Hybrid (sigma)(delta) modulators with adaptive calibration

This paper describes an architecture for stable high-order (sigma)(delta) modulation. The architecture is based on a hybrid (sigma)(delta) modulator, wherein hybrid integrators replace conventional analog integrators. The hybrid integrator, which is a combination of an analog integrator and a digital integrator, offers an increased dynamic range and helps make the resulting high-order (sigma)(delta) modulator stable. However, the hybrid (sigma)(delta) modulator relies on precise matching of analog and digital paths. In this paper, a calibration technique to alleviate possible mismatch between analog and digital paths is proposed. The calibration adaptively adjusts the digital integrators so that their transfer functions match the transfer functions of corresponding analog integrators. Through behavioral-level simulations of fourth-order (sigma)(delta) modulators, the calibration technique is verified.