An 8-Bit Fractional-Order Sigma-Delta Modulator Based on Unity STF Architecture

This work introduces a new type of continuoustime (CT) Sigma-Delta modulator (SDM): the fractional-order type. A fractional-order band-pass filter (BPF) is realized in a feedforward SDM architecture with a unity signal transfer function (STF) using a half-order element. The noise transfer function (NTF) exhibits a shaping of 10 dB slope for the out-ofband spectrum. This will relax digital domain processing while achieving 53.9 dB signal-to-noise-and-distortion ratio (SNDR) and 8.6 effective number of bits (ENOB). This work proves the capabilities and potential of using fractional-order filters in the SDM loops, such as achieving notch noise shaping using only two single-element transfer functions. Theoretical and simulation results on MATLAB using the SIMSIDES toolbox match the results from a Field-programmable Analog Array (FPAA).