level requirements become very tense which in fact yields higher power consumption as the classical chain of integrator filters. Still, we derived possibilities to compensate for loopfilter non-idealities in the presence of SOR. They were also modelled on system level in order to be incorporated into an online design environment, where the non-ideality compen- sation is heuristically done. In terms of power efficient operational amplifiers, both inverter based and ring-amplifier based de- signs have been studied. In final prototype implementation of a high efficiency delta-sigma modulator, still inverter based amplifiers have been chosen as RAMP show inferior power efficiency in older technology nodes. Simulation results show advance state of the art power efficiency and performance.
Publications
- “Design Approach for Ring Amplifiers”. In: IEEE Transactions on Circuits and Systems I: Regular Papers 67.10 (2020), pp. 3444–3457
Joschua Conrad et al.
(See online at https://doi.org/10.1109/tcsi.2020.2986553) - “Compensation of Finite GBW in CT Bandpass SDMs Based on Single- OpAmp Resonators with Positive-Feedback”. In: 2021 IEEE 64rd International Midwest Symposium on Circuits and Systems (MWSCAS). 2021
Johannes Wagner et al.
(See online at https://doi.org/10.1109/mwscas47672.2021.9531770)
