A current-output DAC for low-power low-noise log-domain ΔΣ modulators

In this paper, a novel low-noise current-output DAC suitable for incorporation in multibit log-domain ΔΣ modulators is proposed, eliminating the need for a voltage-to-current conversion stage in the feedback path and the associated resistor thermal noise. The paper demonstrates how appropriately scaled switched-current elements and the introduction of additional current sources enable the realization of a full current swing at the proposed DAC output, and evaluates the design parameters to achieve the required signal swing within a ΔΣmodulator loop. Analysis and simulation of the various design tradeoffs involved is presented, and it is demonstrated that the proposed current-output DAC is suitable for very low-power applications with low-to-medium speed requirements.