A superconducting bandpass sigma-delta modulator and a method for analog-to-digital signal conversion is disclosed. The superconducting bandpass sigma-delta modulator includes coupled resonators having a desired impedance ratio. A first resonator connects to a comparator, which comparator generates single-flux-quantum pulses. A feedback loop links from the comparator to a second resonator and includes a current amplifier. A digital RF receiver system is also disclosed. This system includes a second order bandpass sigma-delta modulator, which has a desired impedance ratio between resonators and a feedback loop with current amplification. The system further has an antenna configured to receive a GHz frequency radio transmission and to yield an analog signal which is accepted by the sigma-delta modulator.