Quadrature Mismatch Shaping Techniques for Fully Differential Circuits

Quadrature ΣΔ ADCs require a feedback path for both the I and the Q part of the complex feedback signal. A complex DAC could give this feedback with near-perfect I/Q balance. Still, the mismatch between the unit elements of the complex DAC introduces mismatch noise that should be shaped out of the signal band with dynamic element-matching (DEM) techniques. In literature, only quadrature DEM techniques for 3-state (I, Q, 0) unit elements are considered. However, in fully differential circuit, also 5-state unit elements are available. In this case, each unit element can be selected ±1, ±Q or 0. When using these 5-state unit elements, the amount of hardware and power consumption can be reduced significantly. In this paper it is shown how the tree structure, the data directed swapper and the vector quantizer structure can be adapted for the use in fully differential circuits with such 5-state unit elements.