Numerical analysis of superconductive oversampling analog-to-digital converters

We have numerically studied oversampling analog-to-digital converters (ADCs) in terms of sensitivity, spurious-free dynamic range, signal-to-noise ratio (SNR) or dynamic range toward the application to a future mobile communication system. These ADCs are based on single-flux-quantum logic. The sensitivity depends on the impedance of the grounded element, while the SNR is less dependent on the architecture of the modulator. A band-pass (sigma)-(delta) modulator is suitable for digital RF radios due to its high sensitivity. The second-order modulator with a feedback gain of 20 and 50 GHz-operation of the single-loop modulator show the same effect on the improvement of SNR. Further improvement required for the digital RF architecture can be realized by using a multi-bit comparator or by higher operating speed.